Stormwater Design Criteria Manual-2000

Town of Kitty Hawk
Stormwater Design Criteria Manual
June, 2000
Submitted by
URS
5606B Virginia Beach Blvd
Virginia Beach, VA 23462
[phone]

0
September 22, 2000
Town of Kitty Hawk
Mr. Timothy W. Owens
Assistant Town Manager
101 Veterans Memorial Drive
Post Office Box 549
Kitty Hawk, North Carolina 27949
Dear Mr. Owens:
As agreed to per your telephone conversation with James Peaco on September 17, 2000,
URS Corporation (URS) is pleased to submit six (6) final copies of the enclosed
Stormwater Design Criteria Manual. The manual has been tailored to assist the Town of
Kitty Hawk in meeting its specific North Carolina stormwater management and
permitting requirements.
• URS appreciates being given the opportunity to assist the Town in meeting its stormwater
management needs. Please call Bud Curtis at [phone] or James Peaco at (757)
321-1255 if you have any questions.
Sincerely,
LWC/jmj
Enclosure
URS Corporation
Executive Cove Center
5606E Virginia Beach Boulevard
Virginia Beach, VA 23462-5631
Tel: [phone]
Fax: [phone]

•
•
FUNDING CREDIT
The preparation of this document was financed in part through a grant provided by
the North Carolina Coastal Management Program, through funds provided by the
Coastal Zone Management Act of 1972, as amended, which is administered by the
Office of Ocean and Coastal Resources Management, National Oceanic and
Atmospheric Administration.

TOWN OF KITTY HAWK
STORMWATER DESIGN CRITERIA MANUAL
1.0 INTRODUCTION................................................................................................................... 1
1.1 Procedure and Submittals.............................................................................................. 1
1.2 Submittal Requirements for Low -density Development/Redevelopment Activities.... 1
1.3 Submittal Requirements for High -Density Development/Redevelopment Activities.. 3
2.0 DESIGN CRITERIA.................................................................................................................. 4
2.1 Stormwater Runoff Calculations...................................................................................
5
2.2 Drainage Conveyance Criteria......................................................................................
6
2.2.1 Channels and Ditches..................................................................................
6
2.2.2 Pipes............................................................................................................6
2.2.3 Culverts.......................................................................................................
7
2.3 Stormwater Best Management Practices (BMPs).........................................................
8
2.3.1 BMP Design Criteria for Low -Density Development ................................. 8
2.3.1.1 Grassed Swales............................................................................... 8
2.3.1.2 Vegetative Buffers.......................................................................... 9
2.3.1.3 Curb Outlet Systems.....................................................................
10
2.3.2 BMP Design Criteria for High -Density Development ..............................
10
2.3.2.1 Wet Detention Ponds....................................................................
10
2.3.2.2 Permanent Water Quality Pool ...........................
2.3.2.3 Temporary Water Quality Pool .....................................................
10
11
2.3.2.4 Determination of the Required Pond Surface Area .......................
11
2.3.2.5 Volume Determination for the Temporary Water Quality Pool....
11
2.3.3 Infiltration Systems...................................................................................
11
2.3.4 Alternative Stormwater Management Systems ........................................
12
2.3.4.1 Stormwater BMP Treatment Efficiencies .....................................
12
FIGURES
Number Follows
1 Building Permit Flowchart Page 1
2 Areas of Environmental Concern Appendices
3 Zoning Districts Appendices
4 Soils Appendices
5 Flood Zones Appendices
0

9 Appendices
A North Carolina Stormwater Management Regulations
B North Carolina Stormwater Management Permit Application
C Rational Method Criteria
D SCS Peak Discharge Method Criteria
E Design of Stable Channels and Divisions
F CAMA Drainage Ditch Criteria Design
G NCDOT Guidelines for Highway Culvert Design
H USDOT Hydraulic Design of Highway Culverts
I Grassed Swale Design Criteria
J Grass -lined Channel Design Criteria
K Wet Detention Pond Design Criteria
L Infiltration Device Design Criteria
M Total Suspended Solids Removal Efficiency Design Criteria
•
0

TOWN OF KITTY HAWK
0 STORMWATER DESIGN CRITERIA MANUAL
1.0 INTRODUCTION
This stormwater design manual was developed for Town administrators to aid
in reviewing proposed site plans and the associated stormwater management
permit applications. Because the Town did not employ a professional
engineer at the time this manual was developed, the information presented
herein was intended for general use by designated Town administrators in the
review of design criteria and runoff calculations submitted with site plans.
The manual contains summarized design criteria that have been consolidated
from various North Carolina design standards.
1.1 PROCEDURE AND SUBMITTALS
This chapter outlines site plan review procedures and submission requirements
for the Town's stormwater management program. Figure 1 shows the steps
involved in the review of proposed site plans and stormwater management
applications as required by the Town Zoning Ordinance for development and
redevelopment activities. Figures 2-5 (preceding the Appendices) are provided
as review aids and illustrate, respectively, Areas of Environmental Concern
(AECs), Zoning Districts, Soil Types, and Flood Zones within the Town limits.
1.2 SUBMITTAL REQUIREMENTS FOR LOW -DENSITY
DEVELOPMENT OR REDEVELOPMENT ACTIVITIES
All applications for building permits for the development or redevelopment of
low -density single-family detached homes, duplexes, and multifamily
residences shall be accompanied by:
• Two (2) copies of a site plan and documented site development
calculations prepared, stamped and endorsed by a registered professional
engineer, surveyor, or or other person duly authorized by the State to
practice as such.
• The following information may be requested for submission to the Town at
the discretion of the Building Inspector.
(1) Two (2) sets of plans showing north arrow, scale, revision date,
property/project boundaries, lot lines, existing and proposed contours,
drainage areas with receiving water classifications, mean high water
line, wetlands, easements, soil types, the required 30 foot minimum
vegetated buffer between impervious areas and surface waters,
existing and proposed impervious areas, road cross -sections, culverts
with pipe sizes indicated, drainage systems, and existing and proposed
stormwater management facilities.

START
RECEIVE PROPOSED SITE
RETURN m
PLAN WITH PROPOSED
DE1hLOPER FCR
DEVELOPMENT OR REDEVELOPMENTSI
DN
SITE PLAN DESIGN
RESIUBMts
ARE SITE DATA AND NO
RUNOFF CALCULATIONS INCLUDED
AS REQUIRED N THE
TOWN ZONING ORDNANCE
YES
IS THE AREA OF THE NO
PROPOSED SITE DISTURBANCE
1-ACRE OR MORE
YES
A NgL1H CARGJNA SEDRiNTATIGI
RETURN AMO EROSION CONTROL PLAN AND
TO
F SITE IS LOCATED N
DEVELOPERSICRYMI WATER DISGIARGE PERT
FOR
AN AEG A CAUA MINOR
ARE REQUIRED. F SITE IS LOCATED
DEVELOPMENT PERMIT
RESUBMISSION N AN AEC, A CAMA MAJOR
IS REQUIRED
DEVELOPMENT PERMIT IS ALSO REQUIRED
IS THE PROPOSED
ISSUE BULDING
PERMIT
DEVELOPMENT SITE NO
LOCATED N ZONNG
DISTRICTS BR-L BR-Y.
BR-3, VR-1. VR-2.
OR VR-4 OR IWW
YES
IS THE PROPOSED
REJECT SIZE PLAN AND lDT COVERAGE FOR
5 THE PROPOSED
REJECT STE RAN AND
REQUIE REDESIGN FOR F'fs•NCPAL USE AND
LOT COVERAGE FOR PRINCIPLE
REQUIRE RIDESGI FOR
LOT COVERAGE OF 3OUL ALL ACCESSORY
USE AND AL ACCESSORY
LOT COVERAGE OF NOR
OR LESS STRUCTURES 30R
STRUCTURES BOX OR LESS
OR LESS
OR LESS
YES
YES
DOES THE
006 TEE
oposm
SITE PLAN AND MEET OEHI9TY STi0R1-
HGM DENSITY STORY-
IE.EC'T SITE FLAN AM
HREJECT
REQUIRE REDESIGJ THAT WATER BIP DEN CPoTFRIA FOR
WATER BP DESIGN CRITEPoA FOR
REQUIRE RAN TNAT
MISTS LAW DENSITY WATERS AS SPEGFlED N
WATERS AS SPECIFED IN
MEETS NOH DENSITY
OMP DESIGMI CPoIE�A TOIMN STOIa1WAlER
MM SIDRYWAIER
BMP DESIGN CPoIERIA
DESIGN MANUAL
DESIGN MANUAL
7
?
YES
YES
140 PERMIT
PERMIT
NO
APPLICA11ON IS
APPLICATION IS
APPROVED BY
APPROVED BY
STATE
STATE
9
?
YES
ISSUE BUILDING
PERMIT
YES
ISSUE BUILDING
PERMIT
4
PREPARATIONTHE THIS AENHIA�
THROUGH AA RANT PROVIDED BY THE NORTH CAOLN
TOWN OF KITTY HAWK
$
COASTAL MANAGEMENT PROGRAM. THROUGH FUNDS PROVIDED
DARE COUNTY. NORTH CAROLINA
BY THE COASTAL ZONE MANAGEMENT ACT OF 197Z AS
AMENDED. WH#CH IS ADMINISTERED BY THE OFFICE OF OCEAN
town;
KLTLTHAWK STORMWATERINANAGEMENTPLAN
AND COASTAL RESOURCES MANAGEMENT. NATIONAL OCEANIC
r` °
BUILDING PERMIT FLOWCHART
AND ATMOSPHERIC ADMINISTRATION,
FIGURE 1
"wf:x '"+}
Woodward —CI a .....209—

(2) Documented calculations of the existing and proposed built -upon
impervious area, the total project area, and the percent built -upon area
for the proposed project. Impervious area calculations shall include a
breakdown of all buildings, streets, parking lots and all other
impervious areas.
(3) A description of the method proposed for stormwater treatment.
(4) For each project site drainage area, documented calculations of
existing and proposed peak runoff rates for the 2-year and 10-year
storm, utilizing the rational method or the SCS curve number method.
Flows that originate from off -site sources and subsequently flow
through the project site must be identified and included in these
calculations.
(5) The number of families, housekeeping units, or rental units the project
is designed to accommodate.
(6) Any other matters which may be necessary to determine conformance
with and provide for the enforcement of this chapter.
• For all proposed development activities which disturb one (1) acre or more
of surface area, two (2) copies of the plans and calculations shall be
submitted by the Developer or Owner to the North Carolina Division of
Water Quality along with one (1) original and one (1) copy of the
completed stormwater management permit application. One (1) copy of
the plans and calculations submitted to the Town shall be returned to the
applicant by the building inspector for all required State stormwater
management permits, after the stormwater management permit has been
approved by the State and the building inspector has marked the copy as
either approved or disapproved and attested to the same by his or her
signature on such copy. No building permit will be issued until a copy of an
approved State stormwater management permit has been received by the
Town. One copy of the plans and calculations, similarly marked, shall be
retained by the Town. A copy of the North Carolina Stormwater
Management Regulations is provided in Appendix A and a copy of a North
Carolina stormwater management permit application form is provided in
Appendix B
• A designated Town administrator shall, unless relieved of this requirement
by the planning board, utilize the services of an engineer and/or surveyor
licensed in the state for the purposes of examining the site plan and
comparing the "as built" site plan to the completed site plan to assure
compliance with all applicable zoning, subdivision, soil sedimentation and
erosion control and flood ordinances and to assure compliance with the
approved North Carolina stormwater management permit as well as any
other regulations of the Town.
2

. 1.3 SUBMITTAL REQUIREMENTS FOR NIGH -DENSITY
DEVELOPMENT OR REDEVELOPMENT ACTIVITIES
All applications for building permits for the development or redevelopment of
high -density permitted projects including multifamily residences, group
development projects, group housing projects, commercial buildings and
commercial sites, as well as changes of use on existing commercial sites or
home occupations or changes from a residential use to a commercial use of
an existing structure shall be accompanied by:
Sixteen (16) copies of a site plan and documented development
calculations, stamped and endorsed by registered engineer, surveyor, or
other person duly authorized by the state to practice as such shall be
submitted no later than twenty (20) days prior to the next regular meeting
of the planning board.
• For all proposed development activities which disturb one (1) acre or more
of surface area, two (2) copies of plans and calculations shall be
submitted by the Developer or Owner to the North Carolina Division of
Water Quality along with one (1) original and one (1) copy of the
completed stormwater management permit application. One (1) copy of
the plans and calculations submitted to the Town shall be returned to the
applicant by the building inspector for all required State stormwater
management permits, after the stormwater management permit has been
approved by the State and the building inspector has marked the copy as
either approved or disapproved and attested to the same by his or her
signature on such copy. No building permit will be issued until a copy of
an approved State stormwater permit has been received by the Town. A
copy of the North Carolina Stormwater Management Regulations is
provided in Appendix A and a copy of a North Carolina stormwater
management permit application form is provided in Appendix B.
Information required to be submitted with the plans and stormwater permit
application include, but are not limited to, the following:
(1) Ten (10) sets of plans showing north arrow, scale, revision date,
property/project boundaries, lot lines, existing and proposed contours,
drainage areas with receiving water classifications, mean high water
line, wetlands, soil types, easements, existing and proposed
impervious areas, road cross -sections, drainage systems with inverts
indicated, culverts with pipe sizes indicated, curb and gutter systems
with inlet and outlet elevations indicated, swale and ditch cross
sections, and existing and proposed stormwater management facilities.
(2) Documented calculations of the existing and proposed built -upon
impervious area, the total project area, and the percent built -upon area
for the proposed project. Impervious area calculations shall include a
3

breakdown of all buildings, streets, parking lots and all other
impervious areas.
(3) A description of the method proposed for post -development
stormwater treatment, along with documented calculations that
demonstrate compliance with high -density Best Management Practice
(BMP) design requirements as per NCAC 2H.1005(b) and the DENR
stormwater BMP design manual.
(4) For each project site drainage area, documented calculations of
existing and proposed peak runoff rates for the 2-year and 10-year
storm, utilizing the rational method or the SCS curve number method.
Flows that originate from off -site sources and subsequently flow
through the project site must be identified and included in these
calculations.
• A designated Town administrator shall, unless relieved of this requirement
by the planning board, utilize the services of an engineer and/or surveyor
licensed in the state for the purposes of examining the site plan and
comparing the "as built" site plan to the completed site plan assure
compliance with all applicable zoning, subdivision, soil sedimentation and
erosion control and flood ordinances and to assure compliance with the
approved North Carolina stormwater management permit as well as any
other regulations of the town.
2.0 DESIGN CRITERIA
This chapter provides summarized criteria and approved methods for design
of stormwater best management practices (BMPs) and drainage systems.
The summarized design criteria have been consolidated from North Carolina
design standards contained in the following documents:
• North Carolina Stormwater Management Regulations
• North Carolina Stormwater BMP Design Manual
• The North Carolina Erosion and Sediment Control Planning and
Design Manual
• The North Carolina Guide to Protecting Coastal Resources Through
The Coastal Area Management Act (CAMA) Permit Program
• The North Carolina Division of Highways Guidelines For Drainage
Studies and Hydraulic Design
n

• The North Carolina Division of Highways Minimum Construction
Standards for Subdivision Roads
• The North Carolina Department of Transportation Policy on Street
and Driveway Access to North Carolina Highways.
2.1 STORMWATER RUNOFF CALCULATIONS
The following steps should be used for calculating stormwater runoff:
1. Use site plans submitted by the developer or owner to verify the delineation
of drainage boundaries for the site, including off -site drainage areas that
discharge runoff through the project site.
2. Verify the following calculations provided by the developer or owner as part
of the project submittal requirements:
(a). The total project area.
(b). The existing and proposed built -upon impervious area. Impervious area
shall include pavement, buildings, roofs and any other surface which
does not allow infiltration of water into the soil. Concrete, asphalt, and
gravel surfaces are considered impervious.
(c). The percent built -upon impervious area for the proposed project site.
3. Based on the project type, select the required design storm as listed below:
• Swales and ditches 10-yr
• Collector systems 10-yr
• Town street cross drainage systems 25-yr
• Primary Roads (U.S. and N.C.) 50-yr
4. Based on the size of the drainage area contributing runoff to the site, select
the required runoff calculation method as listed below:
Rational Method - For all land development drainage areas of 20 acres
or less and all town street collector systems. The minimum time of
concentration (TOC) shall be 10 minutes for all rational method
evaluations.
• SCS Peak Discharge Method - For all land development drainage areas
larger than 20 acres
5. Verify the runoff calculations provided by the developer or owner as part of
the project submittal requirements. Summarized runoff design
methodologies from the North Carolina Erosion and Sediment Control
Planning and Design Manual are provided in the following appendices:
• Rational Method — Appendix C
• SCS Peak Discharge Method — Appendix D
5

2.2 DRAINAGE CONVEYANCE CRITERIA
This chapter provides summarized minimum conveyance criteria for channels
and ditches, pipes, and culverts. The summarized conveyance criteria have
been consolidated from applicable North Carolina standards and are provided in
the following paragraphs.
2.2.1 Channels and Ditches
The minimum design criteria for stable conveyance channels and ditches are as
follows:
(1) The system must have capacity to non-erosively carry the peak flow
expected from the 10-year storm.
(2) The channel lining must be resistant to erosion for the design velocity.
(3) All proposed ditches with dimensions of greater than 6 feet wide by 4 feet
deep must be approved by the Coastal Resources Commission.
A copy of the design methodology for stable channels and ditches, from the
North Carolina Erosion and Sediment Control Planning and Design Manual, is
provided in Appendix E.
A copy of the Coastal Resources Commission requirements for drainage
ditches is provided in Appendix F.
2.2.2 Pipes
1. Invert elevations shall be clearly indicated on proposed site plans for all
pipes entering or leaving drop inlets, catch basins, manholes, etc.
2. Minimum storm sewer pipe diameter shall be eighteen (18) inches. Pipes
shall be sized in an analysis independent from that which locates inlets.
Normally, one proceeds from the upland area toward the outlet, setting pipes
at minimum depth consistent with profile constraints and hydraulic grade
line.
3. Pipes shall be sized to flow just full at the design peak flow in accordance
with Manning's formula:
Q - (1.486/n)AR°-67SO.1; where:
n = roughness coefficient
A = area of pipe
R = hydraulic radius, which is obtained by dividing the area of the pipe by
the wetted perimeter of the pipe
S = pipe slope (assuming uniform flow)
2

The minimum values of the roughness coefficient (n) that shall be used in
the design of pipes are as follows:
• Concrete pipe = 0.013
• Corrugated HDPE pipe = 0.010
4. Pipes shall be designed to maintain self-cleaning velocities. Minimum and
maximum design velocities shall be as follows:
• Minimum velocity = 3 feet per second, where practical
• Maximum velocity = 15 feet per second, when flowing full
5. The distance between points of access in a storm sewer system shall be
limited to 300 feet where the pipe diameter is 18 to 42 inches, and 800 feet
where the pipe diameter is 48 inches or larger. It is mandatory that access
be provided at all pipe junctions and bends.
6. A minimum cover of two feet should be maintained wherever possible.
Designs consisting of multiple or low head pipes or special bedding shall be
provided where cover is decreased below two feet.
7. A hydraulic grade line (water surface profile) shall be determined for the
entire system and shown on the proposed site plan. The grade line shall not
rise above the top of junction facilities (for example, manholes and yard
drains) or the flowline in curb and gutter sections.
8. Concrete pipe shall be the standard material. The use of corrugated high
density polyethylene (HDPE) pipe shall be subject to approval by the Town
on a case -by -case basis. Metal pipe shall not be used.
2.2.3 Culverts
The minimum culvert diameter allowed shall be 15 inches. No one shall fill
in, remove, or block driveway or roadway culverts.
2. A minimum freeboard of one and one-half feet will be provided to safeguard
existing or proposed structures.
3. Culvert material of construction shall be concrete or corrugated high density
polyethylene (HDPE) with the following exceptions:
• The expected fill height over the structure exceeds the maximum values
for concrete as provided by the North Carolina Division of Highways.
• The required invert slope is greater than 10 percent.
• If a majority of the installations for a project require metal culverts, then
all culvert pipe for the project can be metal.
7

4. Culverts shall be adequate to accommodate the design flows for the intended
location. There are four discharge levels that must be evaluated for each
culvert design per the North Carolina Guidelines For Drainage Studies And
Hydraulic Design. A copy of the culvert design portion of this document is
provided in Appendix G. The four discharge levels are as follows:
(1) The "design discharge" as listed in paragraph 2.1.3
(2) Qioo base flood.
(3) 0-overtopping. This discharge is computed after a trial size is selected.
(4) Qio for outlet protection and erosion control measures.
Other discharges may be required on a site -specific basis. Examples are:
(1) Q-average. For permit determination.
(2) Q-bank full. For fish passage, channel stability or floodplain analysis.
The design of drainage culverts requires considerable expertise and
experience. By law, culvert design in Kitty Hawk can only be performed by
professional engineers registered in the State of North Carolina. As a general
guide for review by the Town Planner, a copy of the U.S. Department of
Transportation document entitled Hydraulic Design of Highway Culverts is
provided in Appendix H.
2.3 STORMWA TER BEST MANAGEMENT PRACTICES (BMPs)
North Carolina's approach to stormwater quality management in the 20 coastal
counties is based first on minimizing impervious surfaces and, secondly, on
treating stormwater runoff from these surfaces. The State uses a pollutant
removal BMP design standard of 85% removal for total suspended solids (TSS).
The State requires specific types of stormwater BMPs for low -density and high
density development in the Town of Kitty Hawk. Design criteria for BMPs that
can be utilized by the Town are provided in the paragraphs.
2.3.1 BMP Design Criteria For Low -Density Development
Pollutant removal from stormwater runoff, generated by low -density
development draining to Currituck Sound and Kitty Hawk Bay, is required to be
facilitated by limiting impervious surfaces and by retaining suspended solids
with vegetated conveyances (grassed swales) and vegetated buffers. Discrete
stormwater conveyance systems, such as storm sewer and ditch networks, are
not allowed in low -density development areas; curb outlet systems are not
permitted. Design criteria for grassed swales, vegetative buffers, and curb outlet
systems are provided as follows:
2.3.1.1 Grassed Swales
1. Design criteria for water quality control using grassed swales from the North
Carolina Stormwater BMP Design Manual include, but are not limited to, the
following:
8

• Maximum runoff velocity should be 2 feet per second for the peak
runoff of the 2 year storm.
•
The design must also non-erosively pass the peak runoff rate from the
10- year storm.
•
Swales should be sited in areas where the seasonal high water table is
at least one foot below the bottom of the swale.
•
Swales should not carry dry -weather flows or constant flows of water.
•
Side slopes should be no greater than 3:1 horizontal to vertical.
•
Longitudinal slope should be in the range of 2% to 4%. If the slope
along the flow path exceeds 4%, then check dams must be installed to
reduce the effective slope to below 4%.
•
Length of swale shall be at least 100 feet per acre of drainage area.
•
A vegetation plan shall be prepared in accordance with the
recommendations found in the North Carolina Erosion and Sediment
Control Design and Planning Manual.
•
Swales should be stabilized within 14 days of their construction.
•
Swales should be constructed on permeable, non -compacted soils.
•
Swales should have short contact times or short grass height.
In the North Carolina Stormwater BMP Design Manual, the methodology for
grassed swale design is referred to the North Carolina Erosion and Sediment
Control Planning and Design Manual. A copy of the grassed swale design
criteria section from the North Carolina Stormwater BMP Design Manual is
provided in Appendix I. A copy of the grassed swale design criteria section of
the North Carolina Erosion and Sediment Control Manual is provided in
Appendix J. Note: Appendix J contains various references to the North
Carolina Erosion and Sediment Control Manual, including the channel and
ditch design criteria section which is provided in Appendix E of this document.
2. No one shall fill in or pipe any roadside or lot -line swale, except as
necessary to provide a minimum driveway crossing. In areas where Town -
maintained swales are present in the roadside right-of-way, all driveways and
road entrances shall have culverts, unless a waiver is granted by the Town.
2.3.1.2 Vegetative Buffers
A vegetative buffer zone or buffer strip is a strip of vegetation that has not been
disturbed during development or has been planted along a stream or other area
to be protected. Buffer zones differ from filter strips in that the land surface is
not as level and there are no level spreaders or other constructed devices to
spread the stormwater runoff into thin sheet flow. Because vegetative buffers
consist primarily of undisturbed vegetation, the design criteria for low -density
development are as follows:
• The buffer shall be a minimum of 30 feet wide
• The buffer shall lie between all impervious built -upon areas and adjacent
surface waters.
6

2.3.1.3 Curb Outlet Systems
1. The Town does not permit curb outlet systems.
2.3.2 BMP Design Criteria For High -Density Development
Stormwater control systems for high -density development draining to Currituck
Sound and Kitty Hawk Bay must be wet detention ponds, infiltration systems, or
alternative storrnwater management systems designed in accordance with
NCAC 2H.1008 (see Appendix A). A safety fence is required by the Town for all
wet ponds. State design criteria for these systems are described in the following
paragraphs.
2.3.2.1 Wet Detention Ponds
Wet detention ponds or basins may be used as a primary treatment device or
as a secondary device following an infiltration system. Wet detention basins,
designed to provide water quality benefits to downstream waters, are ponds that
are sized and configured to provide significant removal of pollutants from the
incoming sormwater runoff. Wet detention basins provide a permanent pool of
water that is designed for a target total suspended solids (TSS) removal rate
according to the size and imperviousness of the contributing watershed. Above
the permanent pool of water, they are also designed to hold the runoff that
results from a 1-inch rain and release this over a period of two to five days.
Once the minimum surface area and temporary storage volume of the basin
needed to achieve the stated water quality goals are determined, the principal
outlet and and emergency spillway should be sized for flood and downstream
erosion control. The storage allocated to flood control is located on top of both
water quality pools, while the storage for downstream erosion control includes
the same storage as the temporary water quality pool. In some instances the
temporary water quality pool may also serve as sufficient volume for
downstream erosion control. Wet detention pond design criteria established in
the North Carolina Stormwater BMP Design Manual are provided in Appendix K
and summarized in the following paragraphs.
2.3.2.2 Permanent Water Quality Pool
• Average permanent water quality pool depths should be between 3 to 6 feet.
The minimum required depth is 3 feet.
• The amount of impervious surface used for sizing should be that expected in
the final buildout of the development. Sizing calculations must also include
any offsite runoff that drains to the pond.
• Enough volume should be included in the permanent pool to store the
sediment that will accumulate between cleanout periods.
• A forebay (which may be established by a weir) must be included to
encourage early settling. This allows drainage of only a portion of the basin
in order to excavate accumulated sediment. The forebay volume should
equal about 20% of the basin volume.
10

2.3.2.3 Temporary Water Quality Pool
• The temporary water quality pool is sized to detain the runoff volume from
the first (1) inch of rain. This requirement refers to volume and not a
particular design storm.
• The temporary water quality pool for extended detention must be located
above the permanent water quality pool.
• The outlet device for this temporary water quality pool should be sized to
release the runoff volume associated with the first 1 inch of rainfall over a
drawdown period of 48 to 120 hours (2 to 5 days).
2.3.2.4 Determination of the Required Pond Surface Area
• The surface area required can be determined using the permanent pool
surface area/drainage area (SA/DA) ratios for given levels of impervious
cover and basin depths as outlined in wet detention pond chapter of the
North Carolina Stormwater BMP Design Manual (Appendix K)
2.3.2.5 Volume Determination for the Temporary Water Quality Pool
• The use of the "Simple Method," as described by Schueler in Controlling
Urban Runoff: A Practical Manual for Plannina and Desionina Urban BMPs
1987 is recommended because it offers a conservative estimate of runoff
volume for a broad variety of land uses and impervious cover percentages.
An example of the simple method's application is provided in the wet
detention pond chapter of the North Carolina Stormwater BMP Design
Manual (Appendix K).
2.3.3 Infiltration Systems
Infiltration refers to the process of stormwater entering the soil. Infiltration
systems may be designed to provide infiltration of the entire design rainfall
volume required for a site or a series of successive systems may be utilized.
The North Carolina Stormwater BMP Design Manual discusses three types of
infiltration devices: infiltration basins, infiltration trenches, and dry wells. Design
criteria established in the North Carolina Stormwater BMP Design Manual are
provided in Appendix L and partially summarized as follows:
• Soils must have been tested and shown to infiltrate a minimum of 0.52
inches/hour at the bottom of the device.
• Infiltration devices must capture and infiltrate the runoff from the first 1.0
inches of runoff in Currituck Sound and Kittyhawk Bay drainage areas.
Determination of the runoff volume for the first 1 inch of rainfall should be
accomplished using the "Simple Method" as described above in Paragraph
2.3.2.5.
• The bottom of the infiltration device should be a minimum of 2 feet above the
seasonal high water table, with greater separation desirable.
11

•
• Drawdown of this runoff must occur within five days.
• The maximum drainage area that should flow to one device is 5 acres.
• Pretreatment devices such as catch basins, grease traps, filter strips,
grassed swales and sediment traps must be used to protect infiltration
devices from clogging.
• All infiltration devices should be sited a minimum of 30 feet from surface
water and 100 feet from any water supply wells.
• Infiltration devices must be designed as off-line BMPs. This means that
runoff in excess of the design volume bypasses the system.
• Runoff should not be directed to an infiltration device until the drainage area
is stabilized.
• Infiltration devices work best for smaller drainage areas and drainage areas
that are completely stable or impervious.
• Thick vegetation on the bottom of the infiltration basin should be maintained.
2.3.4 Alternative Stormwater Management Systems
1. In addition to the approved high -density stormwater management practices
described above, stormwater management systems consisting of other control
options or a series of control options may be approved by the State on a case -
by -case basis. Approval shall only be given in cases where the applicant can
demonstrate that the alternative design criteria shall provide equal or better
stormwater control, equal or better protection of State waters, and result in no
increased pollution potential for nuisance conditions. The criteria for approval,
specified in 15A NCAC 2H.1008(h), shall be that:
• The stormwater management system shall provide for 85% average annual
removal of TSS.
• The discharge rate following the 1-inch design storm shall be such that the
runoff volume draws down to the pre -storm stage within 2-5 days.
• The post development discharge rate shall .be no larger than the
predevelopment discharge rate for the 1-year 24-hour storm.
2.3.4.1 Stormwater BMP Treatment Efficiencies
When evaluating the treatment efficiency of proposed alternative treatment
systems, the State design criteria for total suspended solids (TSS) removal
efficiencies should be utilized. A copy of summarized TSS removal efficiencies
for various BMP types, from the North Carolina Stormwater BMP Design
Manual, is provided in Appendix M.
12

•
STATE OF
NORTH CAROLINA_
DEPARTMENT OF D E & N. R
ENVIRONMENT &
.NATURAL RESO URCES
DIVISION OF
WATER QUALITY
Administrative Code Section:
15A NCAC 2H .1000
Stormwater Management
Amended Effective: December 1, 1995
Environmental
Management Commission
Raleigh, North Carolina
STATES
W

EHNR - ENVIRONMENTAL MANAGEMENT ITI5A: 02H .1000
SECTION .1000 - STORNnVATER MANAGEMENT
Is .1001 STORMWATER MANAGEMENT POLICY
The rules in this Section set forth the requirements for application and issuance of permits for stormwater
management systems in accordance with G.S. 143-215.1(d) and 15A NCAC 2H .0200. These requirements
to control pollutants associated with stormwater runoff apply to development of land for residential,
commercial, industrial, or institutional use but do not apply to land management activities associated with
agriculture or silviculture unless specifically addressed in special supplemental classifications and management
strategies adopted by the Commission.
History Note: Statutory Authority G.S. 143-214.1; 143-214.7; 143-215.3(a)(1);
Eff. January 1, 1988;
Amended Ef. . September 1, 1995.
.1002 DEFINITIONS
The definition of any word or phrase in this Section shall be the same as given in Article 21, Chapter 143
of the General Statutes of North Carolina, as amended. Other words and phrases used in this Section are
defined as follows:
(1) "Built -upon Area" means that portion of a development project that is covered by impervious or
partially impervious cover including buildings, pavement, gravel roads and parking areas, recreation
facilities (e.g., tennis courts), etc. (Note: Wooden slatted decks and the water area of a swimming
pool are considered pervious).
(2) "CAMA Major Development Permits" mean those permits or revised permits required by the Coastal
Resources Commission according to 15A NCAC V Sections .0100 and .0200.
(3) "Certificate of Stormwater Compliance" means the approval for activities that meet the requirements
for coverage under a stormwater general permit for development activities that are regulated by this
Section.
(4)
"Coastal Counties" include Beaufort, Bertie, Brunswick, Camden, Carteret, Chowan, Craven,
Currituck, Dare, Gates, Hertford, Hyde, New Hanover, Onslow, Pamlico, Pasquotank, Pender,
Perquimans, Tyrrell, and Washington.
(5)
"Curb Outlet System" means curb and gutter installed in a development which meets low density
criteria [Rule .1003(d)(1) of this Section] with breaks in the curb or other outlets used to convey
stormwater runoff to grassed swales or vegetated or natural areas and designed in accordance with
Rule .1008(g) of this Section.
(6)
"Development" means any land disturbing activity which increases the amount of built -upon area or
which otherwise decreases the infiltration of precipitation into the soil.
(7)
"Drainage Area or Watershed" means the entire area contributing surface runoff to a single point.
(8)
"Forebay" means a device located at the head of a wet detention pond to capture incoming sediment
before it reaches the main portion of the pond. The forebay is typically an excavated settling basin
or a section separated by a low weir.
(9)
"General Permit" means a "permit" issued under G.S. 143-215.1(b)(3) and (4) authorizing a category
of similar activities or discharges.
(10)
"Infiltration Systems" mean stormwater control systems designed to allow runoff to pass or move
(infiltrate/exfiltrate) into the soil.
(11)
"Notice of Intent" means a written notification to the Division that an activity or discharge is
intended to be covered by a general permit and takes the place of "application" used with individual
permits.
(12)
"Off -site Stormwater Systems" mean stormwater management systems that are located outside the
boundaries of the specific project in question, but designed to control stormwater drainage from that
project and other potential development sites. These systems shall designate responsible parties for
operation and maintenance and may be owned and operated as a duly licensed utility or by a local
government.
(13)
"On -site Stormwater Systems" mean the systems necessary to control stormwater within an individual
==-=— ------NORTH CAROLINA ADJUIN STRATIIT CODE 12;1519S Page 1

EIINR - ENVIRONMENTAL MANAGMUMVT TISA: 0217.1000
development project and located within the project boundaries.
(14)
"Redevelopment" means any rebuilding activity which has no net increase in built -upon area or
which provides equal or greater stormwater control than the previous development (stormwater
controls shall not be allowed where otherwise prohibited).
(15)
"Seasonal High Water Table" means the highest level that groundwater, at atmospheric pressure,
reaches in the soil in most years. The seasonal high water table is usually detected by the mottling
of the soil that results from mineral leaching.
(16)
"Sedimentation/Erosion Control Plan" means any plan, amended plan or revision to an approved plan
submitted to the Division of Land Resources or delegated authority in accordance with G.S.
113A-57.
(17)
"Stormwater" is defined in G.S. 143, Article 21.
(18)
"Stormwater Collection System" means any conduit, pipe, channel, curb or gutter for the primary
purpose of transporting (not treating) runoff. A stormwater collection system does not include
vegetated swales, swales stabilized with armoring or alternative methods where natural topography
or other physical constraints prevents the use of vegetated swales (subject to case -by -case review),
curb outlet systems, or pipes used to carry drainage underneath built -upon surfaces that are
associated with development controlled by the provisions of Rule .1003(d)(1) in this Section.
(19)
"10 Year Storm" means the surface runoff resulting from a rainfall of an intensity expected to be
equaled or exceeded, on the average, once in 10 years, and of a duration which will produce the
maximum peak rate of runoff, for the watershed of interest under average antecedent wetness
conditions.
(20)
"Water Dependent Structures" means a structure for which the use requires access or proximity to
or siting within surface waters to fulfill its basic purpose, such as boat ramps, boat houses, docks,
and bulkheads. Ancillary facilities such as restaurants, outlets for boat supplies, parking lots and
boat storage areas are not water dependent uses.
(21)
"Wet Detention Pond" means a structure that provides for the storage and control of runoff and
includes a designed and maintained permanent pool volume.
(22)
"Vegetative Buffer" means an area of natural or established vegetation directly adjacent to surface
waters through which stormwater runoff flows in a diffuse manner to protect surface waters from
degradation due to development activities. The width of the buffer is measured horizontally from
the normal pool elevation of impounded structures, from the bank of each side of streams or rivers.
and from the mean high water line of tidal waters, perpendicular to the shoreline.
(23)
"Vegetative Filter" means an area of natural or planted vegetation through which stormwater runoff
flows in a diffuse manner so that runoff does not become channelized and which provides for control
of stormwater runoff through infiltration of runoff and filtering of pollutants. The defined length of
the filter shall be provided for in the direction of stormwater flow.
Histon- :Vote: Stattuory Authority G.S. 143-213; 143-214.1: 143-214. 7; 143-215.3(a)(1 );
E, ff. January 1, 1988:
Amended Eff. December 1, 1995; September 1. 1995.
.1003 STORMWATER MANAGEMENT: COVERAGE: APPLICATION: FEES
(a) The intent of the Commission is to achieve the water quality protection which low density development
near sensitive waters provides. To that end, the Director, by applying the standards in this Section shall cause
development to comply with the antidegradation requirements specified in 15A hCAC 2B .0=01 by protecting
surface waters and highly productive aquatic resources from the adverse impacts of uncontrolled high density
development or the potential failure of stormwater control measures.
(b) To ensure the protection of surface waters of the State in accordance with G.S. 143-21.3.7, a permit is
required in accordance with the provisions of this Section for any development activities which require a
CAIMA major development permit or a Sedimentation/Erosion .Control Plan and which meet any of the
followin_ criteria:
(1) - development activities located in the 20 coastal counties as defined in Rule .1002(4) of this Section:
(2) development activities draining to Outstanding Resource Waters (ORW) as defined in 15A NCAC
2B .0225; or
(3) development activities within one mile of and draining to High Quality Waters (HQW) as defined
NORTH CAROLLVA AMILVISTRATIVE CODE 12115195 Pate 2

L"im - ENVIRONMENTAL MANAGEMENT T15A: 02II .1000
in 15A NCAC 2B .0101(e)(5).
Projects under a common plan of development shall be considered as a single project and shall require
stormwater management in accordance with this Section. Local governments with delegated
Sedimentation/Erosion Control Programs often implement more stringent standards in the form of lower
thresholds for land area disturbed. In these situations, the requirements of this Rule apply only to those
projects that exceed the state's minimum area of disturbance as outlined in G.S. 113A-57. Specific permitting
options, including general permits for some activities, are outlined in Paragraph (d) of this Rule.
(c) Development activity with a CAMA major development permit or a Sedimentation/Erosion Control Plan
approved prior to January 1, 1988 are not required to meet the provisions of these Rules unless changes are
made to the project which require modifications to these approvals after January 1, 1988.
(d) Projects subject to the permitting requirements of this Section may be permitted under the following
stormwater management options:
(1) Low Density Projects: Projects permitted as low density projects must be designed to meet and
maintain the applicable low density requirements specified in Rules .1005 through .1007 of this
Section. The Division shall review project plans and assure that density levels meet the applicable
low density requirements. The permit shall require recorded deed restrictions and protective
covenants to ensure development activities maintain the development consistent with the plans and
specifications approved by the Division.
(2) High Density Projects: Projects permitted as high density projects must be designed to meet the
applicable high density requirements specified in Rules .1005 through .1007 of this Section with
stormwater control measures designed, operated and maintained in accordance with the provisions
of this Section. The permit shall require recorded deed restrictions and protective covenants to
ensure development activities maintain the development consistent with the plans and specifications
approved by the Division. Stormwater control measures and operation and maintenance plans
developed in accordance with Rule .1005 of this Section must be approved by the Division. In
addition, NPDES permits for stormwater point souses may be required according to the provisions
of 15A NCAC 2H .0126.
(3) Other Projects: Development may also be permitted on a case -by -case basis if the project:
(A) controls runoff through an off -site stormwater system meeting provisions of this Section;
(B) is redevelopment which meets the requirements of this Section to the maximum extent practicable;
(C) otherwise meets the provisions of this Section and has water dependent structures, public roads
and public bridges which minimize built -upon surfaces, divert stormwater away from surface
waters as much as possible and employ other best management practices to minimize water
quality impacts.
(4) Director's Certification: Projects may be approved on a case -by -case basis if the project is certified
by the Director that the site is situated such that water quality standards and uses are not threatened
and the developer demonstrates that:
(A) the development plans and specifications indicate stormwater control measures which shall be
installed in lieu of the requirements of this Rule: or
(B) the development is located such a distance from surface waters that impacts from pollutants
present in stormwater from the site shall be effectively mitigated.
(5) General Permits: Projects may apply for permit coverage under general permits for specific types
of activities. The Division shall develop generai permits for these activities in accordance with
Rule .1013 of this Section. General Permit coverage shall be available to activities including, but
not limited to:
(A) construction of bulkheads and boat ramps;
(B) installation of sewer lines with no proposed built -upon areas;
(C) construction of an individual single family residence; and
(D) other activities that, in the opinion of the Director. meet the criteria in Rule _.1013 of this Section.
Development designed to meet the requirements in Subparagraphs (d)(1) and (d)(3) of this Paragraph must
demonstrate that no areas within the project site are of such high density that stormwater runoff threatens
grater quality.
(e) Applications: Any person with development activity meeting the criteria of Paragraph (b) of this Rule
shall apply for permit coverage through the Division. Previously issued Stormwater Certifications (issued in
accordance with stormwater management rules effective prior to September 1, 1995) revoked due to
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ERNR - ENVIRONMENTAL MANAGEMENT TI SA: 02H .1000
certification violations must apply for permit coverage. Stormwater management permit applications, project
plans, supporting information and processing fees shall be submitted to the appropriate Division of
Environmental Management regional office. A processing fee, as described in Paragraph (f) of this Rule, must
be submitted with each application. Processing fees submitted in the form of a check or money order shall
be made payable to N.C. Department of Environment, Health, and Natural Resources. Applications which
are incomplete or not accompanied by the processing fee may be returned. Permit applications shall be signed
as follows:
(1) in the case of corporations, by a principal executive officer of at least the level of vice-president,
or his authorized representative;
(2) in the case of a partnership, by a general partner and in the case of a limited partnership, by a
general partner;
(3) in the case of a sole proprietorship, by the proprietor;
(4) in the case of a municipal, state or other public entity by either a principal executive officer,
ranking official or other duly authorized employee.
The signature of the consulting engineer or other agent shall be accepted on the application only if
accompanied by a letter of authorization.
(f) Permit Fees:
(I) For every application for a new or revised permit under this Section, a nonrefundable application
processing fee in the amount stated in Subparagraph (f)(2) of this Paragraph shall be submitted at
the time of application.
(A) Each permit application is incomplete until the application processing fee is received;
(B) No processing fee shall be charged for modifications of permits when initiated by the Director;
(C) A processing fee of forty dollars ($40.00) shall be charged for name changes;
(D) No processing fee shall be required for name changes associated with the initial transfer of
property from the developer to property owner or responsible party. Any subsequent changes
in ownership shall be subject to the name change processing fee in Part (C) of this Paragraph.
(2) Schedule of Fees
Permit Application
Processing Fee
. New Timely
Applications/ Renewals
Modifications/ Without
Rate Renewal Modifications
Low Densitv S''=5 N; A
High Density 385
Other 225 N A
Director's Certification 350 N.'A
General Permits 50 N,'A
(g) Supporting Documents and Information. This Paragraph outlines those supporting documents and
information that must be submitted with stormwater applications. Additional information may also be
applicable or required. The applicant shall attempt to submit all necessary information to describe the site.
development and stormwater management practices proposed. The following documents and information shall
be submitted with stormwater applications:
(1) two sets of detailed plans and specifications for the project;
(2) plans and specifications must be dated and sealed as outlined in Rule .10080) of this Section and
show the revision number and date;
(3) general location map showing orientation of the project with relation to at least two references
.FORTH CAROLINA ADAILVISTRATITT CODE 1211.5195 Pare 4

EHNR - ENVIRONMENTAL MANAGEMENT T15A: 02H .1000
(numbered roads, named streams/rivers, etc.) and showing the receiving water (a USGS map
preferable);
(4)
topographic map(s) of the project area showing original and proposed contours and drainage
patterns;
(5)
delineation of relevant boundaries including drainage areas, seasonal high water table, wetlands,
property/project boundaries and drainage easements;
(6)
existing and proposed built -upon area including roads, parking areas, buildings, etc.;
(7)
technical information showing all final numbers, calculations, assumptions, drawing and procedures
associated with the stormwater management measures including but not limited to: built -upon area,
runoff coefficients, runoff volume, runoff depth, flow routing, inlet and outlet configuration (where
applicable), other applicable information as specified;
(8)
- operation and maintenance plan signed by responsible party;
(9)
recorded deed restriction and protective covenants. As an alternative proposed deed restriction and
protective covenants and a signed agreement to provide final recorded articles shall be accepted
when final documents are not available at the time of submittal.
(h)
Permit Issuance and Compliance: Stormwater management permits shall be issued in a manner
consistent
with the following:
(1)
Stormwater management permits issued for low density projects shall not require permit renewal.
(2)
Stormwater management permits issued for projects that require the construction of engineered
stormwater control measures shall be issued for a period of time not to exceed 10 years.
Applications for permit renewals shall be submitted 180 days prior to the expiration of a permit
and must be accompanied by the processing fee described in Paragraph (f) of this Rule.
(3)
Stormwater management permits shall be issued to the developer or owner and shall cover the
entire master plan of the project ("stormwater master plan permit"). The master plan permit shall
include specifications for stormwater management measures associated with each individual lot or
property within the project.
(4)
Any individual or entity found to be in noncompliance with the provisions of a stormwater
management permit or the requirements of this Section is subject to enforcement procedures as set
forth in G.S. 143, Article 21.
History
Note: Statutory Authority G.S. 143-214.1; 143-214.7; 143-215. 1 (d); 143-215.3(a)(1);
Eff. January 1. 1988;
Amended Eff. . December 1, 1995; September 1, 1995.
.1004 STATEWIDE STORIMWATER GUIDELLYES
History Note: Statutory Authority G.S. 143-214.1; 143-214.7.• 143-215.3(a)(1): 143-215.8A;
Eff. January 1. 1988;
Repealed Eff. September 1. 1995.
.1005 STORINIWATER REQUIREMENTS: COASTAL. COUNMES
All development activities within the coastal counties which require a stormwater management permit in
accordance with Rule .1003 of this Section shall manage stormwater runoff as follows:
(1) development activities within the coastal counties draining to Outstanding Resource Waters (ORW)
shall meet requirements contained in Rule .1007 of this Section;
(2) development activities within one-half mile of and draining to SA waters or unnamed tributaries to
SA waters:
(a) Low Density Option: Development shall be permitted pursuant to Rule .1003(d)(1) of this Section
if the development has:
j (i) built -upon area of 25 percent or less: or proposes development of single family residences on lots
! with one-third of an acre or greater with a built -upon area of 25 percent or less;
(ii) stormwater runoff transported primarily by vegetated conveyances; conveyance system shall not
include a discrete stormwater collection system as defined in Rule .1002 of this Section;
(iii) a 30 foot wide vegetative buffer.
(b) High Density Option: Higher density developments shall be permitted pursuant to Rule .1003(d)(2)
NORTH CAROLINA ADMINISTRATIVE CODE 12115195 Page 5

EHNR - ENVIRONMENTAL MANAGEMENT TI5A: 02H .1000
of this Section if stormwater control systems meet the following criteria:
(i) no direct outlet channels or pipes to SA waters unless permitted in accordance with 15A NCAC
2H .0126;
(ii) control systems must be infiltration systems designed in accordance with Rule .1008 of this
Section to control the runoff from all surfaces generated by one and one-half inches of rainfall.
Alternatives as described in Rule .1008(h) of this Section may also be approved if they do not
discharge to surface waters in response to the design storm;
(iii) runoff in excess of the design volume must flow overland through a vegetative filter designed in
accordance with Rule .1008 of this Section with a minimum length of 50 feet measured from
mean high water of SA waters;
(3) development activities within the coastal counties except those areas defined in Items (1) and (2) of
this Paragraph:
(a) Low Density Option: Development shall be permitted pursuant to Rule .1003(d)(1) of this Section
if the development has:
(i) built -upon area of 30 percent or less; or proposes development of single family residences on lots
with one-third of an acre or greater with a built -upon area of 30 percent or less;
(ii) stormwater runoff transported primarily by vegetated conveyances; conveyance system shall not
include a discrete stormwater collection system as defined in Rule .1002 of this Section;
(iii) a 30 foot wide vegetative buffer.
(b) High Density Option: Higher density developments shall be permitted pursuant to Rule .1003(d)(2)
of this Section if stormwater control systems meet the following criteria:
(i) control systems must be infiltration systems, het detention ponds or alternative stormwater
management systems designed in accordance with Rule .1008 of this Section;
(ii) control systems must be designed to control runoff from all surfaces generated by one inch of
rainfall.
History Note: Statutory Authority G.S. 143-214.1; 143-214.7,• 143-215.1; 143-215.3(a);
E, ff. September 1, 1995.
.1006 STORXIWATER REQUIREMENTS: HIGH QUALITY WATERS
All development activities which require a stormwater management permit under Rule .1003 of this Section
and are within one mile of and draining to waters classified as High Quality Waters (HQW) shall manage
stormwater runoff in accordance with the provisions outlined in this Rule. More stringent stormwater
management measures may be required on a case -by -case basis where it is determined that additional measures
are required to protect water quality and maintain existing and anticipated uses of these waters.
(1) All waters classified as WS-I or WS-11 (15A NCAC :B .0212 and .0214) and all waters located in
the coastal counties (Rule .1005 of this Section) are -excluded from the requirements of this Rule
since they already have requirements for stormwater management.
(2) Low Density Option: Development shall be permitted pursuant to Rule .1003(c)(1) of this Section
if the development has:
(a) built -upon area of 12 percent or less or proposes single family residential development on lots of
one acre or greater;
(b) stormwater runoff transported primarily by vegetated conveyances; conveyance system shall not
include a discrete stormwater collection system as defined in Rule .1002 of this Section:
(c) a 30 foot wide vegetative buffer.
(3) High Density Option: Higher density developments :hall be permitted pursuant to Rule .1003(c)(2)
of this Section if stormwater control systems meet the following criteria:
(a) control systems must be wet detention ponds or alternative stormwater management systems
designed in accordance with Rule .1008 of this Section;
(b) control systems must be designed to control runoff from all surfaces generated by one inch of
rainfall.
History Note: Statutory Authorin- G. S. 143-214.1; 143-214. ; ; 143-215.1; 143-215.3(a);
E, f . September 1, 1995,-
Amended EJf. December 1, 1995.
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EHNR - ENVIRONMENTAL MANAGEMENT TI5A: 02H .1000
.1007 STORMWATER REQUIREMEiNTS: OUTSTANDING RESOURCE WATERS
All development activities which require a stormwater management permit under Rule .1003 of this Section
and which drain to waters classified as Outstanding Resource Waters (ORW) shall manage stormwater runoff
in accordance with the provisions of this Rule. Water quality conditions shall clearly maintain and protect
91 the outstanding resource values of waters classified as Outstanding Resource Waters (ORW). Stormwater
management strategies to protect resource values of waters classified as ORW shall be developed on a site
specific basis during the proceedings to classify these waters as ORW. The requirements of this Rule serve
as the minimum conditions that must be met by development activities. More stringent stormwater
management measures may be required on a case -by -case basis where it is determined that additional measures
are required to protect water quality and maintain existing and anticipated uses of these waters.
(1) Freshwater ORWs: Development activities which require a stormwater management permit under
Rule .1003 of this Section and which drain to freshwaters classified as ORW shall manage
stormwater runoff as follows:
(a) Low Density Option: Development shall be permitted pursuant to Rule .1003(d)(1) of this Section
if the development has:
(i) built -upon area of 12 percent or less or proposes single family residential development on lots
of one acre or greater;
(ii) stormwater runoff transported primarily by vegetated conveyances; conveyance system shall not
include a discrete stormwater collection system as defined in Rule .1002 of this Section, and
(iii) a 30 foot wide vegetative buffer.
(b) High Density Option: Higher density developments shall be permitted pursuant to Rule .1003(d)(2)
of this Section if stormwater control systems meet the following criteria:
(i) control systems must be wet detention ponds or alternative stormwater management systems
designed in accordance with Rule .1008 of this Section; and
(ii) control systems must be designed to control runoff from all surfaces generated by one inch of
rainfall.
(2) Saltwater ORWs: Development activities which require a stormwater management permit under Rule
.1003 of this Section and which drain to saltwaters classified as ORW shall manage stormwater
runoff as follows: Cr
(a) Within 575 feet of the mean high water line of designated ORW areas, development activities shall
comply with the low density option as specified in Rule .1005(2)(a) of this Section.
(b) Projects draining to saltwaters classified as ORW that impact the Areas of Environmental Concern
(AEC). determined pursuant to G.S. 113A-113, shall delineate the ORW AEC on the project plans
and conform to low density requirements as specified in Rule .1005(2)(a) of this Section within the
ORW AEC.
(c) After the Commission has received a request to classify Class SA waters as ORW and given
permission to the Director to schedule a public hearing to consider reclassification and until such
time as specific stormwater design criteria become effective, only development which meets the
requirements of Rule .1003(d)(3)(A), (B) and (C) and Rule .1005(2)(a) of this Section shall be
approved within 575 feet of the mean high water line of these waters.
flistory Note: Stanrtory Authoritv G.S. 143-214.1; 143-214.7,- 143-215.1; 143-215.3(a);
Efj: September 1, 1995.
.1003 DESIGN OF STORiVIWATER AL4uNAGENIENT .NfEASURES
(a) Structural Stormwater Control Options. Stormwater control measures which may be approved pursuant
to this Rule and which shall not be considered innovative include:
(1) Stormwater infiltration systems including infiltration basins/ponds, swales, and vegetative filters:
(�) Wet detention ponds; and
(3) Devices approved in accordance with Paragraph (b) of this Rule.
All stormwater management structures are subject to the requirements of Paragraph (c) of.this Rule.
(b) Innovative Systems. Innovative measures for controlling stormwater which are not well established
through actual experience may be approved on a demonstration basis under the following conditions:
(1) There is a reasonable expectation that the control measures will be successful;
(2) The projects are not located near High Quality Waters (HQW):
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EHNR - ENVIRONMENTAL MANAGEMENT TI SA: 02H .1000
(3) Monitoring requirements are included to verify the performance of the control measures; and
(4) Alternatives are available if the control measures fail and shall be required when the Director
determines that the system has failed.
(c) General Engineering Design Criteria For All Projects.
(1) The size of the system must take into account the runoff at the ultimate built -out potential from all
surfaces draining to the system, including any off -site drainage. The storage volume of the system
shall be calculated to provide for the most conservative protection using runoff calculation methods
described on pages A.1 and A.2 in "Controlling Urban Runoff: A Practical Manual For Planning
And Designing Urban BMPs" which is hereby incorporated by reference not including
amendments. This document is available through the Metropolitan Washington (D.C.) Council of
Governments at a cost of forty dollars ($40.00). This method is also described in .the Division's
document "An Overview of Wet Detention Basin Design." Other engineering methods may be
approved if these methods are shown to provide for equivalent protection;
(2) All side slopes being stabilized with vegetative cover shall be no steeper than 3:1 (horizontal to
vertical);
(3) All stormwater management structures shall be located in recorded drainage easements for the
purposes of operation and maintenance and shall have recorded access easements to the nearest
public right-of-way. These easements shall be granted in favor of the party responsible for
operating and maintaining the stormwater management structures;
(4) Vegetative filters designed in accordance with Paragraph (f) of this Rule are required from the
overflow of all infiltration systems and discharge of all stormwater wet detention ponds. These
filters shall be at least 30 feet in length, except where a minimum length of 50 feet is required in
accordance with Rule .1005(2)(b)(iii) of this Section;
(5) Stormwater controls shall be designed in accordance with the provisions of this Section. Other
designs may be acceptable if these designs are shown by the applicant, to the satisfaction of the
Director, to provide equivalent protection;
(6) In accordance with the Antidegradation Policy as defined in 15A NCAC 2B .0201, additional
control measures may be required on a case -by -case basis to maintain and protect. for existing and
anticipated uses, waters with quality higher than the standards; and
(7) Stormwater control measures used for sedimentation and erosion control during the construction
phase must be cleaned out and returned to their designed state.
(d) Infiltration System Requirements. Infiltration systems may be designed to provide infiltration of the
entire design rainfall volume required for a site or a series of successive systems may be utilized. Infiltration
may also be used to pretreat runoff prior to disposal in a wet detention ponds. The following are general
requirements:
(1) Infiltration systems shall be a minimum of 30 feet from surface waters and 50 feet from Class SA
waters;
(2) Infiltration systems shall be a minimum distance of 100 feet from water supply wells:
(3) The bottom of infiltration systems shall be a minimum of two feet above the seasonal high water
table;
(4) Infiltration systems must be designed such that runoff in excess of the design volume by-passes the
system and does not flush pollutants through the system;
(5) Infiltration systems must be designed to complete!%- draw down the design storage volume to the
seasonal high water table under seasonal high water conditions within five days and a
hydrogeologic evaluation may be required to determine whether the system can draw dawn in five
days:
(6) Soils must have a minimum hydraulic conductivity of 0.52 inches per hour to be suitable for
infiltration;
(7) Infiltration systems must not be sited on or in fill material. unless approved on a case -by -case basis
under Paragraph (h) of this Rule;
(S) Infiltration systems may be required on a case -by -case basis to have an observation well to provide
ready inspection of the system;
(9) If runoff is directed to infiltration systems during construction of the project, the system must be
restored to design specifications after the project is complete and the entire drainage area is
stabilized.
NORTH CAROLINA ADMINISTRATITT CODE 12115195 Page 8

EHNR - ENVIRONMENTAL MANAGEMENT TISA: 02H .1000
(e) Wet Detention Pond Requirements. These practices may be used as a primary treatment device or as
a secondary device following an infiltration system. Wet detention ponds shall be designed for a specific
pollutant removal. Specific requirements for these systems are as follows:
(1) The design storage volume shall be above the permanent pool;
(2) The discharge rate from these systems following the one inch rainfall design storm shall be such
that the draw down to the permanent pool level occurs within five days, but not in less than two
days;
(3) The design permanent pool level mean depth shall be a minimum of three feet and shall be
designed with a surface area sufficient to remove 85 percent of total suspended solids. The design
for 85 percent total suspended solids removal shall be based on "Methodology for Analysis of
Detention Basins for Control of Urban Runoff Quality" which is hereby incorporated by reference
not including subsequent amendments. This document is available from the U.S. Environmental
Protection Agency (Document number EPA440/5-87-001) at no cost;
(4) The inlet structure must be designed to minimize turbulence using baffles or other appropriate
design features and shall be located in a manner that avoids short circuiting in the pond;
(5) Pretreatment of the runoff by the use of vegetative filters may be used to minimize sedimentation
and eutrophication of the detention pond;
(6) Wet detention ponds shall be designed with a forebay to enhance sedimentation at the inlet to the
pond;
(7) The basin side slopes for the storage volume above the permanent pool shall be stabilized with
vegetation down to the permanent pool level and shall be designed in accordance with
Subparagraph (c)(2) of this Rule;
(8) The pond shall be designed with side slopes no steeper than 3:1 (horizontal to vertical);
(9) The pond shall be designed to provide for a vegetative shelf around the perimeter of the basin.
This shelf shall be gently sloped (6:1 or flatter) and shall consist of native vegetation;
(10) The pond shall be designed to account for sufficient sediment storage to allow for the proper
operation of the facility between scheduled cleanout periods.
(f) Vegetative Filter Requirements. Vegetative filters shall be used as a non-structural method for providing
additional infiltration, filtering of pollutants and minimizing stormwater impacts. Requirements for these
filters are as follows:
(1) A distribution device such as a swale shall be used to provide even distribution of runoff across
the width of the vegetative filter;
(2) The slope and length of the vegetative filter shall be designed, constructed and maintained so as
to provide a non -erosive velocity of flow through the filter for the 10 year storm and shall have
a slope of five percent or less, where practicable: and
(3) Vegetation in the filter may be natural vegetation, grasses or artificially planted wetland vegetation
appropriate for the site characteristics.
(g) Curb Outlet Systems. Projects that meet the low density provisions of Rules .1005 through .1007 of
this Section may use curb and gutter with outlets to convey the stormwater to grassed swales or vegetated
areas prior to the runoff discharging to vegetative filters or wetlands. Requirements for these curb outlet
systems are as follows:
(1) The curb outlets shall be located such that the swale or vegetated area can carry the peak flow from
. the 10 year storm and the velocity of the flow shall be non -erosive;
(2) The longitudinal slope of the swale or vegetated area shall not exceed five percent, where
practicable;
(3) The side slopes of the swale or vegetated area shall be no steeper than 5:1 (horizontal to vertical).
Where this is not practical due to physical constraints, devices to slow the rate of runoff and
encourage infiltration to reduce pollutant delivery shall be provided:
(4) The minimum length of the swale or vegetated area shall be 100 feet; and
(5) In sensitive areas, practices such as check dams, rock or wooden, may be required to increase
detention time within the swale or vegetated area.
(h) Alternative Design Criteria. to addition to the control measures outlined in Paragraphs (b), (d), (e).
t t) and (g) of this Rule, stormwater management systems consisting of other control options or series of
control options may be approved by the Director on a case -by -case basis. This approval shall only be given
in cases where the applicant can demonstrate that the Alternative Design Criteria shall provide equal or better
.NORTH CAROLINA ADMINISTRATIVE CODE 12/1S19S Page 9

..aa.rn - ZAVIRONMENTAL MANAGEMENT TBA: 02H .1000
stormwater control, equal or better protection of waters of the state, and result in no increased potential for
nuisance conditions. The criteria for approval shall be that the stormwater management system shall provide
for 85 percent average annual removal of Total Suspended Solids and that the discharge rate from the system
meets one of the following:
(1) the discharge rate following the one -inch design storm shall be such that the runoff volume draws
down to the pre -storm design stage within five days, but not less than two days; or
(2) the post development discharge rate shall be no larger than predevelopment discharge rate for the
one year 24 hour storm.
(i) Operation and maintenance plans. Prior to approval of the development by the Division an operation
and maintenance plan or manual shall be provided by the developer for stormwater systems, indicating the
operation and maintenance actions that shall be taken, specific quantitative criteria used for determining when
those actions shall be taken, and who is responsible for those actions. The plan must clearly indicate the steps
that shall be taken and who shall be responsible for restoring a stormwater system to design specifications if
a failure occurs and must include an acknowledgment by the responsible party. Development must be
maintained consistent with the requirements in these plans and the original plans and any modifications to these
plans must be approved by the Division.
0) System Design. Stormwater systems must be designed by an individual who meets any North Carolina
occupational licensing requirements for the type of system proposed. Upon completion of construction, the
designer for the type of stormwater system installed must certify that the system was inspected during
construction, was constructed in substantial conformity with plats and specifications approved by the Division
and complies with the requirements of this Section prior to issuance of the certificate of occupancy.
History Note: Statutory Authority G.S. 143-214.1; 143-214.7; 143-215.1; 143-215.3(a);
Eff. September 1, 1995.
.1009 STAFF REVIEW AND PERMIT PREPARATION
(a) The staff of the permitting agency shall conduct a review of plans, specifications and other project data
accompanying the application and shall determine if the application and required information are complete.
The staff shall acknowledge receipt of a complete application.
(b) If the application is not complete with all required information, the application may be returned to the
applicant. The staff shall advise the applicant by mail:
(1) how the application or accompanying supporting information may be modified to make them
acceptable or complete; and
(2) that the 90 day processing period required in G.S. 143-215.1 begins upon receipt of corrected or
complete application with required supporting information.
(c) If an application is accepted and later found to be incomplete, the applicant shall be advised how the
application or accompanying supporting information may be modified to make them acceptable or complete.
and that if all required information is not submitted within 30 days that the project shall be returned as
incomplete.
History Now Statutory Authority G.S. 143-215.1; 143-21-.3(a);
Eff. September 1, 1995.
.1010 FINAL ACTION ON PERVIIT APPLICATIONS TO THE DIVISION
(a) The Director shall take final action on all applications not later than 90 days following receipt of a
complete application and with required information. All permits or renewals of permits and decisions denying
permits or renewals shall be in writing.
(b) The Director is authorized to:
(1) issue a permit containing such conditions as are necessary to effectuate the purposes of G.S. 143,
Article 21;
(2) issue permit containing time schedules for achieving compliance with applicable water quality
standards and other legally applicable requirements:
(3) deny a permit application where necessary to effectuate:
(A) the purposes of G.S. 143, Article 21;
(B) the purposes of G.S. 143-215.67(a);
.FORTH CAROLMA AD.IILVISTRATIVE CODE 12115195 Page 10

•
•
Criivn - ��v VJAWJYJ)2biVJAL MAMULA1ENT T15A: 02H .1000
(C) rules on coastal waste treatment, disposal, found in Section .0400 of this Subchapter;
(D) rules on "subsurface disposal systems," found in 15A NCAC 18A .1900. Copies of these Rules
are available from the Division of Environmental Health, P.O. Box 29535, Raleigh, North
Carolina 27626-0535; and
(E) rules on groundwater quality standards found in Subchapter 2L of this Chapter.
(4) hold public meetings when necessary to obtain additional information needed to complete the
review of the application. The application will be considered as incomplete until the close of the
meeting record.
(c) If a permit is denied, the letter of denial shall state the reason(s) for denial and any reasonable measures
which the applicant may take to make the application approvable.
(d) Permits shall be issued or renewed for a period of time deemed reasonable by the Director.
History Note: Statutory Authority G.S. 143-215.1; 143-215.3(a);
Eff. September 1, 1995.
.1011 MODIFICATION AND REVOCATION OF PER_tiIITS
Any permit issued by the Division pursuant to these Rules is subject to revocation, or modification upon 60
days notice by the Director in whole .or part for good cause including but not limited to:
(1) violation of any terms or conditions of the permit;
(2) obtaining a permit by misrepresentation or failure to disclose fully all relevant facts;
(3) refusal of the permittee to allow authorized employees of the Department of Environment, Health,
and Natural Resources upon presentation of credentials:
(a) to enter upon permittee's premises on which a system is located in which any records are required
to be kept under terms and conditions of the permit;
(b) to have access to any copy and records required to be kept under terms and conditions of the
permit;
(c) to inspect any monitoring equipment or method required in the permit; or
(d) to sample any discharge of pollutants;
(4) failure to pay the annual fee for administering and compliance monitoring.
History Note: Statutory Authority G.S. 143-215.1; 143-215.3(a);
Eff. September 1, 1995.
.1012 DELEGATION OF AUTHORITY
For permits issued by the Division, the Director is authorized
contained in these Rules except the following:
(1) denial of a permit application;
(2) revocation of a permit not requested by the permittee; or
(3) modification of a permit not requested by the perminee.
History Note: Statutory Authority G.S. 143-215.3(a);
Eff. September 1, 1995.
to delegate any or all of the functions
.1013 GENERAL PERMITS
(a) In accordance with the provisions of G.S. 143.215.1(b)(3) and (4), general permits may be developed
by the Division and issued by the Director for categories of activities covered in this Section. All activities
in the State that received a "Certificate of Coverage" for that category from the Division shall be deemed
covered under that general permit. Each of the general permits shall be issued individually under G.S.
143-215.1. using all procedural requirements specified for state permits including. application and public
notice. Activities covered under general permits, developed in accordance with this Rule, shall be subject to
the same standards and limits, management practices, enforcement authorities, and rights and privileges as
specified in the general permit. Procedural requirements for application and permit approval, unless
specifically designated as applicable to individuals proposed to be covered under the general permits, apply
only to the issuance of the general permits. After issuance of the general permit by the Director, activities
in the applicable categories may request coverage under the general permit, and the Director or his designee
NORTH CAROLLVA ADMINISTRATIVE CODE 12115195 Page 11

EHiVR - ENVIRONMENTAL MANAGEMENT TI SA: 02H .1000
•
shall grant appropriate certification. General permits may be written to regulate categories of other activities
that all:- involve the same or substantially similar operations; have similar characteristics; require the same
limitations or operating conditions; require the same or similar monitoring; and in the opinion of the Director
are more appropriately controlled by a general permit.
(b) No provision in any general permit issued under this Rule shall be interpreted to allow the permittee
to violate state water quality standards or other applicable envirottmental standards.
(c) For a general permit to apply to an activity, a Notice of Intent to be covered by the general permit must
be submitted to the -Division using forms provided by the Division and, as appropriate, following the
application procedures specified in this Section. If all requirements are met, coverage under the general
permit may be granted. If all requirements are not met, a long form application and full application review
procedure shall be required.
(d) General permits may be modified and reissued by the Division as necessary. Activities covered by
general permits need not submit new Notices of Intent or renewal requests unless so directed by the Division.
If the Division chooses not to renew a general permit, all facilities covered under that general permit shall be
notified to submit applications for individual permits.
(e) All previous state water quality permits issued to a facility which can be covered by a general permit,
whether for construction or operation, are revoked upon request of the permittee, termination of the individual
permit and issuance of the Certification of Coverage.
(f) Anyone engaged in activities covered by the general permit rules but not permitted in accordance with
this Section shall be considered in violation in G.S. 143-215.1.
(g) Any individual covered or considering coverage under a general permit may choose to pursue an
individual permit for any activity covered by this Section.
(h) The Director may require any person, otherwise eligible for coverage under a general permit, to apply
for an individual permit by notifying that person that an application is required. Notification shall consist of
a written description of the reason(s) for the decision, appropriate permit application forms and application
instructions, a statement establishing the required date for submission of the application. and a statement
informing the person that coverage by the general permit shall automatically terminate upon issuance of the
individual permit. Reasons for requiring application for an individual permit may be:
(1) the activity is a significant contributor of pollutants:
(2) conditions at the permitted site change, altering the constituents or characteristics of the site such
that the activity no longer qualifies for coverage under a general permit;
(3) noncompliance with the general permit;
(4) noncompliance with Commission Rules:
(5) a change has occurred in the availability of demonstrated technology or practic--s for the control
or abatement of pollutants applicable to the activity: or
(6) a determination that the water of the stream receiving stormwater runoff from the site is not
meeting applicable water quality standards.
6) Anv interested person may petition the Director to take an action under Paragraph (h) of this Rule to
require an individual permit.
,j) General permits may be modified, terminated, or revoked and reissued in accordance v6th the authority
and requirements of Rules .1010 and .1011 of this Section.
Histon• iVote• Statutory Authoring G.S. 143-215.1: 143-21=.3(a);
EJ}: September 1, 1995.
500 copies of this public document were printed at a cost of $ 144.00 or
$.29 per copy.
NORTH CAROLINA ADMINISTRATIVE CODE 12/IS/95 Page 12

Is
OFFICE USE ONLY
Date Received
Fee Paid
Permit Number
State of North Carolina
Department of Environment and Natural Resources
Division of Water Quality
STORMWATER MANAGEMENT PERMIT APPLICATION FORM
This form may be photocopied for use as an original
I. GENERAL INFORMATION
1. Applicants name (specify the name of the corporation, individual, etc. who owns the project):
2. Print Owner/Signing Official's name and title (person legally responsible for facility and compliance):
3. Mailing Address for person listed in item 2 above:
City: State: Zip:
Telephone Number: ( 1
4. Project Name (subdivision, facility, or establishment name - should be consistent with project name on
plans, specifications, letters, operation and maintenance agreements, etc.):
5. Location of Project (street address):
City: County:
6. Directions to project (from nearest major intersection):
7. Latitude: Longitude: of project
8. Contact person who can answer questions about the project:
Name: Telephone Number. (
II. PERMIT INFORMATION:
1. Specify whether project is (check one): New Renewal Modification
Form SWU-101 Version 3.99 Page 1 of 4

2. If this application is being submitted as the result of a renewal or modification to an existing permit, list the
existing permit number and its issue date (if known)
3. Specify the type of project (check one):
Low Density High Density Redevelop General Permit Other
4. Additional Project Requirements (check applicable blanks):
_CAMA Major _Sedimentation/Erosion Control _404/401 Permit _NPDES Stormwater
Information on required state permits can be obtained by contacting the Customer Service Center at
1-877-623-6748.
III. PROJECT INFORMATION
1. In the space provided below, summarize how stormwater will be treated. Also attach a detailed narrative
(one to two pages) describing stormwater management for the project.
2. Stormwater runoff from this project drains to the
3. Total Project Area: acres 4. Project Built Upon Area:
5. How many drainage areas does the project have?
River basin.
6. Complete the following information for each drainage area. If there are more than two drainage areas in the
project, attach an additional sheet with the information for each area provided in the same format as below.
Basin:Infozmatson t . � x i3rauiage:Area1: " " yam, "`, Drauzage�,e��
Receiving Stream Name
Receiving Stream Class
Drainage Area
Existing Impervious* Area
Proposed Im ervious*Area
% Impervious* Area (total)
�rvious Surface�.Q� \< . .aY t..., m. ` : tt " ?.:. 4 i u#i► k L
On -site Buildings
On -site Streets
On -site Parking
On -site Sidewalks
Other on -site
Off -site
Total: Total:
* Impervious area is defined as the built upon area including, but not limited to, buildings, roads, parking areas,
sidewalks, gravel areas, etc. 0
Form SWU-101 Version 3.99 Page 2 of 4

How was the off -site impervious area listed above derived?
•
•
IV. DEED RESTRICTIONS AND PROTECTIVE COVENANTS
The following italicized deed restrictions and protective covenants are required to be recorded for all
subdivisions, outparcels and future development prior to the sale of any lot. If lot sizes vary significantly, a
table listing each lot number, size and the allowable built -upon area for each lot must be provided as an
attachment.
1. The following covenants are intended to ensure ongoing compliance with state stormwater management permit
number as issued by the Division of Water Quality. These covenants may
not be changed or deleted without the consent of the State.
2. No more than square feet of any lot shall be covered by structures or impervious materials.
Impervious materials include asphalt, gravel, concrete, brick, stone, slate or similar material but do not include wood
decking or the water surface of swimming pools.
3. Swales shall not be filled in, piped, or altered except as necessary to provide driveway crossings.
4. Built -upon area in excess of the permitted amount requires a state stormwater management permit modification prior to
construction.
5. All permitted runoff from outparcels or future development shall be directed into the permitted stormwater control
system. These connections to the stormwater control system shall be performed in a manner that maintains the
integrity and performance of the system as permitted.
By your signature below, you certify that the recorded deed restrictions and protective covenants for this project
shall include all the applicable items required above, that the covenants will be binding on all parties and
persons claiming under them, that they will run with the land, that the required covenants cannot be changed or
deleted without concurrence from the State, and that they will be recorded prior to the sale of any lot.
V. SUPPLEMENT FORMS
The applicable state stormwater management permit supplement form(s) listed below must be submitted for
each BMP specified for this project. Contact the Stormwater and General Permits Unit at [phone] for the
status and availability of these forms.
Form SWU-102
Wet Detention Basin Supplement
Form SWU-103
Infiltration Basin Supplement
Form SWU-104
Low Density Supplement
Form SWU-105
Curb Outlet System Supplement
Form SWU-106
Off -Site System Supplement
Form SWU-107
Underground Infiltration Trench Supplement
Form SWU-108
Neuse River Basin Supplement
Form SWU-109
Innovative Best Management Practice Supplement
Form SWU-101 Version 3.99
Page 3 of 4

VI. SUBMITTAL REQUIREMENTS
Only complete application packages will be accepted and reviewed by the Division of Water Quality (DWQ).
A complete package includes all of the items listed below. The complete application package should be
submitted to the appropriate DWQ Regional Office.
1. Please indicate that you have provided the following required information by initialing in the space
provided next to each item.
Initials
• Original and one copy of the Stonmwater Management Permit Application Form
• One copy of the applicable Supplement Form(s) for each BMP
• Permit application processing fee of $420 (payable to NCDENR)
• Detailed narrative description of stormwater treatment/management
• Two copies of plans and specifications, including:
- Development/Project name
- Engineer and firm
-Legend
- North arrow
- Scale
- Revision number & date
- Mean high water line
- Dimensioned property/project boundary
- Location map with named streets or NCSR numbers
- Original contours, proposed contours, spot elevations, finished floor elevations
- Details of roads, drainage features, collection systems, and stormwater control measures
- Wetlands delineated, or a note on plans that none exist
- Existing drainage (including off -site), drainage easements, pipe sizes, runoff calculations
- Drainage areas delineated
- Vegetated buffers (where required)
VII. AGENT AUTHORIZATION
If you wish to designate authority to another individual or firm so that they may provide information on your
behalf, please complete this section.
Designated agent (individual or firm):
Mailing Address:
City: State: Zip:
Phone: i ) Fax: ( )
VIIL APPLICANT'S CERTIFICATION
I, (print or type name of person listed in General Information, item 2)
certify that the information included on this permit application form is, to the best of my knowledge, correct and
that the project will be constructed in conformance with the approved plans, that the required deed restrictions
and protective covenants will be recorded, and that the proposed project complies with the requirements of 15A
NCAC 2H .1000.
Signature:
Date:
Form SWU-101 Version 3.99 Page 4 of 4

Permit No.
(to be provided by DWQ)
State of North Carolina
Department of Environment and Natural Resources
Division of Water Quality
STORMWATER MANAGEMENT PERMIT APPLICATION FORM
LOW DENSITY SUPPLEMENT
This form may be photocopied for use as an original
A low density project is one that meets the appropriate criteria for built upon area and transports stormwater
runoff primarily through vegetated conveyances. Low density projects should not have a discrete stormwater
collection system as defined by 15A NCAC 2H .1002(18). Low density requirements and density factors can
be found in 15A NCAC 2H .1005 through .1007.
I. PROJECT INFORMATION
Project Name :
Contact Person: Phone Number: ( )
Number of Lots: Allowable Built Upon Area Per Lot*:
*If lot sizes are not uniform, attach a table indicating the number of lots, lot sizes and allowable built upon
area for each lot. The attachment must include the project name, phase, page numbers and provide area
subtotals and totals.
H. BUILT UPON AREA
See the Stormwater Management Permit Application for specific language that must be recorded in the deed
restrictions for all subdivisions.
For uniform lot sizes, complete the following calculation in the space provided below where:
• SA Site Area - the total project area above Mean High Water. Wetlands may be excluded when the
development results in high density pockets.
• DF Density Factor - the appropriate percent built upon area divided by 100.
• RA Road Area - the total impervious surface occupied by roadways.
• OA Other Area - the total area of impervious surfaces such as clubhouses, tennis courts, sidewalks, etc.
• No. Lots - the total number of lots in the subdivision.
• BUA/Lot - the computed allowable built upon area for each lot including driveways and impervious
surfaces located between the front lot line and the edge of pavement.
•
Form SWU-104 Rev 3.99 Page 1 of 2

(SA x DF) - RA - OA = BUA
No. Lots Lot
Calculation: .
III. REQUIRED ITEMS CHECKLIST
Initial in the space provided to indicate that the following requirements have been met and supportinf
documentation is provided as necessary. If the applicant has designated an agent on the Stormwater
Management Permit Application Form, the agent may initial below.
Applicants Initials
a. A 30 foot vegetative buffer is provided adjacent to surface waters. Projects in the Neuse
River basin may require additional buffers.
b. Deed restriction language as required on form SWU-101 shall be recorded as a restrictive
covenant. A copy of the recorded document shall be provided to DWQ within 30 days of
platting and prior to sale of any lots.
c. Built upon area calculations are provided for the overall project and all lots.
d. Project conforms to low density requirements within the ORW AEC (if applicable).
[15A NCAC 2H .1007(2)(b)]
•
Form SWU-104 Rev 3.99 Page 2 of 2

Permit No.
(to be provided by DWQ)
State of North Carolina
Department of Environment and Natural Resources
Division of Water Quality
STORMWATER MANAGEMENT PERMIT APPLICATION FORM
INFILTRATION BASIN SUPPLEMENT
This form may be photocopied for use as an original
DMZ Stormwater Management Plan Review:
A complete stormwater management plan submittal includes a stormwater management permit application, an
infiltration basin supplement for each system, design calculations, soils report and plans and specifications
showing all stormwater conveyances and system details.
I. PROJECT INFORMATION
Project Name:
Contact Person: Phone Number: ( 1
This worksheet applies to: Basin No. in Drainage Area
(as identified on plans) (from Form SWU-101)
II. DESIGN INFORMATION - Attach supporting calculations/documentation. The soils report must be
based upon an actual field investigation and soil borings. County soil maps are not an acceptable
source of soils information. All elevations shall be in feet mean sea level (fmsl).
Soils Report Summary
Soil Type
Infiltration Rate in/hr or cf/hr/sf (circle appropriate units)
SHWT Elevation fmsl (Seasonal High Water Table elevation)
Basin Design Parameters
Design Storm inch (1.5 inch event for SA waters, I inch event for others)
Design Volume c.f.
Drawdown Time days
Basin Dimensions
Basin Size
Basin Volume Provided
Basin Elevations
Bottom Elevation
Storage Elevation
Top Elevation
ft. x
c.f.
fmsl
fmsl
fmsl
ft. = sq. ft. (bottom dimensions)
Form SWU-103 Rev 3.99 Page I of 3

III. REQUIRED ITEMS CHECKLIST
The following checklist outlines design requirements per the Stormwater Best Management Practices Manual
(N.C. Department of Environment, Health and Natural Resources, February 1999) and Administrative Code
Section: 15 A NCAC 2H .1008. 0
Initial in the space provided to indicate that the following design requirements have been met and supporting
documentation is attached. If the applicant has designated an agent in the Stormwater Management Permit
Application Form, the agent may initial below. Attach justification if a requirement has not been met.
Applicants Initials
a. System is located 50 feet from class SA waters and 30 feet from other surface waters.
b. System is located at least 100 feet from water supply wells.
C. Bottom of system is at least 2 feet above the seasonal high water table.
d. Bottom of the system is 3 feet above any bedrock or impervious soil horizon.
System is not sited on or in fill material or DWQ approval has been obtained.
System is located in a recorded drainage easement for the purposes of operation and
maintenance and has recorded access easements to the nearest public right-of-way.
Drainage area for the device is less than 5 acres.
Soils have a minimum hydraulic conductivity of 0.52 inches per hour and soils report is
attached.
System captures and infiltrates the runoff from the first 1.0 inch of rainfall (1.5 inch event
for areas draining to SA waters ). Design volume and infiltration calculations attached.
System is sized to take into account the runoff at the ultimate built -out potential from all
surfaces draining to the system, including any off -site drainage. Calculations attached.
All side slopes stabilized with vegetated cover are no steeper than 3:1 (H:V).
A pretreatment device such as a catch basin, grease trap, filter strip, grassed swale or
sediment trap is provided.
in. Bottom of the device is covered with a layer of clean sand to an average depth of 4 inches
or dense vegetative cover is provided.
n. Vegetated filter is provided for overflow and detail is shown on plans (Required minimum
length is 50 feet for SA waters, 30 feet for other waters).
o. Flow distribution mechanism within the basin is provided.
p. A benchmark is provided to determine the sediment accumulation in the pretreatment
device.
q. Runoff in excess of the design volume bypasses off-line systems (bypass detail provided).
r. System is designed to draw down the design storage volume to the proposed bottom
elevation under seasonal high water conditions within five days. A soils report and all
pertinent draw -down calculations are attached.
s. Plans ensure that the installed system will meet design specifications (constructed or
restored) upon initial operation once the project is complete and the entire drainage area*
stabilized.
Form SWU-103 Rev 3.99 Page 2 of 3

IV. INFILTRATION BASIN OPERATION AND MAINTENANCE AGREEIMENT
1. After every runoff producing rainfall event and at least monthly inspect the infiltration system for erosion,
trash accumulation, vegetative cover, and general condition.
is2. Repair eroded areas immediately, re -seed as necessary to maintain adequate vegetative cover, mow
vegetated cover to maintain a maximum height of six inches, and remove trash as needed.
3. After every runoff producing rainfall event and at least monthly inspect the bypass, inflow and overflow
structures for blockage and deterioration. Remove any blockage and repair the structure to approved
design specifications.
4. Remove accumulated sediment from the pretreatment system and infiltration basin annually or when
depth in the pretreatment unit is reduced to 75% of the original design depth. The system shall be restored
to the original design depth without over -excavating. Over -excavating may cause the required water
table separation to be reduced and may compromise the ability of the system to perform as designed.
Removed sediment shall be disposed of in an appropriate manner and shall not be handled in a manner
that will adversely impact water quality (i.e. stockpiling near a stormwater treatment device or stream,
etc.).
A benchmark shall be established in the pretreatment unit. The benchmark will document the original
design depth so that accurate sediment accumulation readings can be taken. The measuring device used
to determine the depth at the benchmark shall be such that it will give an accurate depth reading and not
readily penetrate into accumulated sediments.
When the design depth reads feet in the pretreatment unit, the sediment shall be
removed from both the pretreatment unit and the infiltration basin.
5. If the Division determines that the system is failing, the system will immediately be repaired to original
design specifications. If the system cannot be repaired to perform its design function, other stormwater
control devices as allowed by NCAC 2H .1000 must be designed, approved and constructed.
I acknowledge and agree by my signature below that I am responsible for the performance of the five
maintenance procedures listed above. I agree to notify DWQ of any problems with the system or prior to any
changes to the system or responsible party.
Print Name and Title:
Address:
Phone: Date:
Signature:
Note: The legally responsible party should not be a homeowners association unless more than 50% of the lots have been sold and
a resident of the subdivision has been named the president.
I, , a Notary Public for the State of , County of
, do hereby certify that
personally appeared before me this _
day of , and acknowledge the due execution of the forgoing infiltration basin maintenance
requirements. Witness my hand and official seal,
SEAL My commission expires
Form SWU-103 Rev 3.99 Page 3 of 3

Permit No.
(to be provided by DWQ)
State of North Carolina
Department of Environment and Natural Resources
Division of Water Quality
STORMWATER MANAGEMENT PERMIT APPLICATION FORM
WET DETENTION BASIN SUPPLEMENT
This form may be photocopied for use as an original
DWQ Stormwater Management Plan Review:
A complete stormwater management plan submittal includes an application form, a wet detention basin
supplement for each basin, design calculations, and plans and specifications showing all basin and outlet
structure details.
I. PROJECT INFORMATION
Project Name:
Contact Person:
Phone Number: S 1
For projects with multiple basins, specify which basin this worksheet applies to:
elevations
Basin Bottom Elevation ft.
Permanent Pool Elevation ft.
Temporary Pool Elevation ft.
(floor of the basin)
(elevation of the orifice)
(elevation of the discharge structure overflow)
areas
Permanent Pool Surface Area sq. ft. (water surface area at the orifice elevation)
Drainage Area ac.
Impervious Area ac.
volumes
Permanent Pool Volume cu. ft.
Temporary Pool Volume cu. ft.
Forebay Volume cu. ft.
Other parameters
SA/DA1
Diameter of Orifice in.
Design Rainfall in.
Design TSS Removal 2 %
(on -site and off -site drainage to the basin)
(on -site and off -site drainage to the basin)
(combined volume of main basin and forebay)
(volume detained above the permanent pool)
(approximately 20% of total volume)
(surface area to drainage area ratio from DWQ table)
(2 to 5 day temporary pool draw -down required)
(minimum 85% required)
Form SWU-102 Rev 3.99 Pagel of 4

Footnotes:
When using the Division SA/DA tables, the correct SA/DA ratio for permanent pool sizing should be computed based upon the
actual impervious % and permanent pool depth. Linear interpolation should be employed to determine the correct value for non-
standard table entries.
2 In the 20 coastal counties, the requirement for a vegetative filter may be waived if the wet detention basin is designed to provi
90% TSS removal. The NCDENR BMP manual provides design tables for both 85% TSS removal and 90% TSS removal.
II. REQUIRED ITEMS CHECKLIST
The following checklist outlines design requirements per the Stormwater Best Management Practices Manual
(N.C. Department of Environment, Health and Natural Resources, February 1999) and Administrative Code
Section: 15 A NCAC 2H .1008.
Initial in the space provided to indicate the following design requirements have been met and supporting
documentation is attached. If the applicant has designated an agent in the Stormwater Management Permit
Application Form, the agent may initial below. If a requirement has not been met, attach justification.
Applicants Initials
a. The permanent pool depth is between 3 and 6 feet (required minimum of 3 feet).
b. The forebay volume is approximately equal to 20% of the basin volume.
c. The temporary pool controls runoff from the design storm event.
d. The temporary pool draws down in 2 to 5 days.
e. If required, a 30-foot vegetative filter is provided at the outlet (include non -erosive flow
calculations) 0
f. The basin length to width ratio is greater than 3:1.
g. The basin side slopes above the permanent pool are no steeper than 3:1.
h. A submerged and vegetated perimeter shelf with a slope of 6:1 or less (show detail).
i. Vegetative cover above the permanent pool elevation is specified.
j. A trash rack or similar device is provided for both the overflow and orifice.
k. A recorded drainage easement is provided for each basin including access to nearest right-
of-way.
1. If the basin is used for sediment and erosion control during construction, clean out of the
basin is specified prior to use as a wet detention basin.
m. A mechanism is specified which will drain the basin for maintenance or an emergency.
III. WET DETENTION BASIN OPERATION AND MAINTENANCE AGREEMENT
The wet detention basin system is defined as the wet detention basin, pretreatment including forebays and the
vegetated filter if one is provided.
This system (check one) 0 does 0 does not incorporate a vegetated filter at the outlet.
This system (check one) 0 does 0 does not incorporate pretreatment other than a forebay.
Form SWU-102 Rev 3.99 Page 2 of 4

Maintenance activities shall be performed as follows:
1. After every significant runoff producing rainfall event and at least monthly:
a. Inspect the wet detention basin system for sediment accumulation, erosion, trash accumulation,
vegetated cover, and general condition.
b. Check and clear the orifice of any obstructions such that drawdown of the temporary pool occurs
within 2 to 5 days as designed.
2. Repair eroded areas immediately, re -seed as necessary to maintain good vegetative cover, mow vegetative
cover to maintain a maximum height of six inches, and remove trash as needed.
3. Inspect and repair the collection system (i.e. catch basins, piping, swales, riprap, etc.) quarterly to
maintain proper functioning.
4. Remove accumulated sediment from the wet detention basin system semi-annually or when depth is
reduced to 75% of the original design depth (see diagram below). Removed sediment shall be disposed
of in an appropriate manner and shall be handled in a manner that will not adversely impact water quality
(i.e. stockpiling near a wet detention basin or stream, etc.).
The measuring device used to determine the sediment elevation shall be such that it will give an accurate
depth reading and not readily penetrate into accumulated sediments.
When the permanent pool depth reads
When the permanent pool depth reads
Sediment Rerhoval El.
Bottom Ele'yation
FOREBAY
feet in the main pond, the sediment shall be removed.
feet in the forebay, the sediment shall be removed.
BASIN DIAGRAM
(fill in the blanks)
Permanent Pool Elevation
Sediment Removal Elevation 6 75%
Bottom Elevation ♦ 25%
MAIN POND
5. Remove cattails and other indigenous wetland plants when they cover 50% of the basin surface. These
plants shall be encouraged to grow along the vegetated shelf and forebay berm.
6. If the basin must be drained for an emergency or to perform maintenance, the flushing of sediment
0 through the emergency drain shall be minimized to the maximum extent practical.
Form SWU-102 Rev 3.99 Page 3 of 4

7. All components of the wet detention basin system shall be maintained in good working order.
I acknowledge and agree by my signature below that I am responsible for the performance of the seven
maintenance procedures listed above. I agree to notify DWQ of any problems with the system or prior to a*
changes to the system or responsible party.
Print name:
Title:
Address:
Phone:
Signature:
Date:
Note: The legally responsible party should not be a homeowners association unless more than 50% of the lots have been sold and
a resident of the subdivision has been named the president.
I, , a Notary Public for the State of ,
County of , do hereby certify that
personally appeared before me this day of , and acknowledge the due
execution of the forgoing wet detention basin maintenance requirements. Witness my hand and official seal,
SEAL
My commission expires
•
Form SWU-102 Rev 3.99 Page 4 of 4

Appendices
i
8.03
Estimating peak rate of runoff, volume of runoff, and soil loss are basic to the
design of erosion and sedimentation control facilities.
There are many methods of determining runoff. Two acceptable methods, the
rational method and the Soil Conservation Service (SCS) peak discharge
method, are described in this section.
The rational method is very simple in concept but relies on considerable
judgment and experience to evaluate all factors properly. It is used primarily for
small drainage areas (less than 50 acres). The SCS method is more sophisticated
hydrologically and offers a more accurate approximation of runoff, particularly
for areas larger than 20 acres. Choice of method for small areas depends
primarily on the experience of the designer.
Rational Method
The rational formula. is:
Q = CiA
where:
Q = peak rate of runoff in cubic feet per second (cfs).
C = runoff coefficient, an empirical coefficient representing the
relationship between rainfall rate and runoff rate.
i = average intensity of rainfall in inches/hour, for a storm duration
equal to the time of concentration, TC.
TC= time of concentration, in minutes; the estimated time for runoff
to flow from the most remote part of the watershed to the point
under consideration. It consists of the total time for overland
sheet flow and concentrated flow (channel and/or pipe flow).
A = drainage area in acres.
The general procedure for determining peak discharge using the rational
formula is presented below and illustrated in Sample Problem 8.03a.
Step 1. Determine the drainage area in acres.
Step 2. Determine the runoff coefficient, C, for the.type of soil/cover in the
drainage area (Table 8.03a).
If the land use and soil cover is homogenous over the drainage area, a C value
can be determined directly from Table 8.03a. If there are multiple soil cover
conditions, a weighted average must be calculated, or the area may be
subdivided
Step 3. Determine the time of concentration, Tp, for the drainage area (i.e., the
time of flow from the most remote point in the basin to the design point, in
minutes).
8.03.1

0
Table 8.03a
Value of Runoff Coefficient
(C) for Rational Formula
Land Use
C
Land Use
C
Business:
Lawns:
Downtown areas
0.70-0.95
Sandy soil, flat, 2%
0.05-0.10
Neighborhood areas
0.50-0.70
Sandy soil, ave., 2-7%
0.10-0.15
Sandy soil, steep, 70/6
0.15-0.20
Residential:
Heavy soil, flat, 2%
0.13-0.17
Single-family areas
0.30-0.50
Heavy soil, ave., 2-7%
0.18-0.22
Multi units, detached
0.40-0.60
Heavy soil, steep, 7%
0.25-0.35
Mufti units, attached
0.60-0.75
Suburban
0.25-0.40
Agricultural land:
Bare packed soil
Industrial:
Smooth
0.30-0.60
Light areas
0.50-0.80
Rough
0.20-0.50
Heavy areas
0.60-0.90
Cultivated rows
Heavy soil no crop
0.30-0.60
Parks, cemeteries
0.10-0.25
Heavy soil with crop
0.20-0.50
Sandy soil no crop
0.20-0.40
Playgrounds
0.20-0.35
Sandy soil with crop
0.10-0.25
Pasture
Railroad yard areas
0.20-0.40
Heavy soil
0.15-0.45
Sandy soil
0.05-0.25
Unimproved areas
0.10-0.30
Woodlands
0.05-0.25
Streets:
Asphalt
0.70-0.95
Concrete
0.80-0.95
Brick
0.70-0.85
Drives and walks
0.75-0.85
Roofs
0.75-0.85
NOTE: The designer must use judgment to select the appropriate C value
within the range for the appropriate
land use. Generally, larger areas with
permeable soils, flat slopes, and dense vegetation should have lowest C
values. Smaller areas with slowly
permeable soils, steep slopes,
and
sparse vegetation should be assigned highest C values.
Source: American Society of Civil Engineers
The overland flow portion of flow time may be determined from Figure 8.03a.
The flow time (in minutes) in the channel can be estimated by calculating the
average velocity in feet per minute and dividing the length (in feet) by the
average velocity.
Step 4. Determine the rainfall intensity, frequency, and duration (Figures 8.03b
through 8.03g—source: North Carolina State Highway Commission; Jan.
1973). Select the chart for the locality closest to your location. Enter the
"duration" axis of the chart with the calculated time of concentration, To. Move
vertically until you intersect the curve of the appropriate design storm, then
move horizontally to read the rainfall intensity factor, i, in inches per hour.
Step 5. Determine peak discharge, 0 (fO/sec), by multiplying the previously
determined factors using the rational formula (Sample Problem 8.03a).
4
4
8.03.2

Appendices
Sample Problem 8.03a
Determination of peak runoff
rate using the rational
method.
160
0-CIA
Given:
Drainage area:
20 acres
Graded areas:
12 acres
Woodland:
8 acres
Maximum slope length:
400 ft
Average slope:
3%, area bare
Location:
Raleigh, NC
Find:
Peak runoff rate from 10-yr frequency storm
Solution:
(1) Drainage area: 20 acres (given)
(2) Determine runoff coefficient, C.
Calculate Weighted Average
Area
Graded' 12 x
Woodland —A x
20
C from Table 8.03a
0.45 5.4
0.15 = -12
6.6
C = 6.6/20 = 0.33
(3) Find the time of concentration, Tc, from Figure 8.03a using maximum
length of travel = 400 ft and height of most -remote point above outlet
.400 ft x 3% =12 ft; assume overland flow on bare earth.
TC = 3.2 minutes.
NOTE: Any time of flow in channel should be added to the overland flow
to determine Tc.
(4)Determine the rainfall intensity factor, i.
i = 8.0 inches/hr (from Figure 8.03e) using 5-minute duration
(5)Q = C(i)(A)
Q = 0.33(8.0)(20) = 52.8 cfs; use 53 cis
'For graded areas use C value range for smooth, bare packed soil
(fable 8.03a).
8.033

w
aD
0
m
0
.fl
co
c
0
0.
m
0
E
am
0
E
0
L
QI
•
H (ft)
500 Tc(min)
.— 200
m
ca
b
0
M
rn
c
m
E
E
I Note:
Use nomograph Tc for natural basins with well-defined channels, for overland
flow on bar&garth, and for mowed -grass roadside channels.
i
For overland flow, grassed surfaces, multiply Tc by 2.
i
i For overland flow, concrete or asphalt surfaces, multiply Tc by 0.4.
For concrete channels, multiply Tc by 0.2.
Figure 8.03a Time of concentration of small drainage basins.
100
50
10
5
1
ii
8.03.4

Appendices
--
20
15
10
8
6
0
L
m
4
L
U
C
2
N
C
N
1
0.8
f°
0.6
c
a
0.4
0.2
0.1
�_��;�
�����■�rir•rirr•��riri■ri
mm
ONE
mm
Emm
.
■■II�►c.\�
■■■■■
■�I
■
Minutes Hours
Duration
Figure 8.03b Rainfall intensity duration curves -Wilmington.
20
15
10
8
6
0
L
4
N
-
d
.0
U
c
2
m
c
0.8
CO
0.6
c
m
0.4
c
4.2
01
5 10 20 40 60 2 3 4 6 8 12 18 24
Minutes Hours
_.� Duration
0iFigure 8.03c Rainfall intensity duration curves —Hatteras.
8.035

0
0
SCS Peak Discharge Method
The peak discharge method of calculating runoff was developed by the USDA
Soil Conservation Service and is contained in SCS Technical Release No. 55
(TR-55) entitled Urban Hydrology for Small Watersheds. This method of runoff
calculation yields a total runoff volume as well as a peak discharge. Use of the
SCS method is illustrated in Sample Problem 8.03b and in Chapter 7, Sample
Erosion and Sedimentation Control Plan.
r
Step 1. Measure the drainage area (in acres); the hydraulic length (distance
from most remote point to design point, in feet); and the average slope (percent)
of the watershed.
Step 2. Calculate a curve number, CN, for the drainage area.
The curve number, CN, is an empirical value, which establishes a relationship
between. rainfall and runoff based upon characteristics of the drainage area.
Table 8.03b contains CN values for different land uses, cover conditions, and
hydrologic soil groups. Hydrologic group assignments for most common soils
in North Carolina are given in Appendix 8.01. If the soil name is not known,
judge the soils based on the group description below:
• Soil Group A Represents soil having a low runoff potential due to high
infiltration rates. These soils consistprimarily of deep, well -drained sands
and gravels.
• Soil Group B—Represents soils having a moderately low runoff poten-
tial due to moderate infiltration rates. These soils consist primarily of
moderately deep to deep, moderately well -drained to well -drained soils
with moderately fine to moderately coarse textures.
• Soil Group C—Represents soils having a moderately high runoff poten-
tial due to slow infiltration rates. These soils consist primarily of soils in
which a layer exists near the surface that impedes the downward move-
ment of water, or soils with moderately fine tofine texture.
Soil Group D—Represents soils having a high runoff potential due to
very slow infiltration rates. These soils consist primarily of soils with high
water tables, soils with a claypan or clay layer at or near the surface, and
shallow soils over nearly impervious parent material.
If the watershed is homogeneous (i.e., uniform land use and soils) the CN value
can be determined directly from Table 8.03b. Curve numbers for
nonhomogeneous watersheds may be determined by dividing the watershed into
homogeneous subareas and computing a weighted average.
Step 3. Select design storm and determine runoff depth and volume for erosion
and sediment control using the 10-yr, 24-hr storm.
a. Determine rainfall amount, in inches, from Figures 8.03h through 8.03m
for the selected design storm. (The design storm is based on an SCS Type
II, 24-hr rainfall distribution.)
8.03.8

Appendices
Sample Problem 8.03b Given:
Determination of peak runoff Location: Raleigh, N.C.
rate. using the SCS method. Land use by soil group:
Commercial area: soil group B 8 acres
Newly graded area: soil group C 20 acres
Wooded land: (good stand —good ground cover)
soil group B 12 acres
Total area 40 acres
Avg. watershed slope: 5%
Ratio of drainage area to ponded area (2 acres wooded,
ponded area near center of watershed) 20:1
Hydraulic length: 2,000 It
% hydraulic length modified: none
% impervious area: (8 acres commercial, 85% impervious)17%
Find:
Peak rate of runoff for the 10-yr frequency, 24-hr storm - 0p 10, 24
Solution:
(1) Drainage area - 40 acres (given)
hydraulic length - 2,000 ft
average slope - 5%
(2)Calculate average curve number (CN) using Table 8.03b.
drainage area x CN .
Commercial area 20% x 92 - 1840
Newly graded area 50% x 93 = 4650
Wooded land $Q% x 55 = 1650
100% 8140
CN 8140 = 81.4 Use 82
100
(3) Determine runoff depth
a. Rainfall amount for 10-yr, 24-hr storm; Raleigh, NC = 5.6 inches
(Figure 8.03j)
b. Runoff depth - 3.63 inches (Table 8.03c by double interpolation)
(4) Determine peak rate of runoff for the design storm by adjusting for
watershed shape.
a. Equivalent drainage area - 46 acres (Figure 8.03n; hydraulic
length - 2,000 ft)
b. 01- 40 cfsrnch x 3.63 inches =145 cis (Figure 8.03p; 3% to 8%
slope; CN - 62)
C. 02 -145 x 0 -126 cis
46
(5)Adjust peak discharge rate 02 for percent impervious area and
percent hydraulic length modified
a. Impervious factor =1.08 (Figure 8.03r ;17% impervious)
b. Hydraulic length modification factor - omit (no channel improve-
ment made)
C. 03 -126 x 1.08 =136 cfs
(6)Adjust peak discharge for avg. watershed slope
i' a. Adjustment factor for watershed slope -1.07
(Table 8.03d; 5% avg. slope)
b. 04 -136 x 1.07 -146 cis
(7)Adjust peak discharge for surface ponding
-, a. Adjustment factor for surface ponding - 0.68 (Table 8.03e;
ratio 20:1; center of watershed; 10-yr)
b. 0p io,24 =146 x 0.68 - 99 cis at design point.
8.03.9

0
Table 8.03b
Runoff Curve Numbers (CN)
Hydrologic Soil Group
A
B
C
D
Land Use/Cover
Cultivated land
without conservation
72
81
88
91
with conservation
62
71
78
81
Pasture land
poorcondition
68
79
86
89
good condition
39
61
74
80
Meadow
good condition
30
58
71
78
Wood or forest land
Thin stand - poor cover, no mulch
45
66
77
83
Good stand - good cover
25
55
70
77
Open spaces, lawns, parks, golf courses, cemeteries, etc.
good condition:
grass cover on 75%
or more of the area
39
61
74
80
fair condition:
grass cover..on 50 >
to 75% of the area
49
69
79
84
Commercial and:business
areas (85% Impervious)"
89
92
94
95
Industrial districts
(72% impervious)
81
88
91
93
Residential:' Development completed and vegetation established
Average lot size Average% Impervious
1/8 acre or less 65
77
65
90
92
1/4 acre .38
61
75
83
87
1/3 acre 30
57
72
81
86
112 acre 25
54
70
80
85
1 acre 20
51
68
79
84
2 acre 15
47
66
77
81
Paved parking lots, roofs,
driveways, etc..; '
98
98
98
98
Streets and roads
paved with curbs and
storm sewers
98
98
98
98
gravel
76
85
89
91
dirt
72
82
87
89
Newly graded area
81
89
93
95
Residential: Development underway and no vegetation
Lot sizes'of 1/4 acre
88
93
95
97
Lot sizes of 1/2 acre
85
91
94
96
Lot sizes of 1 acre
82
90
93
95
Lot sizes of 2 acres
81
89
92
94
'Curve.numbers are computed assuming the runoff from the house and driveway is directed toward the street.
source: USDA-SCS
r�
G
8.03.10

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ao
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2-year 1 day precipitation (inches)
Scale in Miles
0 25 SO 76 100
RAINFALL DATA MAP
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5-year 1 day precipitation (inches)
Scots In Mil"
0 25 50 75 100
RAINFALL DATA MAP
3.9
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10-year 1 day precipitation (inches)
ScMe In MH..
0 23 SO 75 100
RAINFALL DATA MAP
5.2 5.4 5.6 %> .E>o» .LADE.
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6
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9
10
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9
10
Im
W---" 0) 0)

Appendices
Table 8.03c
Runoff Depth
7
0i
b. Determine runoff depth (in inches) from the curve number and rainfall
depth using Table 8.03c.
Rainfall
Curve Number (CN)
(inches)
60
65
70
75
80
85
90
95
1.0
0.00
0.00
0.00
0.03
0.08
0.17
0.32
0.56
1.2
0.00
0.00
0.03
0.07
0.15
0.28
0.46
0.74
1.4
0.00
0.02
0.06
0.13
0.24
0.39
0.61
0.92
M
0.01
0.05
0.11
0.20
0.34
0.52
0.76
1.11
1.8
0.03
0.09
0.17
0.29
0.44
0.65
0.93
1.30
2.0
0.06
0.14
0.24
0.38
0.56
0.80
1.09
1.48
2.5
0.17
0.30
0.46
0.65
0.89
1.18
1.53
1.97
3.0
0.33
0.51
0.72
0.96
1.25
1.59
1.98
2.44
4.0
0.7.6
1.03
1.33
1.67
2.04
2.46
2.92
3.42
5.0
1.30
1.65
2.04
2.45
2.89
3.37
3.88
4.41
6.0
1.92
.2.35
2.80
3.28
3.78
4.31
4.85
5.40
7.0
2.60
3.10
3.62
4.15
4.69
5.26
5.82
6.40
8.0
3.33
.3.90
4.47
5.04
5.62
6.22
6.81
7.39
9.0
4.10
4.72
5.34
5.95
6.57
7.19
7.79
8.39
10.0
4.90
5.57
6.23
6.88
7.52
8.16
8.78
9.39
11.0
5.72
6.44
7.13
7.82
8.48
9.14
9.77
10.39
12.0
6.56
7.32
8.05
8.76
9.45
10.12
10.76
11.39
To obtain runoff depths
for CN's and other rainfall amounts not shown
in this table, use an arithmetic interpolation.
The volume of runoff from the site can be calculated by multiplying the
area of the site by the runoff depth.
Step 4. Determine the peak rate of runoff for the design storm by adjusting for
watershed shape as follows:
a. Determine an "equivalent drainage area" from the hydraulic length of the
watershed using Figure 8.03n. Hydraulic length is the length of the flow
path from the mostremotepoint in the watershed to thepointof discharge.
b. Determine the discharge (cfs%mch of runoff) for the equivalent drainage
area from Figure 8.03o through 8.03q:
Figure 8.03o - for average watershed slopes 0-3 %
Figure 8.03p - for average watershed slopes 3-7%
Figure 8.03q - for average watershed slopes 8-50%
Calculate the peak discharge, 01, of the equivalent watershed by multi-
plying equivalent watershed area by runoff from Table 8.03c in Step 3b.
8.03.17

0
w 10000
w
LL
W 5000
w
a
U_ 2000
0
z 1000
w
J
500
I
•-o•1 WHERE
L=HYDRAULIC
o=DRAINAGE AREA, ACRES
�•
J,
-�■�■■■■rem■■■■■■■-
DRAINAGE AREA, ACRES
Figure 8.03n Hydraulic length and drainage area relationship.
!I
)0
c. Compute peak discharge, 02, by multiplying the "equivalent watershed"
peak discharge, Ot, by the ratio of the actual drainage area to the equivce
-
alent drainage area:
02 _ Ot x (actual drainage area)
(equiv. drainage area)
Step S. Adjust peak discharge to account for impervious area and channel
improvements (modified hydraulic length shown in Figure 8.03r).
a. Use the top graph in. Figure 8.03r to determine the peak factor for imper-
vious area in the watershed (Factor nvvip).
b. Use the bottom graph in Figure 8.03r to determine the peak factor based
upon the percentage of hydraulic length that has been modified (i.e.,
deepened, widened, lined, etc.) to increase channel capacity (FactorHLM).
c. Adjust peak discharge, 02, from step 4 by multiplying by the two peak
factors.
03 mod. = 02 x (Factor imp) x (Factor HLM)
6
8.03.18

Appendices
-w
PEAK RATES OF
DISCHARGE FOR
SMALL WATERSHEDS
ON A FLAT SLOPE,
24-HOUR STORM,
TYPE II
DISTRIBUTION
1 2 5 10 20 50 �foo 200 500
DRAINAGE AREA, ACRES
Figure 8 03o Discharge vs equivalent drainage :area for average watershed slopes 0 - 30k.
L
[
PEAK RATES ;OF [
DISCHARGE FOR [
SMALL WATERSHEDS[
ON A MODERATE I
SLOPE, 24-HOUR
STORM, TYPE 11
DISTRIBUTION [
i
c
•M
1 2 5 10 20IN 50 100 200 500 2000
DRAINAGE AREA, ACRES
Figure 8.03p Discharge vs equivalent drainage area for average watershed 3 - 8%.
8.03.19

0
•••
500
STEEP SLOPES
ABOVE 8%
200
a
z
PEAK RATES OF
Cr100
DISCHARGE FOR
o
SMALL WATERSHEDS
ON A STEEP SLOPE,
z 50
24-HOUR STORM,
TYPE II
v�i
DISTRIBUTION
LL
U
w
¢ 20
x
x
U
N
0 10
Y
W
W
m
5
2
1
2 5 10 20 50 100 200
DRAINAGE AREA, ACRES
Figure 8.03q Discharge vs equivalent drainage area for average watershed slopes 8 - 50%.
i
iri
FRI
8.03.20

Appendices
i 10PO
1
I a
0
7
'4 ---
a�
50
a
E
0
C
a�
U
L
N
I a
01.0 1.2 1A 1.6 1.8
Peak Factor
Peak Discharge Adjustment Factor for Impervious Area
10c
U
0 50
-. w
.� O
02
C L
U C)
•- C
CD 0 J
0
I AJ i.c i.ti LID 1.0
Peak Factor
Peak Discharge Adjustment Factor for Hydraulic
Length Modification
Figure 8.03r Peak discharge adjustment factors (source: USDA—SCS).
8.03.21

0
Step 6. Adjust the peak discharge based on the average watershed slope (Table
8.03d).
Enter Table 8.03d with the average percentage of slope and acreage of the
watershed, and read the appropriate slope adjustment factor (interpolate where
necessary). Adjust the peak discharge by multiplying by the slope adjustment
factor.
Qa = 03 x Slope factor
Step 7. Adjust the peak discharge for ponding and swampy areas in the
watershed (Table 8.03e).
Peak flow determined from the previous steps is based on uniform surface flow
in ditches, drains, and streams. Where significant ponding areas occur in the
watershed, make a reduction in the peak runoff value. Table 8.03e provides
adjustment factors based on the ratio of the ponding and swampy areas to the
total watershed area for a range of storm frequencies.
G
To use Table 8.03e, fast calculate the ratio of drainage area to ponded area,
determine generally where the ponded areas occur in the watershed (at the
design point, spread throughout the watershed, or located only in upperreaches),
then select the adjustment factor for the appropriate design storm.
Ad just th a peak discharge by multiplying Qa by the adjustment factor for surface
ponding: 4
Qpeak= Qa x factorfor surface ponding
41
8.03.22

Appendices
Table 8.03d
Slope Adjustment Factors
Slope
10
20
50
100
200
(percent)
acres
acres
acres
acres
acres
Flat 0.1
0.49
0.47
0.44
0.43
0.42
0.2
0.61
0.59
0.56
0.55
0.54
0.3
0.69
0.67
0.65
0.64
0.63
0.4
0.76
0.74
0.72
0.71
0.70
0.5
0.82
0.80
0.78
0.77
0.77
0.7
0.90
0.89
0.88
0.87
0.87
1.0
1.00
1.00
1.00
1.00
1.00
1.5
1.13
1.14
1.14
1.15
1.16
Moderate 3
0.93
0.92
0.91
0.90
0.90
4
1.00
1.00
1.00
1.00
1.00
5
1.04
1.05
1.07
1.08
1.08
6
1.07
1.10
1.12
1.14
1.15
7
1.09
1.13
1.18
1.21
1.22
Steep 8
0.92
0.88
0.84
0.81
0.80
9
0.94
0.90
0.86
0.84
0.83
10
0.96
0.92
0.88
0.87
0.86
11
0.96
0.94
0.91
0.90
0.89
12
0.97
0.95
0.93
0.92
0.91
13
0.97
0.97
0.95
0.94
0.94
14
0.98
0.98
0.97
0.96
0.96
15
0.99
0.99
0.99
0.98
0.98
16
1.00
1.00
1.00
1.00
1.00
20'
1.03
1.04
1.05
1.06
1.07
25
1.06
1.08
1.12
1.14
1.15
30
1.09
1.11
1.14
1.17
1.20
40
1.12
1.16
1.20
1.24
1.29
50
1.17
1.21
1.25
1.29
1.34
source: USDA-SCS
-
8.03.23

0
Table 8.03e
Adjustment Factors for Ponding and Swampy Areas
Adjustment factors
where ponding and
swampy
areas
occur
at the
design
point.
Ratio of drainage
Percentage of
area to ponding
ponding and
Storm frequent
(years)
and swampy area
swampy area
5
10
25
5U
100
500
0.2
0.92
0.94
0.95
0.96
0.97
0.98
200
.5
.86
.87
.88
.90
.92
.93
100
1.0
.80
.81
.83
.85
.87
.89
50
2.0
.74
.75
.76
.79
.82
.86
40
2.5
.69
.70
.72
.75
.78
.82
30
3.3
.64
.65
.67
.71
.75
.78
20
5.0
.59
.61
.63
.67
.71
.75
15
6.7
.57
.58
.60
.64
.67
.71
10
10.0
.53
.54
.56
.60
.63
.68
5
20.0
.48
.49
.51
.55
.59
.64
Adjustment factors
where ponding and
swampy
areas
are spread throughout
the
watershed or occur
in central parts of the watershed.
Ratio of drainage
Percentage of
area to ponding
ponding and
Storm frequency
(years)
and swampy area
swampy area
5
10
Z5
bu
100
500
0.2
0.94
0.95
0.96
0.97
0.98
0.99
200
.5
.88
.89
.90
.91
.92
.94
100
1.0
.83
.84
.86
.87
.88
.90
50
2.0
.78
.79
.81
.83
.85
.87
40
2.5
.73
.74
.76
.78
.81
.84
30
3.3
.69
.70
.71
.74
.77
.81
20
5.0
.65
.66
.68
.72
.75
.78
15
6.7
.62
.63
.65
.69
.72
.75
10
10.0
.58
.59
.61
.65
.68.
.71
5
20.0
.53
.54
.56
.60
.63
.68
4
25.0
.50
.51
.53
.57
.61
.66
Adjustment factors
where ponding and
swampy
areas
are located
only in
upper
reaches of the watershed.
Ratio of drainage
Percentage of
area to ponding
ponding and
Storm frequency
(years)
and swampy area
swampy area
2
5
10
25
50
100
500
0.2
0.96
0.97
0.98
0.98
0.99
0.99
200
.5
.93
.94
.94
.95
.96
.97
100
1.0
.90
.91
.92
.93
.94
.95
50
2.0
.87
.88
.88
.90
.91
.93
40
2.5
.85
.85
.86
.88
.89
.91
30
3.3
.82
.83
.84
.86
.88
.89
20
5.0
.80
.81
.82
.84
.86
.88
15
6.7
.78
.79
.80
.82
.84
.86
10
10.0
.77
.77
.78
.80
.82
.84
5
20.0
.74
.75
.76
.78
.80
.82
4
G
io
8.03.24

Appendices
DESIGN OF=STAB LECHANNELS AND DIVERSIONS"
This section addresses the design of stable conveyance channels and diversions
using flexible linings. A stable channel is defined as a channel which is nonsilt-
ing and nonscouring. To minimize silting in the channel, flow velocities should
remain constant or increase slightly throughout the channel length. This is espe-
cially important in designing diversion channels and can be accomplished by
adjusting channel grade. Procedures presented in this section address the prob-
lems of erosion and scour. More advanced procedures for permanent, unlined
channels may be found elsewhere. (References: Garde and Ranga Raju,1980)
Diversions are channels usually with a supporting ridge on the lower side. They
are generally located to divert flows across a slope and are designed following
the same procedures as other channels. Design tables for vegetated diversions
and waterways are included at the end of this section.
Flexible channel linings are generally preferred to rigid linings from an erosion
control standpoint because they conform to changes in channel shape without
failure and are less susceptible to damage from frost heaving, soil swelling and
shrinking, and excessive soil pore water pressure from lack of drainage. Flex-
ible linings also are generally less expensive to construct, and when vegetated,
are more natural in appearance. On the other hand, flexible linings generally
have higher roughness and require a larger cross section for the same discharge.
0''_ EROSION CONTROL CRITERIA
The minimum design criteria for conveyance channels require that two primary
conditions be satisfied: the channel system must have capacity for the peak flow
expected from the 10-year storm and the channel lining must be resistant to
erosion for the design velocity. In some cases, out -of -bank flow may. be con-
sidered a functional part of the channel system. In these cases, flow capacities
and design velocities should be considered separately for out -of -bank flows and
channel flows.
Both the capacity of the channel and the velocity of flow are functions of the
channel lining, cross -sectional area and slope. The channel system must carry
the design flow, fit site conditions, and be stable.
STABLE CHANNEL DESIGN METHODS
Two acceptedprocedures for designing stable channels with flexible linings are:
(1) the permissible velocity approach; and (2) the tractive force approach. Under
the permissible velocity approach, the channel is considered stable if the design,
mean velocity is lower than the maximum permissible velocity. Under the trac-
tive force approach, erosive stress evaluated at the boundary between flowing
water and lining materials must be less than the minimum unit tractive force that
will cause serious erosion of material from a level channel bed.
8.05.1

0
The permissible velocity procedure is recommended for the design of vegeta-
tive channels because of common usage and the availability of reliable design
tables. The tractive force approach is recommended fordesign of channels with
temporary synthetic liners or riprap liners. The tractive force procedure is
described in full in the U.S. Department of Transportation, Federal Highway
Administration Bulletin, Design of Roadside Channels with Flexible Linings.
Permissible Velocity The permissible velocity procedure uses two equations to calculate flow:
Procedure
Manning's equation,
V _ 1.49 R2/3 S1/2
n
where:
V = average velocity in the channel in ft/sec.
n = Manning's roughness coefficient, based upon the lining of
the channel
R = hydraulic radius, wetted cross -sectional area/wetted perimeter
in ft
S = slope of the channel in ft/ft.
and the continuity equation,
Q=AV
where:
Q = flow in the channel in cfs
A = cross -sectional area of flow within the channel in ft2
V = average velocity in the channel in ft/sec.
Manning's equation and the continuity equation are used together to determine
channel capacity and flow velocity. A nomograph for solving Manning's equa-
tion is given in Figure 8.05a.
Selecting Permanent Channel lining materials include such flexible materials as grass, riprap and
Channel Lining gabions, as well as rigid materials such as paving blocks, flag stone, gunite, as-
phalt, and concrete. The design of concrete and similar rigid linings is general-
ly not restricted by flow velocities. However, flexible channel linings do have
maximum permissible flow velocities beyond which they are susceptible to
erosion. The designer should select the type of liner that best fits site conditions.
Table 8.05a lists maximum permissible velocities for established grass linings
and soil conditions. Before grass is established, permissible velocity is deter-
mined by the choice of temporary liner. Permissible velocities for riprap linings
are higher than for grass and depend on the stone size selected.
•
8.05.2

Appendices
•
•
60
50
40
30
NX
10
2
o.
5
0.0001
c
4
0.0002
0
Q3
0.0005
V)
2
0.001
:3
- �,
0
�
�
z,
0.002
CD
7D
0.005
1.0
CD
\�S
0.01
.D
cn/
�Qp
0.02
0
0
0.5
(n
0.05
0.4
0.1
0.3
0.2
0.3
0.2
C 0.1
Figure 8.05a Nomograph for solution of Manning equation.
50
40
30
20
cn
r«
10
10
h/
0.01Jm
/ -► 5
/ m
Cl, 4
/ m
/ 0 3
oti / L
O/ c <
0.05
/ m
/ rn
i� n 0.1
0
cu .
0
m•
0
Z3
0.5
2
1.0
0.5
8.053

Table 8.05a
Maximum Allowable Design Velocities'
for Vegetated Channels
Typical
Soil
Grass Lining
Permissible Velocity3
Channel Slope
Characteristics2
for Established Grass
Application
Lining (ft/sec)
0-5%
Easily Erodible
Bermudagrass
5.0
Non -plastic
Tall fescue
4.5
(Sands & Silts)
Bahiagrass
4.5
Kentucky bluegrass
4.5
Grass -legume mixture
3.5
Erosion Resistant
Bermudagrass
6.0
Plastic
Tall fescue
5.5
(Clay mixes)
Bahiagrass
5.5
Kentucky bluegrass
5.5
Grass -legume mixture
4.5
5-10%
Easily Erodible
Bermudagrass
4.5
Non -plastic
Tall fescue
4.0
(Sands & Silts)
Bahiagrass
4.0
Kentucky bluegrass
4.0
Grass -legume mixture
3.0
Erosion Resistant
Bermudagrass
5.5
Plastic
Tall fescue
5.0
(Clay Mixes)
Bahiagrass
5.0
Kentucky bluegrass
5.0
Grass -legume mixture
3.5
>10%
Easily Erodible
Bermudagrass
3.5
Non -plastic
Tall fescue
2.5
(Sands & Silts)
Bahiagrass
2.5
Kentucky bluegrass
2.5
Erosion Resistant
Bermudagrass
4.5
Plastic
Tall fescue
3.5
(Clay Mixes)
Bahiagrass
3.5
Kentucky bluegrass
3:5
Source: USDA-SCS Modified
NOTE: 'Permissible Velocity based on 10-yr storm peak
runoff
2Soil erodibility based
on resistance to soil movement from concentrated flowing water.
36efore grass is established, permissible velocity is determined by the type of temporary liner used.
Selecting Channel To calculate the required size of an open channel, assume the design flow is
uniform and does not vary with time. Since actual flow conditions change
Cross -Section throughout the length of a channel, subdivide the channel into design reaches,
Geometry and design each reach to carry the appropriate capacity.
•
•
The three most commonly used channel cross -sections are "W-shaped, par-
abolic, and trapezoidal. Figure 8.05b gives mathematical formulas for the area,
hydraulic radius and top width of each of these shapes. 0
8.05.4

Appendices
•
V-Shape
j= T
d
Z=e
�• e
Cross -Sectional Area (A) = Zd2
Top Width (T) = 2dZ
Hydraulic Radius (R) _ �Zd-
2 Z� `+ 1
Parabolic Shape
T
Cross -Sectional Area (A) = 3 Td
Top Width (T) =1.5d A
Hydraulic Radius = T2d
1.5T2 + 4d2
0
Trapezoidal Shape
T
i
ta-- b---.ram e
Cross -Sectional Area (A) = bd + Zd2
Top Width (T) = b + 2dZ
Hydraulic Radius = bd + Zd2
b + 2d 4 Z2+ 1
Figure 8.05b Channel geometries for v-shaped, parabolic and trapezoidal channels.
Z=d
8.05.5

0
Design Procedure- The following is a step-by-step procedure for designing a runoff conveyance
Permissible Velocity channel using Manning's equation and the continuity equation:
Table 8.05b
Manning's n for Structural
Channel Linings
Step 1. Determine the required flow capacity, Q, by estimating peak runoff rate
for the design storm (Appendix 8.03).
Step 2. Determine the slope and select channel geometry and lining.
Step 3. Determine the permissible velocity for the lining selected, or the desired
velocity, if paved.
Step 4. Make an initial estimate of channel size —divide the required Q by the
permissible velocity to reach a "first try" estimate of channel flow area. Then
select a geometry, depth, and top width to fit site conditions.
Step 5. Calculate the hydraulic radius, R, from channel geometry (Figure 8.05b).
Step 6. Determine roughness coefficient n.
Structural Linings —see Table 8.05b
Grass Lining:
a. Determine retardance class for vegetation from Table 8.05c. To meet
stability requirement, use retardance for newly mowed condition (gen-
erally C or D). To determine channel capacity, use at least one retardance
class higher.
b. Determine n from Figure 8.05c.
Step 7. Calculate the actual channel velocity, V, using Manning's equation
(Figure 8.05a), and calculate channel capacity, Q, using the continuity equation.
Step 8. Check results against permissible velocity and required design capacity
to determine if design is acceptable.
Step 9. If design is not acceptable, alter channel dimensions as appropriate. For
trapezoidal channels, this adjustment is usually made by changing the bottom
width.
Channel Lining
Recommended
n values
Asphaltic concrete, machine placed
0.014
Asphalt, exposed prefabricated
0.015
Concrete
0.015
Metal, corrugated
0.024
Plastic
0.013
Shotcrete
0.017
Gabion
0.030
Earth
0.020
Source: American Society of Civil Engineers (modified)
0
•
i
8.05.6

Appendices
•
0-
.4
.3
.2
rn
c .I
�C
.08
CO
.06
.04
.02
.I
Step 10. For grass -lined channels once the appropriate channel dimensions
have been selected for low retardance conditions, repeat steps 6 through 8 using
a higher retardance class, corresponding to tall grass. Adjust capacity of the
channel by varying depth where site conditions permit.
NOTE 1: If design velocity is greater than 2.0 ft/sec., a temporary lining
may be required to stabilize the channel until vegetation is established.
The temporary liner may be designed for peak flow from the 2-yr storm.
If a channel requires temporary lining, the designer should analyze shear
stresses in the channel to select the liner that provides protection and
promotes establishment of vegetation. For the design of temporary liners,
use tractive force procedure.
NOTE 2: Design Tables —Vegetated Channels and Diversions at the end
of this section.may be used to design grass -lined channels with parabolic
cross -sections.
Step 11. Check outlet for carrying capacity and stability. If discharge velocities
exceed allowable velocities for the receiving stream, an outlet protection struc-
ture will be required (Table 8.05d).
Sample Problem 8.05a illustrates the design of a grass -lined channel.
10113,
6" to 101,
2' to 611
than 2"
�1I
I
Ik
IIII,b
bLess
��������
.2 .4 .6 .8 1.0 2 4 6 8 10 20
VR, Product of Velocity and Hydraulic Radius
Figure 8.05c Manning's n related to velocity, hydraulic radius, and vegetal retardanoe.
8.05.7

0
Table 8.05c
Retardance Classiflcation for Vegetal Covers
Retardance
Cover .
Condition
A
Reed canarygrass
Excellent stand, tall (average 36")
Weeping lovegrass
Excellent stand, tall (average 30")
B
Tall fescue
Good stand, uncut, (average 18")
Bermudagrass
Good stand, tall (average 12")
Grass -legume mixture
(tall fescue, red
fescue, sericea
lespedeza)
Good stand, uncut
Grass mixture
(timothy, smooth
bromegrass or
orchardgrass)
Good stand, uncut (average 20")
Sericea lespedeza
Good stand, not woody, tall (average 19")
Reed canarygrass
Good stand, cut (average 12-15")
Alfalfa
Good stand, uncut (average 11 ")
C
Tall fescue
Good stand (8-12")
Bermudagrass
Good stand, cut (average 6")
Bahiagrass
Good stand, uncut (6-8")
Grass -legume mixture --
summer (orchardgrass,
redtop and annual
Good stand, uncut (6-8")
lespedeza)
Centipedegrass
Very dense cover (average 6")
Kentucky bluegrass
Good stand, headed (6-12")
Redtop
Good stand, uncut (15-20")
D
Tall fescue
Good stand, cut (3-4")
Bermudagrass
Good stand, cut (2.5")
Bahiagrass
Good stand, cut (3-4")
Grass -legume mixture --
fall -spring (orchard -
grass, redtop, and
annual lespedeza)
Good stand, uncut (4-5")
Red fescue
Good stand, uncut (12-18")
Centipedegrass
Good stand, cut (3-4")
Kentucky bluegrass
Good stand, cut (3-4")
E
Bermudagrass
Good stand, cut (1.5")
Bermudagrass
Burned stubble
Modified from: USDA-SCS, 1969. Engineering Field Manual.
•
•
8.05.8

Appendices
•
•
Table 8.05d
Maximum Permissible
Velocities for Unprotected
Soils in Existing Channels.
Sample Problem 8.05a
Design of a
grass -lined channel.
Materials
Fine Sand (noncolloidal)
Sand Loam (noncolloidal)
Silt Loam (noncolloidal)
Ordinary Firm Loam
Fine Gravel
Stiff Clay (very colloidal)
Graded, Loam to Cobbles (noncolloidal)
Graded, Silt to Cobbles (colloidal)
Alluvial Silts (noncolloidal)
Alluvial Silts (colloidal)
Course Gravel (noncolloidal)
Cobbles and Shingles
Shales and Hard Pans
Given:
Design 010 =16.6 cis
Maximum Permissible
Velocities (fps)
2.5
2.5
3.0
3.5
5.0
5.0
5.0
5.5
3.5
5.0
6.0
5.5
6.0
Proposed channel grade = 2%
Proposed vegetation: Tall fescue
Soil: Creedmoor (easily erodible)
Permissible velocity, Vp = 4.5 ft/s (Table 8.05a)
Retardance class: "B" uncut, "D" cut (Table 8.05c).
Trapezoidal channel dimensions:
designing for low retardance condition (retardance class D)
design to meet Vp,
Find:
Channel dimensions
Solution:
Make an initial estimate of channel size
A = ON; 16.6 cfs/4.5 ft/sec = 3.691?
Try bottom width = 3.0 ft
Z=3
A=bd+Zd2
P=b+2d
An iterative solution using Figure 8.05a to relate flow depth to
Manning's n proceeds as follows: Manning's equation is used
to check velocities
d (ft) A (ft) R (ft) n V (fps) Q (cfs) Comments
0.8 4.32 0.54 0.043 3.25 14.0 V<Vp OK,
Q<Q10,
(too small, try deeper channel)
0.9 5.13 0.59 0.042 3.53 18.10 V<Vp, OK,
Q>Qto, OK
Now design for high retardance (class B):
Try d = 1.5 ft and trial velocity, Vt = 3.0 ft/sec
d (ft) A (ft2) R (ft) Vt (fps) n V (fps) Q (cfs)
Comments
1.5 11.25 0.90 3.0 0.08 2.5
reduce Vt
2.0 0.11 1.8
reduce Vt
1.6 0.12 1.6 18
Q>Qto OK
Channel summary:
Trapezoidal shape, Z=3, b=3 it, d=1.5 It, grade = 2%
8.05.9

0
Tractive Force
Procedure
Table 8.05e
Manning's Roughness
Coefficients for Temporary
Lining Materials
The design of riprap-lined channels and temporary channel linings is based on
analysis of tractive force.
NOTE: This procedure is for uniform flow in channels and is not to be
used for design of deenergizing devices.
To calculate the required size of an open channel, assume the design flow is
uniform and does not vary with time. Since actual flow conditions change
through the length of a channel, subdivide the channel into design reaches as
appropriate.
PERMISSIBLE SHEAR STRESS
The permissible shear stress, Td, is the force required to initiate movement of
the lining material. Permissible shear stress for the liner is not related to the
erodibility of the underlying soil. However, if the lining is eroded or broken, the
bed material will be exposed to the erosive force of the flow.
COMPUTING NORMAL DEPTH
The first step in selecting an appropriate lining is to compute the design
flow depth (the normal depth) and determine the shear stress.
Normal depths can be calculated by Manning's equation as shown for trap-
ezoidal channels in Figure 8.05d. Values of the Manning's roughness coeffi-
cient for different ranges of depth are provided in Table 8.05e for temporary
linings and Table 8.05f for riprap. The coefficient of roughness generally
decreases with increasing flow depth.
n value for Depth Ranges
0-0.5 ft
0.5-2.0 it
>2.0 it
Lining Type
Woven Paper Net 0.016
0.015
0.015
Jute Net 0.028
0.022
0.019
Fiberglass Roving 0.028
0.021
0.019
Straw with Net 0.065
0.033
0.025
Curled Wood Mat 0.066
0.035
0.028
Synthetic Mat 0.036
0.025
0.021
r
•
8.05.10

[7
•
S
0.1
0.08
0.06
0.05
0.04
0.03
0.02
0.01
0.008
0.006
0.005
0.004
0.002
NOTE: Project hori
d 1 to obtain va
Z I
B i
On
(Fig/S)
-10
8.0
6.0
5.0
4.0
3.0
quo
0.8
0.6
0.5
0.4
aD
J
c
F—
Appendices
d
n
B
N c� �.
of
Example:
0.1
—0.001
0.08
Given:
Find:
Solution:
S-0.01
d
Qn = 0.3
0.06
Q = 10 fig/S
d/B = 0.14
0.05
n = 0.03
d = 0.14(4) = 0.56 ft
B=4ft
0.04
Z = 4
0.03
0.02
Figure 8.05d Solution of Manning's equation
for trapezoidal channels of various side slopes.
8.05.11

Table 8.05f
Manning's Roughness Coefficient for Riprap and Gravel
n value for Depth Ranges
Material d50 (inches)
0-0.5 ft
0.5-1.0 ft 1.0-2.0 ft
> 2.0 ft
Gravel 1
0.033
0.028 0.026
0.025
2
0.045
0.034 0.034
0.031
Riprap 6
0.106
0.054 0.044
0.041
9
0.215
0.068 0.062
0.047
12
0.797
0.084 0.060
0.053
15
-
0.104 0.068
0.059
18
-
0.127 0.076
0.064
21
-
0.158 0.085
0.070
24
-
0.199 0.095
0.076
DETERMINING SHEAR STRESS
Shear stress, T, at normal depth is computed for the lining by the following
equation:
T = yds
where:
T = shear stress in lb/ftz
y = unit weight of water, 62A lb/ft3
d = flow depth in ft
s = channel gradient in ft/ft.
If the permissible shear stress, Td, given in Table 8.05g is greater than the com-
puted shear stress, the Rprap or temporary lining is considered acceptable. If a
lining is unacceptable, select a lining with a higher permissible shear stress and
repeat the calculations for normal depth and shear stress. In some cases it may
be necessary to alter channel dimensions to reduce the shear stress.
Computing tractive force around a channel bend requires special considerations
because the change in flow direction imposes higher shear stress on the chan-
nel bottom and banks. The maximum shear stress in a bend, Tb, is given by the
following equation:
Tb = KbT
where:
Tb = bend shear stress in lb/ft2
Kb = bend factor
T = computed stress for straight channel in lb/ft2
The value of Kb is related to the radius of curvature of the channel at its center
line, Rc, and the bottom width of the channel, B, Figure 8.05e. The length of
channel requiring protection downstream from a bend, Lp, is a function of the
roughness of the lining material and the hydraulic radius as shown in Figure
8.05f.
8.05.12

Appendices
•
•
Table 8.05g
Permissible Shear Stresses
for Riprap and Temporary
Liners
Permissible Unit Shear Stress, T�
Lining Category
Lining Type
(lb/ft )
Temporary
Woven Paper Net
0.15
Jute Net
0.45
Fiberglass Roving:
Single
0.60
Double
0.85
Straw with Net
1.45
Curled Wood mat
1.55
Synthetic Mat
2.00
dso Stone Size (inches)
Gravel Riprap
1
0.40 .
2
0.80
Rock Riprap
6
2.50
9
3.80
12
5.00
15
6.30
18
7.50
21
8.80
24
10.00
Design Procedure- The following is a step-by-step procedure for designing a temporary liner for a
channel. Because temporary liners have a short period of service, the design 0
Temporary Liners may be reduced. For liners that are needed for six months or less, the 2-yr fre-
quency storm is recommended.
Step 1. Select a liner material suitable for site conditions and application. Deter-
mine roughness coefficient from manufacturer's specifications or Table 8.05e.
Step 2. Calculate the normal flow depth using Manning's equation (Figure
8.05d). Check to see that depth is consistent with that assumed for selection of
Manning's n in Figure 8.05d.
Step 3. Calculate shear stress at normal depth.
Step 4. Compare computed shear stress with the permissible shear stress for
the liner.
Step 5. If computed shear is greater than permissible shear, adjust channel
dimensions to reduce shear or select a more resistant lining and repeat steps 1
through 4.
Design of a channel with temporary lining is illustrated in Sample Problem
8.05b.
8.05.13

0
Sample Problem 8.05b
Design of a Temporary Liner
for a Vegetated Channel.
Given:
02=7.6cfs
Bottom width = 3.0 ft
Z=3
n = 0.02 (Use basic n value for channels cut in earth (Table 8.05b).
Vp = 2.0 ft/sec maximum allowable velocity for bare soil
Channel gradient = 2%
Find:
Suitable temporary liner material
Solution:
Using Manning's equation:
b(ft) d(ft) A(W) R(ft) V(fps) Q(cfs) Comments
3.0 0.40 .1.68 0.304 4.77 8.00 V>Vp,
(needs protection)
Q>Qz, OK
Velocity > 2.0 fps channel requires temporary liner:
Calculate channel design with straw with net as temporary liner.
n = 0.033 (Table 8.05e). Td = 1.45 (Table 8.05g)
b(ft) d(ft) A(ft) R(ft) V(fps) Q(cfs) Comments
3.0 0.6 2.88 0.42 3.60 10.38 T<Td, OK
Calculate shear stress for 02 conditions:
T = yds where y - unit weight of water (62A lb,4t3)
d - flow depth in ft
s = channel gradient in Wit
T = (62.4)(0.6)(0.02) = 0.75 T <Td OK
Temporary liner: straw with net
DESIGN OF RIPRAP LINING -MILD GRADIENT
The mild gradient channel procedure is applicable for channel grades less than
10%. The method assumes that the channel cross section is already designed
and that the remaining problem is to provide a stable riprap lining.
Side slope stability. As the angle of the side slope approaches the angle of
repose of the channel lining, the lining material becomes less stable. The
stability of a side slope is given by the tractive force ratio, K2, a function of the
side slope and the angle of repose of the rock lining material.
The rock size to be used for the channel lining can be determined by compar-
ing the tractive force ratio, an indicator of side slope stability, to the ratio of
shear stress on the sides and shear stress on the bottom of the channel. The angle
of repose for different rock shapes and sizes is shown in Figure 8.05g. The re-
quired rock size (mean diameter of the gradation, d5o) for the side slopes is
determined from the following equation:
d5o (sides) = K2 d5o (bottom)
where:
Kf = ratio of shear stress on the sides, Ts, and bottom, T, of a
trapezoidal channel (Figure 8.05h),
K2 = tractive force ratio (Figure 8.05i).
E
•
r�
8.05.14

Appendices
0-
2.0
1.9
1.8
1.7
1.6
Kb 1.5
1.4
1.3
1.2
1.1
Rc
B
Figure 8.05e Kb factor for maximum shear stress on channel bends.
Tb = KbT
8.05.15

El
nb
0.
0.01,
0.01
kO
MINI
IN
ME
MN
MEN
I •V 5.0 10.0 50.0
Lp/R
Figure 8.05f Protection length, LP, downstream from a channel bend.
•
r
is
8.05.16

•
•
Appendices
43
Q 41
0
(D 39
O
C.
(D 37
0
a� 35
rn
c
Q 33
31
Mean Stone Size d50, ft
ITOW"
N
==ME■■■
F1 I
0
11
-
�ZN��!
Mc:000�
Mean Stone Size, d50, mm
Figure 8.05g Angle of repose for different rock shapes and sizes.
Selection of riprap gradation and thickness. Riprap gradation should have a
smooth size distribution curve. The largest stone size in the gradation should
not exceed 1.5 times the d5o size. The most important criterion is that interstices
formed by larger stones be filled with smaller sizes in an interlocking fashion,
preventing the formation of open pockets. These gradation requirements apply
regardless of the type of filter design used.
In general, riprap constructed with angular stone performs best. Round stones
are acceptable as riprap provided they are not placed on side slopes steeper than
3:1. Flat, slab -like stones should be avoided since they are easily dislodged by
the flow. An approximate guide to stone shape is that neither the breadth nor
the thickness of a single stone be less than one-third its length.
The thickness of a riprap lining should equal 1.5 times the diameter of the
largest rock size in the gradation.
Filter design. When rock riprap is used, an appropriate underlying filter
material must be selected. The filter material may be either a granular, gravel
or sand filter blanket, or a geotextile fabric.
8.05.17

0
For a granular filter blanket, the following criteria must be met: 0
dt5filter < 5
day base
5 < dt5 filter < 40
d15 base
dso filter 40
dso base
Where "filter" refers to the overlying riprap or gravel and "base" refers to the
underlying soil, sand, or gravel. The relationship must hold between the filter
blanket and base material and between the riprap and filter blanket.
The minimum thickness for a filter blanket should not be less than 6 inches.
In selecting a filter fabric, the fabric should have a permeability at least equal
to the soil and a pore structure that will hold back the base soil. The following
properties are essential to assure performance under riprap:
• For filter fabric covering a base with granular particles containing 50 per-
cent or less (by weight) of fine particles (less than U.S. Standard Sieve
No. 200):
a. d85 base(mm)/EOS* filter cloth (mm) > 1.
b. Total open area of filter is less than 36%.
• Filter fabric covering other soils:
a. EOS less than U.S. Standard Sieve No. 70.
b. Total open area of filter less than 10%.
* EOS - Equivalent Opening Size to a U.S. Standard Sieve Size
Design Procedure- The following is a step-by-step procedure for designing a riprap channel lining
Riprap Lining, Mild with mild gradients.
Gradient Step 1. Select a riprap size and look up the Manning's n value (Table 8.05f)
. and permissible shear stress, Td (Table 8.05g).
Step 2. Calculate the normal flow depth in the channel, using Manning's equa-
tion (Figure 8.05d). Check that the n value for the calculated design depth is
consistent with that determined in step 1.
Step 3. Calculate shear stress at design depth.
Step 4. Compare the calculated shear stress with the permissible shear stress.
If the calculated shear stress is less than the permissible shear stress, then the
selected riprap size is acceptable. Otherwise, the procedure must be repeated
using a larger size riprap with a higher permissible shear stress.
Step S. For riprap linings on side slopes steeper than 3:1, execute the sup-
plemental procedure for steep side slope design presented below. 0
8.05.18

Appendices
•
•
•
1.1
1.0
ChIH 0.9
Y 0.8
0.7
0.6
0.5
0
Supplemental Procedure for Riprap Channel With Steep Side Slopes.
This procedure should be used when side slopes are steeper than 3:1.
Step 1. From Figure 8.05g, determine the angle of repose for the rock size and
shape. NOTE: The side slopes selected for the channel must be stable for the
soil conditions.
2 4 6 8 10
B/d
Figure 8.05h Ratio of side shear stress to bottom shear stress , Ki.
Step 2. From Figure 8.05h, determine Kt, the ratio of maximum side shear to
maximum bottom shear for a trapezoidal channel, based on bottom width to
depth ratio, b/d, and side slope, Z.
Step 3. From Figure 8.05i, determine K2, the tractive force ratio, based on side
slope and the stone angle of repose.
Step 4. The required d50 for side slopes is given by the following equation:
d5o (sides) = K2 d5o (bottom)
where:
Ki = ratio of shear stress on the sides, Ts, and bottom, T, of a
trapezoidal channel (Figure 8.05h),
K2 = tractive force ratio (Figure 8.05i).
8.05.19

13
45
40
35
6
(D 8 30
C
N
0 25
m
Fn 20
0
15
Q
10
ON
Angle of Re�ose, O'Deg.
I — I __
No
M
Sim. -4
1.10
M
0
0
mom
WIN
%Z"h§M
NONE
'ObBIR
0
IF
�1
10
0.2 0.4 0.6 0.8 1.0
K2
Figure 8.051 Tractive force ratio, K2.
Sample Problem 8.05c demonstrates the tractive force procedure for the design
of mild gradient riprap channels.
DESIGN OF RIPRAP LINING -STEEP GRADIENTS
This section outlines the design of riprap channel lining for steep gradients.
Achieving channel stability on steep gradients,10% or more, usually requires
some type of channel linings except where the channels can be constructed in
durable bedrock.
Rigid channel linings may be more cost effective than riprap in steep slope con-
ditions. Ripmp stability on a steep slope depends on the average weight of the
stones and the lift and drag forces induced by the flow. To resist these forces,
steep channels require larger stones than mild slope channels, and the size of
riprap linings increases quickly as discharge and channel gradient increase. The
decision to select a rigid or flexible lining may be based on other site conditions,
such as foundation material and maintenance requirements.
Transition sections protect transition regions of the channel both above and
below the steep gradient section. The transition from a steep gradient to a culvert
r
1]
8.05.20

Appendices
•
0".
Sample Problem 8.05c
Design of a mild gradient
channel with riprap lining.
Determine the mean riprap size and flow depth for a mild
gradient channel:
Given:
O = 30 cis
s = 0.07 ft/ t
b = 4.0 it
Z =3
Find:
Flow depth and mean riprap size
Solution:
(1) Try dso = 6 inches, depth 1.0 It
From Table 8.05f; select n = 0.054
From Table 8.05g; permissible unit shear stress = 2.5 Witt
(2) From Figure 8.05d determine channel flow depth
On = (30)(0.054) =1.6; d/b = 0.22 d = (0.22)(4.0) = 0.9 it
NOTE: Calculated depth is within selected depth range.
(3) Calculate shear stress
T .- yds
T - (62.4 Ib/113)(0.9)(0.07) - 4 0 IMF
Exceeds allowable of 2.5 Ib/ftl.
Try dso =1.0 it, depth 1.0 it
(1) n - 0.084; permissible unit shear stress = 5.0 IMF
(2) On = (30)(0.084) = 2.5; d/b = 0.26
d = (0.26)(4.0) =1.04
(3) Shear stress (62.4) (1.04) (0.07) = 4.6 Ib/ft2 < 5.0 lb /ft2 O.K.
Use dso - 1.0 it
Determine maximum stone size and riprap thickness
(1) dmax =1.5 x dso = (1.5)(12 in) - 18 in
(2) Thickness of riprap (installed below finished grade)
- 1.5 x dmax - (1.5) x (18 in) = 27 in
Continuing with the same problem
Given a channel bend of radius Rc = 30 it
(1) Kb - 1.25 (Figure 8.05e)
(2) Tb - T x Kb = 4.6 IMF x 1.25 = 5.75. This exceeds the permissible
shear stress for dso = 1.0 it
(3) Try d5o =15 inches to armor the channel bend; Td = 6.30 (Table
8.05g)
(4) For hydraulic radius, R = 0.79 and nb . 0.1 the protection length
downstream of the channel bend (LP)- 7 it (Figure 8.05f).
should allow room for some movement of riprap to prevent blockage of the cul-
vert opening. Riprap should be placed flush with the invert of a culvert. The
break between the steep slope and culvert entrance should equal three to five
times the mean rock diameter. The transition from a steep gradient to a mild
gradient channel may require an energy dissipation structure. The transition
from a mild gradient to a steep gradient should be protected against local scour
upstream from the transition for a distance approximately five times the uniform
depth of flow in the downstream channel.
Channel alignment and freeboard. Bends should be avoided on steep gradient
channels. A design requiring a bend in a steep channel should be redesigned if
possible to eliminate the bend, or replaced by a conduit system.
8.05.21

0
4
U 3
CD
_U)
3
N 2
CT
ca
-r— 21
U
N
0 1!
CT
C
0
n_An t_nn I to
Riprap Mean Diameter, (ft)
2.50
50
=
WJ
WA
I
Channel
WAVAEMPAWAMIN
MIWIA
- I
�
VEM
FA
WN
mm
P �Vm
mm
u.zo v.ov 0.75
Flgure 8.051 Steep slope riprap design, B = 2, Z = 3.
1.00 1.25 1.50
Depth, d(ft)
{5
t0
15 0
Cn
10 SD
CO
CD..
'6
0
CD
6
0
•
Freeboard should equal the mean depth of flow, since wave height may reach
approximately twice the mean depth. 0
Riprap gradation, thickness, and filter requirements. Riprap gradation, thick
ness and filter requirements are the same as those for mild slopes. It is impor-
tant to note that riprap thickness is measured normal to the channel gradient.
Design The design procedure for steep gradient channel linings is summarized below.
Procedure-Riprap
Lining, Steep Gradient Step 1. Based on a known discharge and channel slope, use Figures 8.05j-8.051
p to select a channel bottom width and channel size and determine the mean riprap
size and flow depth. For intermediate channel widths not given in these figures,
interpolate between charts.
Step 2. To determine flow depth and riprap size for side slopes other than 3: 1,
proceed as follows:
a. Find the flow depth by the following equation:
d = A do
where values of the A3/Az ratio are found from Table 8.05h (the subscript refers
to the side slope Z-value) and do is the flow depth from the design charts for
side slopes of 3: 1. 1*
8.05.22

•
Appendices
Riprap Mean Diameter, (ft)
0 0.50 1.00 1.50 2.00 2.50
50
46
46
35
n
30 W
(a
(D
25 Q
o
(D
Q
5
0
5
-0.00 -0.26 - "0 0.76 1.00 1.25
Figure 8.05k Steep slope riprap design, B = 4, Z = 3. Depth, d(ft)
Riprap Mean Diameter, (ft)
0 .50 1.00 1.50 2.00
50
45
40
CD 35
U)
30
C 25
L
ns
U 20
N
0 15
10
5
0
5
4
4
U 3
to
C`�... 3
Oj 25
20
U
N
0 15
10
5
O
WAFAFM
p
PIMA
V
WAS,
I-MAMMM
MORRIAMOMMIAWAM'
=FwR#A=FA=IFIIAFM=
Channel
Slope, S
WAYMAMMMENAMMM
Wf4vM=E=P/'/A===
Figure 8.051 Steep slope riprap design, B = 6, Z = 3.
60
45
40
96 0
n
S
30 w
tQ
(D
25 0
20 CD
(D
n
16
10
6
0
0 .25 .60 .75 1.00 1.25
Depth, d(ft)
8.05.23

0
Table 8.05h 9
Values of A3/Az for Selected Side Slopes and Depth -to -Bottom Width Ratios'
A3/Az
d/b
2:1
3:1
4:1
5:1
6:1
0.10
1.083
1.000
0.928
0.866
0.812
0.20
1.142
1.000
0.888
0.800
0.727
0.30
1.187
1.000
0.853
0.760
0.678
0.40
1.222
1.000
0.846
0.733
0.647
0.50
1.250
1.000
0.833
0.714
0.625
0.60
1.272
1.000
0.823
0.700
0.608
0.70
1.291
1.000
0.815
0.688
0.596
0.80
1.307
1.000
0.809
0.680
0.586
0.90
1.321
1.000
0.804
0.672
0.578
1.00
1.333
1.000
0.800
0.666
0.571
1.10
1.343
1.000
0.796
0.661
0.565
1.20
1.352
1.000
0.793
0.657
0.561
1.30
1.361
1.000
0.790
0.653
0.556
1.40
1.368
1.000
0.787
0.650
0.553
1.50
1.378
1.000
0.785
0.647
0.550
1.60
1.381
1.000
0.783
0.644
0.547
1.70
1.386
1.000
0.782
0.642
0.544
1.80
1.391
1.000
0.780
0.640
0.542
1.90
1.395
1.000
0.779
0.638
0.540
2.00
1.400
1.000
0.777
0.636
0.538
1 Based on the following equation:
1 + 3 d/b
A3/Az = 1 + Z(d/b)
b. Find the riprap size using the following equation:
d5o = Ond50c
where do and d5oc are values from the design charts (Figures 8.05j, 8.05k,
and 8.051).
Sample Problem 8.05d demonstrates the tractive force procedure for design of
riprap channels on steep grade.
Stability Evaluation Determining flow capacity and velocity in a natural channel involves detailed
for Natural Channels analysis and evaluation. Variations in channel cross section, alignment, grade
and roughness, and often changing conditions of in -bank and out -of -bank flow
make accurate determination of channel capacity and velocity difficult.
The following procedure uses Manning's equation and the continuity equation
to estimate stream channel capacity and velocity. Flow constrictions caused by
culverts or bridges must be evaluated separately.
•
•
8.05.24

Appendices
Sample Problem 8.05d
Design of a steep gradient
channel with riprap lining.
Survey of the Stream
10 ,
Channel
• _�
Determine the mean riprap size and flow depth for a steep gradient
channel.
Given:
Q=30cfs
s = 0.15 Wit
b = 3.0 It
Z= 3
Find:
Flow depth and mean riprap size.
Solution:
(1) Enter Figure 8.05j,
for b = 2.0 given Q - 30 cis and s = 0.15 ft/ft,
d - 0.92 ft
dso = 1.1 ft
Enter Figure 8.05k,
for b - 4.0 given 0 - 30 ft3/sec and S - 0.15 ft/ft,
d = 0.70 ft
d5o - 0.9 ft
(2) Interpolating for a 3.0 ft bottom width gives,
d - 0.81 ft
dso - 1.0 ft
To apply Manning's equation to a natural stream, a field survey is necessary to
determine the relevant channel characteristics. The field survey should identify
the following:
• Control points along the channel to define channel reaches to be evaluated.
These include confluences with tributaries, points of significant change
in grade or cross section, bridges, or culverts that restrict the flow.
• The profile of the channel bottom along the centerline of the stream.
• Selected cross sections, at right angles to the channel centerline in each
reach, to determine average channel cross section. The survey should also
include elevation of the flood plain and valley abutments if out -of -bank
flow is anticipated. An accurate topographic map may provide addition-
al stream valley sections and profile points to supplement the field sur-
vey.
• Descriptions of relevant physical characteristics of the channel between
control points, such as channel bed and bank materials, vegetation, ob-
structions, meander and other factors that determine the roughness coef-
ficient n.
Determining an n An n value for each channel reach can be determined by following the proce-
Factor for a Natural dure outlined in Appendix 8.04.
Channel
8.05.25

0
Permissible Velocity in Natural channels seldom have uniform vegetative lining, especially those with
Natural Channels continuous stream flow. Typical natural channels have beds of exposed soil,
gravel deposits, rock outcroppings and water bars, and banks ranging from ex-
posed soil to dense native vegetation.
The permissible velocity in natural channels should be determined for the most
erodible soil condition along the evaluation reach. Table 8.05d gives permis-
sible velocities for existing channels in specified soil materials.
Evaluation Procedure After the channel has been divided into reaches, the following procedure may
be used to determine stability. The procedure should be applied to each evalua-
tion reach, beginning at the lowest stable section and progressing upstream.
Step 1. Determine the peak runoff rate for a 10-year storm after site develop-
ment, based on the entire contributing drainage area at the downstream end of
each reach.
Step 2. Determine average cross -sectional area, hydraulic radius, slope and per-
missible velocity in the channel reach.
Step 3. Determine roughness coefficient, n, for the reach.
Step 4. Calculate bankfull velocity, V, and capacity, 0, using Manning's equa-
tion and the continuity equation.
Step 5. Compare actual bankfull channel capacity, 0, with the peak rate of
runoff from step 1, and compare velocity, V, with the permissible velocity from
step 2.
a. Calculated channel velocities for the 10-year peak must be equal to or less
than the allowable velocity or channel stabilization will be necessary
(Practice Standards and Specifications: 6.72, Vegetative Streambank
Stabilization; 6.73, Structural Streambank Stabilization).
b. If the capacity of the channel exceeds the peak runoff rate from the 10-
year storm, compute the velocity, V, for the depth at which the 10-year
storm discharge will flow for stability comparison.
c. If capacity of the channel is less than the peak runoff rate from the 10-
year storm, a deeper flow depth must be determined (considering the
quantity of out -of -bank flow) to provide the necessary capacity. The chan-
nel velocity at this stage must be calculated and compared to the allow-
able velocity to determine if the reach will require stabilization.
•
8.05.26

Appendices
•
•
Design Tables for Tables 8.05i through 8.05o may be used to facilitate the design of grass -lined
Grass -lined Channel channels with parabolic cross -sections. These design tables are based on a retar-
dance of "D" (vegetation newly cut) to determine Vt for stability considerations.
The top width, depth and veloctiy, V2, are based on a retardance of "C" (vegeta-
tion at normal cutting height for proper maintenance). Channel capacity is deter-
mined by these considerations.
Sample Problem 8.05e
Design of grass -lined channel
with a parabolic cross-
section using Design Table
8051 through 8.05o.
Table 8.05c provides retardance classifications for selected vegetal covers.
Table 8.05a gives maximum allowable velocities for grass -lined channels for
various grasses, soil conditions, and slopes. The velocities in Table 8.05a guide
the selection of Vt in the Design Tables and should not be exceeded. It is good
practice to use a value for VI that is significantly less than the maximum allow-
able when choosing a design cross section. The maximum allowable design
velocity should only be used when soils will readily support vegetation, special
care will be taken in establishing and maintaining grass linings, and a wider,
shallower channel cannot be constructed due to site limitations. Riprap-lined
and paved channels shouldbe considered when design velocities approach max-
imum allowable for vegetation.
Sample Problem 8.05e illustrates the design of grass -lined channels with par-
abolic cross -sections.
Determine the top width and depth for a vegetated channel.
Given:
0: 40 cis
Grade: 4%
Soil: easily erodible
Grass: bermudagrass
Site will allow a top width of 25 ft.
Find:
Channel top width and depth that will be stable and fit site conditions.
Solution:
From Table 8.05a use maximum permissible velocity = 5.0 ft/sec
From Design Table 8.05n use retardance "D" and "C"; grade 4.0%
Top width = 20.8 ft
Depth - 0.83 ft
V2 - 3.42
NOTE: A design velocity V1 of 4.0 fVsec was used as it was less than
maximum allowable and gave a top width that would fit site limitations.
Wide, shallow vegetated channels are less subject to erosion, are less
costly to maintain, and blend more readily into the natural landscape.
8.05.27

0
Design Tables for Tables 8.05p through 8.05y may be used to facilitate the design of grass -lined
Grass -lined Diversions diversions with parabolic cross -sections. These tables are based on a retardance
of "D" (vegetation newly cut) to determine V1 for stability considerations. To
determine channel capacity, chose a retardance of "C" when proper maintenance
is expected; otherwise, design channel capacity based on retardance "B". Table
8.05c provides retardance classifications for selected vegetal covers. Table
8.05a gives maximum allowable velocities for grass -lined channels. The per-
missible velocities guide the selection of V1 and should not be exceeded. It is
good practice to use a value for V1 that is significantly less than the maximum
allowable when choosing a design cross-section. When velocities approach the
maximum allowable, flatter grades should be evaluated or a more erosion resis-
tant liner such as riprap should be considered.
Sample Problem 8.05f
Design of grass -lined
diversion with a parabolic
cross-section using Design
Tables 8.05p through 8.05y.
Determine the top width and depth for a vegetated diversion.
Given:
0: 30 cis
Grade:1 %
Soil: easily erodible
Grass: Tall fescue
Maintenance: low, will be cut only twice a year. Site will allow a top
width of 18 ft.
Find:
Diversion top width and depth that will be stable and fit site condtions.
Solution:
From Table 8.05a use maximum permissible velocity = 4.5 ft/sec
From Table 8.05c use Design Tables for capacity based on
retardance "B"
From Table 8.05r use retardance "D" and "B"; grade 1 %
Top width -15 ft
Depth - 2.4 ft
V2 =1.8 ft/sec
NOTE: V1 < 4.5 ft/sec; Top width < 18 ft, design OK.
NOTE: In this case any other cross-section shown opposite 0 = 20
would have been stable. It is good practice, however, to select a cross-
section that will give a velocity, V1, well below the maximum allowable
whenever site conditions permit. Wide, shallow cross -sections are more
stable and require less maintenance. It is also prudent to evaluate flatter
design grades in order to best fit diversions to the site and keep
velocities well below maximum allowable.
•
r
•
8.05.28

Table 8.051
Parabolic Waterway Design (Retardance "D" and "C', Grade 0.25%)
Q
Vl
- 2.0
Vl
- 2.5
V1
- 3.0
V1
- 3.5
Vl
- 4.0
VI - 4.5
VI - 5.0
Vl - 5.5
V1 - 6.0
efa
T
D
V2
T
D
V2
T
D
V2
T
D
V2
T
D
V2
T D V2
T D V2
T D V2
T D V2
15
20
25
9.6
2.36
1.63
30
11.4
2.31
1.68
35
.13.2
2.27
1.73
40
15.0
2.25
1.76
10.4
2.67
2.13
45
16.8
2.23
1.78
11.6
2.62
2.19
50
18.6
2.21
1.80
12.8
2.59
2.24
55
20.4
2.20
1.82
14.0
2.56
2.28
60
22.2
2.19
1.83
15.2
2.53
2.31
65
24.0
2.18
1.84
16.5
2.54
2.30
70
25.8
2.18
1.85
17.7
2.52
2.33
12.6
3.05
2.70
75
27.6
2.17
1.86
18.9
2.51
2.35
13.4
3.00
2.76
80
29.4
2.17
1.87
20.1
2.50
2.37
14.3
3.01
2.76
90
33.1
2.17
1.86
22.6
2.49
2.38
16.0
2.97
2.81
100
36.7
2.17
1.87
25.1
2.49
2.38
17.7
2.95
'2.85
110
40.3
2.16
1.88
27.5
2.47
2.41
19.4
2.93
2.88
120
43.9
2.16
1.89
30.0
2.47
2.41
21.1
2.91
2.91
15.2
3.58
3.28
130
47.6
2.16
1.88
32.3
2.48
2.41
22.8
2.89
2.93
16.4
3.55
3.32
140
51.2
2.16
1.88
34.9
2.46
2.43
24.6
2.91
2.91
17.6
3.53
3.35
150
54.8
2.16
1.89
37.4
2.47
2.42
26.3
2.90
2.93
18.8
3.51
3.39
160
58.4
2.16
1.89
39.9
2.47
2.42
28.0
2.89
2.95
20.0
3.49
3.41
170
62.0
2.16
1.89
42.3
2.46
2.43
29.7
2.88
2.96
21.2
3.47
3.44
16.7
4.03
3.75
180
65.6
2.16
1.90
44.8
2.47
2.43
31.4
2.87
2.97
22.4
3.46
3.46
17.6
4.00
3.81
190
69.2
2.16
1.90
47:2
2.46
2.44
33.1
2.87
2.98
23.6
3.45
3.48
18.5
3.97
3.85
200
72.8
2.16
1.90
49.7
2.46
2.44
34.9
2.88
2.97
24.8
3.44
3.49
19.4
3.94
3.90
220
80.0
2.16
1.90
54.6
2.46
2.44
38.3
2.87
2.99
27.2
3.42
3.53
21.3
3.92
3.92
240
87.3
2.16
1.90
59.5
2.46
2.45
41.7
2.86
3.00
29.6
3,40
3.55
23.1
3.88
3.99
260
94.5
2.16
1.90
64.5
2.46
2.44
45.2
2.86
3.00
32.1
1.41
3.54
25.0
3.87
4.01
19.5 4.57 4.34
280
101.7
2.16
1.90
69.4
2.46
2.45
48.6
2.85
3.01
34.5
3.40
3.56
26.9
3.86
4.02
'21.0 4.57 4.34
300
108.9
2.16
1.90
74.3
2.46
2.45
52.1
2.86
3.00
36.9
3.39
3.58
28.7
3.83
4.07
22.4 4.53 4.40
a
b

00
0
tA
0
Table 8.05j
Parabolic Waterway Design (Retardance "D" and "C", Grade 0.5%)
Q
efS
Vl
- 2.0
V1
-
2.5
Vl
-
3.0
Vl
- 3.5
V1
- 4.0
Vl
- 4.5
Vl
- 5.0
Vl 5.5
Vl - 6.0
T
D
V2
T
D
V2
T
D
V2
T
D
V2
T
D
V2
T
D
V2
T
D
V2
T D V2
T
D V2
15
8.6
1.63
1.58
20
11.3
1.58
1.66
25
14.1
1.57
1.67
9.0
1.91
2.14
30
16.9
1.56
1.68
10.7
1.87
2.21
8.2
2.18
2.48
35
19.6
1.55
1.71
12.4
1.85
2.26
9.4
2.10
2.62
40
22.4
1.55
1.71
14.1
1.83
2.30
10.7
2.08
2.66
45
25.1
1.54
1.73
15.8
1.82
2.33
11.9
2.03
2.76
50
27.9
1.54
1.73
17.5
1.80
2.35
13.2
2.02
2.78
9.6
2.42
3.19
55
30.7
1.54
1.72
19.2
1.80
2.37
14.5
2.02
2.79
10.5
2.39
3.25
60
33.4
1.54
1.74
20.9
1.79
2.38
15.8
2.01
2.80
11.4
2.37
3.30
65
36.1
1.53
1.75
22.7
1.80
2.36
17.0
1.99
2.86
12.3
2.35
3.34
70
38.9
1.54
1.74
24.4
1.80
2.37
18.3
1.99
2.86
13.2
2.33
3.38
75
41.6
1.54
1.75
26.1
1.'1
2.38
19.6
1.99
2.86
14.1
2.32
3.41
11.2
2.71
3.66
80
44.3
1.53
1.75
27.8
1.74
2.39
20.9
1.99
2.86
15.0
2.31
3.43
11.8
2.65
3.80
90
49.8
1.53
1.75
31.2
1.78
2.41
23.5
1.99
2.8
16.9
2.31
3.42
13.3
2.65
3.78
100
55.3
1.53
1.75
34.6
1.78
2.42
26.0
1.97
2.9
18.7
2.29
3.47
14.7
2.63
3.85
11.9
3.02
4.13
110
60.8
1.54
1.75
38.1
1.78
2.41
28.6
1.97
2.9
20.5
2.28
3.50
16.1
2.60
3.90
13.0
2,98
4.22
120
66.3
1.54
1.75
41.5
1.78
2.42
31.2
1.98
2.9
22.4
2.29
3.49
17.5
2.58
3.94
14.1
2.94
4.30
130
71.7
1.53
1.76
44.9
1.78
2.42
33.7
1.97
2.9
24.2
2.28
3.51
18.9
2.57
3.98
15.2
2.91
4.36
140
77.2
1.54
1.76
48.3
1.78
2.43
36.3
1.97
2.9
26.0
2.27
3.54
20.4
2.58
3.95
16.4
2.93
4.34
150
82.6
1.54
1.76
51.7
1.78
2.43
38.9
1.97
2.91
27.9
2.28
3.52
21.8
2.57
3.98
17.5
2.90
4.39
14.0
3.34
4.77
160
88.0
1.53
1.76
55.1
1.78
2.44
41.4
1.97
2.9
29.7
2.27
3.54
23.2
2.56
4.01
18.6
2.88
4.44
14.9
3.33
4.80
170
93.4
1.53
1.77
58.5
1.78
2.44
44.0
1.97
2.9
31.5
2.26
3.55
24.6
2.55
4.03
19.8
2.89
4.41
15.7
3.27
4.92
180
98.8
1.53
1.77
61.9
1.78
2.44
46.5
1.96
2.9
33.3
2.26
3.57
26.1
2.56
4.01
20.9
2.88
4.45
16.6
3.26
4.94
190
104.2
1.54
1.77
65.3
1.78
2.44
49.1
1.97
2.9
35.2
2.27
3.55
27.5
2.56
4.03
22.0
2.86
4.49
17.5
3.26
4.96
200
109.6
1.54
1.77
68.7
1.78
2.44
51.6
1.96
2.9
37.0
2.26
3.56
28.9
2.55
4.04
23.1
2.85
4.52
18.4
3.25
4.98
15.3 3.72 5.23
220
120.5
1.54
1.77
75.5
1.78
2.44
56.8
1.97
2.9
40.7
2.26
3.56
31.8
2.55
4.04
25.4
2.85
4.53
20.2
3.24
5.01
16.7 3.66 5.36
240
131.3
1.54
1.77
82.3
1.78
2.45
61.9
1.97
2.94
44.3
2.26
3.58
34.6
2.54
4.07
'27.7
2.85
4.53
22.0
3.23
5.04
18.2 3.65 5.38
260
142.1
1.54
1.77
89.1
1.78
2:45
67.0
1.97
2.9
48.0
2.26
3.58
37.5
2.55
4.06
30.0
2.85
4.54
23.8
3.22
5.06
19.7 3.64 5.39
280
152.9
1.54
1.78
95.9
1.78
2.45
72.1
1.97
2.91
51.6
2.25
3.59
40.3
2.54
4.08
32.2
2.83
4.58
25.6
3.21
5.08
21.1 3.61 5.48
17.5 4.14 5.75
300
163.7
1.54
1.78
102.6
1.78
2.46
77.2
1.97
2.95
55.3
2.26
3.59
43.2
2.54
4.08
34.5
2.83
4.58
27.3
3.18
5.15
22.6 3.60 5.49
18.7 4.12 5.80
0
• f •

Table 8.05k
Parabolic Waterway Design (Retardance "D" and "C", Grade 1.0%)
Q
V1
- 2.0
V1
- 2.5
Vl
- 3.0
VI
- 3.5
V1
- 4.0
Vl
- 4.5
VI
- 5.0
VL
- 5.5
Vl
. 6.0
efe
T
D
V2
T
D
V2
T
D
V2
T
D
V2
T
D
V2
T
D
V2
T
D
V2
T
D
V2
T
D
V2
15
13.4
1.13
1.47
8.4
1.30
2.03
20
17.8
1.12
1.49
11.1
1.27
2.10
7.6
1.52
2.55
25
22.2
1.11
1.50
13.9
1.27
2.09
9.4
1.49
2.64
7.6
1.62
2.99
30
26.6
1.11
1.50
16.6
1.26
2.13
11.2
1.46
2.71
9.1
1.61
3.03
35
30.9
1.11
1.52
19.3
1.25
2.15
13.0
1.45
2.75
10.5
1.57
3.14
8.0
1.80
3.59
40
35.3
1.11
1.52
22.1
1.26
2.13
14.8
1.44
2.79
12.0
1.57
3.14
9.1
1.78
3.65
45
39.7
1.11
1.52
24.8
1.25
2.15
16.7
1.45
2.76
13.4
1.55
3.21
10.2
1.76
3.70
50
44.0
1.11
1.52
27.5
1.25
2.16
18.5
1.44
2.79
14.9
1.55
3.21
11.3
1.75
3.74
8.7
2.02
4.20
55
48.3
1.11
1.53
30.2
1.25
2.16
20.3
1.43
2.80
16.3
1.54
3.26
12.4
1.75
3.76
9.5
1.99
4.30
60
52.7
1.11
1.52
32.9
1.25
2.17
22.1
1.43
2.82
17.8
1.54
3.25
13.5
1.74
3.79,
10.4
2.01
4.26
65
57.0
1.11
1.53
35.6
1.25
2.17
23.9
1.43
2.83
19.2
1.53
3.29
14.6
1.73
3.81
11.2
1.98
4.33
9.3
2.22
4.66
70
61.3
1.11
1.53
38.3
1.25
2.17
25.7
1.43
2.84
20.7
1.53
3.27
15.6
1.71
3.90
12.0
1.96
4.40
10.0
2.21
4.69
75
65.6
1.11
1.53
41.0
1.25
2.18
27.5
1.42
2.85
22.1
1.53
3.31
16.7
1.71
3.90
12.8
1.95
4.46
10.7
2.21
4.71
80
69.8
1.11
1.54
43.7
1.25
2.18
29.3
1.42
2.85
23.6
1.53
3.29
17.8
1.71
3.91
13.7
1.96
4.42
11.3
2.16
4.85
90
78.5
1.11
1.54
49.1
1.25
2.18
32.9
1.42
2.87
26.5
1.53
3.31
20.0
1.70
3.93
15.3
1.93
4.52
12.7
2.16
4.87
10.6
2.42
5.20
100
87.1
1.11
1.54
54.5
1.25
2.18
36.6
1.43
2.85
29.4
1.52
3.32
22.2
1.70
3.94
17.0
1.93
4.52
14.1
2.15
4.89
11.7
2.39
5.31
110
95.6
1.11
1.54
59.9
1.25
2.18
40.2
1.42
2.86
32.3
1.52
3.33
24.4
1.70
3.94
18.7
1.93
4.52
15.4
2.12
5.00
12.9
2.40
5.28
11.1
2.59
5.67
120
104.2
1.11
1.54
65.2
1.25
2.19
43.8
1.42
2.87
35.2
1.52
3.33
26.6
1.70
3.95
20.3
1.92
4.59
16.8
2.12
5.00
14.0
2.37
5.36
12.1
2.59
5.69
130
112.7
1.11
1.55
70.6
1.25
2.19
47.4
1.42
2.87
38.1
1.52
3.34
28.8
1.70
3.95
22.0
1.92
4.58
18.2
2.13
5.00
15.1
2.35
5.44
13.0
2.55
5.83
140
121.2
1.11
1.55
76.0
1.25
2.19
51.0
1.42
2.87
41.0
1.52
3.34
30.9
1.69
3.99
23.7
1.92
4.57
19.6
2.13
5.00
16.2
2.34
5.50
14.0
2.55
5.83
150
129.7
1.11
1.55
81.3
1.25
2.19
54.6
1.42
2.87
43.9
1.52
3.34
33.1
1.69
3.99
25.3
1.91
4.62
20.9
2.11
5.07
17.4
2.35
5.46
15.0
2.55
5.84
160
138.1
1.11
1.55
86.6
1.25
2.20
58.2
1.42
2.88
46.8
1.52
3.34
35.3
1.69
3.99
27.0
1.91
4.61
22.3
2.11
5.06
18.5
2.33
5.51
15.9
2.52
5.95
170
146.6
1.11
1.55
91.9
1.25
2.20
61.7
1.42
2.89
49.7
1.52
3.34
37.5
1.69
3.99
28.7
1.92
4.60
23.7
2.11
5.05
19.6
2.32
5.56
16.9
2.52
5.94
180
155.0
1.11
1.55
97.2
1.25
2.20
65.3
1.42
2.89
52.5
1.52
3.36
39.6
1.69
4.01
30.3
1.91
4.63
25.0
2.10
5.10
20.7
2.31
5.60
17.9
2.52
5.93
190
163.4
1.11
1.55
102.5
1.25
2.20
68.9
1.42
2.89
55.4
1.52
3.36
41.8
1.69
4.01
32.0
1.91
4.62
26.4
2.10
5.09
21.9
2.32
5.56
18.8
2.50
6.02
200
171.7
1.11
1.56
107.8
1.25
2.20
72.4
1.42
2.90
58.3
1.52
3.35
44.0
1.69
4.00
33.6
1.91
4.65
27.8
2.11
5.08
23.0
2.32
5.59
19.8
2.50
6.01
220
188.7
1.11
1.56
118.4
1.25
2.21
79.6
1.42
2.89
64.0
1.52
3.37
48.4
1.70
4.00
37.0
1.91
4.63
30.5
2.10
5.12
25.3
2.32
5.59
21.7
2.48
6.08
240
205.5
1.11
1.56
129.0
1.25
2.21
86.7
1.42
2.90
69.8
1.52
3.37
52.7
1.69
4.01
40.3
1.91
4.65
33.3
2.10
5.11
27.5
2.30
5.65
23.6
2.47
6.13
260
222.4
1.11
1.56
139.6
1.25
2.21
93.9
1.42
2.90
75.5
1.52
3.38
57.1
1.69
4.01
43.6
1.91
4.66
36.0
2.10
5.14
29.8
2.30
5.64
25.6
2.48
6.11
280
239.1
1.11
1.56
150.2
1.25
2.22
101.0
1.42
2.91
81.3
1.52
3.37
61.4
1.69
4.02
46.9
1.90
4.68
38.8
2.10
5.12
32.1
2.31
5.63
27.5
2.47
6.15
300
255.9
1.11
1.56
160.8
1.25
2.22
108.1
1.42
2.91
87.0
1.52
3.38
65.7
1.69
4.03
50.3
1.91
4.66
41.5
2.10
5.14
34.3
2.30
5.68
29.5
2.48
6.12
00
b
u
a
b

Table 8.051
Parabolic Waterway Design (Retardance "D" and "C", Grade 2.0%)
Q
efs
Vl
- 2.0
Vl
-
2.5
Vl
-
3.0
V1
- 3.5
V1
- 4.0
VI
- 4.5
V1
- 5.D
Vl - 5.5
VI - 6.0
T
D
V2
T
D
V2
T
D
V2
T
D
V2
T
D
V2
T
D
V2
T
D
V2
T
D
V2
T
D
V2
15
20.8
0.81
1.32
12.8
0.91
1.90
9.3
1.00
2.37
6.7
1.15
2.85
20
27.6
0.80
1.33
17.1
0.91
1.89
12.3
0.99
2.43
8.8
1.12
3.00
6.5
1.29
3.51
5.4
1.41
3.84
25
34.5
0.81
1.33
21.3
0.91
1.91
15.4
0.99
2.43
11.0
1.11
3.01
8.0
1.25
3.69
6.7
1.38
3.96
30
35
41.3
48.0
0.81
1.34
25.5
0.9.1
1.92
18.4
0.98
2.46
13.2
1.11
3.02
9.6
1.24
3.71
7.9
1.33
4.20
6.6
1.49
4.48
40
54.8
0.80
0.80
1.33
29.7
0.91
1.93
21.5
0.99
2.44
15.3
1.10
3.08
11.1
1.22
3.82
9.2
1.33
4.23
7.6
1.45
4.68
45
61.5
0.80
1.34
1.35
33.9
38.1
0.91
0.91
1.93
1.93
24.5
27.5
0.98
0.98
2.46
2.47
17.5
19.6
1.10
3.07
12.7
1.22
3.81
10.5
1.32
4.26
8.7
1.45
4.67
7.2
1.65
4.96
50
68.2
0.80
1.35
42.3
0.91
1.93
30.5
0.98
2.48
21.8
1.10
1.10
3.11
3.09
14.3
15.8
1.23
1.22
3.80
3.86
11.8
13.1
1.32
1.32
4.27
9.7
1.43
4.80
8.0
1.61
5.16
55
74.9
0.81
1.35
46.4
0.91
1.94
33.5
0.98
2.48
23.9
1.09
3.12
17.4
1.22
3.84
14.4
1.32
4.28
4.29
10.8
11.8
1.43
1.42
4.78
4.87
8.8
9.7
1.57
5.33
7.5
1.74
5.64
60
81.5
0.81
1.36
50.6
0.91
1.93
36.5
0.98
2.49
26.1
1.10
3.10
18,9
1.21
3.89
15.6
1.30
4.38
12.9
1.42
4.84
10.6
1.58
1.59
5.30
5.28
8.2
9.0
1.72
1.74
5.75
5.65
65
70
88.1
94.7
0.81
0.81
1.36
1.36
54.7
0.91
1.94
39.5
0.98
2.49
28.2
1.10
3.12
20.5
1.22
3.87
16.9
1.30
4.38
13.9
1.41
4.92
11.4
1.56
5.40
9.7
1.73
5.74
75
101.2
0.81
1.36
58.8
62.9
0.91
0.91
1.94
1.94
42.5
45.5
0.98
0.99
2.49
2.49
30.3
1.09
3.14
22.0
1.21
3.90
18.2
1.31
4.37
15.0
1.42
4.89
12.3
1.57
5.37
10.4
1.71
5.82
80
107.8
0.81
1.36
67.0
0.91
1.95
48.4
0.98
2.50
32.4
34.6
1.09
1.10
3.13
3.13
23.6
1.22
3.88
19.5
1.31
4.37
16.0
1.41
4.95
13.1
1.55
5.46
11.1
1.70
5.89
90
121.0
0.81
1.37
75.2
0.91
1.95
54.4
0.98
2.50
38.8
1.09
3.15
25.1
28.2
1.21
1.21
3.91
3.92
20.7
1.30
4.42
17.1
1.41
4.91
14.0
1.56
5.43
11.8
1.69
5.95
100
134.2
0.81
1.37
83.4
0.91
1.96
60.4
0.99
2.50
43.1
1.10
3.15
31.3
1.21
3.93
23.3
25.9
1.30
1.30
4.41
4.40
19.2
21.3
1.41
4.94
15.7
1.55
5.48
13.3
1.69
5.92
110
147.3
0.81
1.37
91.6
0.91
1.96
66.3
.0.98
2.51
47.4
1.10
3.15
34.4
1.21
3.93
28.4
1.30
4.44
23.4
1.41
1.40
4.96
4.98
17.4
19.1
1.55
1.54
5.52
5.55
14.7
16.2
1.68
6.02
120
160.3
0.81
1.38
99.8
0.91
1.96
72.2
0.98
2.51
51.6
1.10
3.16
37.5
1.21
3.93
31.0
1.30
4.42
25.5
1.40
4.99
20.8
1.54
5.58
17.6
1.68
1.67
5.99
6.06
130
173.3
0.81
1.38
107.9
0.91
1.96
78.1
0.98
2.51
55.8
1.09
3.17
40.6
1.21
3.93
33.5
1.30
4.45
27.6
1.40
5.00
22.5
1.53
5.60
19.1
1.68
6.03
140
186.3
0.81
1.38
116.0
0.91
1..97
84.0
0.99
2.52
60.1
1.10
3.16
43.6
1.21
3.96
36.0
1.29
4.47
29.7
1.40
5.00
24.2
1.53
5.62
20.5
1.67
6.08
150
199.2
0.81
1.38
124.1
0.91
1.97
89.9
0.99
2.52
64.3
1.10
3.16
46.7
1.21
3.96
38.6
1.30
4.45
31.8
1.40
5.00
25.9
1.53
5.63
21.9
1.66
6.13
160
212.0
0.81
1.38
132.1
0.91
1.97
95.7
0.99
2.52
68.5
1.10
3.17
49.8
1.21
3.95
41.1
1.30
4.47
33.8
1.40
5.05
27.6
1.53
5.64
23.4
1.67
6.09
170
224.8
0.81
1.39
140.2
0.91
1.97
101.6
0.99
2.32
72.7
1.10
3.17
52.8
1.21
3.97
43.6
1.30
4.48
35.9
1.40
5.05
29.3
1.53
5.65
24.8
1.66
6.13
180
237.5
0.81
1.39
148.2
0.91
1.98
107.4
0.99
2.53
76.8
1.10
3.18
55.9
1.21
3.96
46.2
1.30
4.46
38.0
1.40
5.04
31.0
1.53
5.65
26.3
1.67
6.10
190
250.2
0.81
1.39
156.1
0.91
1.98
113.2
0.99
2.53
81.0
1.10
3.18
58.9
1.21
3.97
48.7
1.30
4.47
40.1
1.40
5.04
32.7
1.53
5.65
27.7
1.67
6.13
200
262.8
0.81
1.39
164.1
0.91
1.98
119.0
0.99
2.53
85.2
1.10
3.18
61.9
1.21
3.98
51.2
1.30
4.48
42.2
1.40
5.03
34.4
1.53
5.66
29.1
1.66
6.16
220
288.5
0.81
1.40
180.2
0.91
1.99
130.7
0.99
2.5
93.6
1.10
3.18
68.1
1.21
3.97
56.3
1.30
4.48
46.3
1.40
5.06
37.8
1.53
5.67
32.0
1.66
6.16
240
314.1
0.81
1.40
196.2
0.91
1.99
142.4
0.99
2.54
102.0
1.10
3.19
74.2
1.21
3.98
61.3
1.30
4.50
50.5
1.40
5.06
41.2
1.53
5.68
34.9
1.66
6.16
260
339.5
0.81
1.40
212.2
0.91
1.99
154.0
0.99
2.54
110.3
1.10
3.20
80.3
1.21
3.98
66.4
1.30
4.49
54.7
1.40
5.05
44.6
1.53
5.68
37.8
1.66
6.16
280
364.9
0.81
1.40
228.2
0.92
1.99
165.6
0.99
2.55
118.7
1.10
3.19
86.3
1.21
4.00
71.4
1.30
4.50
58.8
1:40
5.07
48.0
1.53
5.68
40.6
1.66
6.20
300
390.2
0.81
1.40
244.1
0.92
2.00
177.2
0.99
2.55
127.0
1.10
3.20
92.4
1.21
4.00
76.4
1.30
4.51
63.0
1.40
5.06
51.4
1.53
5.68
43.5
1.66
6.19
0

Table 8.05m
Parabolic Waterway Design (Retardance "D" and "C", Grade 3.0%)
Q
V1
- 2.0
V1
- 2.5
V1
- 3.0
V1
3.5
V1
4.0
V1
4.5
V1
5.0
V1
5.5
V1
6.0
ofS
T
D
V 2
T
D
V2
T
D
V2
T
D
V2
T
D
V2
T
D
V2
i
D
V2
i
D
V2
T
D
V2
15
23.6
0.69
1.35
16.3
0.76
1.80
11.4
0.83
2.33
8.8
0.90
2.77
6.5
1.01
3.37
5.0
1.16
3.78
20
31.4
0.69
1.36
21.7
0.76
1.81
15.2
0.83
2.34
11.7
0.90
2.81
8.6
0.99
3.48
6.6
1.13
3.14
5.9
1.19
4.17
25
39.2
0.69
1.36
27.0
0.75
1.83
19.0
0.83
2.33
14.6
0.90
2.83
10.8
0.99
3.44
8.1
1.09
4.18
7.3
1.16
4.33
6.0
1.27
4.80
30
46.9
0.69
1.37
32.4
0.75
1.82
22.7
0.83
2.36
17.4
0.88
2.89
12.9
0.98
3.49
9.7
1.08
4.22
8.7
1.15
4.44
7.1
1.24
5.03
5.8
1.41
5.37
35
54.6
0.69
1.37
37.7
0.75
1.83
26.4
0.83
2.38
20.3
0.89
2.88
15.0
0.98
3.53
11.3
1.08
4.25
10.1
1.13
4.51
8.3
1.24
5.02
6.7
1.38
5.55
40
62.2
0.69
1.37
43.0
0.75
1.83
30.2
0.83
2.37
23.2
0.89
2.88
17.1
0.98
3.55
12.9
1.08
4.26
11.5
1.13
4.57
9.4
1.22
5.17
7.6
1.36
5.70
45
69.9
0.70
1.37
48.3
0.75
1.83
33.9
0.83
2.37
26.0
0.88
2.90
19.2
0.97
3.57
14.5
1.08
4.27
12.9
1.12
4.61
10.6
1.22
5.14
8.5
1.34
5.81
50
77.4
0.69
1.38
53.5
0.75
1.84
37.6
0.83
2.38
28.9
0.89
2.89
21.3
0.97
3.58
16.0
1.06
4.36
14.3
1.12
4.63
11.7
1.21
5.24
9.4
1.33
5.90
55
85.0
0.70
1.38
58.7
0.75
1.85
41.2
0.83
2.40
31.7
0.89
2.91
23.4
0.97
3.58
17.6
1.06
4.35
15.7
1.11
4.66
12.5-
1.21
5.20
10.4
1.35
5.80
60
92.5
0.70
1.38
64.0
0.75
1.84
44.9
0.83
2.40
34.5
0.88
2.92
25.5
0.97
3.59
19.2
1.07
4.35
17.1
1.11
4.67
14.0
1.20
5.28
11.3
1.34
5.87
65
99.9
0.69
1.39
69.1
0.75
1.85
48.6
0.83
2.39
37;3
0.88
2.93
27.6
0.97
3.59
20.8
1.07
4.34
18.5
1.11
4.69
15.2
1.21
5.24
12.2
1.33
5.93
70
107.3
0.69
1.39
74.3
0.75
1.86
52.2
0.83
2.40
40.1
0.88
2.93
29.7
0.98
3.59
22.3
1.06
4.39
19.9
1.11
4.69
16.3
1.20
5.30
13.1
1.32
5.98
75
114.7
0.70
1.39
79.4
0.75
1.86
55.8
0.83
2.41
42.9
0.88
2.94
31.8
0.98
3.59
23.9
1.06
4.38
21.3
1.11
4.70
17.5
1.21
5.26
14.0
1.32
6.02
80
122.1
0.70
1.40
84.5
0.75
1.87
59.4
0.83
2.42
45.7
0.88
2.94
33.9
0.98
3.58
25.5
1.07
4.36
22.7
1.11
4.70
18.6
1.20
5.31
15.0
1.33
5.94
90
137.0
0.70
1.40
94.9
0.75
1.87
66.7
0.83
2.42
51.4
0.89
2.93
38.0
0.97
3.61
28.6
1.06
4.40
25.5
1.11
4.72
20.9
1.20
5.33
16.8
1.32
6.01
100
151.8
0.70
1.40
105.2
0.75
1.87
74.0
0.83
2.42
57.0
0.89
2.94
42.2
0.98
3.61
31.7
1.06
4.42
28.3
1.11
4.73
23.2
1.20
5.34
18.6
1.31
6.08
110
166.6
0.70
1.41
115.5
0.75
1.87
81.3
0.83
2.42
62.6
0.89
2.95
46.4
0.98
3.61
34.9
1.06
4.40
31.0
1.10
4.78
25.5
1.20
5.34
20.5
1.32
6.04
120
181.3
0.70
1.41
125.7
0.75
1.88
88.5
0.83
2.43
68.2
0.89
2.95
50.5
0.98
3.62
38.0
1.06
4.42
33.8
1.11
4.78
27.7
1.19
5.40
22.3
1.32
6.08
130
195.9
0.70
1.41
135.9
0.76
1.88
95.7
0.83
2.43
73.7
0.89
2.96
54.6
0.98
3.63
41.1
1.06
4.43
36.6
1:11
4.77
30.0
1.19
5.40
24.2
1.32
6.04
140
210.5
0.70
1.41
146.1
0.76
1.88
102.8
0.83
2.44
79.3
0.89
2.96
58.8
0.98
3.62
44.2
1.06
4.44
39.4
1:11
4.77
32.3
1.20
5.39
26.0
1.32
6.08
150
225.0
0.70
1.42
156.2
0.76
1.89
110.0
0.83
2.44
84.8
0.89
2.96
62.9
0.98
3.63
47.3
1.06
4.44
42.1
1.11
4.80
34.6
1.20
5.38
27.8
1.31
6.11
160
239.4
0.70
1.42
166.2
0.76
1.89
117.1
0.83
2.45
90.3
0.89
2.97
67.0
0.98
3.63
50.4
1.06
4.45
44.9
1.11
4.79
36.8
1.19
5.42
29.6
1.31
6.13
170
253.7
0.70
1.42
176.2
0.76
1.90
124.2
0.83
2.45
95.8
0.89
2.97
71.1
0.98
3.64
53.5
1.06
4.45
47.7
1.11
4.78
39.1
1.20
5.41
31.5
1.32
6.09
180
268.0
0.70
1.43
186.2
0.76
1.90
131.2
0.83
2.46
101.3
0.89
2.97
75.2
0.98
3.64
56.6
1.06
4.45
50.4
1.11
4.80
41.3
1.19
5.44
33.3
1.32
6.11
190
282.2
0.70
1.43
196.1
0.76
1.90
138.3
0.83
2.46
106.7
0.89
2.98
79.2
0.98
3.65
59.7
1.07
4.45
53.1
1.11
4.81
43.6
1.20
5.42
35.1
1.32
6.12
200
296.3
0.70
1.43
206.0
0.76
1.90
145.3
0.83
2.46
112.2
0.89
2.98
83.3
0.98
3.65
62.7
1.06
4.47
55.9
1.11
4.80
45.8
1.19
5.45
36.9
1.32
6.14
720
325.1
0.70
1.44
226.1
0.76
1.91
159.5
0.83
2.47
123.2
0.89
2.98
91.5
0.98
3.65
68.9
1.06
4.47
61.4
1.11
4.81
50.4
1.20
5.43
40.6
1.32
6.12
240
353.8
0.70
1.44
246.2
0.76
1.91
173.7
0.83
2.47
134.2
0.89
2.99
99.7
0.98
3.65
75.1
1.07
4.47
66.9
1.11
4.81
54.9
1.20
5.44
44.2
1.32
6.15
260
382.4
0.70
1.44
266.1
0.76
1.92
187.8
0.83
2.48
145.1
0.89
2.99
107.8
0.98
3.67
81.3
1.07
4.47
72.4
1.11
4.82
59.4
1.20
5.45
47.8
1.31
6.17
280
410.8
0.70
1.45
286.0
0.76
1.92
201.9
0.83
2.48
156.0
0.89
3.00
116.0
0.98
3,66
87.4
1.07
4.48
77.9
1.11
4.82
63.9
1.20
5.46
51.5
1.32
6.15
300
439.0
0.70
1.45
305.8
0.76
1.92
215.9
0.83
2.49
166.9
0.89
3.00
124.1
0.98
3.67
93.6
1.07
4.47
83.3
1.11
4.83
68.4
1.20
5.46
55.1
1.32
6.17
'M

Table 8.05n
Parabolic Waterway Design (Retardance "D" and "C", Grade 4.0%)
Q
eiE
V1
- 2.0
V1
2.5
Vl
3.0
Vl
3.5
V1
4.0
VY
4.5
Vl
5.0
V1
5.5
Vl
6.0
T
D
V2
T
D
V2
i
D
V2
T
D
V2
T
D
V2
T
D
V2
T
D
V2
i
D
V2
T
D
Y2
15
27.9
0.62
1.29
19.9
0.66
1.68
13.9
0.73
2.20
10.3
0.79
2.73
7.9
0.85
3.28
6.3
0.92
3.78
4.9
1.06
4.21
20
25
37.1
46.2
0.62
0.62
1.29
1.30
26.3
33.0
0.66
0.66
1.69
18.5
0.72
2.21
13.7
0.78
2.76
10.5
0.84
3.33
8.4
0.92
3.81
6.4
1.01
4.52
5.5
1.09
4.88
30
55.3
0.62
1.30
39.5
0.66
1.70
1.70
23.0
27.6
0.72
0.72
2.24
2.23
17.1
20.4
0.78
2.77
13.1
0.84
3.35
10.5
0.92
3.82
8.0
1.01
4.55
6.8
1.06
5.09
5.7
5.7
1.20
5.34
35
0.62
1.31
0.66
1.71
32.6
0.72
2.25
27.8
0.77
0.78
2.82
2.81
15.7
18.3
0.84
0.84
3.36
12.5
0.91
3.92
9.5
0.99
4.71
8.2
1.07
5.09
1.20
5.34
71
40
73.3
73.3
0.62
1.31
52.4
52.4
0.66
1.71
36.6
0.72
2.25
27.1
0.77
2.83
20.8
0.83
3.37
3.42
I4.6
16.6
0.91
0.90
3.90
3.96
11.1
12.7
0.99
1.00
4.70
4.68
9.5
1.06
5.15
7.8
1.15
5.77
45
50
82.2
99.9
0.62
1.32
58.8
0.66
1.72
41.1
0.72
2.26
30.4
0.77
2.85
23.4
0.84
3.41
18.7
0.91
3.94
14.2
0.98
4.77
10.8
12.2
1.04
1.05
5.24
5.17
8.9
18.9
1.14
1.14
5.81
5.81
55
99.9
0.62
0.62
1.32
1.72
71.5
71.5
0.66
0.66
1.73
1.13
0.72
2.26
33.0
0.77
2.86
26.0
0.84
3.40
20.7
0.90
3.97
15.8
0.99
4.74
13.5
1.05
5.24
I1.1
1.14
5.85
60
108.7
0.62
1.32
77.8
0.66
1.73
50.1
50.1
54.5
0.72
0.72
2.26
2.26
37.0
40.3
0.77
0.77
2.86
2.87
28.5
0.84
3.43
22.8
0.91
3.95
17.3
0.98
4.80
14.8
1.04
5.28
12.2
1.14
5.87
31.0
0.83
3.45
24.8
0.90
3.97
18.9
0.99
4.77
16.1
1.04
5.32
13.3
1.14
5.88
65
70
117.4
126.1
0.62
0.62
1.33
1.33
84.1
90.3
0.66
1.73
58.9
0.72
2.27
43.6
0.77
2.87
33.6
0.84
3.43
26.8
0.90
3.99
20.4
0.98
4.81
17.5
1.05
5.26
14.3
1.12
6.00
75
134.7
0.62
1.33
96.5
0.66
0.66
1.74
1.74
63.3
67.7
0.72
0.72
2.27
2.28
46.9
50.1
0.77
2.86
36.1
0.84
3.44
28.8
0.90
4.01
21.9
0.98
4.85
18.8
1.04
5.29
15.4
1.12
6.00
80
143.3
0.62
1.34
102.7
0.66
1.74
72.1
0.72
2.28
53.3
0.77
0.77
2.88
2.89
38.6
41.1
0.84
0.84
3.45
30.9
0.91
3.98
23.5
0.98
4.82
20.1
1.04
5.31
16.5
1.13
5.99
90
160.8
0.62
1.34
115.2
0.66
1.75
80.9
0.72
2.28
59.9
0.77
2.89
46.2
0.84
3.46
3.46
32.9
36.9
0.91
0.90
3.99
4.01
25.0
28.1
0.98
4.84
21.4
1.04
5.33
17.6
1.13
5.98
100
178.2
0.62
1.34
127.7
0.66
1.75
89.7
0.72
2.29
66.4
0.77
2.90
51.2
0.84
3.47
41.0
0.91
4.00
31.2
0.98
0.98
4.85
4.85
24.0
26.7
1.04
5.38
19.7
1.12
6.07
110
195.4
0.62
1.35
140.1
0.66
1.76
98.5
0.72
2.29
72.9
0.77
2.90
56.2
0.84
3.48
45.0
0.90
4.02
34.3
0.98
4.85
29.3
1.04
1.04
5.35
5.37
21.9
24.1
1.12
6.05
120
212.6
0.62
1.35
152.5
0.66
1.76
107.2
0.72
2.30
79.4
0.77
2.90
61.2
0.84
3.49
49.0
0.90
4.03
37.3
0.98
4.88
31,9
1.04
5.40
26.2
1.12
1.12
6.03
6.09
130
229.6
0.62
1.35
164.8
0.66
1.76
115.9
0.72
2.30
85.9
0.77
2.91
66.2
0.84
3.49
53.0
0.90
4.03
40.4
0.98
4.87
34.6
1.04
5.36
28.4
1.12
6.07
140
246.6
0.62
1.36
177.0
0.66
1.77
124.5
0.72
2.30
92.3
0.77
2.91
71.2
0.84
3.49
57.0
0.90
4.04
43.4
0.98
4.90
37.2
1.04
5.38
30.5
1.12
6.10
150
263.5
0.62
1.36
189.1
0.66
1.77
133.2
0.73
2.30
98.7
0.77
2.92
76.2
0.84
3.49
61.0
0.91
4.04
46.5
0.98
4.88
39.8
1.04
5.39
32.7
1.12
6.08
160
280.3
0.62
1.36
201.2
0.66
1.78
141.7
0.73
2.31
105.1
0.77
2.92
81.1
0.84
3.50
65.0
0.91
4.04
49.5
0.98
4.90
42.4
1.04
5.40
34.8
1.12
6.11
170
296.9
0.62
1.37
213.3
0.67
1.78
150.3
0.73
2.31
111.5
0.78
2.92
86.0
0.84
3.51
68.9
0.91
4.05
52.5
0.98
4.91
45.0
1.04
5.40
36.9
1.12
6.13
180
313.5
0.62
1.37
225.3
0.67
1.78
158.8
0.73
2.32
117.8
0.78
2.93
90.9
0.84
3.52
72.9
0.91
4.05
55.6
0.98
4.90
47.6
1.04
5.40
39.1
1.12
6.11
190
330.0
0.62
1.37
237.2
0.67
1.79
167.3
0.73
2.32
124.2
0.78
2.93
95.8
0.84
3.52
76.8
0.91
4.06
58.6
0.98
4.90
50.2
1.04
5.40
41.2
1.12
6.12
200
346.4
0.62
1.37
249.1
0.67
1.79
175.7
0.73
2.32
130.5
0.78
2.93
100.7
0.84
3.52
80.7
0.91
4.07
61.6
0.98
4.91
52.7
1.04
5.43
43.3
1.12
6.14
22C
380.0
0.62
1.38
273.3
0.67
1.79
192.9
0.73
2.33
143.3
0.78
2.93
110.6
0.84
3.53
88.7
0.91
4.07
67.6
0.98
4.93
57.9
1.04
5.44
47.6
1.12
6.14
240
413.3
0.62
1.38
297.4
0.67
1.80
209.9
0.73
2.33
156.0
0.78
2.94
120.4
0.84
3.53
96.6
0.91
4.07
73.7
0.98
4.93
63.1
1.04
5.44
51.9
1.12
6.14
260
446.5
0.62
1.39
321.4
0.67
1.80
227.0
0.73
2.33
168.7
0.78
2.94
130.2
0.84
3.54
104.5
0.91
4.08
79.7
0.98
4.94
68.3
1.04
5.44
56.2
1.12
6.13
280
479.5
0.62
1.39
345.3
0.67
1.80
243.9
0.73
2.34
181.3
0.78
2.95
140.0
0.84
3.54
112.3
0.91
4.09
85.8
0.99
4.93
73.5
1.04
5.44
60.4
1.12
6.15
300
512.3
0.62
1.39
369.0
0.67
1.81
260.8
0.73
2.34
193.9
0.78
2.95
149.8
0.84
3.55
120.2
0.91
4.09
91.8
0.99
4.94
78.6
1.04
5.46
64.7
1.12
6.14
a
9 0 0

•
Table 8.05o
Parabolic Waterway Design (Retardance "D" and "C", Grade 5.0%)
Q
Vl
- 2.0
VI
- 2.5
Vl
- 3.0
Vl
- 3.5
VI
- 4.0
VI
- 4.5
V1
- 5.0
Vl
- 5.5
Vl
. 6.0
efs
T
D
V2
T
D
V2
T
D
V2
T
D
V2
T
D
V2
T
D
V2
T
D
V2
T
D
V2
T
D
V2
15
29.3
0.57
1.33
21.1
0.60
1.74
15.0
0.66
2.23
12.2
0.70
2.58
9.0
0.75
3.25
7.2
0.83
3.70
5.8
0.93
4.09
4.6
0.99
4.81
20
39.0
0.57
1.33
28.1
0.61
1.74
19.9
0.66
2.26
16.2
0.70
2.62
12.0
0.75
3.26
9.5
0.81
3.84
7.6
0.89
4.35
6.1
0.97
4.95
5.3
1.06
5.21
25
48.6
0.57
1.34
35.1
0.61
1.73
24.8
0.66
2.28
20.3
0.70
2.59
15.0
0.75
3.27
11.9
0.81
3.82
9.5
0.89
4.37
7.6
0.96
5.03
6.5
1.02
5.56
30
58.1
0.57
1.34
42.0
0.61
1.74
29.7
0.66
2.28
24.3
0.70
2.61
18.0
0.76
3.26
14.2
0.80
3.89
11.3
0.87
4.49
9.1
0.96
5.08
7.8
1.01
5.59
35
67.6
0.57
1.35
48.8
0.61
1.75
34.6
0.66
2.28
28.2
0.70
2.64
20.9
0.75
3.30
16.6
0.81
3.86
13.2
0.88
4.47
10.5
0.94
5.26
9.1
1.01
5.60
40
77.0
0.57
1.35
55.7
0.61
1.75
39.5
0.66
2.28
32.2
0.70
2.64
23.9
0.75
3.29
18.9
0.80
3.90
15.1
0.88
4.46
12.0
0.94
5.26
10.3
0.99
5.77
45
86.4
0.57
1.35
62.5
0.61
1.75
44.3
0.66
2.29
36.1
0.70
2.65
26.8
0.75
3.31
21.3
0.81
3.87
16.9
0.87
4.52
13.5
0.94
5.25
11.6
1.00
5.75
50
95.7
0.57
1.36
69.2
0.61
1.76
49.1
0.66
2.30
40.1
0.70
2.64
29.7
0.75
3.32
23.6
0.81
3.89
18.8
0.88
4.50
15.0
0.94
5.25
12.9
1.00
5.73
55
105.0
0.57
1.36
75.9
0.61
1.77
53.9
0.66
2.30
44.0
0.70
2.65
32.6
0.75
3.33
25.9
0.81
3.90
20.6
0.87
4.54
16.5
0.94
5.24
14.1
0.99
5.84
60
114.2
0.57
1.36
82.6
0.61
1.77
58.7
0.66
2.30
47.9
0.70
2.66
35.5
0.75
3.34
28.2
0.81
3.92
22.4
0.87
4.57
17.9
0.93
5.32
15.4
0.99
5.81
65
123.4
0.57
1.36
89.3
0.61
1.77
63.4
0.66
2.31
51.8
0.70
2.66
38.4
0.75
3.34
30.5
0.81
3.92
24.3
0.87
4.54
19.4
0.94
5.30
16.7
1.00
5.78
70
132.4
0.57
1.37
95.9
0.61
1.77
68.2
0.66
2.31
55.6
0.70
2.67
41.3
0.75
3.34
32.8
0.81
3.93
26.1
0.87
4.56
20.8
0.93
5.36
17.9
0.99
5.85
75
141.5
0.57
1.37
102.4
0.61
1.78
72.9
0.66
2.31
59.4
0.70
2.68
44.1
0.75
3.36
35.1
0.81
3.93
27.9
0.87
4.58
22.3
0.93
5.34
19.2
1.00
5.82
80
150.5
0.57
1.37
109.0
0.61
1.78
77.5
0.66
2.32
63.3
0.70
2.68
47.0
0.75
3.36
37.4
0.81
3.92
29.7
0.87
4.60
23.8
0.94
5.32
20.4
0.99
5.88
90
168.8
0.57
1.38
122.3
0.61
1.79
87.0
0.66
2.33
71.0
0.70
2.69
52.8
0.75
3.36
42.0
0.81
3.93
33.4
0.87
4.59
26.7
0.94
5.35
22.9
0.99
5.91
100
187.0
0.57
1.38
135.5
0.61
1.79
96.5
0.66
2.33
78.7
0.70
2.70
58.5
0.75
3.37
46.5
0.81
3.96
37.0
0.87
4.62
29.6
0.93
5.38
25.5
0.99
5.86
110
205.1
0.57
1.38
148.7
0.61
1.79
105.9
0.66
2.33
86.4
0.70
2.70
64.3
0.75
3.37
51.1
0.81
3.96
40.1
0.87
4.61
32.5
0.93
5.39
28.0
0.99
5.88
120
223.1
0.57
1.39
161.8
0.61
1.80
115.3
0.66
2.33
94.1
0.70
2.70
70.0
0.75
3.38
55.7
0.81
3.96
44.3
0.87
4.62
35.4
0.93
5.41
30.5
0.99
5.89
130
240.9
0.57
1.39
174.8
0.61
1.80
124.6
0.66
2.34
101.7
0.70
2.71
75.7
0.76
3.38
60.2
0.81
3.97
47.9
0.87
4.64
38.3
0.93
5.41
33.0
0.99
5.90
140
258.7
0.57
1.40
187.7
0.61
1.81
133.9
0.66
2.34
109.3
0.70
2.71
81.3
0.75
3.39
64.7
0.81
3.98
51.5
0.87
4.64
41.2
0.93
5.42
35.5
0.99
5.91
150
276.4
0.58
1.40
200.6
0.61
1.81
143.1
0.66
2.35
116.8
0.70
2.72
87.0
0.76
3.39
69.3
0.81
3.97
55.1
0.87
4.65
44.1
0.93
5.42
37.9
0.99
5.96
160
293.9
0.58
1.40
213.4
0.61
1.81
152.3
0.66
2.35
124.3
0.70
2.72
92.6
0.76
3.40
73.7
0.81
3.99
58.7
0.87
4.65
47.0
0.94
5.42
40.4
0.99
5.95
170
311.4
0.58
1.40
226.1
0.61
1.82
161.5
0.66
2.35
131.8
0.70
2.73
98.2
0.76
3.41
78.2
0.81
3.99
62.3
0.87
4.65
49.9
0.94
5.41
42.9
0.99
5.95
180
328.7
0.58
1.41
238.8
0.61
1.82
170.6
0.66
2.36
139.2
0.70
2.73
103.8
0.76
3.41
82.7,
0.81
3.99
65.9
0.87
4.65
52.7
0.93
5.44
45.4
0.99
5.94
190
346.0
0.58
1.41
251.4
0.61
1.83
179.7
0.67
2.36
146.6
0.70
2.74
109.4
0.76
3.41
87.1
0.81
4.00
69.4
0.87
4.67
55.6
0.94
5.43
47.8
0.99
5.97
200
363.1
0.58
1.42
263.9
0.61
1.83
188.7
0.67
2.37
154.0
0.70
2.74
114.9
0.76
3.42
91.6
0.81
4.00
73.0
0.87
4.66
58.4
0.94
5.45
50.3
0.99
5.96
220
398.3
0.58
1.42
289.6
0.62
1.83
207.1
0.67
2.37
169.0
0.70
2.75
126.1
0.76
3.43
100.6
0.81
4.00
80.1
0.87
4.68
64.2
0.94
5.45
55.2
0.99
5.99
240
433.2
0.58
1.42
315.0
0.62
1.84
225.4
0.67
2.37
184.0
0.70
2.75
137.4
0.76
3.43
109.5
0.81
4.01
87.3
0.87
4.68
69.9
0.94
5.46
60.2
0.99
5.98
260
467.9
0.58
1.43
340.4
0.62
1.84
243.7
0.67
2.38
198.9
0.70
2.76
148.5
0.76
3.44
118.5
0.81
4.01
94.4
0.87
4.69
75.6
0.94
5.47
65.1
0.99
5.99
280
502.5
0.58
1.43
365.6
0.62
1.84
261.8
0.67
2.38
213.7
0.70
2.76
159.7
0.76
3.44
127.4
0.81
4.02
101.5
0.87
4.70
81.4
0.94
5.46
70.0
0.99
6.01
300
536.7
0.58
1.43
390.7
0.62
1.85
279.9
0.67
2.38
228.5
0.71
2.77
170.7
0.76
3.45
136.2
0.81
4.03
108.6
0.87
4.70
87.0
0.94
5.48
74.9
0.99
6.01
I

Table 8.05P
Parabolic Diversion Design (Retardance "D" and "B", Grade 0.25%)
Q Vl = 2.0 V1 = 2.5 Vl = 3.0 Vl = 3.5 Vl = 4.0 Vl = 4.5 V1 = 5.0 Vl = 5.5 Vl = 6.0
cfs
T
D
V2
T
D
V2
T
D
V2
T
D
V2
T D
V2
T D V2 T
D V2 T D V2 T r V2
15
20
T
25
12
3.8
1.0
1 s
30
14
3.6
1.1
35
17
3.5
1.1
-F
_
40
19
3.5
1.2
13
4.1
1.4
D
-_ 0.5 Freeboard
45
21
3.4
1.2
14
4.0
1.4-
50
23
3.4
1.2
16
3.9
1.5
T
= Top width, Retardance "B"
55
26
3.4
1.2
17
3.9
1.5
D
= Depth, Retardance "B"
60
28
3.4
1.2
19
3.9
1.5
V2
= Velocity, Retardance "B"
65
30
3.4
1.2
20
3.8
1.6
V1
= Velocity, Retardance "D"
70
32
3.4
1.2
22
3.8
1.6
15
4.5
1.8
75
34
3.4
1.2
23
3.8
1.6
16
4.4
1.9
(Settlement to be added
80
37
3.4
1.2
25
3.8
1.6
17
4.4
1.9
to top of ridge.)
90
41
3.4
1.2
28
3.8
1.6
19
4.3
1.9
100
46
3.4
1.2
31
3.7
1.6
21
4.3
2.0
110
50
3.4
1.2
34
3.7
1.6
23
4.2
2.0
120
55
3.4
1.3
37
3.7
1.6
26
4.2
2.0
18
5.0
2.3
130
59
3.4
1.3
40
3.7
1.6
28
4.2
2.0
19
4.9
2.4
140
64
3.3
1.3
43
3.7
1.7
30
4.2
2.0
21
4.9
2.4
150
68
3.3
1.3
46
3.7
1.7
32
4.2
2.0
22
4.8
2.5
160
73
3.3
1.3
49
3.7
1.7
34
4.2
2.0
24
4.8
2.5
170
77
3.3
1.3
52
3.7
1.7
36
4.2
2.1
25
4.8
2.5
20
5.5
2.8
180
82
3.3
1.3
55
3.7
1.7
38
4.2
2.1
26
4.7
2.6
21
5.4
2.8
190
86
3.3
1.3
58
3.7
1.7
40
4.2
2.1
28
4.7
2.6
22
5.4
2.8
200
91
3.3
1.3
61
3.7
1.7
42
4.2
2.1
29
4.7
2.6
23
5.3
2.9
220
67
3.7
1.7
46
4.2
2.1
32
4.7
2.6
25
5.3
2.9
240
73
3.7
1.7
50
4.1
2.1
35
4.7
2.6
27
5.2
3.0
260
79
3.7
1.7
54
4.1
2.1
38
4.7
2.6
29
5.2
3.0
22 6.0 3.3
280
85
3.7
1.7
59
4.1
2.1
40
4.6
2.6
31
5.1
3.1
24 5.9 3.4
300
91
3.7
1.7
63
4.1
2.1
43
4.6
2.7
33
5.1
3.1
26 5.9 3.4
G

Table 8.05q
Parabolic Diversion Design (Retardance "D" and "B", Grade 0.5%)
Q
Vl
- 2.0
Vl
- 2.5
Vl
= 3.0
Vl
- 3.5
Vl
- 4.0
Vl
- 4.5
Vl = 5.0
Vl = 5.5 Vl
= 6.0
cfe
T
D
V2
T
D
V2
T
D
V2
T
D
V2
T
D
V2
T
D
V2
T D
V2
T D V2 T
D V2
15
12
2.8
1.0
20
15
2.7
1.0
25
18
2.7
1.1
12
3.1
1.4
30
22
2.6
1.1
14
3.0
1.4
10
3.4
1.6
35
25
2.6
1.1
16
3.0
1.5
12
3.3
1.7
T =
Top width,
Retardance "B"
40
29
2.6
1.1
18
2.9
1.5
13
3.2
1.8
D =
Depth,
Retardance "B"
45
33
2.6
1.1
20
2.9
1.5
15
3.2
1.8
V2 =
Velocity, Retardance "B"
50
36
2.6
1.1
22
2.9
1.5
17
3.1
1.9
12
3.7
2.1
Vl -
Velocity, Retardance "D"
55
40
2.6
1.1
24
2.9
1.6
18
3.1
1.9
13
3.6
2.2
60
43
2.6
1.1
27
2.9
1.6
20
3.1
1.9
14
3.6
2.2
(Settlement
to be added to top
65
47
2.6
1.1
29
2.9
1.6
21
3.1
1.9
15
3.5
2.3
of ridge.)
70
50
2.6
1.1
.31
2.9
1.6
23
3.1
1.9
16
3.5
2.3
75
54
2.6
1.1
33
2.9
1.6
25
3.1
1.9
17
3.5
2.3
14
4.0
2.5
80
58
2.6
1.1
35
2.9
1.6
26
3.1
1.9
18
3.5
2.4
15
3.9
2.6
90
65
2.6
1.1
40
2.9
1.6
29
3.1
2.0
21
3.5
2.4
16
3.9
2.6
100
72
2.6
1.1
44
2.8
1.6
32
3.1
2.0
23
3.4
2.4
18
3.8
2.7
14
4.3
3.0
110
79
2.6
1.1
48
2.8
1.6
36
3.1
2.0
25
3.4
2.4
20
3.8
2.8
16
4.2
3.1
120
86
2.6
1.1
52
2.8
1.6
39
3.1
2.0
27
3.4
2.5
21
3.7
2.8
17
4.1
3.1
130
93
2.6
1.1
57
2.8
1.6
42
3.1
2.0
30
3.4
2.5
23
3.7
2.8
18
4.1
3.2
140
61
2.8
1.6
45
3.1
2.0
32
3.4
2.5
25
3.7
2.8
19
4.1
3.2
150
65
2.8
1.6
48
3.1
2.0
34
3.4
2.5
26
3.7
2.9
21
4.1
3.2
17 4.6
3.5
160
70
2.8
1.6
52
3.0
2.0
36
3.4
2.5
28
3.7
2.9
22
4.0
3.3
18 4.5
3.6
170
74
2.8
1.6
55
3.0
2.0
39
3.4
2.5
30
3.7
2.9
24
4.0
3.3
19 4.5
3.6
180
78
2.8
1.6
58
3.0
2.0
41
3.4
2.5
31
3.7
2.9
25
4..0
3.3
20 4.5
3.7
190
83
2.8
1.6
61
3.0
2.0
43
3.4
2.5
33
3.7
2.9
26
4.0
3.3
21 4.5
3.7
200
87
2.8
1.6
64
3.0
2.0
45
3.4
2.5
35
3.7
2.9
27
4.0
3.3
22 4.4
3.8
18 5.0 4.0
220
95
2.8
1.6
71
3.0
2.0
50
3.4
2.5
38
3.7
2.9
30
4.0
3.4
24 4.4
3.8
19 4.9 4.1
240
77
3.0
2.0
54
3.4
2.5
42
3.7
2.9
33
4.0
3.4
26 4.4
3.8
21 4.9 4.1
260
83
3.0
2.0
59
3.4
2.5
45
3.7
3.0
36
4.0
3.4
28 4.3
3.9
23 4.8 4.2
280
90
3.0
2.0
63
3.4
2.5
48
3.7
3.0
38
4.0
3.4
30 4.3
3.9
24 4.8 4.2 20
5.4 4.5
0 300
96
3.0
2.0
68
3.4
2.5
52
3.6
3.0
41
4.0
3.4
32 4.3
3.9
26 4.8 4.3 21
5.3 4.6
tA
W
4

Table 8.05r
Parabolic Diversion Design (Retardance "D" and "B", Grade 1.0%)
Q Vl = 2.0 Vl = 2.5 Vl = 3.0 Vl = 3.5 Vl = 4.0 Vl = 4.5 Vl = 5.0 Vl = 5.5 Vl = 6.0
cfs T D V2 T D V2 T D V2 T D V2 T D V2 T D V2 T D V2 T D V2 T D V2
15 18 2.1 0.9 11 2.3 1.2
20 24 2.0 0.9 15 2.2 1.3 10 2.5 1.7
25 30 2.0 0.9 19 2.2 1.3 12 2.5 1.7 10 2.7 1.9 T = Top width, Retardance "B"
30 36 2.0 0.9 22 2.2 1.4 15 2.4 1.8 12 2.6 2.0 D = Depth, Retardance "B"
35 42 2.0 0.9 26 2.2 1.4 17 2.4 1.8 14 2.6 2.1 10 2.9 2.4 V2 = Velocity, Retardance "B"
40 48 2.0 1.0 29 2.2 1.4 19 2.4 1.8 15 2.5 2.1 12 2.8 2.5 Vl = Velocity, Retardance " D"
45 54 2.0 1.0 33 2.2 1.4 22 2.4 1.8 17 2.5 2.1 13 2.8 2.5
50 59 2.0 1.0 37 2.2 1.4 24 2.4 1.9 19 2.5 2.2 14 2.8 2.5 11 3.1 2.9 (Settlement to be added to
55 65 2.0 1.0 40 2.2 1.4 26 2.4 1.9 21 2.5 2.2 16 2.8 2.6 12 3A 2.9 top of ridge.)
60 71 2.0 1.0 44 2.2 1.4 29 2.4 1.9 23 2.5 2.2 17 2.7 2.6 13 3.0 3.0
65 77 2.0 1.0 47 2.2 1.4 31 2.4 1.9 25 2.5 2.2 18 2.7 2.6 14 3.0 3.Q 11 3.4 3.2
70 83 2.0 1.0 51 2.2 1.4 33 2.4 1.9 26 2.5 2.2 20 2.7 2.6 15 3.0 3.0 12 3.3 3.3
75 88 2.0 1.0 54 2.2 1.4 36 2.4 1.9 28 2.5 2.2 21 2.7 2.7 16 3.0 3.1 13 3.3 3.4
80 94 2.0 1.0 58 2.2 1.4 38 2.4 1.9 30 2.5 2.2 23 2.7 2.7 17 3.0 3.1 14 3.2 3.4
90 65 2.2 1.4 43 2.4 1.9 34 2.5 2.2 25 2.7 2.7 19 3.0 3.1 16 3.2 3.5 13 3.5 3.8
100 72 2.2 1.4 47 2.4 1.9 38 2.5 2.2 28 2.7 2.7 21 3.0 3.1 17 3.2 3.6 14 3.4 3.9
110 79 2.2 1.4 52 2.4 1.9 41 2.5 2.3 31 2.7 2.7 23 2.9 3.2 19 3.2 3.6 16 3.4 3.9 13 3.7 4.1
120 86 2.2 1.4 57 2.4 1.9 45 2.5 2.3 34 2.7 2.7 25 2.9 3.2 21 3.2 3.6 17 3.4 4.0 15 3.7 4.2
130 94 2.2 1.4 61 2.4 1.9 49 2.5 2.3 36 2.7 2.7 27 2.9 3.2 22 3.1 3.6 18 3.4 4.0 16 3.6 4.3
140 66 2.4 1.9 52 2.5 2.3 39 2.7 2.7 29 2.9 3.2 23 3.1 3.6 20 3.4 4.1 17 3.6 4.3
150 71 2.4 1.9 56 2.5 2.3 42 2.7 2.7 31 2.9 3.2 26 3.1 3.7 21 3.4 4.1 18 3.6 4.4
160 75 2.4 1.9 60 2.5 2.3 45 2.7 2.7 33 2.9 3.2 27 3.1 3.7 22 3.4 4.1 19 3.6 4.4
170 80 2.4 1.9 63 2.5 2.3 47 2.7 2.7 35 2.9 3.3 29 3.1 3.7 24 3.4 4.1 20 3.6 4.5
180 84 2.4 1.9 67 2.5 2.3 50 2.7 2.7 38 2.9 3.3 31 3.1 3.7 25 3.3 4.1 21 3.5 4.5
190 89 2.4 1.9 71 2.5 2.3 53 2.7 2.7 40 2.9 3.3 32 3.1 3.7 26 3.3 4.2 22 3.5 4.5
200 94 2.4 1.9 74 2.5 2.3 55 2.7 2.7 42 2.9 3.3 34 3.1 3.7 28 3.3 4.2 24 3.5 4.6
220 82 2.5 2.3 61 2.7 2.7 46 2.9 3.3 37 3.1 3.7 30 3.3 4.2 26 3.5 4.6
240 89 2.5 2.3 66 2.7 2.8 50 2.9 3.3 41 3.1 3.1 33 3.3 4.2 28 3.5 4.6
260 96 2.5 2.3 72 2.7 2.8 54 2.9 3.3 44 3.1 3.8 36 3.3 4.2 30 3.5 4.7
280 77 2.7 2.8 58 2.9 3.3 47 3.1 3.8 38 3.3 4.2 .33 3.5 4.7
300 83 2.7 2.8 62 2.9 3.3 50 3.1 3.8 41 3.3 4.2 35 3.5 4.7
a
•

0
w
b
Table 8.05s
Parabolic Diversion Design (Retardance "D" and "B", Grade 1.5%)
Q Vl = 2.0 Vl = 2.5 Vl = 3.0 V1 = 3.5 V1 = 4.0 Vl = 4.5 V1 = 5.0 V1 = 5.5 V1 = 6.0
cfs T D V2 T D V2 T D V2 T D V2 T D V2 T D V2 T D V2 T D V2 T D V2
15 24 1.8 0.9 15 1.9 1.2 10 2.2 1.5 .
20 32 1.8 0.9 20 1.9 1.2 14 2.1 1.6
25 39 1.8 0.9 25 1.9 1.2 17 2.1 1.6 11 2.3 2.1
30 47 1.8 0.9 31 1.9 1.2 20 2.1 1.6 13 2.3 2.2 11 2.4 2.4
35 55 1.8 0.9 36 1.9 1.2 23 2.1 1.7 16 2.2 2.2 13 2.4 2.5 10 2.6 2.7
40 63 1.8 0.9 41 1.9 1.2 27 2.1 1.7 18 2.2 2.2 14 2.3 2.6 12 2.5 2.8
45 70 1.8 0.9 46 1.9 1.2 30 2.1 1.7 20 2.2 2.2 16 2.3 2.6 13 2.5 2.8 10 2.8 3.2
50 78 1.8 0.9 51 1.9 1.2 33 2.1 1.7 22 2.2 2.2 18 2.3 2.6 15 2.5 2.9 11 2.8 3.3
55 86 1.8 0.9 55 1.9 1.2 36 2.1 1.7 24 2.2 2.3 20 2.3 2.6 16 2.5 2.9 12 2.7 3.4 10 3.0 3.5
60 93 1.8 0.9 60 1.9 1.2 40 2.0 1.7 26 2.2 2.3 21 2.3 2.6 17 2.5 2.9 13 2.7 3.4 11 3.0 3.6
65 65 1.9 1.2 43 2.0 1.7 29 2.2 2.3 23 2.3 2.6 19 2.5 3.0 14 2.7 3.4 12 2.9 3.7
70 70 1.9 1.2 46 2.0 1.7 31 2.2 2.3 25 2.3 2.6 20 2.5 3.0 15 2.7 3.4 13 2.9 3.8 11 3.1 4.0
75 75 1.9 1.2 49 2.0 1.7 33 2.2 2.3 26 2.3 2.7 22 2.5 3.0 16 2.7 3.5 14 2.9 3.8 12 3.1 4.0
80 80 1.9 1.2 52 2.0 1.7 35 2.2 2.3 28 2.3 2.7 23 2.5 3.0 18 2.7 3.5 15 2.9 3.8 13 3.1 4.2
90 90 1.9 1.2 59 2.0 1.7 39 2.2 2.3 32 2.3 2.7 26 2.5 3.0 20 2.7 3.5 16 2.8 3.9 14 3.0 4.2
100 65 2.0 1.7 44 2.2 2.3 35 2.3 2.7 29 2.4 3.0 22 2.7 3.5 18 2.8 4.0 15 3.0 4.3
110 72 1.0 1.7 48 2.2 2.3 39 2.3 2.7 31 2.4 3.0 24 2.7 3.5 20 2.8 4.0 17 3.0 4.4
120 78 2.0 1.7 52 2.2 2.3 42 2.3 2.7 34 2.4 3.0 26 2.6 3.6 22 2.8 4.0 18 3.0 4.4
130 85 2.0 1.7 57 2.2 2.3 45 2.3 2.7 37 2.4 3.0 28 2.6 3.6 23 2.8 4.0 19 3.0 4.4
140 91 2.0 1.7 61 2.2 2.3 49 2.3 2.7 40 2.4 3.1 30 2.6 3.6 25 2.8 4.0 21 3.0 4.5
150 97 2.0 1.7 65 2.2 2.3 52 2.3 2.7 43 2.4 3.1 32 2.6 3.6 27 2.8 4.0 22 2.9 4.5
160 69 2.2 2.3 56 2.3 2.7 45 2.4 3.1 34 2.6 3.6 29 2.8 4.1 24 2.9 4.5
170 74 2.2 2.3 59 2.3 2.7 48 2.4 3.1 37 2.6 3.6 30 2.8 4.1 25 2.9 4.5
180 T = Top width, Retardance "B" 78 2.2 2.3 63 2.3 2.7 51 2..4 3.1 39 2.6 3.6 32 2.8 4.1 27 2.9 4.6
190 D = Depth, Retardance "B" 82 2.2 2.3 66 2.3 2.7 54 2.4 3.1 41 2.6 3.7 34 2.8 4.1 28 2.9 4.6
200 V2 = Velocity, Retardance "B" 86 2.2 2.3 69 2.3 2.7 56 2.4 3.1 43 2.6 3.7 M 2.8 4.1 30 2.9 4.6
220 Vl = Velocity, Retardance " D" 95 2.2 2.3 76 2.3 2.7 62 2.4 3.1 47 2.6 3.7 39 2.8 4.1 33 2.9 4.6
240 83 2.3 2.7 68 2.4 3.1 51 2.6 3.7 43 2.8 4.1 35 2.9 4.6
260 (Settlement to be added to 90 2.3 2.7 73 2.4 3.1 55 2.6 3.7 46 2.8 4.1 38 2.9 4.6
280 top of ridge.) 97 2.3 2.7 79 2.4 3.1 60 2.6 3.7 50 2.8 4.1 41 2.9 4.6
300 84 2.4 3.1 64 2.6 3.7 53 2.8 4.1 44 2.9 4.7
�M
fo
y

00
0
ut
:ca
Table 8.05t
Parabolic Diversion Design (Retardance "D" and "B", Grade 2.0%)
Q Vl = 2.0 Vl = 2.5 V1 = 3.0 V1 = 3.5 V1 = 4.0 V1 = 4.5 V1 = 5.0 V1 = 5.5 V1 = 6.0
cfs T D V2 T D V2 T D V2 T D V2 T D V2 T D V2 T D V2 T D V2 T D V2
15 30 1.6 0.8 18 1.8 1.2 13 1.9 1.4 9 2.1 1.8
20 39 1.6 0.8 24 1.8 1.2 17 1.9 1.5 12 2.0 1.9
25 49 1.6 0.8 30 1.7 1.2 21 1.9 1.5 15 2.0 2.0 11 2.2 2.4
30 59 1.6 0.8 35 1.7 1.2 25 1.9 1.5 18 2.0 2.0 13 2.1 2.5 10 2.3 2.8
35 68 1.6 0.8 41 1.7 1.2 29 1.9 1.5 21 2.0 2.0 15 2.1 2.5 12 2.2 2.9 10 2.4 3.0
40 78 1.6 0.8 47 1.7 1.2 34 1.9 1.5 23 2.0 2.0 17 2.1 2.5 14 2.2 2.9 11 2.4 3.2
45 88 1.6 0.8 53 1.7 1.2 38 1.9 1.5 26 2.0 2.0 19 2.1 2.5 15 2.2 2.9 13 2.4 3.2 10 2.6 3.5
50 97 1.6 0.8 59 1.7 1.2 42 1.9 1.6 29 2.0 2.0 21 2.1 2.6 17 2.2 2.9 14 2.4 3.2 11 2.5 3.6
55 64 1.7 1.2 46 1.8 1.6 32 2.0 2.0 23 2.1 2.6 19 2.2 2.9 15 2.4 3.3 12 2.5 3.7 10 2.7 4.0
60 70 1.7 1.2 50 1.8 1.6 35 2.0 2.0 25 2.1 2.6 20 2.2 3.0 17 2.4 3.3 13 2.5 3.7 11 2.7 4.0
65 76 1.7 1.2 54 1.8 1.6 38 2.0 2.0 27 2.1 2.6 22 2.2 3.0 18 2.3 3.4 15 2.5 3.7 12 2.7 4.1
70 81 1.7 1.2 58 1.8 1.6 41 2.0 2.1 29 2.1 2.6 24 2.2 3.0 19 2.3 3.4 16 2.5 3.8 13 2.7 4.1
75 87 1.7 1.2 62 1.8 1.6 43 2.0 2.1 31 2.1 2.6 25 2.2 3.0 21 2.3 3.4 17 2.5 3.8 14 2.7 4.1
80 93 1.7 1.2 68 1.8 1.6 46 2.0 2.1 33 2.1 2.6 27 2.2 3.0 22 2.3 3.4 18 2.5 3.8 15 2.6 4.2
90 74 1.8 1.6 52 2.0 2.1 37 2.1 2.6 30 2.2 3.0 25 2.3 3.4 20 2.5 3.8 17 2.6 4.2
100 83 1.8 1.6 58 2.0 2.1 41 2.1 2.6 34 2.2 3.0 27 2.3 3.4 22 2.5 3.9 18 2.6 4.3
110 91 1.8 1.6 63 2.0 2.1 45 2.1 2.6 37 2.2 3.0 30 2.3 3-4 24 2.5 3.9 20 2.6 4:3
120 99 1.8 1.6 69 2.0 2.1 49 2.1 2.6 40 2.2 0.0 33 2.3 3.4 26 2.4 3.9 22 2.6 4.3
130 75 2.0 2.1 53 2.1 2.6 44 2.2 3.0 35 2.3 3.4 29 2.4 3.9 24 2.6 4.3
140 80 2.0 2.1 57 2.1 2.6 47 2.2 3.0 38 2.3 3.5 31 2.4 3.9 26 2.6 4.4
150 86 2.0 2.1 61 2.1 2.7 50 2.2 3.0 41 2.3 3.5 33 2.4 3.9 27 2.6 4.4
160 91 2.0 2.1 65 2.1 2.7 53 2.2 3.0 43 2.3 3.5 35 2.4 3.9 29 2.6 4.4
170 97 2.0 2.1 69 2.1 2.7 57 2.2 3.1 46 2.3 3.5 37 2.4 4.0 31 2.6 4.4
180 T = Top width, Retardance "B" 73 2.1 2.7 60 2.2 3.1 49 2.3 3.5 39 2.4 4.0 33 2.6 4.4
190 D = Depth, Retardance "B" 77 2.1 2.7 63 2.2 3.1 51 2.3 3.5 41 2.4 4.0 34 2.6 4.5
200 V2 = Velocity, Retardance "B" 81 2.1 2.7 66 2.2 3.1 54 2.3 3.5 44 2.4 4.0 36 2.6 4.5
220 Vl = Velocity, Retardance "V' 89 2.1 2.7 73 2.2 3.1 59 2.3 3.5 48 2.4 4.0 40 2.6 4.5
240 97 2.1 2.7 79 2.2 3.1 65 2.3 3.5 52 2.4 4.0 43 2.6 4.5
260 (Settlement to be added to 86 2.2 3.1 70 2.3 3.5 56 2.4 4.0 47 2.6 4.5
280 top of ridge.) 92 2.2 3.1 75 2.3 3.5 61 2.4 4.0 .50 2.6 4.5
300 99 2.2 3.1 81 2.3 3.5 65 2.4 4.0 54 2.6 4.5
0
9 s 0

Table 8.05u
Parabolic Diversion Design (Retardance "D" and "B", Grade 0.25%)
Q Vl = 2.0 Vl = 2.5 Vl = 3,0 Vl = 3.5 V1 = 4.0 V1 = 4.5 V1 = 5.0 V1 = 5.5 V1 = 6.0
cfs
T
D
V2
T
D
V2
T
D
V2
T
D
V2
T
D
V2
T D V2
T D V2 T D V2 T D V2
15
20
25
11
2.9
1.6
1
T
30
13
2.8
1.7
1
_I
35
15
2.8
1.7
40
17
2.8
1.8
11
3.2
2.1
-
_-
45
19
2.7
1.8
13
3.1
2.2
_
D -"
_ 0.5 Freeboard
50
21
2.7
1.8
14
3.1
2.2
77
55
23
2.7
1.8
15
3.1
2.3
T
= Top width, Retardance " C'
60
25
2.7
1.8
17
3.0
2.3
D
= Depth, Retardance " C'
65
27
2.7
1.8
18
3.0
2.3
V2
= Velocity, Retardance "Cl
70
29
2.7
1.9
19
3.0
2.3
14
3.6
2.7
V1
= Velocity, Retardance 'IV'
75
31
2.7
1.9
21
3.0
2.3
15
3.5
2.8
80
33
2.7
1.9
22
3.0
2.4
16
3.5
2.8
(Settlement to be added to
90
37
2.7
1.9
25
3.0
2.4
17
3.5
2.8
top of ridge.)
100
41
2.7
1.9
28
3.0
2.4
19
3.5
2.9
110
45
2.7
1.9
30
3.0
2.4
21
3.4
2.9
120
49
2.7
1.9
33
3.0
2.4
23
3.4
2.9
16
4.1
3.3
130
53
2.7
1.9
36
3.0
2.4
25
3.4
2.9
18
4.1
3.3
140
57
2.7
1.9
38
3.0
2.4
27
3..4
2.9
19
4.0
3.4
150
61
2.7
1.9
41
3.0
2.4
29
3.4
2.9
20
4.0
3.4
160
65
2.7
1.9
44
3.0
2.4
30
3.4
3.0
21
4.0
3.4
170
69
2.7
1.9
46
3.0
2.4
32
3.4
3.0
23
4.0
3.4
18
4.5
3.8
180
73
2.7
1.9
49
3.0
2.4
34
3.4
3.0
24
4.0
3.5
19
4.5
3.8
190
77
2.7
1.9
52
3.0
2.4
36
3.4
3.0
25
4.0
3.5
20
4.5
3.9
200
81
2.7
1.9
55
3.0
2.4
38
3.4
3.0
27
3.9
3.5
21
4.4
3.9
220
89
2.7
1.9
60
3.0
2.4
42
3.4
3.0
29
3.9
3.5
23
4.4
3.9
240
97
2.7
1.9
65
3.0
2.5
45
3.4
3.0
32
3.9
3.6
25
4.4
4.0
260
71
3.0
2.5
49
3.4
3.0
34
3.9
3.6
27
4.4
4.0
21 5.1 4.3
280
76
3.0
2.5
53
3.4
3.0
37
3.9
3.6
29
4.4
4.0
22 5.1 4.3
300
82
3.0
2.5
57
3.4
3.0
40
3.9
3.6
31
4.3
4.1
24 5.0 4.4
ft
ss;
ep
y

0
Table 8.05v
N Parabolic Diversion Design (Retardance "D" and "C", Grade 0.5%)
Q Vl = 2.0 Vl = 2.5 Vl = 3.0 Vl = 3.5 Vl = 4.0 Vl = 4.5 Vl = 5.0 Vl = 5.5 Vl = 6.0
cfs
T
D
V2
T
D
V2
T
D
V2
T
D
V2
T
D
V2
T
D
V2
T D
V2
T D
V2
T D V2
15
10
2.1
1.6
20
13
2.1
1.7
25
16
2.1
1.7
10
2.4
2.1
30
20
2.1
1.7
12
2.4
2.2
9
2.7
2.5
35
23
2.1
1.7
14
2.4
2.3
11
2.6
2.6
T
= Top Width,
Retardance
" C'
40
26
2.1
1.7
16
2.3
2.3
12
2.6
2.7
D
= Depth,
Retardance
" C'
45
29
2.0
1.7
18
2.3
2.3
13
2.5
2.8
V2
= Velocity,
Retardance "
C'
50
32
2.0
1.7
20
2.3
2.4
15
2.5
2.8
11
2.9
3.2
Vl
= Velocity,
Retardance "
Dd'
55
35
2.0
1.7
22
2.3
2.4
16
2.5
2.8
12
2.9
3.3
60
39
2.0
1.7
24
2.3
2.4
18
2.5
2.8
13
2.9
3.3
(Settlement
to be added to
65
42
2.0
1.8
26
2.3
2.4
19
2.5
2.9
14
2.9
3.3
top of
ridge.)
70
45
2.0
1.8
28
2.3
2.4
21
2.5
2.9
15
2.8
3.4
75
48
2.0
1.8
30
2.3
2.4
22
2.5
2.9
16
2.8
3.4
12
3.2
3.7
80
51
2.0
1.8
32
2.3
2.4
23
2.5
2.9
17
2.8
3.4
13
3.2
3.8
90
57
2.0
1.8
35
2.3
2.4
26
2.5
2.9
19
2.8
3.4
15
3.2
3.8
100
64
2.0
1.8
39
2.3
2.4
29
2.5
2.9
21
2.8
3.5
16
3.1
3.9
13
3.5
4.1
110
70
2.0
1.8
43
2.3
2.4
32
2.5
2.9
23
2.8
3.5
18
3.1
3.9
14
3.5
4.2
120
76
2.0
1.8
47
2.3
2.4
35
2.5
2.9
25
2.8
3.5
19
3.1
3.9
15
3.4
4.3
130
83
2.0
1.8
51
2.3
2.4
38
2.5
2.9
27
2.8
3.5
21
3.1
4.0
17
3.4
4.4
140
89
2.0
1.8
55
2.3
2.4
41
2.5
2.9
29
2.8
3.5
22
3.1
4.0
18
3.4
4.3
150
95
2.0
1.8
59
2.3
2.4
44
2.5
2.9
31
2.8
3.5
24
3.1
4.0
19
3.4
4.4
15 3.8
4.8
160
62
2.3
2.4
46
2.5
2.9
33
2.8
3.5
25
3.1
4.0
20
3.4
4.4
16 3.8
4.8
170
66
2.3
2.4
49
2.5
2.9
35
2.8
3.6
27
3.1
4.0
22
3.4
4.4
17 3.8
4.9
180
70
2.3
2.4
52
2.5
2.9
37
2.8
3.6
29
3.1
4.0
23
3.4
4.5
18 3.8
4.9
190
74
2.3
2.4
55
2.5
2.9
39
2.8
3.6
30
3.1
4.0
24
3.4
4.5
19 3.8
5.0
200
78
2.3
2.4
58
2.5
2.9
41
2.8
3.6
32
3.1
4.0
25
3.4
4.5
20 3.8
5.0
16 4.2
5.2
220
86
2.3
2.4
64
2.5
2.9
45
2.8
3.6
35
3.1
4.0
28
3.4
4.5
22 3.7
5.0
18 4.2
5.3
240
93
2.3
2.4
69
2.5
2.9
49
2.8
3.6
38
3.0
4.1
.30
3.4
4.5
24 3.7
5.0
20 4.2
5.4
260
75
2.5
2.9
53
2.8
3.6
41
3.0
4.1
33
3.4
4.5
26 3.7
5.0
21 4.1
5.4
280
81
2.5
3.0
57
2.8
3.6
44
3.0
4.1
35
3.3
4.6
28 3.7
5.0
23 4.1
5.5
19 4.6 5.8
300
87
2.5
3.0
61
2.8
3.6
47
3.0
4.1
38
3.3
4.6
30 3.6
5.0
24 4.1
5.5
20 4.6 5.8
0

00
0
w
•
e
Table 8.05w
Parabolic Diversion Design (Retardance "D" and "C", Grade 1.0%)
Q Vl = 2.0 Vl = 2.5 V1 = 3.0 Vl = 3.5 V1 = 4.0 V1 = 4.5 Vl = 5.0 V1 = 5.5 V1 = 6.0
cfs T D V2 T D V2 T D V2 T D V2 T D V2 T D V2 T D V2 T D V2 T D V2
•
15 16 1.6 1.5 10 1.8 2.0
20 22 1.6 1.5 13 1.8 2.1 T = Top Width, Retardance " C'
25 27 1.6 1.5 17 1.8 2.1 11 2.0 2.6 D = Depth, Retardance " C'
30 32 1.6 1.5 20 1.8 2.1 13 2.0 2.7 11 2.1 3.0 V2 = Velocity, Retardance " C'
35 37 1.6 1.5 23 1.8 2.2 15 2.0 2.8 12 2.1 3.1 V1 = Velocity, Retardance "IY'
40 43 1.6 1.5 26 1.8 2.2 17 1.9 2.8 14 2.1 3.1 10 2.3 3.7
45 48 1.6 1.5 29 1.8 2.2 19 1.9 2.8 16 2.1 3.2 12 2.3 3.7 (Settlement to be added to
50 53 1.6 1.5 33 1.8 2.2 22 1.9 2.8 17 2.1 3.2 13 2.3 3.7 10 2.5 4.2 top of ridge.)
55 58 1.6 1.5 36 1.8 2.2 24 1.9 2.8 19 2.0 3.3 14 2.3 3.8 11 2.5 4.3
60 64 1.6 1.5 39 1.8 2.2 26 1.9 2.8 21 2.0 3.3 15 2.2 3.8 12 2.5 4.3
65 69 1.6 1.5 42 1.8 2.2 28 1.9 2.8 22 2.0 3.3 17 2.2 3.8 .13 2.5 4.3 10 2.7 4.7
70 74 1.6 1.5 45 1.8 2.2 30 1.9 2.8 24 2.0 3.3 18 2.2 3.9 14 2.5 4.4 11 2.7 4.7
75 79 1.6 1.5 49 1.8 2.2 32 1.9 2.9 26 2.0 3.3 19 2.2 3.9 15 2.5 4.5 12 2.7 4.7
80 84 1.6 1.5 52 1.8 2.2 34 1.9 2.9 27 2.0 3.3 20 2.2 3.9 16 2.5 4.5 13 2.7 4.9
90 95 1.6 1.5 58 1.8 2.2 38 1.9 2.9 31 2.0 3.3 23 2.2 3.9 17 2.4 4.5 14 2.7 4.9 12 2.9 5.2
100 65 1.8 2.2 43 1.9 2.9 34 2.0 3.3 25 2.2 3.9 19 2.4 4.5 16 2.7 4.9 13 2.9 5.3
110 71 1.8 2.2 47 1.9 2.9 37 2.0 3.3 28 2.2 3.9 21 2.4 4.5 17 2.6 5.0 14 2.9 5.3 12 3.1 5.7
120 77 1.8 2.2 51 1.9 2.9 41 2.0 3.3 30 2.2 4.0 23 2.4 4.5 19 2.6 5.0 16 2.9 5.4 13 3.1 5.7
130 84 1.8 2.2 55 1.9 2.9 44 2.0 3.3 33 2.2 4.0 25 2.4 4.5 20 2.6 5.0 17 2.9 5.4 14 3.1 5.8
140 90 1.8 2.2 59 1.9 2.9 47 2.0 3.3 35 2.2 4.0 27 2.4 4.5 22 2.6 5.0 18 2.8 5.5 15 3.1 5.8
150 96 1.8 2.2 64 1.9 2.9 51 2.0 3.3 38 2.2 4.0 29 2.4 4.5 23 2.6 5.0 19 2.8 5.5 17 3.1 5.8
160 68 1.9 2.9 54 2.0 3.3 40 2.2 4.0 30 2.4 4.5 25 2.6 5.0 20 2.8 5.5 18 3.0 6.0
170 72 1.9 2.9 57 2.0 3.3 43 2.2 4.0 32 2.4 4.5 26 2.5 5.0 22 2.8 5.5 19 3.0 6.0
180 76 1.9 2.9 61 2.0 3.4 45 2.2 4.0 34 2.4 4.5 28 2.6 5.0 23 2.8 5.5 20 3.0 6.0
190 80 1.9 2.9 64 2.0 3.4 48 2.2 4.0 36 2.4 4.5 29 2.6 5.0 24 2.8 5.5 21 3.0 6.0
200 84 1.9 2.9 67 2.0 3.4 50 2.2 4.0 38 2.4 4.5 31 2.6 5.0 25 2.8 5.5 22 3.0 6.0
220 93 1.9 2.9 74 2.0 3.4 55 2.2 4.0 42 2.4 4.5 34 2.6 5.0 28 2.8 5.5 24 3.0 6.0
240 81 2.0 3.4 60 2.2 4.0 45 2.4 4.5 37 2.6 5.0 30 2.8 5.5 26 3.0 6.0
260 87 2.0 3.4 65 2.2 4.0 49 2.4 4.5 40 2.6 5.0 33 2.8 5.5 28 3.0 6.0
280 94 2.0 3.4 70 2.2 4.0 53 2.4 4.5 43 2.6 5.0 36 2.8 5.5 30 3.0 6.0
300 75 2.2 4.0 57 2.4 4.5 46 2.5 5.0 38 2.8 5.5 32 3.0 6.0

00
0
tA
A
p Table 8.05x
Parabolic Diversion Design (Retardance "D" and "C", Grade 1.5%)
Q Vl = 2.0 V1 = 2.5 V1 = 3.0 Vl = 3.5 V1 = 4.0 Vl = 4.5 V1 = 5.0 V1 = 5.5 V1 = 6.0
cfs T D V2 T D V2 T D V2 T D V2 T D V2 T D V2 T D V2 T D V2 T D V2
15 21 1.4 1.4 14 1.6 1.9
20 28 1.4 1.4 18 1.5 1.9 12 1.7 2.5
25 35 1.4 1.4 23 1.5 1.9 15 1.7 2.6 10 1.9 3.2
30 42 1.4 1.4 27 1.5 1.9 18 1.7 2.6 12 1.8 3.2 10 2.0 3.6
35 49 1.4 1.4 32 1.5 2.0 21 1.6 2.6 14 1.8 3.3 11 1.9 3.7 10 2.1 4.1
40 56 1.4 1.4 36 1.5 2.0 24 1.6 2.6 16 1.8 3.3 13 1.9 3.7 11 2.1 4.2
45 63 1.4 1.4 41 1.5 2.0 27 1.6 2.6 18 1.8 3.4 15 1.9 3.8 12 2.0 4.3
50 70 1.4 1.4 45 1.5 2.0 30 1.6 2.7 20 1.8 3.4 16 1.9 3.9 13 2.0 4.3 10 2.3 4.8
55 76 1.4 1.5 50 1.5 2.0 33 1.6 2.7 22 1.8 3.4 18 1.9 3.9 14 2.0 4.3 11 2.3 4.9
60 83 1.4 1.5 54 1.5 2.0 35 1.6 2.7 24 1.8 3.4 19 1.9 3.9 16 2.0 4.4 12 2.3 4.9 10 2.4 5.2
65 90 1.4 1.5 58 1.5 2.0 38 1.6 2.7 26 1.8 3.4 21 1.9 3.9 17 2.0 4.4 13 2.2 5.0 11 2.4 5.3
70 97 1.4 1.5 63 1.5 2.0 41 1.6 2.7 28 1.8 3.4 22 1.9 3.9 18 2.0 4.4 14 2.2 5.0 12 2.4 5.4 10 2.6 5.6
75 67 1.5 2.0 44 1.6 2.7 30 1.8 3.4 24 1.9 3.9 19 2.0 4.4 15 2.2 5.0 12 2.4 5.4 11 2.6 5.6
80 72 1.5 2.0 47 1.6 2.7 32 1.8 3.4 26 1.9 3.9 21 2.0 4.4 16 2.2 5.0 13 2.4 5.J# 12 2.5 5.8
90 80 1.5 2.0 53 1.6 2.7 36 1.8 3.5 29 1.9 3.9 23 2.0 4.4 18 2.2 5.0 15 2.4 5.4 13 2.5 5.9
100 89 1.5 2.0 59 1.6 2.7 39 1.8 3.5 32 1.9 3.9 26 2.0 4.5 20 2.2 5.0 17 2.4 5.4 14 2.5 6.0
110 98 1.5 2.0 64 1.6 2.7 43 1.8 3.5 35 1.9 3.9 28 2.0 4.5 22 2.2 5.0 18 2.3 5.5 15 2.5 6.0
120 70 1.6 2.7 47 1.8 3.5 38 1.9 4.0 31 2.0 4.5 24 2.2 5.0 20 2.3 5.5 17 2.5 6.0
130 76 1.6 2.7 51 1.8 3.5 41 1.9 4.0 33 2.0 4.5 26 2.2 5.0 21 2.3 5.5 18 2.5 6.0
140 82 1.6 2.7 55 1.8 3.5 44 1.9 4.0 36 2.0 4.5 27 2.2 5.0 23 2.3 5.5 19 2.5 6.0
150 87 1.6 2.7 59 1.8 3.5 47 1.9 4.0 39 2.0 4.5 29 2.2 5.0 25 2.3 5.5 21 2.5 6.0
160 93 1.6 2.7 63 1.8 3.5 51 1.9 4.0 41 2.0 4.5 31 2.2 5.0 26 2.3 5.5 22 2.5 6.0
170 99 1.6 2.7 67 1.8 3.5 54 1.9 4.0 44 2.0 4.5 33 2.2 5.0 28 2.3 5.5 23 2.5 6.0
180 70 1.8 3.5 57 1.9 4.0 46 2.0 4.5 35 2.2 5.0 29 2.3 5.5 25 2.5 6.0 .
190 74 1.8 3.5 60 1.9 4.0 49 2.0 4.5 37 2.2 5.0 31 2.3 5.5 26 2.5 6.0
200 T = Top width, Retardance " C" 78 1.8 3.5 63 1.9 4.0 51 2.0 4.5 39 2.2 5.0 33 2.3 5.5 27 2.5 6.0
220 D = Depth, Retardance " C' 86 1.8 3.5 69 1.9 4.0 56 2.0 4.5 43 2.2 5.0 36 2.3 5.5 30 2.5 6.0
240 V2 = Velocity, Retardance " C' 93 1.8 3.5 75 1.9 4.0 61 2.0 4.5 47 2.2 5.0 39 2.3 5.5 33 2.5 6.0
260 Vl = Velocity, Retardance " D" 82 1.9 4.0 66 2.0 4.5 51 2.2 5.0 42 2.3 5.5 35 2.5 6.0
280 (Settlement to be added to 88 1.9 4.0 71 2.0 4.5 54 2.2 5.0 46 2.3 5.5 38 2.5 6.0
300 top of ridge.) 94 1.9 4.0 76 2.0 4.5 58 2.2 5.0 49 2.3 5.5 41 2.5 6.0
0

Table 8.05y
Parabolic Diversion Design (Retardance "D" and "C', Grade 2.0%)
Q Vl = 2.0 Vl = 2.5 Vl = 3.0 Vl = 3.5 Vl = 4.0 Vl = 4.5 Vl = 5.0 Vl = 5.5 Vl = 6.0
cfs T D V2 T D V2 T D V2 T D V2 T D V2 T D V2 T D V2 T D V2 T D V2
15 27 1.3 1.3 16 1.4 1.9 11 1.5 2.4
20 35 1.3 1.3 21 1.4 1.9 15 1.5 2.4 11 1.6 3.0
25 44 1.3 1.3 27 1.4 1.9 19 1.5 2.4 13 1.6 3.0 10 1.8 3.7
30 53 1.3 1.3 32 1.4 1.9 23 1.5 2.5 16 1.6 3.0 11 1.7 3.7 10 1.8 4.2
35 61 1.3 1.3 37 1.4 1.9 26 1.5 2.5 19 1.6 3.1 13 1.7 3.8 11 1.8 4.2
40 70 1.3 1.3 42 1.4 1.9 30 1.5 2.5 21 1.6 3.1 15 1.7 3.8 12 1.8 4.3 10 2.0 4.7
45 78 1.3 1.4 48 1.4 1.9 34 1.5 2.5 24 1.6 3.1 17 1.7 3.8 14 1.8 4.3 11 1.9 4.8
50 87 1.3 1.4 53 1.4 1.9 38 1.5 2.5 26 1.6 3.1 19 1.7 3.8 15 1.8 4.3 13 1.9 4.8 10 2.1 5.3
55 95 1.3 1.4 58 1.4 1.9 41 1.5 2.5 29 1.6 3.1 21 1.7 3.8 17 1.8 4.3 14 1.9 4.9 11 2.1 5.3
60 63 1.4 1.9 45 1.5 2.5 32 1.6 3.1 23 1.7 3.9 18 1.8 4.4 15 1.9 4.9 12 2.1 5.3 10 2.2 5.7
65 68 1.4 1.9 49 1.5 2.5 34 1.6 3.1 24 1.7 3.9 20 1.8 4.4 16 1.9 4.9 13 2.1 5.4 11 2.2 5.7
70 73 1.4 1.9 52 1.5 2.5 37 1.6 3.1 26 1.7 3.9 22 1.8 4.4 18 1.9 4.9 14 2.1 5.4 12 2.2 5.8
75 78 1.4 1.9 56 1.5 2.5 39 1.6 3.1 28 1.7 3.9 23 1.8 4.4 19 1.9 4.9 15 2.1 5.4 13 2.2 5.9
80 83 1.4 2.0 60 1.5 2.5 42 1.6 3.1 30 1.7 3.9 24 1.8 4.4 20 1.9 4.9 16 2.1 5.4 14 2.2 5.9
90 94 1.4 2.0 67 1.5 2.5 47 1.6 3.2 34 1.7 3.9 28 1.8 4.4 22 1.9 4.9 18 2.1 5.5 15 2.2 5.9
100 74 1.5 2.5 52 1.6 3.2 37 1.7 3.9 31 1.8 4.4 25 1.9 5.0 20 2.1 5.5 17 2.2 6.0
110 81 1.5 2.5 57 1.6 3.2 41 1.7 3.9 34 1.8 4.4 27 1.9 5.0 22 2.0 5.5 19 2.2 6.0
120 89 1.5 2.5 62 1.6 3.2 45 1.7 3.9 37 1.8 4.4 30 1.9 5.0 24 2.0 5.5 20 2.2 6.0
130 96 1.5 2.5 67 1.6 3.2 48 1.7 3.9 40 1.8 4.5 32 1.9 5.0 26 2.0 5.5 22 2.2 6.0
140 73 1.6 3.2 52 1.7 4.0 42 1.8 4.5 35 1.9 5.0 28 2.0 5.5 23 2.2 6.0
150 78 1.6 3.2 56 1.7 4.0 46 1.8 4.5 37 1.9 5.0 30 2.0 5.5 25 2.2 6.0
160 83 1.6 3.2 59 1.7 4.0 48 1.8 4.5 39 1.9 5.0 32 2.0 5.5 27 2.2 6.0
170 88 1.6 3.2 63 1.7 4.0 51 1.8 4.5 4e 1.9 5.0 34 2.0 5.5 28 2.2 6.0
180 93 1.6 3.2 67 1.7 4.0 54 1.8 4.5 44 1.9 5.0 36 2.0 5.5 30 2.2 6.0
190 T = Top width, Retardance " C' 98 1.6 3.2 70 1.7 4.0 57 1.8 4.5 47 1.9 5.0 38 2.0 5.5 32 2.2 6.0
200 D = Depth, Retardance "C' 74 1.7 4.0 60 1.8 4.5 49 1.9 5.0 40 2.0 5.5 33 2.2 6.0
220 V2 = Velocity, Retardance " C' 81 1.7 4.0 66 1.8 4.5 54 1.9 5.0 44 2.0 5.5 37 2.2 6.0
240 Vl = Velocity, Retardance "D" 88 1.7 4.0 72 1.8 4.5 59 1.9 5.0 48 2.0 5.5 40 2.2 6.0
260 96 1.7 4.0 78 1.8 4.5 64 1.9 5.0 51 2.0 5.5 43 2.2 6.0
280 (Settlement to be added to top of ridge.) 84 1.8 4.5 69 1.9 5.0 55 2.0 5.5 46 2.2 6.0
300 90 1.8 4.5 73 1.9 5.0 59 2.0 5.5 50 2.2 6.0
IM-

0
•
r
•
8.05.46

lates slowly and present a threat to marine life
and public health, human waste from boats is
better disposed of on land at appropriate sites.
If a marina includes a substantial number of
boats or is in a critical area, permit conditions
to require installation of pumpout facilities
may be imposed. Generally, no discharges
from boats are allowed in marinas.
Drainage Ditches
Drainage ditches are used throughout North
Carolina's coastal region to lower the water
table on a particular piece of land so it can be
safely built upon or cultivated. Drainage ditches
are also used to dry out areas where mosquitoes
breed. The ditches play a part in making some
areas more enjoyable and more livable.
However, drainage ditches can cause a lot of
damage to coastal resources. They can alter the
flow of water through productive marshlands
and disturb the natural balance there. They can
create stagnant bodies of water where sedi-
ments, pollutants, and vermin accumulate. They
can introduce sediment into adjacent estuarine
waters that can smother valuable habitats, cloud
the water to keep light from reaching submerged
vegetation, and choke fish and shellfish:
The Coastal Resources Commission's stand-
ards for drainage ditches and nonagricultural
drainage are designed to lessen these problems.
Drainage ditches must meet the specific stand-
ards listed below as well as the general use
standards for coastal wetlands, estuarine waters,
and public trust areas (which are officially stated
in Title 15, Subchapter 7H, Section .0208(b)(3)
and (4) of the N.C. Administrative Code. The
Coastal Resources Commission must approve
all proposed ditches with maximum dimensions
greater than six feet wide by four feet deep. If
the CRC determines that the ditch will affect es-
tuarine or navigable waters, a major develop-
ment permit is required. The dimensions of all
ditches are measured at the ground level.
No drainage ditch in and through marshes
shall exceed six feet by four feet deep unless
Drainage Canal
Ii' - ^ y :,t�'�". 'ALLOWED
IWITHOUT CRC
IPREALITHEAUTHORIZATION
V
- 6. it
Figure 27. Maximum allowable size of drainage
ditches.
DRAINAGE CANAL as
oYtj
--• ^BASIw`-'�'` -
:-
-- °` '.ESTUARINEi
WATERFLOW ; -1a x� WATERFLOW WATERS
VEGETATION
BUFFER
WATERFLOW STRIP
,-. -•ram`
OS
- -•
d ESTUARINE'
DRAINAGE CANAL
; ' WATER
Figure 28. Retention devices used with drainage
ditches.
the applicant can show that a larger ditch is
needed for adequate drainage (see Figure 27).
Six feet by four feet is the standard size of
drainage ditches in the coastal region. A ditch
this size should be enough to drain the land
and cause the least possible damage to sur-
rounding wetlands.
No drainage ditch can cause significant
damage to primary nursery areas, shellfish
beds, submerged grass beds, or other impor-
tant estuarine habitats.
The Division of Coastal Management's field
representative can tell you where these areas
are and how you can design a project to avoid
them.
In designing and digging a drainage ditch it is
necessary to be aware of the damage it can
cause to the productive estuarine system. This
damage comes not only from releasing fresh
water, sediments, and nutrients into the wet-
lands and estuarine waters. Large releases of
fresh water can alter the water's salinity,
49

which is the key to the whole system's ability
to support abundant plant and animal life.
Sediment coming from the ditch and sur-
rounding lands can smother valuable habitats,
cloud the water to keep light from reaching
submerged vegetation, and choke fish and
shellfish. Nutrients from lands that are
drained by the ditch can cause algae blooms
that rob the estuarine waters of light and
oxygen.
Settling basins, water gates, and other runoff
retention structures are examples of devices
that can be used to reduce the amount of sedi-
ments and nutrients that wash into the
drainage ditch and then into the wetlands and
estuarine waters (see Figure 28). The
Division of Soil and Water Conservation (see
appendix for address) administers a cost -shar-
ing program that can help pay for some of
these devices.
The excavation of new ditches through high
ground must occur landward of a temporary
earthen plug or other device to reduce silta-
tion of adjacent water bodies.
Spoil from the construction or maintenance
of drainage ditches through a regularly
flooded marsh must be placed landward of
the marsh to prevent the introduction of sedi-
ment into the marsh or water. Where
feasible, spoil from ditches through an ir-
regularly flooded marsh must be placed on
non -wetland areas (including former disposal
sites).
Ditches must be designed to minimize diver-
sions or reductions in the volume of flow to
both surface waters and groundwater. No
non-agricultural ditch may divert or restrict
the flow of water to important wetlands or
marine habitats.
Ditches must provide water of sufficient
depth to allow the free passage of finfishes,
juvenile shrimp, and other migratory animals.
Ditches may not create stagnant pools of
water or significant changes in the velocity of
flow.
Exemption
Small ditches used for agricultural or commer-
cial forestry with dimensions less than six feet
by four feet do not require a LAMA permit.
This exemption applies only for agriculture and
forestry and does not apply to permits required
under the State Dredge and Fill Act.
Nourishment of Estuarine
Beaches
North Carolina's broad sounds and tidal rivers
are lined with numerous sand beaches that are
used for recreation. At times the beach migrates
or erodes, and loses its value as a recreational
resource. The beach's usefulness for recreation
can be temporarily restored by replenishing its
supply of sand. However, such a project must be
carefully carried out to prevent the deterioration
of wetlands, shellfish beds, nursery areas,
navigation channels, and water quality in the
state's estuaries.
Estuarine beach nourishment projects must
meet specific standards in addition to the
general use standards for coastal wetlands, es-
tuarine waters, and public trust areas. These
standards (which are officially stated in Title 15,
Subchapter 7H, Section .0208(b)(8) of the N.C.
Administrative Code) are listed here.
Beach creation and/or maintenance may be
allowed to enhance water -related recreation-
al facilities for public, commercial, and
private uses. Placing unconfined sand in the
water and along the shoreline will not be al-
lowed as a method for controlling shoreline
erosion.
Beaches can be created and/or maintained
where they historically have been found due
to natural processes. They will not be allowed
in areas with high erosion rates where fre-
quent maintenance will be needed.
•
50

VIII
Page 1 of 5
VIII. CULVERTS
A culvert is a conduit that conveys flow through the embankment. The most
commonly used shapes are circular, rectangular, elliptical, pipe arch and
arches. They range in size from large multiple barrel box culverts and metal
arch structures to single 18 inch pipes. The design process for culverts as well
as all drainage structures is much like the bridge crossing in that it involves:
data collection, hydrologic analysis, formulation, evaluation and selection of
an alternate, and documentation of the design. Some of the larger structures
must be analyzed by the same procedures and methods as a bridge crossing. The
procedure presented here is summary in nature and is intended for the common box
or pipe culvert crossing. The extent of design effort for a particular culvert
must be commensurate to its cost and potential risk to the public. The engineer
should reference FHWA, Hydraulic Design Series No. 5 (15), for more detailed
guidance. He must also reference this document for nomograph charts and tables
required for a manual design process.
The forms used for documentation and the information required differ for box and
pipe size culverts. Any culvert structure providing conveyance greater than a
single 72 inch pipe will follow the design procedure and documentation on the
"Culvert Survey and Hydraulic Design report" (Appendix F). Smaller culvert design
will be documented on a pipe data sheet (Appendix G).
(1) Data Collection Information gathered during the pre -design study and field
survey relative to each particular crossing or all crossings in general is to be
assembled. This process will include:
(a) For all box culverts or any other structure that preliminary
estimates indicate requiring a total crossing conveyance greater than
a single 72 inch pipe, plot a plan and profile view of the stream
crossing on the "Culvert Survey and Hydraulic Design Report" (Appendix
F) PAGE 1 of 3,PAGE 2 of 3,Page 3 of 3 (PDF FORMAT - see note below).
NOTE: These PDF files may give an initial error message when opened;
however, they are viewable by zooming in. Printing may be problematic,
but it is possible. Be sure the "shrink to fit" toggle is on, and be
prepared to wait about 5 minutes for the printing to complete. The
problem has something to do with the graphics copied from the
Microstation File to the PDF file.
(Click here for Microstation *.DGN file.(contains both Bridge &
Culvert Survey and Hydraulic Design Reports)
The drawing scale is to be 1 inch = 50 feet horizontal and 1 inch = 10
feet vertical. Existing features are to be in ink with manmade
features shown with dashed lines. This information is to be limited to
that which is pertinent to the structure sizing and location.
Information to be provided on the profile view:
(1) There are to be two profiles - one along the centerline
of the roadway showing the flood plane section and roadway
profile both existing and proposed. The second profile is
to be along the centerline of the structure showing the
stream bed grade, top of bank and normal water surface
profile.
(2) The centerline of the roadway profile should show:
ground line, channel base and banks, grade line, water
surface elevations (date of survey, normal if different),
flood plain limits, historical flood elevations (including
date of occurrence, and estimated frequency), utility
elevations, controlling backwater feature elevations
(building floor levels, yards, cultivated fields, roadways,
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VIII Page 2 of 5
drives, other drainage structures, overtopping controls),
general classification of stream bed and bank materials
(clay, silt, sand, gravel, cobble, rock), plot rock line if
identified
(3) The centerline of structure should show: stream bed,
top of bank, existing and proposed roadway cross-section,
normal water surface profile, historical flood levels,
controlling feature elevations properly positioned along
the profile, rock line if identified.
(4) Any additional stream cross -sections utilized for
design or needed for structural excavation estimates are to
be plotted on the survey report. The drawing scale for
these sections can be adjusted as needed to fit the report.
Information to be provided on the plan view:
(1) Natural features - stream channel showing
base and banks, limits of the floodplain
(2) Type of cover
(3) Manmade features -buildings, houses,
highways, existing drainage structures, utilities
(4) The proposed roadway section and fill slope
limits
(b) For 72 inch pipe size and smaller, the site data will be
summarized on the pipe data sheet. The engineer will also need to
reference the drainage plans for topographical and proposed layout
information.
(2) Hydrologic Analysis - There are four discharge levels that must be evaluated
for each culvert design. These are:
(a) A "design discharge" as listed and defined in the hydrology
section (Table 4-3,Chapter VI)
(b) Q100 base flood
.(c) Q-overtopping. This discharge is computed after a trial size is
selected.
(d) Q10 for outlet protection and erosion control measures.
Other discharges may be required on a site specific basis. Examples
are:
(a) Q-average - for permit determination
(b) Q-bank full- for fish passage, channel stability or floodplain
analysis.,
(3) Hydraulic Design
(a) The first step in hydraulically analyzing a culvert is to address
criteria and information that must be quantified prior to commencing
actual structural sizing and location. This would include:
Material Selection M
A material selection recommendation must be provided for each pipe
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VIIl
Page 3 of 5
culvert. The general selection policy is as follows.
Culvert pipe shall be concrete with the following
exceptions :
• The expected fill height over the structure exceeds
the maximum values for concrete as provided in the
N.C. Division of Highways charts,(Appendix H)
• The required invert slope is greater than 10%.
• If a majority of the installations for a project
require metal, then all culvert pipe for the project
can be metal.
Other site or project specific factors such as, corrosive
conditions, accessibility, environmental requirements,
handling and initial cost may dictate the use of a
particular material.
Box culverts are generally cast in place or precast
concrete. There are large metal structures, arches and box
shapes, with and without bottom plates, that can be
considered for sites requiring large openings and/or spans.
The primary source of information on available sizes and
structural details is the manufactures literature.
Appendix H provides gage requirements and fill limitations
for metal and concrete structures.
[LINK TO APPENDIX H,SHEETS 1,2,3,4,5,6,7,8,9,10,1l1
End Treatment
Headwalls are generally used on the inlet end of pipe
culverts 36 inch or larger. The outlet end does not require
a headwall unless site specific conditions such as
right-of-way limitation warrant placement of an outlet
headwall. For guidance on end treatment of parallel pipes,
reference section 5-20, of the Roadway Design Manual (16).
Allowable Headwater
The allowable headwater elevation is established based on
an evaluation of natural flooding depths, upstream
structures and land use, as well as the proposed roadway
elevations.
Multiple Openings (width)
When the width of the structure opening is significantly
wider than the natural channel, an evaluation must be made
of the affect on flow capacity which will occur when the
low flow area is restricted to its natural width by
artificial or natural means.
Alignment
As near as is practicable, a culvert should intercept an
outlet flow within the natural channel. When channel
realignment is required, a natural channel design should be
btilized (see section X).
Length and Slope
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2/10/2000

VIII
Page 4 of 5
The slope of a culvert should approximate that of the
natural channel. The invert elevation should be slightly
below the natural bed ranging from 0.1 +/- feet for small
pipes to 1.0 +/- feet for large box culvert. Where fish
passage is a consideration, the invert should be a minimum
of 1.0 feet below the natural bed. Baffles may be placed in
the invert to promote retention of bed material and
formation of a low flow channel. When a shallow (3-5 foot
max. depth) non -erosive rock foundation is found throughout
the proposed site, the structure can be built on footings
without a bottom allowing retention of the natural channel
bed. The Geotechnical Unit must confirm the foundation
acceptability prior to final selection of the "bottomless"
culvert.
Potential channel cleanout and improvements should also be
considered particularly in the coastal plain. The length is
established by the geometry of the roadway embankment, the
bed elevation and skew.
Tailwater
The computed normal channel depth for each discharge level
being evaluated generally establishes the tailwater. This
can be determined by a simple single section analysis.
Effects of downstream controls and constrictions must also
be considered.
0
Debris
The structure opening should be reasonably sized to provide
for debris. The limitation of structural height to
headwater depths in the HW/D = 1.2+/- range has proven to
limit problems of this nature to acceptable levels. Where
experience or physical evidence indicates the water course
will transport a greater than normal size or volume of
debris, special debris controls should be developed and/or
the estimated capacity of the structure reduced to reflect
the potential for blockage.
(b)A trial size culvert can be determined using the design discharge,
inlet control nomographs (HDS-5 ref.- 12)and an assumed HW/D = 1.2.
Multiple openings may be selected by dividing the discharge.
(c)When a trial size selection is reasonable in regard to available
sizes (see Appendix H) and allowable headwater limitations, the full
inlet/outlet control analysis is performed. The higher of the computed
headwaters governs.
(d)If the analyzed size is acceptable in regard to controls and
criteria relative to the design discharge, verify it being the minimum
acceptable by checking the performance of a smaller structure.
(e)If inlet control governs, improved inlet design must be
investigated. This will be performed for all inlet control box
culverts and for pipe culverts 36 inch and larger with lengths > 150
ft. If as much as one nominal size reduction can be achieved for box
culverts, the improved inlet option can be selected. For pipe
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VIII
Page 5 of 5
culverts, an economic analysis is required to justify the selected
option.
(f) Determine the design values and acceptability of the selected
culvert for the Q100 and overtopping flood.
(g)Outlet velocities shall be determined for the Q10 discharge. If
this velocity exceeds the scour velocity for the receiving stream, rip
rap outlet protection is required.
(1) See channel chapter for permissible velocity guidelines
(2) Use whichever is greater, tailwater depth or normal
flow depth for culvert to determine outlet velocity.
(4) Design Documentation
All information pertinent to the culvert design shall be documented on either
the "Culvert Survey and Hydraulic Design Report"; or the "Pipe Data Sheet". This
will include:
(a) For box culverts, plot the proposed structure in plan and profile
views. Note centerline station and skew. Show invert elevations and
skew, or top of footing elevations.
(b) Show design water surface elevation on all views.
(c) Complete fill-in of data for selected structure on report or data
sheet.
(d) If design is accomplished by computer program, private engineering
firms must submit data file summaries on an IBM compatible disk.
(e) For large culverts (>72 inch), a plot of the performance curve for
the selected structure with a plot of the natural stage -discharge
relations is desirable.
(f) Provide stream classification.
IX. Storm Drainage System
•
http://www.doh.dot.state.nc.uslpreconstructlhighwaylhydrolg10399weblviii.culverts.htm 2/10/2000

3.9.2
HYDRAULIC DESIGN OF HIGHWAY
CULVERTS.
Note: EDS-5 is an updated version of
EMC loos. 5 and U. Sections
3.9.2 and 3.9.2.1 are covered
by EDS-5
USOeparfrrlerlt
Fedw HkjlmOy•
A�T>iHSlrlOtbfl
liesearcn. Oeverooment.
am Tec mi Ny
Turner•Farbank Hynway
aese*rcn center
6= G*orNetown Pic*
McLean. Virginia 22101
Hydraulic Ossign
Series No. 5 (»S-5)
Report No.
FH W A-IP-85-16
. September 1985
3-12

•
This Implementation Package provides practical hydraulic design methods. and
techniques for the analysis and sizing of highway culverts. These procedures
should be of interest to hydraulic, bridge, and highway design engineers.
Sufficient copies of the report are being distributed to provide a minimum of
one copy to each FHWA Region office, Division office, and each State highway
agency. Additional copies will be available to public agencies from the FHWA
Off i a of Engineering (HNG-31).
Ronald E. Heinz R. J. Betsold
Director, Office of Director, Office of
Engineering Implementation
•
NOTICE
This document is disseminated under the sponsorship of the Department of
Transportation in the interest of information exchange. The United States
Government assumes no liability for its contents or use thereof. The contents
of this report reflect the views of the contractor, who is responsible for
the accuracy of the data presented herein. The contents do not necessarily
reflect the official policy of the Department of Transportation. This report
does not constitute a standard, specification, or regulation.
The United States Government does not endorse products or manufacturers.
Trade or manufacturers' names appear herein only because they are considered
essential to the object.of this document.-
-

•
III. CULVERT DESIGN
A. Culvert Flow.
1. General. An exact theoretical
analysis of culvert flow is extremely
complex because the flow is usually non-
uniform with regions of both gradually
varying and rapidly varying flow. An
exact analysis involves backwater and
drawdown .calculations, energy and mo-
mentum balance, and application of the
results of hydraulic model studies. For
example, the U.S. Geological Survey has
defined 18 different culvert flow types
based on inlet and outlet submergence,
the flow regime in the barrel, . and the
downstream brink depth. (20) Often,
hydraulic jumps form inside or downstream
of the culvert barrel. . In addition, the
flow types change in a given culvert as
the flow rate and tailwater elevations
change.
In order to systematically analyze
culveit flow, the procedures of this
publication have been developed, wherein
the various types of flow are classified
and analyzed on the basis of 'control
section. A control section is a location
where there is a unique relationship
between the flow rate and the upstream
water surface elevation. Many different
flow conditions exist over time, but at
a given time the flow is 'either governed
by the inlet geometry (inlet control);.
or by a combination of the culvert inlet
configuration, the characteristics of
.the barrel, and the tailwater (outlet
control). Control may oscillate from
inlet to outlet; however, in this publica-
tion, the concept of •minimum perform-
ance' applies. That is, while the culvert'
may operate more efficiently at times (more.'
flow for a given headwater level), it
will never operate at a lower level of
performance than calculated.
The culvert design method presented
in this publication is based on the use
of design charts and nomographs. These
25
charts and nomographs are, in turn, based
on data from numerous hydraulic tests
and on theoretical calculations. At each
step of the process, some error is intro-
duccd. For example, there is scatter in
the test data and the selection of a
best fit design equation involves some
error. Also, the correlation between
the design equations and the design homo-
graphs is not exact. Reproduction of
the design charts introduces additional
error. Therefore, it should be assumed
that the results of the procedure are
accurate to within plus or minus ten per-
cent, in terms of head. Additional infor-
mation on the precision of the design
charts is provided in appendix A.
Table 1 in chapter I shows the factors
which must be considered in culvert design
for inlet and outlet -control. In inlet
control, only the inlet area, the edge
configuration, and the shape influence
the culvert performance for a given head-
water elevation. The headwater depth is
measured from the inlet invert, and the
tailwater • elevation has no influence on
performance. In outlet control, all of
the -factors listed in table 1 affect
culveit performance. Headwater depth is
measured from the outlet invert, and the
difference between headwater and tailwater
elevation represents the energy which
conveys the flow through the culvert.
L Types of Control. A general
description of the characteristics of
inlet and outlet control flow is given
below. A culvert flowing in inlet control
has shallow, high velocity flow categor-
ized as 'supercritical.' For supercriti-
cal flow, the control section is at the
upstream end of the barrel. (the inlet).
Conversely, a culvert flowing in outlet
control will have relatively deep, lower
velocity flow termed 'subcritical' flow.
For subcritical flow the control is at the
downstream end of the culvert (the
outlet). The tailwater depth is either

A
WATER SURFACE
Off
OUTLET UNSUBMERGED
e
WATER SURFACE
HW —
OUTLET SUBMERGED
INLET UNSUBMERGED
C
HW WATER SURFACE
INLET SUBMERGED
MEDIAN DRAIN
HW
WATER SURFACE
OUTLET SUBMERGED
Figure III-1—Types of Inlet control.
126
R

•
critical depth at the culvert outlet or
the downstream channel depth, whichever
is higher. In a given culvert, the type
of flow is dependent on all of the factors
listed in table 1.
a. Inlet Control.
1) Examples of Inlet Control.
Figure III-1 depicts several different
examples of inlet control flow. The
type of flow depends.on the submergence
of the inlet and outlet ends of the cul-
vert. In all of these examples, the
control section is at the inlet end of
the culvert. Depending on the tailwa=
ter, a hydraulic jump may occur down-
stream of the inlet.
Figure III-1-A depicts a condition
where neither the inlet nor the outlet
end of the culvert are submerged. The
flow passes through critical depth just
downstream of the culvert entrance and
the flow in the barrel is supercritical.
The barrel flows partly full over its
length, and the flow approaches normal
depth at the outlet end.
Figure III-1-B shows that submergence
of the outlet end of the culvert does
not assure outlet control. In this case,
the flow just downstream of the inlet is
supercritical and a hydraulic jump forms
in the culvert barrel.
Figure 11I-1-C is a more typical design
situation. The inlet end is submerged
and the outlet end flows freely. Again,
the flow is supercritical and the barrel
flows partly full over its length. Crit-
ical depth is located just downstream of
the culvert entrance, and the flow is
approaching normal depth at the down-
stream end of the culvert.
Figure III-1-D is an unusual condi-
tion illustrating the fact that even
submergence of both the inlet and the
outlet ends of the culvert does not assure
full flow. In this case, a hydraulic jump
will form in the barrel. The median
inlet provides ventilation of the culvert
barrel. If the barrel were not . venti-
27
laced, sub -atmospheric pressures could
develop which might create an unstable
condition during which the barrel would
alternate between full flow and partly
full flow.
2) Factors Influencing Inlet
Control. Since the control is at the
upstream end in inlet control, only the
headwater and the inlet configuration
affect the culvert performance. (table
1) The headwater depth is measured from
the invert of the inlet control section
to the surface of the upstream pool.
The inlet area is the cross -sectional
area of the face of the culvert. General-
ly, the inlet face area is the same as
the barrel area, but for tapered inlets
the face area is enlarged, and the control
section is at the throat. The i.UJS1
Figure III-2— Flow contractions
for various culvert Inlets.

edge configuration describcs the entrance
type. Some typical inlet edge configu-
rations are thin edge projecting, mitered,
square edges in a headwall and beveled
edge. The inlet shave is usually the
same as the shape of the culvert barrel;
however, it may be enlarged as in the
case of a tapered inlet. Typical shapes
are rectangular, circular. and elliptical.
Whenever the inlet face is a different
size or shape than the culvert barrel.
the possibility of an additional control
section within the barrel exists.
An additional factor which influences
inlet control performance is the barrel
slope. The effect is small. however,
and it can be ignored or a small slope
correction factor can be inserted in the
inlet control equations. (appendix A)
The inlet edge configuration is a
major factor in inlet control performance,
and it can be modified to improve perfor-
mance. Various inlet edges are shown in
figure III-2. Figure III-2-A is a this
edge projecting inlet typical of metal
pipe, figure III-2-B is a projecting
thick-walled inlet (about the same perfor-
mance as a square edge in a headwall)
which is typical of concrete pipe without
a groove end, and figure II1-2-C is a
groove end or socket inlet which is typical
of a concrete pipe joint. Note that as
the inlet edge condition improves (from
figure III-2-A to III-2-C), the flow
contraction at the inlet decreases.
This reduced flow contraction indicates
increased inlet performance and more
flow through the barrel for the same
headwater.
1.5 : 1 TOP BEVEL
33.7 • TOP
I.5:1 SIDE BEVEL
W/33.T'ANGLE
AND SIDE
W/33.7'ANGLE
BEVELS
OF BARREL.
HEIGHT
1 i•/ft
Of T
I
BARREL
WIDTH
ti 3L 1
_
.D
B
_ I
1:1 TOP BEVEL
450 MP
1:1 SIDE BEVEL
W/4S•ANGLE
AND SIDE
W/45.•ANGLE
BEVELS
I in /ft
of 4�
BARREL
HEIGHT
in/fit
1
OF BARREL ` I
OF WRCL
1
HEIGHT
WIDTH-
I
4S'
fib'
D
1
. e
i
.
1
Figure III-3--Beveled edges.
28
•

•
A method of increasing inlet perfor-
mance is the use of beveled edges at the
entrance of the culvert. Beveled edges
reduce the contraction of the flow by
effectively enlarging the face of the
culvert. Although any beveling will
help the hydraulics, design charts are
available for two bevel angles, 45 degre-
es and 33.7 degrees, as shown in figure
III-3.
The larger, 33.7-degree bevels require
some structural modification, but they
provide slightly better inlet performance
than the 45-degree bevels. The smaller,
45-degree bevels require very minor struc-
tural modification of the culvert headwall
and increase both inlet and outlet con-
trol performances. Therefore, the use
of 45 degree bevels is recommended on
all culverts, whether in inlet or outlet
control, unless the culvert has a groove
end. (The groove end provides about
the same performance as a beveled edge.)
3) Hydraulics of Inlet Control.
Inlet control performance is defined by
the three regions of flow shown in Figure
III4: unsubmerged, transition and sub-
merged. For low headwater conditions,
as shown in figures III-1-A and III-1-B,
the entrance of the culvert operates as
a weir. A weir is an unsubmerged flow
control section where the upstream water
surface elevation can be predicted for a
given flow rate. The relationship between
flow and water surface elevation must be
determined by model tests of the weir
geometry or by measuring prototype dis-
charges. These tests or measurements
are then used to develop equations for
unsubmerged inlet control flow. Appendix
A contains the equations which were devel-
oped from the NBS model test data.
For headwaters submerging the culvert
entrance, as are shown in figures III-1-C
and III-1-D, the entrance of the culvert
operates as an orifice. An orifice is
an opening, submerged on the upstream
side and flowing freely on the downstream
side, which functions as a control sec-
tion. The relationship between flow and
headwater can be defined based on results
29
from model tests. Appendix A contains
the submerged flow equations which were
developed from the NBS test data.
The flow transition zone between the
low headwater (weir control) and the
high headwater flow conditions (orifice
control) is poorly defined. This zone
is approximated by plotting the unsub-
merged and submerged flow equations and
connecting them with a line tangent to
both curves, as shown in figure I11.4.
OVERALL INLET
CONTROL CURVE-,_-�/'
MMERG E0(OR NFNCE] FLOW
UNSU•YEROUMCIR1 FLOW
Figure III-4-.Inlet flow control curves.
The inlet control flow versus headwater
curves . which are established using the
above procedure .are the basis for con-
structing . the • inlet control design
homographs. Note that the approach velo-
city head can be included as a part of
the available headwater in the inlet
control relationships.
4) Inlet Depressions. The inlet
control equations or nomographs provide
the depth of headwater above ' the inlet

invert required to convey a given discharge
through the inlet. This relationship
remains constant regardless of the elev-
ation of the inlet invert. If the entrance
end of the culvert is depressed below the
stream bed, more head can be exerted on
the inlet for the same headwater eleva-
tion.
Two methods of depressing the entrance
ends of culverts are shown in figures
III-S and lII-6. Figure III-S depicts
the use of a depressed approach apron
with the fill retained by wingwalls.
Paving the apron is desirable. Figure
III-6 shows a sump constructed upstream
of the culvert face. Usually the sump
ELEVATION
Figure III-S—Colrert with depressed apron and wingwalls.
.30
•
4
•

S
•
10 "
ELEVATION
n i_
'GT
(MIN.)
III
I
IT
f
x
a�2
m
e
i
PLAN
Figure III-6—Culvert with inlet sump.
is paved, but for small depressions, an at the face to the throat invert. Tapered
unpaved excavation may be adequate. inlets will be discussed further in chapter
IV.
When a culvert is depressed . below the
stream bed at the inlet, the depression b. Outlet Control
is called the FALL. For. culverts without
tapered inlets, the FALL is defined as 1) Examples of Outlet Control.
the depth from the natural stream bed at Figure III-7 illustrates various outlet
the face to the inlet invert. For culverts control • flow conditions. In all cases,
with tapered inlets, the FALL is defined the control section is at the outlet end
as the depth from the natural stream bed of the culvert or further downstream.
31

HW
•
W.
w'
_-
c
—"i—
Hw
o
HW H
W s.
E
Hw
T
Figure III-7— Types of outlet control.
32

•
(0 -
P -
For the partly full flow situations. the
flow in the barrel is subcritical.
Condition III-7-A represents the clas-
sic full flow condition, with both inlet
and outlet submerged. The barrel is in
pressure flow throughout ' its length.
This condition is often assumed in calcula-
tions, but seldom actually exists.
Condition III-7-B depicts the outlet
submerged with the inlet unsubmerged. For
this case, the headwater is shallow so
that the inlet crown is exposed as the
flow contracts into the culvert.
Condition III-7-C. shows the entrance
submerged to such a degree that the cul-
vert flows full throughout its entire
length while the exit is unsubmerged.
This is a rare condition. It requires
an extremely high headwater to maintain
full barrel flow with no tailwater. The
outlet velocities are usually high under
this condition,
Condition III-7-D is more typical. The
culvert entrance is submerged by the
headwater and the outlefend flows freely
with a low tailwater. For this condition,
the barrel flows partly full over at
least part of its length (subcritical
flow) and the flow passes through critical
depth just upstream of the outlet.
Condition ' III-7-E is also typical,
with neither the inlet nor the outlet
end of the culvert submerged. The barrel
flows partly full over its entire length,
and the flow profile is subcritical.
2) Factors Influencing Outlet
Control. All of the factors influencing
the performance of a culvert in inlet
control also influence culverts in outlet
control. In addition, the barrel charac-
teristics (roughness, area, shape, length,
and slope) and the tailwater elevation
affect culvert performance in outlet
control. (table 1) .
The barrel roughness is- a function of
the material used to fabricate the bar-
rel. Typical materials include concrete
33
and corrugated metal. The roughness is
represented by a hydraulic resistance
coefficient such as the Manning n value.
Typical Manning a values for culverts
are presented in table 4. Additional
discussion on the sources and derivations
of the Manning a values are contained in
appendix B.
The barrel area and barrel shape are
§elf explanatory.
The barrel length is the total culvert
length from the entrance to the exit of
the culvert. Because the design height
of the barrel and the slope influence
the actual length, an approximation of
barrel length is usually necessary to
begin the design process.
The barrel slope is the actual slope
of the culvert barrel. The barrel slope
is often the saw,- as the natural stream
slope. However, when the culvert inlet
is raised or lowered, the barrel slope
is different from the stream slope. ..
The tailwater elevation is based on
the downstream 'water surface elevation.
Backwater calculations from a downstream
control, a normal depth approximation,
or field observations are used to. define
the tailwater elevation.
3) Hydraulics of Outlet Control.
Full flow in the culvert barrel, as
depicted in figure III-7-A, is the best
type of flow for describing outlet control
hydraulics.
Outlet control flow conditions can be
calculated based on energy balance. The
total energy (HL) required to pass the
flow through the culvert barrel is made
up of the entrance loss (Ha, the friction
losses through the barrel (Ht), and the
exit loss (H,). Other losses, including
bend losses (Hb), losses at junctions
(HP, and loses at grates (H ) should be
included as appropriate. These losses
are discussed in chapter VI.
HL = He + Ht + Ho + Hb + Hit Hg (1)

Table 4. Manning a values for culverts.
Type of
Conduit
Wall & Joint
pescriotion
Concrete Pipe
Good joints, smooth
walls
Good joints, rough
walls
Poor joints, rough
walls
Concrete Box
Good joints, smooth
finished walls
Poor joints, rough,
unfinished walls
Corrugated Metal
2-2/3 by 1/2
Pipes and Boxes,
in corrugations
Annular Corrugations
(Manning n varies
6 by I inch
with barrel size)
corrugations
5 by 1 inch
corrugations
3 by 1 inch
corrugations
6 by 2 inch
structural
plate corrugations
9 by 2 1/2
inch structural
plate corrugations
Corrugated Metal
2-2/3 by 1/2
Pipes, Helical
inch corruga-
Corrugations,
tions, 24 inch
Full Circular Flow
plate width
Spiral Rib Metal PiFe
3/4 by 3/4 in
recesses at
12 inch spacing,
good joint
34
Hannina n
0.011-0.013
0.014-0.016
0.016-0.017
0.012-0.015
0.014-0.018
0.027-0.022
0.0254.022
0.026-0.025
0.028-0,027
0.035-0.033
0.037-0.033
0.012-0.024
0.012-0.013
•
•
•

•
r
t
The barrel velocity is calculated as
follows:
Q
A
V is the average velocity in
the culvert barrel, ft/s (m/s)
Q is the flow rate. ft3/s (m3/3)
A is the full cross sectional
area of the flow, ft2 (m3)
The velocity head is:
Vs
H, • (3)
2g
g is the acceleration due to
gravity. 32.2 ft/s/s (9.8
• m/s/s)
The entrance loss is a function of
the velocity head in the barrel, and can
be expressed as a coefficient times the
velocity head.
V2
He • ke --- (4a)
(22)
-Values of ke based on various inlet
configurations are given in table 12,
appendix D.
.The friction loss in the barrel is
also a function of the velocity head. Based.
on the Manning equation, ttie friction
loss is:
29 n2 L V=
Ht •------------- (4b)
RL33 2g
n is the Manning roughness coeffi-
cient (table 4)
3S•
L is the length of the culvert
barrel, ft (m)
R is the hydraulic radius of the
full culvert barrel • A/p, ft (m)
A is the cross -sectional area of
the barrel. ft2 W)
p is the perimeter of the barrel.
f t (m)
V is the velocity in the barrel.
ft/s (m/s)
The exit loss is a function of the
change in velocity at the outlet of the
culvert barrel. For a sudden expansion
such as an endwall, the exit loss is:
V2 Vd=
He • 1.0 ---- - — (4c)
2g 2g
Vd is the channel• velocity down-
stream of the culvert, ft/s (m/s)
Equation (4c) may overestimate exit losses,
and a multiplier of less than 1.0 can be
used. (40) The downstream velocity is
usually neglected, in which * rase the
exit loss is equal to the full now velo-
city head in the 'barrel, as shown in
equation (4d).
Vz
He • H, -• (4d)
2g
Bend losses, junction . losses, grate
losses and other losses are discussed in
chapter VL •These other losses are added
to -the total losses using equation (1).
Inserting the above relationships for
entrance loss, friction loss, and. exit loss
(equation •4d) into equation (1). the
following equation for loss is obtained:
29 n= L V=
H • 1 + ko + 29 -- (5)
R1.ss 2g

V2
124
/01
V M f Hll
\_'000' -........ Hot
1.
SECTION lO
TW
SECTION
Figure III-8—Full flow energy and hydraulic grade lines.
Figure III-8 depicts the energy grade
line and the hydraulic grade line for
full flow in a culvert barrel. The energy
grade line represents the . total energy
at any point along the culvert barrel.
HW is the depth from the inlet invert to
the energy grade line.The hydraulic grade
line is the depth to which water would
rise in vertical tubes connected to the
sides of the culvert barrel. In full
flow, the energy grade line 'and the hyd-
raulic grade line are parallel straight
lines -separated by the velocity head lines
except in the vicinity of the inlet where
the flow passes through a contraction.
The headwater and tailwater condi-
tions as well as the entrance, friction,
and exit losses are also shown in figure
1114. Equating the total energy at
sections 1 and 2, upstream and downstream
of the culvert barrel in figure III-8,
the following relationship results:
V= V2
HWo + n W TW + e + HL (6)
2g 2g
HW. ' is the' headwater depth above
the outlet invert, ft (m)
Va is the approacl} velocity, ft/s
(m/s)
TW is the tailwater depth above
the outlet invert, ft (m)
Vd is the downstream velocity,
ft/s (m/s)
36
I
V2
HL is the sum of all losses in-
cluding entrance (Hj, friction
(W. exit (H,) and other
losses, (Hb), (H), etc.,
ft (m)
Note that the total available upstream
energy (HW) includes the depth of the
upstream water surface above the outlet
invert and the approach velocity head.
In most instances, the approach velocity
is low, and the approach velocity head is
neglected. However, it can be considered
to be a part of the available headwater
and used to convey the now through the
culvert.
Likewise, the velocity downstream of
the culvert (Vd) is usually neglected.
When both approach and downstream veloci-
ties are neglected, equation (6) becomes
HWo im TW + HL (7)
In this case, HL is the difference in
elevation between the watei surface eleva-
tion at the outlet (tailwater elevation)
and the water surface elevation at the
inlet (headwater elevation). If it is
desired to include the approach and/or
downstream velocities, use equation (4c) .
for exit losses and equation (6) instead
of equation (7) to calculate the headwater.

c�
t
ENTRAN-I_
CE LOSS
HEADWATER
A, FULL FLOW
S. PARTLY FULL FLOW
C. FREE SUFtFAC E FLOW
D. HYDRAULIC GRADE LINE APPROXIMATION
Figure III-9--Outlet control energy and hydraulic grade lines.
37
EXIT
LOSS
TAILWATER

Figure III-10--Roadway overtopping.
Equations (1) through (7) were devel-
oped for full barrel flow, shown in figure
III-7-A. The equations also apply to
the flow situations shown in figures
III-7-B and C, which are effectively
full flow conditions. Backwater calcu-
lations may be required for. the partly
full flow conditions shown in figures
III-7-D and E. These calculations begin
at the water surface at the downstream
.end of the culvert and proceed upstream —
to the entrance of the culvert The
downstream water surface is based on
critical depth, at the culvert outlet or
on the tailwater depth, whichever is
higher. ' If the calculated backwater
profile intersects the top of the barrel,
as in figure III-7-1), a straight, full
flow hydraulic grade line extends from
that point upstream to the culvert en-
trance- From equation (4b), the full
flow friction slope is
Hr 29 n= V2
g = .---
a L RIM 2g
In order to avoid tedious backwater
calculations, approximate . methods' have
been developed to analyze partly full
flow conditions. Based on numerous back-
water calculations performed by the FHWA
38
Qlop• Qo
staff, it was found that a downstream
extension of the full flow hydraulic
grade line for the flow condition shown
in figure III-9-B pierces the plane of
the culvert outlet at a point one-half
way between critical depth and the top
of the barrel. Therefore, it is possible
to begin the hydraulic grade line at a
depth of (dC + D)/2 above the outlet
invert and extend the straight, full
flow. hydraulic grade line upstream to
the inlet of the culvert at a slope of
Sw (figure III-9-D) If the tailwater
exceeds (d. + D)/2, the tailwater is
used to set the downstream end of the
extendedJull flow hydraulic grade line.
The inlet losses and the velocity head
are added to the elevation of the hydraulic
grade line at the inlet to obtain the
headwater elevation.
This approximate method works best
when the barrel flows full over at least
part of its length. (figure III-9-B)
When the barrel is partly full over its
entire length (figure III-9-C), the method
becomes increasingly inaccurate as the
headwater falls further below the top of
the barrel at the inlet Adequate results
are obtained down to i headwater of 0.75D.
For lower headwaters, backwater calcu-
lations are required to obtain accurate
headwater elevations.

•
10
Cr
HWr
FLOW
Lr
1105damoll
ii1111 11
A) DISCHARGE COEFFICIENT FOR
Hwr /Lr > 0.15
3.10
3.00
2.90
cr 2.60
2.70
2.60
2.50 r
0
1.0 2.0 a.0. 4.0
Hwr #_
8) DISCHARGE COEFFICIENT FOR
Hwr /Lr AO.15
C 4 2 IttCr
1.010
0.90
0.80
0.70
0.60
0.50
ht
0.6 0.7 0.6 . 0.9 1.0
h t/ Hwr
C) SUBMERGENCE FACTOR
Figure III-I1—Discharge coefficients for roadway overtopping.
The outlet control nomographs in appen-
dix D provide solutions for equation (5)
for entrance, friction, and exit losses
in full barrel flow. Using the approximate
backwater method, the losses (H) obtained
from the nomographs can be applied for
the partly full flow conditions shown -in
figures III-7 *and III-9. The losses are
added to the elevation of the extended
full flow hydraulic grade line at the
barrel outlet in order to obtain the
headwater elevation. The extended hy-
draulic grade line is set at the higher
of (dc .+ D)/2 or the tailwater elevation
at the culvert outlet. Again, the approxi-
mation works best when the barrel flows
full over at least part of its length.
39
I Roadway Overtopping. Overtop-
ping will begin when the headwater rises
to the elevation of the roadway. (figure
III-10) The overtopping will usually
occur at the low point of a sag vertical
curve on the roadway. The flow will be
similar to flow over a broad crested
weir. Flow coefficients for flow over-
topping roadway embankments are found in
HDS No. 1, Hydraulics of Bridge Waterways
(21), as well as in the documentation of
HY-7, the Bridge Waterways Analysis Model
(22). Curves from reference (22) are
shown in figure III-11. Figure III-11-A
is for deep overtopping, figure III-11-B
is for shallow overtopping, and figure
1II-11-C is a correction factor for down-

stream submergence. Equation (8) defines
the flow across the roadway.
Qa M Cd L HWI.t.s (8)
Q, is the overtopping flow rate
in fts/s (ms/s)
Cd is the overtopping discharge
coefficient
L is the length of the roadway
crest, ft (m)
HWr is the upstream depth,
measured from the roadway
crest to the water surface
upstream of the weir draw -
down, ft (m)
A.rtTma 6- WACIVIsio■ wm SUMIENTs
. cuv.TION OF dKST
.................................
&119TM00 t- at W A 51"U9 39449PT
Figure III-12—Weir crest length
determinations for roadway. overtopping.
The length and elevation of the roadway -
crest are difficult to. determine when
the crest is defined by a roadway sag
vertical curve. The sag vertical curve
can be broken into a series of horizontal
segments as shown in figure III42-A.
Using equation (8), the flow over each
segment is calculated for a given head-
water. Then, the incremental flows for
40
each segment are added together, result.
ing in the total flow across the roadway.
Representing the sag vertical curve
by_ a single horizontal line (one segment)
is often adequate for culvert design.
(figure III-12-B) The length of the
weir can be taken as the horizontal length
of this segment or it can be based on
the roadway profile and an acceptable
variation above and below the horizontal
line. In effect, this method utilizes
an average depth of the upstream pool
above the roadway crest for the flow
calculation.
It is a simple matter to calculate
the flow across the roadway for a given
upstream water surface elevation using
equation (8). The problem is that the
roadway overflow plus the culvert flow
must equal the total design flow. A
trial and error process is necessary to
determine the amount of the total flow
passing through the culvert and the amount
flowing across the roadway. Performance
curves may also be superimposed for the
culvert flow and the road overflow to
yield an overall solution as is discussed
later in this chapter.
l
4. Outlet Velocity. Culvert outlet
velocities should be calculated to deter-
mine the need for erosion protection at
the culvert exit. Culverts usually result
in outlet velocities which are higher than
the natural stream velocities. These
outlet velocities may require flow
readjustment or energy dissipation to
prevent downstream erosion.
In inlet control, backwater (also
called drawdown). calculations may be
necessary to determine the outlet
velocity. These calculations begin at
the. culvert entrance and proceed down-
stream to . the exit. The flow velocity
is obtained from the flow and the
cross -sectional area at the exit.
(equation (2))
An approximation may be used to avoid
backwater calculations in determining
the outlet velocity for culverts oper-
ating in inlet control. The water surface

•
YOr11M • & AV 0 AMtA wr rww rnwam v---- --
A# BARREL GEOMETRY ANO OEPTH
EOUAL TO NORMAL DEPTH
Figure III-13--Outlet velocity - Inlet control.
Vow • 0 ; AP • AREA OF FLOW PRISM BASED ON BARREL
ro GEOMETRY AND 4
Figure III-14»Outlet velocity - outlet control.
profile converges toward normal depth as
calculations proceed down the culvert
barrel. Therefore, if the culvert is of
adequate length, normal depth will exist
at the culvert outlet. Even in short
4I
w
.PTH
culverts, -normal depth can be assumed
and used to define the area of flow at
the outlet and obtain the outlet velo-
city. (figure III-13) The velocity
calculated in this manner may be slightly

higher than the actual velocity at the
outlet. Normal depth in common culvert
shapes may be calculated using a trial
and error solution of the Manning equa-
tion. The known inputs are flow rate,
barrel resistance, slope and geometry.
Normal depths may also be obtained from
design aids in publications such as HDS
No. 3. (23)
In outlet control, the cross section-
al area of the flow is defined by the
geometry of the outlet and either critical
depth, tailwater depth, or the height of
the conduit. (figure III-14)
Critical depth is used when the tail -
water is less than critical depth and
the tailwater depth is used when tailwater
is greater than critical depth but below
the top of the barrel. The total barrel
area is used when the tailwater exceeds
the top of the barrel.
B. Performance Curves.
Performance curves are representa-
tions of flow rate versus headwater depth
or elevation for, a given now control
device, such as a weir, an orifice, or a
culvert. A weir constricts open channel
flow so that the flow prism through
critical depth just upstream of the weir.
An orifice is a flow control device,
fully submerged on the upstream side,
through which the flow passes. Performance
curves and equations for these two basic
types of now control devices are shown
in figure III-15.
When a tailwater exists, the control
device may be submerged so that more
than one flow -versus -elevation relation-
ship exists Then, the performance curve
is dependent on the variation of both
tailwater and headwater. In the case of
a weir or orifice, the device is called
a submerged weir or a submerged orifice,
respectively. For some cases, submergence
effects have been analyzed and correction
factors have been developed. (21,22,24)
Culvert performance curves are similar
to weir and/or orifice performance curves
42
In fact, culverts often behave as weirs
or orifices. However, due to the C.
that a culvert has several possible control
sections (inlet, outlet, throat), a given
installation will have a performance
curve for each control section and one
for roadway overtopping. The overall
culvert performance curve is made up of
the controlling portions of the individual
performance curves for each control sec-
tion.
1. Inlet Control. The inlet control
performance curves are developed using
either the inlet control equations of
appendix A or the inlet control nomography
of appendix D. If the equations of
appendix A are used, both unsubmerged
(weir) and submerged (orifice) flow head-
waters must be calculated for a series
of flow rates bracketing the design flow.
The resultant curves are then connected
with a line tangent to both curves (the
transition zone). If the inlet control
nomographs are used, the headwaters corre-
sponding to the series of flow rates are
determined and then plotted. The transi-
tion zone is inherent in the nomography.
2. Outlet Control. The outlet control
performance curves are developed using
equations (1) through (7) of this chapter,
the outlet control nomographs of appendix
D. or backwater calculations. Flows
bracketing the design flow are selected.
For these flows, the total losses through
the barrel are calculated or read from
the outlet control nomographs. The losses
are added to the elevation of the hydraulic
grade line at the culvert outlet to obtain
the headwater.
If backwater calculations are performed
beginning at the downstream end of the.
culvert, friction losses are - accounted
for in the calculations. . Adding . the
inlet loss to the energy grade line in
the barrel at the inlet results in the
headwater' elevation for each flow rate.
3., Roadway Overtopping. A perfor-
mance curve showing the culvert flow as
well as the flow across the roadway is a
useful analysis tool Rather than using
•
•

it
Z
0
Q
W
..J
W
t
v
Z
0
Q
W
_j
W
FLOW RATE (0)
WEIR .
Equation: Q = CdL(HW�3/2
Q = flow rate, fts/s (m3/s)
Cd = weir coefficient
L = length of weir, ft (m)
HWr _ -driving :iead above
weir crea:, f t (m)
FLOW RATE (0)
ORIFICE
Equation: Q = kahi/2
Q = flow rate, fts/s (ms/s)
k = coefficient '
a = area of orifice,ft2 (m2)
h = driving head above
center of orifice, ft (m)
Figure III -IS —Performance curves
and equations for weirs and orifices.
a trial and error procedure to determine
the flow division between the overtop.
ping flow and the culvert flow, an overall
performance curve can be developed. The
performance curve depicts the sum of the
flow through the culvert and the flow
across the roadway.
The overall performance curve can be
determined by performing the following
steps.
1. Select a- range of flow rates and
determine the corresponding headwater
elevations 'for the culvert now alone.
43
These flow rates should fall above and
below the design dis:harge and cover the
entire now range of interest. Both
inlet and outlet control headwaters should
be calculated.
2. Combine the inlet and outlet control
performance curves to define a single
performance curve for the culvert.
3. When the culvert headwater ele-
vations exceed the roadway crest eleva-
tion, overtopping will begin. Calculate
the equivalent upstream water surface
depth above the roadway (crest of weir)

for each selected flow rate. Use these
water surface depths and equation (8) to
calculate flow rates across the roadway.
4. Add the culvert flow and the roadway
overtopping. flow at the corresponding
headwater elevations to obtain the overall
culvert performance curve.
Using the combined culvert perfor-
mance curve, it is an easy matter to
determine the headwater elevation for
any flow rate, or to visualize the per-
formance of the culvert installation
over a range of flow rates. When roadway
overtopping begins, the rate of headwater
increase will flatten severely. The
headwater will rise very slowly from
that point on. Figure III-16 depicts an
overall culvert performance curve with
roadway overtopping. Example problem
1114 illustrates the development of an
overall culvert performance curve-
ouLVMT RW
.,Ao.„
aC RTOOM:
CMS
1.11
sarnaL
FLOW RAT[ (tt%s)
Figure III-16--Culvert performance
curve with roadway overtopping.
C. Culvert Desian Method.
The culvert design method provides- a
convenient and organized procedure for
44
designing culverts, considering inlet
and outlet control. While it is possible
to follow the design method without an
understanding of culvert hydraulics,
this is not recommended. The result
could be an inadequate and possibly unsafe
structure.
1. Culvert Design Form. The Culvert
Design Form, shown in figure III-17, has
been formulated to guide the user through
the design process. Summary blocks are
provided at the top of the form for the
project description, and the designer's
identification. Summaries of hydrologic
data of the form are also included. At
the top right is a small sketch of the
culvert with blanks for inserting important
dimensions and elevations.
The central portion of the design form
contains lines for inserting the trial
culvert description and calculating the
inlet control and outlet control headwater
elevations. Space is provided at the
lower center for comments and at the
lower right for a description of the
culvert barrel selected.
The first step in the design process
is to summarize all known data for the
culvert at the top of 'the Culvert Design
Form. This information will have been
collected or calculated prior to per-
forming theactual culvert design. The
next step is to select a preliminary
culvert material, shape, size, and entrance
type. The user then enters the design
now rate and proceeds with the inlet
control calculations.
L Inlet Control. The inlet control
calculations determine the headwater
elevation required to pass the design
flow through the selected culvert configu-
ration in inlet control. The approach
velocity head may be included as part of
the headwater, if desired. The inlet con-
trol nomographs of appendix D are used
in the design process. For the following
discussion, refer to the schematic inlet
control nomograph shown in figure III-18.
•
•

e
r
PROJECT
fiatlo{
_•
CULVERT DES-; ►I °0-+
ocslaNEl/Daft
s.Ecr
or
■cYlc.c■.o.Tt •--
■VOAOIOCICAL faTa
taY �•■H�
AOAONAV ELEVATION .�
C .t..00
E■aI■aat aa<A. l: trot Go fil
—ioll
�. CIr.■ta. fa.t'
1.
,at2ran PLMfLA&V Z
taI
Iln .w -...L
a. I•ta■tl •a l..tla1 701■I
fIa.-PA &I I. �t►,_tN
t•
I,
CKYUIT LOCAV11d1•
'�'a
R■■
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f
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...t• t■.I■a
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# l :
: z
CONVENTS
an
.{,I■
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Iau
ta.,
.'
,I
.■
y
.t
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t•r
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jt
Tg111.CJ1 /OOT.OT[!:
NI ty' ■�,• 44.6-4 T all
{/ a, . A • It, • Alt/l.I.c■lYta { t.Gtp1
W"T EO■T■■► UCTMI
RI .• L• U / A� ]Y t /p
III wE aI■■ /0■ O W CwAtm
a,I Itf.t
Itf ■., IO • .{ •{ a• �,I■ MM KtNN O M
d •. ■am a W— S"K—
r ty ta,.....
C0.1■Oa Ell /l0■ K■T■�
,Y ►ft► w, . t►•,. A,II, •w{ no
C■a■Iltl.
!ValCNI/r atn{ITtO{{ :
COYNENTS
/Ogcutllolt:
S,:Ilrelr !a■{[L saECr[e �.
list
` at■t. raar�
•a Nat■••t■ . uokffl Co.
• V. data NaII�
utl alai �
w i•rlWa/•IW
tate MCC
Figure III-17--Culvert design form.
a. Locate the selected culvert
size (point 1) and flow rate (point 2)
on the appropriate scales of* the inlet
control nomograph. (Note that for box
culverts, the flow rate per foot of barrel
width is used.)
b. Using a straightedge, carefully
extend a straight line from the culvert
size (point 1) through the flow rate
(point 2) and mark a point on the first
headwater/culvert height (HW/D) scale
(point 3). The first HW/D scale is also
a turning line.
(NOTE: If the nomography are put into a
notebook, a clean plastic sheet with a
matte finish can be used to mark on so
that the nomographs can be preserved.)
c. If another HW/D scale is required,
extend a horizontal line from the first
HW/D scale (the turning line) to the
desired scale and read the result.
45
d. Multiply HW/D by the culvert
height, D, to obtain the required head-
water (HW) from the invert of the control
section to the energy grade line. If
the approach velocity is neglected , HW
equals the required headwater depth (HWI).
If the approach velocity is included in
the calculations, deduct the approach
velocity head from HW to determine HWP
e. Calculate the required depres-
sion (FALL) of the inlet control section
below the stream bed as follows:
HWd - ELhd - ELd
FALL s HWI - HWd
HWd is the design headwater
depth, ft (m)
ELbd is the design headwater
elevation, ft (m)

r0 '
O
A
H
H
M4
r
A
w
A
O
p
A »
kl
O
Q
�Op
M
M
y
x
n
H
M
Y 1J�
CULVERT SIZE
w +
FLOW RATE (0)
a
r
{A a y O 10
a
'0 0
0 0
HEADWATER DEPTH / BARREL HEIGHT (HW/0)
1 =
N ..1
y0 O
~ O N w l+ + q O y 0 .. '
1
1 n
y o ,o
9

0
ELdis the elevation of the
streambed at the face, ft (m)
HWJs the required headwater
depth, ft (m)
Possible results and consequences of
this calculation are:
1) If the FALL is negative or
zero, set FALL equal to zero and proceed
to step f.
2) If the FALL is positive, the
inlet control section invert must be
depressed below the streambed at the
face by that amount. If the FALL is
acceptable, proceed to step f.
3) If the FALL is positive and
greater than is judged to be acceptable,
select another culvert configuration and
begin again at step a.
f. Calculate the inlet control
section invert elevation as follows:
ELt = ELd - FALL
where ELt is the invert elevation at
the face of a culvert (ELr) or at the
throat of a culvert with a tapered inlei
(ELF.
3. Outlet Control. ' The outlet control
calculations result in the headwater
elevation required to convey the design
discharge through the selected culvert
in outlet control. The approach and
downstream velocities may be included
in the design process, if desired. The
critical depth charts and outlet control
nomographs of appendix D are used in the
design process. For illustration, refer
to the schematic critical depth chart
and outlet control nomograph shown in
figures III-19 and 1I1-20, respectively.
a. Determine the tailwater depth
above the outlet invert (TW) at the design
flow rate. This is obtained from backwater
or normal depth calculations, or from
field observations.
47
L�f �
i
too wo No no woo
FLOW RATE (0)
Figure III-19--Critical depth
chart (schematic).
b. Enter the appropriate critical
depth chart (figure III-19) with the
now rate and read the critical depth
(d,). do cannot exceed D!
(Note:. The do curves are truncated
for convenience when they converge. If
an accurate d. is required for do > .91)
consult the Handbook_ of Hydraulics or
other hydraulic references. (24))
e. Calculate (dc + D)/2
d. Determine the depth from the
culvert outlet invert to the hydraulic
grade line (hd.
ho = TW or (dc + D/2), whichever is
larger.
e. From table 12, appendix D, obtain
the appropriate entrance loss coefficient,
k., for the culvert inlet configuration.

t)
W
to
N
0
J
Figure III-20--Outlet control nomograph (schematic).
49
•

0
f. Determine the losses through the
culvert barrel, H, using the outlet control
nomograph (figure 111.1-0) or equation
(5) or (6) if outside the range of the
nomograph.
l) If the Manning n value given
in the outlet control nomograph* is dif-
ferent than the Manning n for the culvert,
adjust the culvert length using the
formula:
n =
t
Lt = L ...---- (9)
n
Lt is the adjusted culvert length,
ft (m)
1 is the actual culvert length,
ft (m)
nt is the desired Manning n value
n is the Manning a value from the
outlet control chart.
Theti, use Lt rather than the actuat
culvert length when using the outlet
control nomograph.
. 2) Using a straightedge, connect
the culvert size (point 1) with the cul-
vert length on the appropriate k. scale
(point 2). This defines a point on the
turning line (point 3).
3) Again using the straight-
edge, extend a line from the discharge
(point 4) through the point on the turning
line (point 3) to the Head Loss (H) scale.
Read H. H is the energy loss through
the culvert, including entrance, friction,
and outlet losses.
Note: Careful alignment of the
straightedge in necessary to obtain good
results from the outlet control nomo-
graph.
g. Calculate the required outlet
control headwater elevation.
ELAo = EL, + H + h, (10)
where EL, is the invert elevation at
49.
the outlet. or it is desired to include
the approach and downstream velocities
in the calculations, add the downstream
velocity head and subtract the approach
velocity head from the right side of
equation (10). Also, use equation (4c)
instead of equation (4d)' to calculate
the exit losses and equation (1) to cal-
culate total losses.)
h. If the outlet control headwater
elevation exceeds the design headwater
elevation, a new culvert configuration
must be selected and the process repeated.
Generally, an enlarged barrel will be
necessary since inlet improvements are
of limited benefit in outlet control.
4. Evaluation of Results. Compare
the headwater elevations calculated for
inlet and outlet control. The higher of
the two. is designated the controlling
headwater elevation. The culvert can be
expected to operate with that higher
headwater for at least part of the time.
The outlet velocity is calculated as
follows:
a. If the controlling headwater is
based on inlet control, determine the
normal depth and velocity in the culvert
barrel. The velocity at normal depth is
assumed to be the outlet velocity.
b. If the controlling headwater is
in outlet control, determine the area of
flow at the outlet based on the barrel
geometry and the following:
1) Critical depth if the tail -
water is below critical depth.
2) The. tailwater depth if the
tailwater is between critical depth and
the top of the barrel.
3) The height of the barrel if
the tailwater -is above the top of the
barrel.
Repeat the design process until an
acceptable culvert configuration is deter-
mined. Once the barrel is selected it

must be fitted into the roadway cross
section. The culvert barrel must have
adequate cover, the length should be
close to the approximate length, and the
headwalls and wingwalls must be dimen-
sioned.
If outlet control governs and the headwater
depth (referenced to the inlet invert)
is less than 1.21), it is possible that
the barrel flows partly full though its
entire length. In this case, caution
should be used in applying the approximate
method of setting the downstream elevation
based on the greater of tailwater or
(dc + D)/2. If an accurate headwater is
necessary, backwater calculations should
be used to check the result from the
approximate method. If the headwater
depth falls below 0.75D, the approximate
method should not be used.
If the selected culvert will not fit the
site, return to the culvert design pro-
cess and select another culvert. If
neither tapered inlets nor flow routing
are to be applied, document the design.
An acceptable design should always be
accompanied by a performance curve which
displays culvert behavior over a range.
of discharges. If tapered inlets are to
be investigated, proceed . to chapter - IV.
50
If storage routing will be utilized
proceed to chapter V.
Special culvert installations, such as
culverts with safety grates, junctions,
or bends are discussed in chapter VI.
Unusual culvert configurations such as
'broken -back' culverts. siphons, and low
head installations are also discussed.
S. Example Problems. The following
example problems illustrate the use of
the design methods and charts for selected
culvert configurations and hydraulic
conditions. The problems cover the fol-
lowing situations:
Problem No. 1: Circular pipe cul-
vert, standard 2-2/3 by 1/2 in (6.8 by
1.3 cm) CMP with beveled edge and rein-
forced concrete pipe with grbove end.
No FALL.
Problem No. 2: Reinforced cast -
in -place concrete box culvert with square
edges and with bevels. No FALL.
Problem No. 3: Elliptical pipe
culvert with groove end and a FALL. 1
Problem No. 4: Analysis of an
existing reinforced concrete box culvert
with square edges,-
C

Table 11 • MANNING a FOR SMALL NATURAL STREAM CHANNELS
(Surface width at flood stage less than 100 ft.)
1. Fairly regular section:
a. Some grass and weeds. little or no brush
0.030--0.035
b. Dense growth of weeds, depth of flow
materially greater than weed height . . . .
. . 0.035--0.05
c. Some weeds, light brush on banks . . . . . .
. . 0.035--0.05
d. Some weeds, heavy brush on banks. . . . . .
. . 0.05 --0.07
e. Some weeds, dense willows on banks . . . . .
. . 0.06 - 0.08
f. For trees within channel, with branches
submerged at high stage, increase all
above values by
0.01 --0.02
. . . . . . . . . .
. .
t 2. Irregular sections, with pools, slight channel
meander; increase values given above about . . .
. . 0.01 - 0.02
3. Mountain streams, no vegetation in channel,
banks usually steep, trees and brush along
banks submerged at - high stage:
a. Bottom of gravel, cobbles, and few boulders
. , 0.04 - 0.05
b. Bottom of cobbles, with large boulders . . . .
. . 0.65 - 0.07
178

TABLE 12 - ENTRANCE LOSS COEFFICIENTS
Outlet Control, Full or Partly Full Entrance head loss
He a ke V=
2g
Type of Structure and Design of Entrance
Pipe, Concrete
Projecting from fill, socket end (groove -end)
Projecting from fill, sq. cut end . . .
Headwall or headwall and wingwalls
Socket end of pipe (groove -end) . . .
Square -edge . . . . . . . .
Rounded (radius - 1 / 12D) . . . . .
Mitered to conform to fill slope
"End -Section conforming to fill slope
Beveled edges, 33.70 or 450 bevels . . .
Side -or slope -tapered inlet
. . . . . . . 02
. . . . . . . 0.5
. . . . . . . 0.2
. . . . . . 0.5
. . . . . 0.2
. . . . . . . 0.7
. . . . . . . 0.5
. . . . . . . . 02
. . . . . . . 02
Projecting from fill (no headwall) . . . . . . . . . . . 0.9
Headwall or headwall and wingwalls square -edge . . . . . . 0.5 .
Mitered to conform to fill slope, paved or unpaved slope . . . '0.7
'End -Section conforming to fill slope ' . . . . . . . . . . 0.5
Beveled edges, 33.70 or 45° bevels . ' 0.2
Side -or slope -tapered inlet . . . . . . . . . . . . . 02
•
r
Headwall parallel to embankment (no wingwalls)
Square -edged on 3 edges . . . , , , ,
0.5
Rounded on 3 edges to radius of 1/12 barrel
dimension, or beveled edges on 3 sides . . . . . . .
6.2
Wingwalls at 300 to 75° to barrel
Square -edged at crown
0.4
Crown edge rounded to radius of 1/12 barrel
. dimension, or beveled top edge . . . . . . . . . .
02
Wingwall at 10° to 25° to barrel
Square -edged at crown . .. . . . . . . . . .
0.5
Wingwalls parallel (extension of sides)
Square -edged at crown . . . . . . . . . . . . .
0.7
Side -or slope -tapered inlet . . . . . . ... . . . . .
02
'Note: 'End Section conforming to fill slope,' made of either metal or
concrete,
are the sections commonly available from manufacturers. From limited
hydrau-
lic tests they are equivalent in operation to a hcadwall in both
iw�l and
ooutleett control. Some end sections, incorporatin aoscd taper
in their
sign have a superior hydraulic performance. ese aT aei sections
can be
�
179

CHART 10
ISO
10,000
1611
8,000
EXAMPLE
(1) (2) (3)
Iss
6,000
0.42 i.ta.. (3.3 her)
6.
s•� -
0.120 do144
s.
4.000
NJ 4 Rw
6• s.
.
132
.3,000
a few
4.
s'
120
111 2.5 Le
4.
2,000
m 2.1 T,4
(3) 2.2 T.T
4.
IOA
3.
•a i• low
3.
96
1.000
3.
600
84
600
/
.. _
2• 2-
S00
�
T2
400
/-
e
2.
t»
_
300
/
*�
3
1.s Ls
i
amin
/
fr
_
60
v
200
/�
1.3
c
34
C
/
W
46
/ n
100
x
/
a:
so
�
ti
42
a
V
60
=
W
1.0 1.0
o
SO HW SCALE ENTRANCE
1.0
�
40
0Ic
TYPE'
W
•
36
30
(I1 s4aera eye sin
33
t►eadnwl
<
G
Zp
e
t2) Glee"esod wits
t
i
30«d..n
• S e
(3) Creere sad
•S
2T
Prelaatlp
t0
24
•
.T .T
.T
a
Ta use "of. (2) er (3foralect
21
s
Nriteatally to asefe (I), like*
4
*so ffrelfN tactlaed Itas tbeeo
a sad 0 stale$, er reverse as
3
ilherrlted.
'6 .6
'
16
2
Is
_
L..s
1.0
12
HEADWATER DEPTH FOR
CONCRETE
PIPE CULVERTS '
HEADWATER SCALES 253
FlEVISED MAY*64 WITH
INLET CONTROL
DUREw a Puu.tC RO�0! xw "m
181

OCHART
2
160
1
10,000
16B
1
e,OOO
EXAMPLE
IS6
6.000
0. 36 inches 43.0 feel)
5,000
6.66 ctc
(3)
144
4,000
N� 6
b.
6•
132
3.000
is
120
2,000
0 2.1 6.3
4
S.
s
01 2.2 La
1os
c0intoo
3•
4.
J
s•
1.000
3.
Boo
3•
04
a
600
Z,
500
72
400
-4
2.
Z.
°3
us300
z
200
o
54
H
ul
4B
W
100
/
`
Bow
60
1.0
42
SO
�.
40
G
3s
30 NW SCALE ENTRANCE
0 TYPE
Us
,6
<
33
20
111 Ilc.c..11
C
.t
•
C
30
tt1 tllla►ed to ccctctm
<
S
B_
t6 cic"
d
i
27
10
(31 hcjcctic6
•
B
0
F
24
.7
6
s
To ccc wIs (2) cr (3) Protect
21
4
Ntilcctcllf to M•16 III, them
�6
cN tftciqhl imc11Nt u" t61cc66
•�
3
0 cw 6 scales, or Itttc/N M
`
1 e
111c.tr6/c•.
,
2
1s
.s
1.0
s
12
HEADWATER DEPTH
FOR
C. M.
PIPE
CULVERTS
WITH
INLET
CONTROL
6u6Cau OF ftM.ICft"S
JAIC IM3
182

•
ISO
1
1
1
164
TT PC
'- 12
ARAL MI"4Y AO#MNISTAATION
• MAY 19?3
183
CHART3 O44
A 8
3.6 3.0
3.0
0
2.0
S
2.0
W
h•
I.s
0
_2
S
r-
4
W
0
W
t.0 c 1.0
W
9 .e
.s r •s
.s2 L-.S2
HEADWATER DEPTH FOR
CIRCULAR PIPE CULVERTS
WITH BEVELED RING
INLET CONTROL

a
CHART 4
3
2
0
0 10 20 30 40 50 ao 70 so 90 100
DISCHARGE-C-CFS
e
s
W
W
u4
0
W
3
C
J
t� 2
mommi
ONE
USE0■//%
■
/_�
■�M■P//0M■
0,!��C0
HIM
■■
momma.■■■■■
•
"CEED
TOP
Of
PIPE
Mir
.. goo goo 10.
184
•

O
CHART
5
—�
.4
1000
=
7,
sus"cRao ovncT uLvcRT nIOMIGc rumLL s
i
Boo
t20
. o.N Pew G
!M *Dow cm. re 04OW904ww
Goo
100
.e
s00
96
1.0
400
64
300
72
��Q
200
60
,p W 2
4.
u
s 4
/ O /� 2
•/ O 00' i
2
W_
46nO
_w
U j' 3
IOOo.ta
42
W
�=
ti� = 4
O
G
h s
3
-b00
G0
33
6.
o
s0
►.--
40
30
00 s G
�'
C
27
i O
30
d 'N 10
24
20
21
is
120
10
13
s
G
12
s
4
HEAD FOR
CONCRETE PIPE CULVERTS
FLOWING FULL
lsumm
or Pustc Roos im ns3
n i 0.012
�_
185

O CHART 6
E2000
M
1000
N
i
M•
•oo
SNSrCR6t0 OYTLCT CULV9RT I &MNG FULL
600
120
SOO
IOs
Per mew cww no ww.r"N. =wows Mr b
mobw r we R0060 /heMw .
400
9s
300
•4
0
a
o0
0
200
72
ss
° to
yor
o� ,gyp
y��
W
2
•0
O
= 100 =
4 s
.pP, ^�,
3
o so
W =
s0
42
4
zso
36
�/ sa°
s
40 °C
lk so W
3 3
/�
i
o — W
30
`-- [i4rrtt __
Z7
a
20
10
24 400
21 too
10 Is '
s
IS
s
s
4
IZ
3
2
suam or PUBLIC ROADS AM a"
186
20
HEAD FOR
STANDARD
C. K PIPE CULVERTS
FLOWING FULL
n = 0.024
7
M

•
$000
1000
3000
160
t000
In
CHART 7
O
i N
N�
1
Smog so -+
umble o ourttr uxvar r1Av►►►4 ruLl
Fw ee►Ie1 ennA .M �Mwegee. cswwn Nw
.ab.0 eeeenbe/ w M see.p p oftre
2
Ik
M
w
s
a
3
3
1000 =
120
0 f,
�J �0A
e
000
114
as
w
90 y
4
v
T00
at
90 _
S
400 w
_
6
no ca
go
AA.
T
s
400 i
~
<
S
M
_
To
00
CPS t yp0
10
0
300
ds
Z00
=
r 600
IS
F
1500 20
Ong • 40
r aoat•
r C.O32O
►V aO31 ► SO
►s• no�o:
HEAD FOR
STRUCTURAL PLATE
CORR. METAL PIPE CULVERTS
FLOWING FULL
n = 0.0328 TO 0.0302
*Mau or ruK1C ROAN im ►SA
187

F-1
CHART 8
li
(2)
(3)
500
EXAMPLE
6
!
10
10
400
11' 12' In o e 75 cts
T
6
0/8 a 10 NM/•t
T
6
s
9
300
orw
1.1a o to"
6
T
S
s
(1) 1.75 3.3
S
6
ZOO
(2) 1.90 3. •
4
S
(3) 2.D5 4, 1
4
1
T
3
3
3
6
S
2
p
IOo
O
6a
2
-.
2
s
3
el
2
1`
so
x
40
=
I.S
O
30
W
3
I.O
'
x
1.0
io
10-- nu. o
.9
.9
.•
W
df
o
O
S Nw WINawALL
SCALE
•T
.T
4 0 FLARE s
6
t
3 R1 "-Mw 1r
(A a (afewbMM
.S
2 of ow.ml
T. "e scale (21 or 131 Mel"•
eerisMMfemy to "a" (1), them,
ess' straight ieeliMed one three"
.4
I 0 Me/ a "Miss. M revers a
.•
.4
.4
.6
L 30
.35 t
.33
.S
HEADWATER DEPTH
FOR BOX CULVERTS
WITH INLET CONTROL
SUN" w PUB" XCIACS is^ PM

�p
C HART 9)
I= 4.0
400
„
SO
300
LO,
EXAMPLE
SCALE ENTRANCE rpE
L3
10
3,s S' sox as 250 cps
UI 450 WIMGWALL iLA1R
Q/Ns.SO Cf3/pT
200
WITH t, .0430
F
r,
20
!
(2) 140TO 33.7• WINGWALL
s
INLET Mr
/LAIR WITH d •.O430
La,t
/0 O'MW
O) 1.41 7.1
Ls Z
I.t
S.
c2) 1.33 4.7
~
1.6
IOr
100
=
1.4
� i
W
Z
H
�
W
i
40
=
1.0
2
O.
Lit
10 tl
30
p
1••
t
x
3
43
p
20
TOP EDGE
t
►-
LEVEL ANGLE
yl
REQUIRED
tFE
O
4/0 ANGLE
_
F�
S
4
t
S
0.042 49•
f.
•7
o
ca
ODG3 t@ -33.rlot
7 W
=
p
10
FACE
•OR 33.7•
30
G
! TOP KVM d
W.
<
t
p
s
'
MOOM O IN nmT
7
L
t
.
` •
MIN.
=
3
G
BEVEL d
s GENCL ANGLE
p
.S
.s
4
LONGITUDINAL SECTION
Ls
'
3
4
.4
Ll
HEADWATER DEPTH FOR INLET CONTROL
1
RECTANGULAR BOX CULVERTS
FLARED WINGWALLS 18 • TO 33.7. & 4 S •
WITH BEVELED EDGE AT MP OF INLET
189

0
CHART 10
EXAMPLE
o.Trr o•orr. *.so*cn Wwo .ns
INLET FACE —ALL EDGES:
HW HW
IMIT KVIEL333J U:1.31 —
ALL On$ p as..
VI INOT stvcu as• 11:11
CMMn 1 304• 2.31 N.f
L44101 c11Y.7tms
•
L4 ulrT trd 2.09 104
1101"KV916 I.N s.4
600
10
,
7
11
300 �
!
•
i
t
b
400300
•
3
4
4
200
H
3
3
130
c
a
_
IWW►
t
100
so
Q c
O�
2
Wso
J
6
1�
G
1.9
�_ Q
R`
W
so
46
C
is
40
i
30
4 w p
=
= C
w
d
c '
20
Lo
lom yam le
W
IA
Fla "mmsm or ALL y�
q
{
a2
sloe rw ror ocrcLS
s"" .or oc Less "on
3 si a ro corer oc" L
"1 o�llcc AMP a°� OW.
i
a•
as
OTnd1 IW—*CA3I 40411.00
09000A24 TMM 311KL Aa14LAL
•
r
�
wwwr
at
a�
�a 33.7 fv4+Ia0
9
_ _
o r "
4 !O•
at '
2 as- For r0.
.7... as
317' M
at
3T4f MIr
�assw Mr
a3
rYll� , r NIA
�.
"a on+crso+s 1p Aw4 cr
2
o
a3
ICVW AM LN01 NUAM TO
"4 omme oulummom 4T
MR AIIIM3 TO 7119 IM
HEADWATER DEPTH FOR INLET CONTROL
RECTANGULAR BOX CULVERTS
90• HEADWALL
rsa""` "'°""''''1 "°""""T""r°"
MAY 1o7a CHAMFERED OR BEVELED INLET EDGES
190
•
r
•

7 i �
Z�
B�W
p�Dm
o
�11 7O
OD ;a
CD
MTMO
i
vex-
r
FF r
m mn
-4 L
N 3'
a
N w . W w r w r a N
HEIGHT OF BARREL (DI IN FEET
DISCHARGE PER FOOT OF BARREL WIDTN;O/Ne11N CFS PER FOOT
w• u w rw.a al; . g
HEADWATER
DEPTH INTERM5OF
HE
HT (tlW/D)
I
•� 6
e e
0
r
1�
w V
e
O
Y
N , 4 ♦ Y
V w
r
�.
w .
w.•

WX
CHART 12
EXAMPLE
827FT 0■SFT. O=3000FS
30' SKEW��L...�1
: T's
L INLETS
a
WINGWrALL FLARE-43'
18.4-
18.4'
INLET IlWW �(W
HW
8
NORMAL IV
FT
8
8
45•wW 2.18
Q9
SoO
T
T
T
U%4•WW 227
U.4
6
12 SKEWED W-4eF
300
6
6
18.4 OR MORE
11
400
3
S
3
ww 2.20
1.0
p
300
0
4
4
4
3
9
200
3
3
e
(so
0
a
2
2
100
EXpMi 16
2
_
90
�Z___
W
G cc
6Q/
To
a
i
_
J
60
I.s
1.3
I.S
so4-40
;
W
~
C
yOW
O W
36
46
W
o
20
LO
1.0
1.0
�.
W
ar
Is
3
g
0.9
09
_
W
<
w 3
Gc
10
=
0.8
0.8
Q8
_
<
9
s
8
o
i
NOT[:
0T•
0.T
0.T
6
HEADWATER SCALE FOR SKEWED
INLETS iS CONSTRUCTED FOR 30•
s
SKEW AND 3:1 WINGWALL FLARE
ENtlQI�
4
(Ias•)
A GOOD AMBLE
FOR AN
06
Q6
0.6
2 �s,f•
SKKEEW FROM�130
TO 43' AND FOR GREATER FLYIE
[FLQUAl
3
ANGLES OF WINGWALL3.
AB[
ANGLES ;.
QS
QS
0.3
• wNGRatL ��
NOT OFFSET
EQUAL—L —
FLAB[
ANGLES
ISM DON
40• ---
NORMAL
WINGWALL INLETS
sun EAU OF FU0.10 ROAOS
OFFICL Of R a 0• AUGUST 1968
HEADWATER DEPTH FOR INLET CONTROL
RECTANGULAR BOX CULVERTS
. FLARED WINGWALLS
NORMAL AND SKEWED INLETS
3/4 0 CHAMFER AT TOP OF OPENING
192
•
•
•

CHART 13
EXAMPLE
8 = 7 FT. 0=5FT. Q= 600
CF.S
18.4•WW & d a 0.063D
9 s TI.9
33r W W a d= a0830
WINGWALL TOP EDGE HW
Hw
45•WWBd=0.0420
8
FLARE ANGLE BEVEL `)T
Ft
8
12 4 5 • VL INJF . 2A6 K 3
600
500
BEVEL EDGE
8
S
s
11 33r I I!l/F7. L90 35
400
REQUIRED
S
4
•
18.40 1IN/F7 1.82 s0
,..
4
10
o
300
Q
1 ANGLE �
4
3
9
a042 45• 33
ao83 33.r
3
a
200
r
m
ISO
2
►-
cui
i
--
2
IV
0
,�i'�► y.
0
�Y�M�P
i C
6 Z
6Oi �'•
o
I.S
r
TO
1.5
60
1.6
•
—' —'
SO
J
W
z
W
C
40
'-
ac
�
=
�
s
a
30
t-
W
4
0
C
2Q
W
1.0
1.0
10
x
~
W15
G
a9
0.9
0.9
IL
3
W
x
0.8
0.8
i
9
WINGWALLS
=
v
T FLARE ANGLE MN.CFFSET
O.T
aT
O.T
a
6
1:1 45• W44 8 (FT)
o
S
t:ls 33.T0 1":8
2
4
1: 3 18.4' I- V2": B
Ob
0 6
0�6
3 +
USE 33.T*xa00630TOP
MIELIEDGE
Z
O
BEVEL AN READ
HMI ON SCALE FOR 16.40
Q3
WW
O.S
O3
LON TWIN SECTION
EQUAL
MimiFLARE
atlCif.3
-
��--
w
s--•
---�'--
wtrowALL
°FFsT
HEADWATER DEPTH FOR INLET CONTROL
PLAN
RECTANGULAR BOX CULVERTS
BUREAU OF PUBLX ROAD$
OFFSET FLARED WINGNALLS
OFFICE OF Rs 0 mmusr It"
• AND BEVELED EDGE AT TOP OF INLET
193
F0

5CHART 14
4
u. 3
z
0 2
V
1
0
16
IS
14
13
12
F; I 1
W6
? 10
9
S
T
6
5
4
CRITICAL DEPTH
RECTANGULAR SECTION
0 10 20 30 40
0/8 -
50 60
SO 100 ISO 200 250 300 350
O�B
CRITICAL DEPTH
�`�` "'•" "" s-ss RECTANGULAR SECTION
194
r
•

•
3
.3000
-4000
-3000
-2000
12x12
1000
' •00
10 x10
wo W
w
•o16
4010:xf
300
w •x•
W s
.400
IXT
Soo
•
-300
$ sxs
_
w
30 p
�200
3xf
s
to s
M
J
41410
i
� 3
s
u
.100
s
3x3
10
a
•
•so
• s0
2Sx2.3
6
axi
�4
-!O
.!0
CHART 15
SWAOG" GVR[T axvcaT RA06 Rti&,
w wfw "woo am arwr"M, wawa •* IN
r r«r• wshrw
4
s
s
l0
2�3
110
,,p44/
tapN
:
20
HEAD FOR
CONCRETE BOX CULVERTS
FLOWING FULL
n s 0.012
195

CHART 29- *
ISI , 97
3000 EXAMPLE
S-Sa• 3oo,r,
136 a 6T 2000 (2) (3)
treeq 4.0
121277 t1) Ltl 11.1
m 1.1 4.6 4.0 3.0
113 a 72 1000 (3) L3 92 - 3.0
eoo • o . feet
106 a s6 3.0 _ ...r
600 i 2.0
9a , 63 40o s��V � � � 2.0
912 56 2.0
1.6
W 63 a S3
s
200 i 1�
= a 46 W
To "on now t:) r to a
W b 0"+9W9 "rMe s
4.68243 aMM t"aw tow" loo 16
of t•et wM f►ee"rp J = 60 of +fr"w SUN (1).
O 60 a 36 O 60 anteet " meaf " ft fi !
W W ta"ttla" w slow sew W 9 !
p So W r (3). 3'
a 53 a 34 < 40_ • 6 •6
19 n 30 ` 6
r 49 a 3L
z _ O O T 7
0 4d a 29 20
7
mw /D ENTRANCE
N 42 s 27 SCALE TYPE 3C ` .6 .6
a
10 lry SNp w•" W
36 a 24 6 "aw.af S
its i•eew W ma
4 ,faNar
30 a 19 3
2 .4 .4
_T
� o
— i
23 a 14 1.0
HEADWATER DEPTH FOR
OVAL CONCRETE PIPE CULVERTS
LONG AXIS HORIZONTAL
rwcw Or .usuc "o.oa JAIL M3
WITH INLET CONTROL
209

CHART 30
!T .1s1
s000
4000 EXAMPLE (2)
iT.13i (3)
3000 ab.: 3r a w-
e 100 aft
TT a Its 2000 jv a I1NV i !
?2 a 113 4 4
Ist :•o a.o
H s IOi 1000 I31 9.9 q.f 4 3 3.—
i3 a !• 000 • e is seat
3
too
S0 a !1 SOO oe E
• •• � 400
= 53 a !3
= 300 /
40 a 7i LS
_ moo s
To aw Ma1a M w (3) C
/ L 43 s IN �. '/ / an. a Idf101 1sea ftwp booms .algae M
2 of me a" ehasarya i
t / 100 se .lnwaaat see" Ili. l0 1.0
O 30 AGO. 80 From DOW es geese (1) p. LO
` .eapat r ffte"oly 1a at! !
O e i0 wk~ N Msar web .!
�~m _ .i .�
W 34 a ss .4 so �
a a a
40
W
32 a 4! p 30 0 .1 .T
Z MM it ENTRANCE h T
a 2! a 4S 20 SCALE TYPE
Ill aaaara eNa with ; i .i._
27 a 42 yehraM <
g aaw 6_)lad WON=
10 8
24 s 30 (
0 131 Stew" ead
a.alwn.a
i
3
4
I! a 30 3 1.4 L 4
e
14a23 LO
HEADWATER DEPTH FOR
OVAL CONCRETE PIPE CULVERTS
LONG AXIS VERTICAL
WITH INLET CONTROL
210

CHART 31 •
3.4
3.0
2.0
1.0
0 20 40 60 SO 100 120 140 160 ISO 200 is
�i DISCHARGE- 0-CFS
J
■■■■■■■■■■■■■■■■■■■■
DISCHARGE-0-CFS
BUREAU OF PUSUG ROADS CRITICAL DEPTH
JAI. 1964 OVAL CONCRETE PIPE
LONG AXIS HORIZONTAL
211

CHART 32
s
a
3
2
t
F�
W
W
0, -
NEON
NONE�.������:�i�����
������%
NEONmom
00mom��■
VIA
■■■■■■■■■■■■■■■■■■■■
mom NONE
ME Elm MIN - Bann
smomm!� MEMO 00�
EINIO■% - INSIMENSIENINE
mom
Wf
illoommom NEON
r
is
212

:000
r 1000
r000
F
Goo
r soo
F- 400
300
C
Isa a97
- 136 a •7
• 1211177
•113a72
• 106 a 6•
96 ss3
-!lass
-l3as3
76 a 46
ss a 43
-G0a36
-��3,,�33a.3,4
-r9a32
4S 129
-4tat7
36 a 24
30s 19
20
23 a 14
10
6
s
s
•uotau or rwaa: aoaos Jatc. t943
c
CHART 33•
�- 0.4
Sbr. S. �+
.
su•1t OfAc OVTLtT CYLYtor .wpuc4 FULL
Aar mew cnc■ we ra..w"o, a■.w. ns A
— 0.6
mMMM c.una.• • rM 400" RctNwc
�
— 0.7
i 0.•
r 0.9
1.0
i.
.f
rr
o
/49 x
' 3
top
op
acp
-4
a+oTi
``
6
o"NowoM an on Koo we
order" for bq an .w""
7
attwNlNa rhey NwiM M
•
n.tW ter wag aces wrt*GL
9
10
20
HEAD FOR
OVAL CONCRETE PIPE CULVERTS
LONG AXIS HORIZONTAL OR VERTICAL
FLOWING FULL
n = 0.012
213

MIMEMMEM
WIMEMERIM
■IMEMERIw
■IMEMEM■
■INNOME■
■IMEMEM■
OMEN
NONE
MEN
■UMM■
No
n
■ommommmummm
suedmommomom
2momMEMEME■
no
MENEENUMMME2.
■momom
mwm�

24
LU
O 10
O
w is
In
L !6
4
L4 14
O'
8
i�
W m
4
Z
. . .. .. ... ... ...
AMEL
. .. .. :.. .. ...
MIMME
Mwu'�-I
M
No
PUPME
MEMEMPOPMEN
MEN
FAFMMMM
No
DAFEEMEN
MEWMEMEMEN
MM,MMMMMMM
MIFAAMENEEME
SAME
mm�
VMM1
1 This nomograph is taken. ficm Ma
FAN
C�W:r
Matic�E=rin
=�4ifieIt
0
stone size to be used at the outlet end oF
culverts. The stone would be placed in
accordance with St'd EC-1.
MEN
0 / 2 3 4•
EQUI YAL ENT SPHERICAL DIAMETE0 OF 570/YE, 11Y FEET
R I PQAP SIZE FOP USE D0 w/Y.5 TQEAM
OF ENERGY DUSIPAToaS
3-6A
•

. 0.
LO-269
Rev 3.63
Project __ Plan Sheet No. Designs, - ..
Sheet of
Revs Dots Dale
HYDROLOGICAL DATA:
AHW Controls STATICN,
D.A. • AC.
100yr. Flood plain slay. --
-
Design AHW depth elev.
_
Structures elev.
freq. TWelev
l
Shoulder slay.Z•
slay:
Skew ' Cov r
DISCHARGES USED
RISK ASSESSMENT ADT
0 • CFS
Detours Available ,Length
Q _ • CFS
Overtopping Stage
0 — • CFS
Flood Plain Management
Inv. El. So • Inv E I.
0 • CFS
Criteria and Significant Impact
Q CFS
Orig.Gr. Elev. L • Orig.Gr. Elev.
HEADWATER COMPUTATIONS
CONT.
OUTLET
End
INLETCONT.
OUTLET CONTROL
CULVERT TYPE 9SIZE
0
0/0
HW.
VELOCITY
COMMENTS
ELEV.
Treat.
HW/D
HW
Ke
do
'
ho
H
LSO
HW
C.M.
Srmooth
DestgnFlood ExceedProb. Elev
A.--"- C1--A C..._.A M-k Cl...

•
Chapter 5 Grassed Swales
I. Introduction
Grassed swales are shallow trapezoidal or parabolic earthen channels covered with a dense growth of a
hardy grass such as Reed Canary or Tall Fescue. Grassed swales are sometimes classed as a type of biofilter
because the vegetation on the swale takes up some pollutants and helps filter sediment and other solid
particles out of the runoff. Tbese channels convey stormwater and provide some stormwater management for
small storms by retarding peak flow rates, lowering velocities of runoff a ad by infiltrating runoff water into
the soil. Swales are used primarily in single-family residential developments, at the outlets of mad culverts,
and as highway medians.
Enhanced grassed swales are ordinary swales with small check dams and wide basins along their course
(Schueler, et al 1992). The check dams and the wide areas create small pools of water, which slow the
water's flow, encourage the water to infiltrate into the soil and enhance pollutant removal. Figure 16. show
an example of an enhanced grass swale.
The Erosion and Sediment Control Planning and Design Manual for North Carolina describes the process of
swale design in detail, and the designer should consult it for general design and vegetation specifications.
When a swale is designed and installed for the purpose of water quality protection in addition to the basic
purpose of transporting stormwater, the design velocities are lower. The requirements for reduced
velocities are to allow a greater contact time with the vegetation and to allow for more infiltration.
Grassed swales have a long history of use for stormwater conveyance, and they normally provide long-term
water quality protection. However, because of their limited pollutant removal ability; grassed swales are not
a sufficient means to reach the 85 % TSS removal requirement, but they can be used as one of a series of
BMPs that when combined with other BMPs, can provide sufficient protection to surface waters. An
example would be a development that used a combination of grassed swales and extended dry detention to
achieve the required 85% TSS removal. For the purposes of satisfying the requirements for stormwater
treatment found in NCAC 15A 2H.1000, a properly designed and constructed grass swale is assumed to
have a TSS removal of 35%.
II. General Characteristics
Grassed swales have had mixed results in removing particulate pollutants such as sediment and trace metals.
They are generally unable to remove significant amounts of soluble plant nutrients. Swales have proven to
be very reliable with few failures. However, formation of gullies or thinning of the vegetative cover will
reduce pollutant removal and cause the swale to fail as a pollutant -removing device.
M. Advantages
The primary advantages of grassed swales include relatively low construction and maintenance costs,
increased infiltration, additional wildlife habitat In some cases, elimination of curbs and gutters which collect
and deliver pollutants to receiving waters, and a pleasing appearance. In areas with low amounts of
impervious surface, such as single-family residential areas, curbs and gutters can be replaced by swales,
resulting in increased stormwater pollutant removal and improved aesthetics.
68

•
IV. Disadvantages
Disadvantages of swales include limited pollutant removal, increased nutrient concentrations in runoff due to
fertilization of the grass in the swales, and standing water, which may cause safety, odor and/or mosquito .
problems.
V. Costs
Swales cost less to construct than curbs, gutters, .md underground pipes; however, swales take up more land
area. Zbe costs of maintaining swales are usually minimal. However, special maintenance such as extensive
sediment removal or erosion repair may become expensive.
VI. Design Requirements:
• Longitudinal slope should be in the range of 2 to 4%. If slope along the flow path exceeds 4%,
then checkdams must be installed to reduce the effective slope to below 4%.
• Side slopes should be no greater than 3:1 horizontal to vertical.
• Maximum runoff velocity should be 2 fps for the peak nmoff of the 2 year storm.
• Design must also nonerosivly pass the peak runoff rate from the 10 yr. storm.
• Length of swale shall be at least 100 feet per .acre of drainage area.
• A vegetation plan shall be prepared in accordance with the recommendation found in
Sediment Control Planning and Desal. .
• Swales should be stabilized within 14 da:Is of the swales construction.
Other general tecommendation.for design and construction of grassed swales for pollutant removal follow:
• Swales should be,constructed on permeable, noncompacted soils.
• Swales dxxdd;be!sitel'In-areas here=the'seasonal-high=water table Is at least one foot below the
bottom of the. swab.
• Swales dxxddnot carry dry-weaftr;tlow.; ors roustant ilows,of water, and
• Swales should.i?axc sM cou*W:times cr short grass height.
VII. Maintenance
Swale maintenance basically involves normal grass management growing activities such as mowing and
resodding when necessary and periodic sediment removal, if significant deposition occurs. Maintenance
shall be performed as follows:
• At least once annually, remove excess sediment, especially from the upstream edge, to maintain
original contours and grading.
• At least once annually, repair any erosion and regrade the swale to ensure that the runoff flows
evenly in a thin street through the swale.
• At least o®ce annually, inspect vegetation and revegetate the swale to maintain a dense growth of
vegetation.
• Grassed swales shall be mowed at least twice amually to a minimum height of six inches.
70

•
VIII. References
Arnold, J.A., ed. D.E. Line, S.W. Coffey, and J. Spooner. 1993. Stormwatcr Management Guidance
Manual. North Carolina Cooperative Extension Service and North Carolina Division of Environmental
Management. Raleigh, NC
Berman, Laurel, C. Hardine, N. Ryan, and J.D. Thorne, P.E.1991. Urban Runoff- Water Quality
Solutions. The American Public Works Association Research Foundation. 58 pp.
Birch, P.B., Ph.D. and H.E. Pressley (eds.)1992. Stormwater Management Manual for the Puget Sound
Basin. Review Draft. Dept. of Ecology. Publication number 90-73.
Gibb, A., B. Bennett, and A. Birkbeck.1991. Urban Runoff Quality and Treatment: A Comprehensive
Review. File number 2-51-246(242). British Columbia Research Corporation. Vancouver, British
Columbia.
North Carolina Department of Environment. Health, and Natural Resources, Division of Land Quality,
Raleigh, NC. September 1988. Erosion and Sediment Control Planning and Design Manual.
Schueler, T.R., P. A. Kumble, and M. A. Heraty.1992. A Current Assessment of Urban Best Management
Practices: Techniques for Reducing Non -Point Source Pollution in the Coastal Zone. Publication number
92705. Metropolitan Washington Council of Governments. Washington, DC.127 pp.
Schueler, T.R.1987. Controlling Urban Runoff: A Practical Manual for Planning and Designing Urban
BMPs. Publication number 87703. Metropolitan Washington Council of Governments. Washington, DC.
275 pp.
Stahre, P. and B. Urbonas.1990. Stormwater Detention For Drainage, Water Quality, and CSO
Management Prentice Hall, Inc. Englewood Cliffs, NJ. 338 pp.
U.S. EPA. 1990. Urban Targeting and BMP Selection. Information and Guidance Manual for State
Nonpoint Source Program Staff Engineers and Managers. The Tertene Institute. EPA No. 68-C8-0034.54
PP.
U.S. EPA. 1992. Stormwater Management for Industrial Activities: Developing Pollution Prevention Plans
and Best Management Practices. Office of Water. Government Institutes, Inc. Rockville, MD.
Urbonas, B. and LA. Roesner, eds. 1986. Urban Runoff Quality —Impact and Quality Enhancement
Technology. American Society of Civil Engineers. New York, NY. 477 pp.
Whipple, W., N.S. Grigg, T. Grizzard, C. W. Randall. R. P. Shubinski, and L S. Tucker. 1983.
Stormwater Management in Urbanizing Areas. Prentice Hall, Inc. Englewood Cliffs, NJ. 234 pp.
71

Practice Standards and Specifications
i., 6.30 -,
Definition A channel with vegetative lining constructed to design cross section and grade
for conveyance of runoff.
Purpose To convey and dispose of concentrated surface runoff without damage from
erosion, deposition, or flooding.
Conditions Where This practice applies to construction sites where:
Practice Applies
• concentrated runoff will cause damage from erosion or flooding;
• a vegetative lining can provide sufficient stability for the channel cross
section and grade;
• slopes are generally less than 5%;
• space is available for a relatively large cross section.
Typical uses include roadside ditches, channels at property boundaries, outlets
for diversions, and other channels and drainage of low areas.
Planning LOCATION
Considerations Generally, channels should be located to conform with and use the natural
drainage system. Channels may also be needed along development boundaries,
roadways, and backlot lines. Avoid channels crossing watershed boundaries or
y ridges.
Plan the course of the channel to avoid sharp changes in direction or grade. Site
development should conform to natural features of the land and use natural
drainageways rather than drastically reshape the land surface. Major recon-
figuration of the drainage system often entails increased maintenance and risk
of failure.
Grass -lined channels must not be subject to sedimentation from disturbed
areas.
An established grass -lined channel resembles natural drainage systems and,
therefore, is usually preferred if design velocities are below 5 ft/sec. Velocities
up to 6 ft/sec can be safely used under certain conditions (Table 8.05a, Appen-
dix 8.05).
Establishment of a dense, resistant vegetation is essential. Construct and veg-
etate grass -lined channels early in the construction schedule before grading and
paving increase the rate of runoff.
Geotextile fabrics or special mulch protection such as fiberglass roving or straw
and netting provide stability until the vegetation is fully established. These
protective liners must be used whenever design velocities exceed 2 ft/sec for
bare soil conditions. It may also be necessary to divert water from the channel
until vegetation is established or to line the channel with sod. Sediment traps
may be needed at channel inlets and outlets.
•
630.1

n
V-shaped grass channels generally apply where the quantity of water is small,
such as in short reaches along roadsides. The V-shaped cross section is least
desirable because it is difficult to stabilize the bottom where velocities may be
high.
Parabolic grass channels are often used where larger flows are expected and
space is available. The swale-like shape is pleasing and may best fit site condi-
tions.
Trapezoidal grass channels are used where runoff volumes are large and slope
is low so that velocities are nonerosive to vegetated linings.
Subsurface drainage, or riprap channel bottoms, may be necessary on sites that
are subject to prolonged wet conditions due to long duration flows or high water
tables (Practice 6.81, Subsurface Drain and Practice 6.31, Riprap-lined and
Paved Channels).
OUTLETS
Outlets must be stable. Where channel improvement ends, the exit velocity for
the design flow must be nonerosive for the existing field conditions. Stability
conditions beyond the property boundary should always be considered (Prac-
tice 6A 1. Outlet Stabilization Structure).
AREA
Where urban drainage area exceeds 10 acres, it is recommended that grass -lined
channels be designed by an engineer experienced in channel design.
Design Criteria Capacity As a minimum, grass -lined channels should carry peak runoff from
the 10-yr storm without eroding. Where flood hazard exists, increase the
capacity according to the potential damage. Channel dimensions may be deter-
mined by using design tables with appropriate retardance factors or by
Manning's formula using an appropriate "n" value. When retardance factors are
used, the capacity is usually based on retardance "C" and stability on retardance
"D" (References: Appendix, 8.05).
Velocity —The allowable design velocity for grass -lined channels is based on
soil conditions, type of vegetation, and method of establishment (Table 8.05a,
Appendix 8.05).
If design velocity of a channel to be vegetated by seeding exceeds 2 ft/sec, a
temporary channel liner is required. The design of the liner may be based on
peak flow from a 2-yr storm. If vegetation is established by sodding, the per-
missible velocity for established vegetation shown in Table 8.05a may be used
and no temporary liner is needed. Whether a temporary lining is requried or not
permanent channel linings must be stable for the 10-yr storm. A design approach
based on erosion resistance of various liner materials developed by the Federal
Highway Administration is presented in Appendix 8.05.
Cross section —The channel shape may be parabolic, trapezoidal, or V-shaped,
depending on need and site conditions (Figure 6.30a).
630.2

Practice Standards and Specifications
•
Figure 6.30a Cross section geometry of
triangular, parabolic, and trapezoidal Triangular "\/"
channels.
T
d
T
e 10
x-section area (A) = Z02
top width (T) = 2dz Z — d
Parabolic
--A
T
d
x-section area (A) = 2/3 Td
top width (T) =1.5A
d
Trapezoidal
T
�d
b e
x-section area (A) = bd + Zd2
top width m = b + 2dz Z — d
Hydraulic grade line —Examine the design water surface if the channel sys-
tem becomes complex.
Side slopes —Grassed channel side slopes generally are constructed 3:1 or flat-
ter to aid in the establishment of vegetation and for maintenance. Side slopes of
V-shaped channels are usually constructed 6:1 or flatter along roadways for
safety.
Depth and width —The channel depth and width are proportioned to meet the
needs of drainage, soil conditions, erosion control, carrying capacity and site
conditions. Construct channels a minimum of 0.2 ft larger around the periphery
to allow for soil bulking during seedbed preparations and sod buildup.
Grade —Either a uniform or gradually increasing grade is preferred to avoid
sedimentation. Where the grade is excessive, grade stabilization structures may
be required or channel linings of riprap or paving should be considered (Prac-
tice 6.82, Grade Stabilization Structure).
6.303

W
Drainage —Install subsurface drains in locations with high water tables or
seepage problems that would inhibit establishment of vegetation in the channel.
Stone channel bottom lining may be needed where prolonged low flow is an-
ticipated.
Outlets —Evaluate the outlets of all channels for carrying capacity and stability
and protect them from erosion by limiting the exit velocity (Practice 6.41, Out-
let Stabilization Structure).
Sedimentation protection —Protect permanent grass channels from sediment
produced in the watershed, especially during the construction period. This can
be accomplished by the effective use of diversions, sediment traps, protected
side inlets, and vegetative filter strips along the channel.
Construction 1. Remove all trees, brush, stumps, and other objectionable material from the
Specifications foundation area and dispose of properly.
2. Excavate the channel and shape it to neat lines and dimensions shown on the
plans plus a 0.2-ft overcut around the channel perimeter to allow for bulking
during seedbed preparations and sod buildup.
3. Remove and properly dispose of all excess soil so that surface water may
enter the channel freely.
4. The procedure used to establish grass in the channel will depend upon the
severity of the conditions and selection of species. Protect the channel with
mulch or a temporary liner sufficent to withstand anticipated velocities during
the establishment period (Appendix 8.05).
Maintenance During the establishment period, check grass -lined channels after every rain-
fall. After grass is established, periodically check the channel; check it after
every heavy rainfall event. Immediately make repairs. It is particularly impor-
tant to check the channel outlet and all road crossings for bank stability and
evidence of piping or scour holes. Remove all significant sediment accumula-
tions to maintain the designed carrying capacity. Keep the grass in a healthy,
vigorous condition at all times, since it is the primary erosion protection for the
channel (Practice 6.11, Permanent Seeding).
References Surface Stabilization
6.11, Permanent Seeding
6.12, Sodding
6.14, Mulching
Outlet Protection
6.41, Outlet Stabilization Structure
Other Related Practices
6.81. Subsurface Drain
6.82, Grade Stabilization Structure
6.30.4

Practice Standards and Specifications
Appendices
8.02, Vegetation Tables
8.03, Estimating Runoff
8.05, Design of Stable Channels and Diversions
•
6305

a
0
❑c�

Chapter 1 Wet Detention Ponds
0 I. Introduction
Wet detention basins, designed to provide water quality benefits to downstream waters, are ponds that are
sized and configured to provide significant removal of pollutants from the incoming stormwater runoff.
They maihtaia a-permannea pool of water that is designed for a target TSS removal ratio according to the
size and imperviousness of the contributing: Watershed.., Above. this permanen4-pool of water, they. are also
designed to hold the runoff that results from a 1 inch rain and release this over a period of two to'$ve days.
These two basic requirements result in a pond where a majority of the suspended sediment and pollutants . .
attached to the sediment are allowed to settle out of the water. In addition, water is released at a rate such,:
that downstream erosion is lessened for smaller storms. Benefits of wet detention ponds over other
stormwater devices are many. Dry detention basins, for example, are less efficient in removing suspended
solids and other pollutants (US ff%.1983; Metropolitan Washington COG,1983) and bold little aesthetic .
value (Maryland DNR,1986). Wet detention basins are also appropriate in areas where infiltration is
impractical due to low infiltration rates of the underlying soils. In addition to water quality benefits, wet
detention ponds can reduce the peak runoff rate from a developed site and control downstream erosion
'The design of wet detention basins is based on controlling the design runoff volume from the long-term
average storm in order to settle out suspended solids and pollutants (such as heavy metals and nutrients).
Biological treatment also occurs when aquatic vegetation uses the nutrients found in the water and
sediment. DEM uses Driscoll's model (US EPA., 1986) to determine the appropriate size of the permanent
pool. This model uses as input a long-term average storm statistically calculated from the historical
rainfall record. By using this storm and the appropriate watershed characteristics (e.g... impervious cover
and drainage area size), a permanent water quality pool is sized to detain the storm long enough to attain
the target TSS. The model incorporates settling that occurs during the storm (dynamic) and between
storms (quiescent) to determine the long-term removal efficiency. The movement of the storm runoff
through the basin is assumed to occur as plug flow.
In addition to the permanent water quality pool, the basin must also have a temporary water quality pool
for extended detention: designed to control runoff from a 1" rainfall. Ibis temporary water quality storage
Is located above the permanent pool and is necessary for a number of reasons. First being for periods when
runoff entering the basin is significantly warmer than the permanent water quality pool. During these
periods, plug flow will occur to a lesser extent, and the temporary water quality volume will allow some of
the suspended solids to fall out of suspension before being released The detrimental effects of this will be
decreased because the runoff from the 1 inch storm is slowly released over a period of two to five days.
Secondly, the slow release of this small storm runoff volume also helps to reduce downstream erosion.
Once the minimum surface area and temporary storage volume of the basin neerleli to- achieve the stated
water quality goals is determined, the.principal outlet and emergency spillway should be sized for flood and
downstream erosion control. The storage allocated to flood control is located on top of both water quality
pools, while the storage for downstream erosion control includes the same.storage as the temporary water
quality pool. In some instances the temporary water quality pool may also serve as sufficient volume for
downstream erosion control.
0

Each locality should decide whether a policy based solely on flood control (i.e., peak flow reduction) or on
erosion control (i.e., bed -material load reduction or velocity control, both of which may also control
flooding) is appropriate. An example of a flood control goal might be to reduce the 10-yr. -
post -development peak discharge to the 10-yr. pre -development peak discharge and safely pass the 100-yr.
storm. However research has shown that detention practices which only control the after -development peak
discharge of large storms are not effective in reducing downstream erosion. The peak flow reduction does
not control bed -material loadings or reduce the duration during which the discharge velocity exceeds the
critical velocity of the receiving channel (McCuen and Moglen,1987; Schueler, 1987).
Smaller more frequent storms (those that produce a banldull flood) are responsible for the majority of
streambank erosion (McCuen,1987; Andersen, I97Q. Leopold 12 AL,1964). In a natural watershed this
bankfull flood is caused by a storm which occurs on average every 1.5 to 2 years. However, as the
watershed develops and stormwater volumes and peaks increase banldull floods occur mote frequently and
channel erosion is more probable. Therefore, designs based on detaining runoff from a small storm, such
as a 1-inch storm, for 48-120 hours should reduce the probability of downstream erosion (Schueler,1987).
A stormwater routing technique should be executed to assure that each outlet (principal and emergency)
performs satisfactorily for its design storm. The wetted perimeter of the basin should be planted with
aquatic vegetation (Maryland DNR, 1987; Schueler, 1987; Florida DEP,1986). 'This vegetation not only
enhances pollutant removal but provides wildlife and waterfowl habitat, and protects the shoreline from
erosion.
In addition to proper design, the basin must be routinely maintained to satisfy long-term water quality and
flood control goals. The basins maybe maintained either by private ownedhomeowners associations or by .
a local government or muniapality. Lake gas, electricity, icity, and sanitary sewers, stormwater management
may be designated as a public "utility." Under this approach, property owners within a jurisdiction are
assessed a monthly user -fee which covers capital and operation and maintenance costs for the stormwater
management program (Hartigan.1986 and Charlotte Mecklenburg Stormwater Utilities,1993). Regardless
of the approach, a key to any maintenance program is the allocation of adequate funding and the
designation of the responsible party.
The following material consists of an outline of guidance for designing or reviewing a wet detention basin
(with references) and an outline of specific wet pond requirements. Figure 1, following the references shows
a cross-section of a typical wet detention pond. .
U. Design Requirements
Design For Water Quality Control
1. Permanent Water Quality Pool
a. The surface area required can be determined using the permanent pool surface area /
drainage area (SAIDA) ratios for given levels of impervious cover and basin depths as
outlined in Table I.105A NCAC 211.1000).
b. Average permanent water quality pool depths should be between 3 to 6 feet. Required
minimum of 3 feet.
c. Impervious levels used for sizing should be those that are expected in the final buildout of
the development, and any offsite runoff that drains to the pond
0

d. Enough volume should be included in the permanent pool to store the sediment that will
accumulate between cleanout periods.
e. A farebay (which may be established by a weir) must be included to encourage early
settling. This allows drainage of only a portion of the basin in order to excavate
accumulated sediment. The forebay volume should equal about 20% of the basin volume.
2. Temporary Water Quality Pool
a. The temporary water quality pool is sized to detain the runoff volume from the fast inch of
rain. Ibis requirement refers to volume and not a particular design storm.
b. 7be temporary water quality pool for extended detention must be located above the
permanent water quality Pool.
c. 7be outlet device for this temporary water quality pool should be sized to release the
runoff volume associated with the first 1-inch of rainfall over a drawdown period of 48 to
120 hours (2 to S days). _.
3. General
a. Basin shape should minimize dead storage areas and short circuiting. Length to width
ratios should be 3:1 or greater. (Barfield, !9 11., 1981, pp. 426-429; Florida DEP, 1982,
pg. 6-289).
b. If the basin is used as a sediment trap during construction. all sediment deposited during
construction must be removed before normal operation begins.
c. Aquatic vegetation should be included for a wetland type detention basin (Maryland DNR.
March 1987; Schueler, 1987, Chapter 4 and 9). A minimum ten foot wide shallow sloped
shelf is needed for the edge of the basin for safety and to provide appropriate conditions
for aquatic vegetation (Schueler, 1987). Ibis shelf should be sloped 6:1 or flatter and
extend to a depth of 2 feet below the surface of the permanent pool (Shaver and Maxted,
DNREC,1994). A list of suitable wetland species and propagation techniques are
provided in Schueler (1987) and Maryland DNR (1987), and can be found
d. An emergency drain (with a pipe sized to drain the pond in less than 24 hours) should be
installed in all ponds to allow access for riser repairs and sediment removal (Schueler,
1987).
An Example of the basics of design for water quality follows.
0

Surface Area to Drainage Area Ratio (SAIDA) For Permanent Pool Sizing
For 85% Pollutant Removal EfSdency
Table I.1
3.0 4.0 5.0 6.0• 0
•
/ •
/
•
�•TI
' '.•
WMW
M
�1-
Numbers given in the body of the table are given in percentages
** Please note that SAIDA ratio numbers in the table above do not apply to ponds constructed in the twenty
coastal counties due to differences in soils. rainfall etc. Please contact the appropriate DEM Regional
Office for information on pond designs for these areas.
M. Example Basin Design
Using the Table 1.1 How:1011nd the Staface Area gf the PermanemPool
The numbers in the Table I.1 represent surface area (SA) to drainage area (DA) percentages. SA= the wet detention
pond permanent pool surface area required to provide an expected 85% Total Suspended Solids removal. The chart is
based on the amount of impervious cover as a percentage of the area draining to the pond and the depth of the
permanenrpool. Impervious percentages are in the left hand column of the chart and depths are given across the table
from 3 feet to 9 feet in one foot increments. If needed, one can interpolate to find the SAIDA ratio that is needed in a
particular case.
To determine the required permanent pool size, use the following steps:
1. Calculate the percent impervious cover of the site draining to the pond
[amount of impervious area / total site area]
2. Determine the average permanent pool depth (or select a depth far comparison purposes).
3. Go to Table I.1 and find the number corresponding to the impervious percentage found above and the depth
assumed This number, taken from the body of the table, represents the permanent pool surface area as it
percentage of the drainage area.
•
5 is

•
4. To determine the required surface area of the permanent pool, take the number from the table, divide by 100
and multiply this number by the contributing drainage area
Example: assume a 10 acre site with 3 acres of Impervious cover.
1. % impervious = 3/10 = 0.30 or 30%
2. Assume an average permanent pool depth of 4 feet
3.. From the. chart, with 30% Impervious and a 4 foot depth, the SA/DA ratio Is given as 1.08%
4. The required surface area would then be;
(1.08 / 100) * 10 acres = 0.108 acres or 4,705 square feet
5. The design runoff volume (the temporary water quality pool) to be controlled must be held in the pond
above this pool permanent pool level. An example of finding this volume is shown below.
Example: Again, on the same 10 acre, 30% Impervious site.
Using the runoff volume calculations in the "Simple Method" as described by Schueler (1987):
Rv=0.05 + 0.009(l)
Rv = runoff coefficient = storm runoff (inches) / storm rainfall (inches)
I = Percent Impervious = Drainage area (acres) / Impervious portion of the drainage area (acres)
In this example:
Rv = 0.05 + 0.009 (30)
Rv = 0.32 (in./in.)
For the volume that must be controlled:
Volume = (Design rainfall) (RvxDrainage Area)
Volume = 1" rainfall * 0.32 (inches /) * 1/12 (feet / incises) * 10 acres
Volume = 0.267 acre feet or 11,616 ft
This volume must be drawn down over a period of two to five days.
NOTE: Other methods may be used to determine the volume of rrmoff from the 1" storm, but care must be taken
because all methods have their limitations and applications. The method shown is used because it offers a
conservative estimate of runoff volume for a broad variety of land uses and impervious cover percentages.
0

Iv. Operation And Maintenance
2.
3.
4.
5.
6.
7.
8.
9.
48
Routine maintenance is vital to the proper operation of the wet detention basin Schueler, 1987 .4. -4
P Pe Pe ( � PF 13 .17;
Maryland DNR, 1986). No two ponds are the same, but every pond will require maintenance at some point,
and their maintenance needs will vary with the size, type of watershed, location, etc.
Adequate funding is one of the most important factors in a successful operation and maintenance program
(Maryland DNR, 1986).
Designation of a responsible party(ies) is important to assure proper inspection and maintenance.
Estimated annual operation and maintenance (O&M) costs for wet detention basins of 5% of construction
costs were found in a survey conducted by the State of Maryland on their wet detention basins (Maryland
DNR, 1986, pg. 37). In addition the NURP study in Washington, D.C., estimated O&M costs to be 5% of
construction costs (Metropolitan Washington COG, 1983, Chapter 3).
A study of Maryland basins found that, in general, people had more favorable impressions of wet detention
basins, were less likely to throw litter in them, and were more likely to clean and perform routine maintenance
on these basins when they were provided a prominent position in the development (Maryland DNR, 1986).
A permanent easement must be provided to assure easy access for maintenance. Care should be taken to
secure all appropriate legal agreements for the easement.
A benchmark for sediment removal should be established to assure adequate storage for water quality and
flood control functions.
The maintenance needs of any particular wet pond are highlyependent on the condition of the watershed that
contributes runoff to the pond. Maintenance should always include minimizing erosion problems and pollutant
export to the pond from the contributing watershed.
Again, one must remember that while general maintenance tasks are identified here, actual needs will vary
from site to site. In general, plans must indicate what operation and maintenance actions are needed, what
criteria will be used to determine when these actions are necessary, and who is responsible for these actions.
Examples of items that should be included on an Operation and Maintenance plan include, but are not limited
to the following:
a. Debris and litter control checks for inlet, outlet and orifice obstruction after every storm producing runoff.
b. Provisions for routine vegetation management/mowing and a schedule for these activities.
c. Checks every 6 months, or more frequently, for:
1) sediment buildup and the need for removal,
2) erosion along the bank and the need for reseeding or stabilization and, if reseeding is
necessary, a reseeding schedule,
3) erosion at the inlet and outlet and methods of stabilization,
4) seepage through the dam, and
5) operation of any valves or mechanical components.
d. Agreement signed and notarized by the responsible party to perform the tasks specified in the plan, including
inspections, operation, and any needed maintenance activities.
LI

V. Inspections
1. North Carolina's stormwater Hiles require annual inspections by the regulating agency of wet detention ponds
as a minimum. More frequent inspections by the land owner, or pond operator are stongly encouraged to
ensure the proper operation of a wet detention pond. Local governments can require more frequent
Inspections, and all local codes should be consulted
2. The Division of Environmental Management and several local governments have developed inspection streets
that serve as checklists for inspectors. At a =J=m. an inspection should include review of the following:
a. obstructions of the inlet and outlet devices by trash and debris,
b. excessive erosion or sedimentation in or around the basin,
C. cracking or settling of the dam,
d. deterioration of inlet or outlet pipes,
e. condition of the emergency spillway, - -
f. stability of side -slopes,
g. up and downstream channel conditions, and
IL woody vegetation in or on the dam.
3. An example Inspection sheet follows:
•
•
0

•
POND MAINTENANCE REQUIREMENTS
Project Name: Project Number:
Party:
Phone Number.
I. Inspect monthly, or after every runoff -producing rainfaff event, whichever comes first
A- Remove debris from the trash rack.
B. Check and clear the orifice of any obstructions. If a pump is used as the drawdown mechanism, check for
pump operation-
C. Check the pond side slopes; remove trash, repair eroded areas before the next rainfall event.
D. If the pond is operated with a vegetated filter, check the filter for sediment accumulation, erosion and
proper operation of the flow spreader mechanism. Repair as necessary.
111. Quarterly
A Inspect the collection system (i.e., catch basins, piping, grassed swales) for proper functioning. Clear
accumulated trash from basin grates and basin bottoms, and check piping for obstructions.
B. Check pond inlet pipes for undercutting, replace riprap, and repair broken pipes.
C. Reseed grassed swales, including the vegetated filter if applicable, twice a year as necessary. Repair
eroded areas immediately.
III. Every 6 months
A Remove accumulated sediment from the bottom of the outlet structure.
B. Check the pond depth at various points in the pond. If depth is reduced to 75% of original design depth,
sediment will be removed to at least original design depth
•
E

•
•
•
POND MAINTENANCE REQUIREMENTS CONTINUED
PAGE 2
A. Maw the side slopes, not including normally submerged vegetated shelf, according to the season. Maximum gmw
height wID be 6".
B. Cattalls, and other indigenous wetland plants, are encouraged along the pond perimeter; however, they nest be
removed when they cover the entire surface area-af the pond
C. Tir orifice is designed to draw dawn the pond in 2-5 days. If drawdown is not accomplished in that time, the
system may be clogged The sauce of the clogging must be found and eliminated
D. All components of the detenmon pond system must be kept in good working order.
V. Special Requirements
I, . hereby acknowledge that I am the financially
responsible party for maimeaame of this detention pond. I will perform the maintenance as outlined
above, as part of the Certification of Compliance with Stormwater Regulations received for this project.
Signature: Date:
I, a Notary Public for the State of . County Of
.do hereby certify that pasonariy appeared before me
this day of - 19 . and acknowledge the due execution of the foregoing instrumait. Witness my
hand and official seal,
10

VI.
VU.
Peak Flow Reduction
The designer should consult with the appropriate local government for specific design or performance requirements.
In general, any flood control or peak flow volumes must be calculated using the elevation of the permanent pool as
a base. This will include the temporary water quality pool which provides attenuation of the one inch storm.
Certincation/Approval
All basins must be designed, stamped, and certified that they are built as designed by a N.C. registered profes..1onal.
Wet detention ponds designed for projects In High Quality Waters, Outstanding Resource Waters, and Coastal
Waters are be reviewed and approved by staff In the DEM Regional Offices. Wet detetion ponds designed for
Watersupply watersheds will be reviewed and approved by the appropriate local government.
VIII. Deflnitions
1. Forebay- 7be forebay is an excavated settling basin or a section separated by a low weir at the head of the
primary impoundment. 7be forebay serves as a depository for a large portion of sediment and facilitates
draining and excavating the basin. Please see Figure 1.
2. Plug flow- Fluid particles pass through the basin and are discharged In the same sequence in which they enter.
The particles remain in the tank for a time equal to the theoretical detention time. This type of flow is
especially appropriate for basins with high length -to -width ratios (Metcalf and Eddy, Inc., 1979).
3. Primary outlet- Mie primary outlet is often constructed of a riser/barrel assembly and provides flood praection
(i.e., for the 10-yr. storm) or reduces the frequency of the operation of the emergency spillway.
4. Impervious surface- Surfaces providing negligible infiltration such as pavement, buildings, recreation
facilities, and covered driveways. This will include porous pavement, gravel, and precast concrete grid In
most cases.
11
•
•
•

Sadment
Fombar
Marsh plants
Embarkment with marsh plants
and spillway to main pod
Level of 1
kk�
nxwff volume
i / p
Romp
Normal
'�, Pool level
Raw prnvnnts
ov
inlet protection
Revarsn-afoPed
a
emban nwt<
1 at
..
orison b slowly
releew sbrtnweter
embankment
mr
Peensrk pod
•'xt r ROMP
.
Conennte
- anti4oltation
Anti -seep
adhor
collars
•
J.
Stormwater
Wet k
outlet
spal"ay -%Ik Outlet/
Figure 1. Wet Detention Pond Schematic (Stormwater Guidance Manual, NC, Arnold et. al.)
12

VIH. References
11
1. Andersen, L.W. 1970. Effects of Urban Development of Floods in Northern Virginia. United States Geological
Survey. Water Supply Paper 2001-C. Washington, D.C.
2. Arnold, J.A., ed., D.E. Line, S.W. Coffey, and J. Spooner.1993. Stormwater Management Guidance ManuaL
North Carolina Cooperative Extension Service and Notch Carolina Division of Environmental Management
Raleigh, N.C.
3. Barfield, BJ., R.C. Warner and C.T. Haan. 1981. Applied Hydrology and Sedimentology for Disturbed Areas.
Oklahoma Technical Press, Stillwater, Oklahoma.
4. Brater, E.F. and H.W. King. 1976. Handbook of Hydraulics. 6th edition, McGraw-Hill, USA.
5. Charlotte Mecklenburg Stormwater Utilities, 1993, Charlotte Mecklenburg Storm Water Design Manual, July
6. Florida Department of Environmental Regulation, Nonpoint Source Management Section, Tallahassee, FL.
1984 Draft. The Florida Development Manual: A Guide to Sound Land and Water Management
7. Florida Department of Environmental Regulation, Nonpoint Source Management Section, Tallahassee, FL.
1986. Current DER Criteria for Wet Detention Systems.
8. Harrington, B.W. 1987a. Design Procedures for Stormwater Management Extended Detention Structures.
Maryland Department of the Environment, Sediment and Stormwater Division, Annapolis, MD.
9. Harrington, B.W.1987b. Design Procedures for Stormwater Management Detention Structures. Maryland
Department of the Environment, Sediment and Stormwater Division, Annapolis, MD.
10. Harrington, B.W. 1986. Feasibility and Design of Wet Ponds to Achieve Water Quality Control. Maryland
Water Resources Administration, Sediment and Stormwater Division, Annapolis, MD.
11. Hartigan, J.P. 1986. Regional BMP Master Plans. In: Urban Runoff Quality- Impact and Quality
Enhancement Technology. Urbonas, B. and L.A. Roesner, Eds. American Society of Civil Engineers, USA.
12. Hartigan, J.P. and T.F. Quasebarth. 1985. Urban Nonpoint Pollution Management for Water Supply
Protection: Regional vs. Onsite BMP Plans. In: Proceedings of Twelfth International Symposium on Urban
Hydrology, Hydraulics, and Sediment Control, University of Kentucky, Lexington, Kentucky, pp. 121-130.
13. James, W.P., J.F. Bell and D.L Leslie.1987. Size and Location of Detention Storage. Journal of Water
113(1): 15-28.
14. Janna, W.S. 1983. Introduction to Fluid Mechanics. Wadsworth, Inc., USA.
15. Leopold, L.B., M.G. Wolman and J.P. Miller. 1964. Fluvial Processes in Geomorphology. W.H. Freeman and
Sons. San Francisco, CA.
13

•
16. Lindsley, R.K and J.B. Franzini. 1972. Water -Resources Engineering. McGraw-Hill, USA.
17. Malcom, H.R., ME. Avera, C.M. Bullard and C.C. Lancaster.1986. Stormwater Management in Urban
Collector Streams. Water Resources Research Institute of the University of North Carolina, Raleigh, NC. Repots
No. 226.
18. Malcom, H.R. and V.E. New. 1975. Design Approaches For Stormwater Management in Urban AwAM
prepared for CE383 at NCSU, Raleigh, NC.
19. Maryland Department of Natural Resources, Sediment and Stormwater Division, Water Resources
Administration, Annapolis, MD. 1986. Maintenance of Stormwater Management Structures, A Departmental
Summary.
20. Maryland Department of Natural Resources, Sediment and Stormwater Division, Water Resources
Administration, Annapolis, MD. 1987. Guidelines for Constructing Wetland Stormwater Basins.
21. McCuen, R.H. and G.E. Moglen. 1987. Design of Detention Basins to Control Erosion. Presented at Sediment
and Stormwater Management Conference, Chestertown, Maryland August 12,1987.
22. McCuen, R.H.198Z A Guide to Hydrologic Analysis Using SCS Methods. Prentice -Hall, Inc., Englewood
Cliffs, New Jersey.
23. Metcalf and Eddy, Inc.1979. Wastewater Engineering: Treatment/DisposaUReuse.-McGraw-Hill, USA, 920
24. Metropolitan Washington Council of Governments. Department of Environmental Programs. 1983. Urban
Runoff in the Washington Metropolitan Area, Final Report. Prepared for US, EPA Nationwide Urban Runoff
Program under Grant No. PO-003208-01.
25. North Carolina Department of Natural Resources and Community Development, Raleigh, NC. November 1,
1985. Dam Safety. Title 15, Subchapter 2K
26. North Carolina Department of Natural Resources and Community Development, Raleigh, NC. August 1,
1985. Sedimentation Control. Title 15, Chapter 4.
27. North Carolina Department of Environment, Health, and Natural Resources, Division of Land Quality, Raleigh,
NC. September 1988. Erosion and Sediment Control Planning and Design Manual.
28. Schueler, T.R. 1987. Controlling Urban Runoff. A Practical Manual for Planning and Designing Urban BMPs.
Department of Environmental Programs, Metropolitan Washington Council of Governments.
29. Shaver and Maxted. 1993. Construction of Wetlands for Stormwater Treatment. Department of Natural
Resources and Environmental Control. Stormwater Design Manual. Chapter Six.
14

30. United States Department of Agriculture, Soil Conservation Service, North Carolina 1987. Pond. Technical
Guide, Section IV. No. 378-1. 0
31. United States Department of Agriculture, Soil Conservation Service. 1986. Engineering Field Manual for
Conservation Practices.
32. United States Department of Agriculture, Soil Conservation Service. 1986. Urban Hydrology for Small
Watersheds. Technical Release No. 55.
33. United States Department of Agriculture, Soil Conservation Service.1970. Soil Survey, Wake County, North
Carolina.
34. United States Department of Agriculture, Soil Conservation Service. National Engineering Handbook.
35. United States Department of Commerce, Bureau of Public Roads. December 1965. "Hydraulic Charts for the
Selection of Highway Culverts," Hydraulic Engineering Circular No. 5, USGPO, Washington, D.C.
36. United States Environmental Protection Agency. 1986. Methodology for Analysis of Detention Basins for
Control of Urban Runoff. EPA 440l5-87-WI.
37. United States Environmental Protection Agency. 1983. Final Report of the Nationwide Urban Runoff
Program, Volume 1.
38. Urbonas, B. and W.P. Ruzzo. 1986. "Standardization of Detention Pond Design for Phosphorus Control." In
Urban Runoff Pollution. Ed. by H.C. Torno, J. Marsalek and M. Desbordes. NATO ASI Series, Vol. G10.
Springer-Veriag, New York, New York.
39. Viessman, W. Jr., J.W. Knapp, G.L. Lewis and T.E. Harbaugh. 1977. Introduction to Hydrology. Harper and
Row, Publishers, Inc., New York, New Yak.
•
15

•
Chapter 9 Infiltration Devices
I. Introduction
Infiltration refers to the process of stormwater entering the soil. A number of infiltration devices with
differing designs have been used in various locations throughout the country. Ibis chapter discusses only
three devices: infiltration basins, infiltration trenches, and dry wells.
Infiltration basins are normally dry basins, much like dry detention basins, with the exception that the
stormwater does not flow out into a receiving stream. Rather, the stormwater is allowed to ex lltrate, or exit
the basin by infiltrating into the soil. Obviously, infiltration basins can be used only where the soils are
permeable enough to empty the basins within a reasonable time interval. Figure 19. shows an example of a
traditional infiltration basin
Infiltration trenches are ditches that fill with stormwater runoff and allow the water to exfiltrate into the
soil. Some versions of infiltration trenches are filled with large crushed stone to create storage for the
merawater in the voids between the stones. Other versions use precast concrete chambers to provide a
large storage volume to bold stormwater for exfiltration into the soil. Infiltration trenches are usually used
to handle the water from parking lots and buildings.
Dry wells are constructed similarly to infiltration trenches but are usually more compact and not elongated.
Dry wells are mostuseful for receiving 'the runoff from roofs of buildings and allowing it to exfiltrate into
the soil. Dry wells that receive runoff from either roofs or completely impervious areas show the most
promise for long-term water quality benefit.
North Carolina -rule§ permit the use of � cxf�fal -€Andes+and as;attaltetnafive
practice.in 01 er w+eas.to satisfythe requirement for 85% TSS removal. Infiltration devices must meet the
design-iega ementsdiscusseShete, of which the geotechnical iavestTgatiobiare anImportant part. -.[See
15A NCAC 2H.1008 for details.]
Infiltration devices are thought to have high removal efficiencies of sediment and pollutants that are
adsorbed to sediment particles. Biological degradation in the soil'duxdd help reduce dissolved pollutants,
depending on soil type. Data is available on actual removal capability for most dissolved pollutants.
At present, many infiltration devices seem to fail rather quickly. ,It appears that the soil becomes clogged
with sediment, preventing infiltration. Newer designs are incorporating enhancements to remove more.
sediment before the sediment enters the Infiltration device. Regular maintenance and proper siting will
extend the life of an infiltration device.
H. Advantages
Infiltration devices put more stormwater into the soil, which more closely mimics the natural hydrology of
the area Increasing the amount of water entering the soil reduces the frequency of flooding and helps to
maintain the shallow ground water that will support dry weather flows In streams. In general, pollutant
removal should be as good as the best stormwater control practices.
82

CO
•
A
'O
ct:
o °o
9
�6
Velocity dissipation
blocks and flow spreader
Maximum water
surface elevation
F1
e A
/
Riprap inlet Sand filter t
(low spreaders
�.00i
Dense
_ _ _ �
go
grass cover
:ss':.- :. •.:� Inlet
_
MI US"
• mil'
Perforated pipe filter
to
underdrains carry
runoff water to basin
9
E
8
' P
I

0 M. Disadvantages
A problem associated with the past high failure rate Is that when a BMP fails, the stormwater receives little
treatment. Also, devices which use infiltration are restricted to those auras with permeable soils, deep
water tables, deep bedrock and stable areas where the stormwater contains little sediment. The greatest
potential concern about infiltration practices is that infiltration of stormwater may contaminate ground
water. To date, no major contamination has occurred (Se-ueler, et al. 1992).
IV. Casts
Infiltration devices are less expensive than large wetlandL% but mode expensive than a simple dry detention
basin. Given that Infiltration devices can often St into -areas with limited spm they may be the most cost-
effective control available in some situations:. Also, there are situations where an infiltration device may be
constructed beneath an Impervious surface, thereby consuming no developable land.
V. Design Requirements
• Soils must have been tested and shoWn'tn`infiltrate a minimum of 0.52 Inches/h= at the bottom of
device. 041 j
• Infiltration devices must capture ap I infiltrate the runoff from first; U.dis of rainfall for areas that
drain to SA classified waters, �d(kz. i f l dther'Weat
• Drawdown ofttlls ronoffoc°days.
• The maximum drainage area that should flow to a single device is 5 acres.
• Pretreatment devices such as catch basins,: grease traps, filter strips, grassed swales and sediment traps
must be used to protect infiltration devices from clogging..
• All infiltration devices should be sited a minimum of 30 feet from surface water. 50 feet from Class SA
waters, and 190 feet from any water supply wells.
• The bottom of iM 1tt GtQ ilidrbe°a<minimum of Ueet4bb the sessonak bi�kw
table, vv'Ifi2greaet sepioaiesirab e:
• The bottom of the infiltration device must be a minimum of 3 feet above any bedrock or impervious
soil horizon.
• The bottom of the device must be lined with a layer of clean sand with an average depth of four inches.
• The sides of an infiltration trench must be lined with geotextile filter fabric.
• The rock used In infiltration trenches must be free of fins (washed stone) and have as large a void
ratio as possible. Rounded stone, such as beach gravel, has a larger void ratio than angular crushed
stone.
• Infiltration devices must be designed as off-line BMPs. This means that runoff In excess of the design
volume by-passes the system.
• Infiltration devices should not be constructed on fill material, but would be allowed on a case -by -case
basis.
• At least one observation well should be included In the design of an infiltration device and may be
required on a case -by -case basis.
• Runoff should not be directed to an infiltration device until the drainage area is stabilized
0 Other Design Guidelines:
84

• Infiltration devices work best for smaller drainage area and drainage areas that are completely stable '-- -
ac�
• Thick vegetation on the bottom of infiltration basin should be maintained
• Infiltration trenches should be wide and shallow rather than deep and narrow. The ratio of side -to -
bottom area should be less than 4:1. The sides and bottom should be lined with falter fabric (geotextile
fabric) to prevent clogging.
• Infiltration devices should be located away from foundation of buildings and other sensitive strucu=
Failure rates far infiltration devices appear to be high Sc bueler cites studies which indicate that only about;::
half of the infiltration trenches and even fewer infiltration basins functioned as long as five years (Schueler; --
et al.1992). Many of these devices failed due to clogging and lack of maintenance.
VL Peak Flow Reduction -
Infiltration devices are used to improve the quality of the starmwata and are not primarily directed to
reducing peak flows or stormwater volume, especially from larger storms that are bypassed around the
system. However, because they prevent some water from running off, they will reduce the peak flows.
VH. Maintenance
While there should be little routine maintenance needed for most infiltration devices, the maintenance that
Is required is very Important, and property owners must be educated in the function and maintenance
requirements of the infiltration device. Especially important is the maintenance of vegetated areas that
drain to the infiltration system. Areas that are allowed to become bare and unvegetated will contribute
excess sediment to the infiltration system and hasten its failure.
• Annual inspections must be conducted after a storm event to ensure infiltration performance.
• Grass filters leading to infiltration basins should be mowed at least twice a year.
• Sediment deposits should be removed from pretreatment devices at least annually.
• Removal and reconstruction of the infiltration device will be necesary when the infiltration rate drops to
unacceptable levels.
V1H. References
Arnold, J.A, eel D.E. Line, S.W. Coffey, and J. Spooner.1993. Stocmwater Management Guidance Manual.
North Carolina Cooperative Extension Service and North Carolina Division of Environmental Management
Raleigh, NC
Berman, Laurel, C. Hartline, N. Ryan, and J.D. Thane, P.E.1991. Urban Runoff: Water Quality
Solutions. The American Public Works Association Research Foundation. 58 pp.
Birch, P.B., PhD. and H.E. Pressley (eds.)1992. Stocmwater Management Manual for the Puget Sound
Basin. Review Draft. Dept. of Ecology. Publication number 90-73.
85

is
Gibb, A., B. Bennett, and A. Blrkbeck.1991. Urban Runoff Quality and Treatment: A Comprd=sive
Review. File number 2-51-246(242). British Columbia Research Corporation. Vancouver, British
Columbia.
North Carolina Department of Environment. Health, and Natural Resources, Division of Land Quality,
Raleigh, NC. September 1988. Erosion and Sediment Control Planning and Design Manual.
Schueler. T.R., P. A. Kumble, and M. A. Heraty.1992. A Current Assessment of Urban Best Management
Fbwdces: Techniques for Reducing Non -Point Source Pollution in the Coastal Zone. Publication number
92705. Metropolitan Washington Council of Governments. Washingtob, --DC.127 pp: `
Schueler, T.R.1087. Controlling Urban Runoff A Practical Manual for Planning and Designing Urban
BMPs. Publication number rnn Metropolitan Washington Council of Governments. Washington, DC.
275 pp. — -
Stahre, P. and B. Urbonas. 1990. Stocmwater Detention For. Drainage, Water Quality, and CSO
Management. Prentice Hall, Inc. Englewood Cliffs, NJ. 338 pp.
U.S. EPA. 1990. Urban Targeting and BMP Selection. Information and Guidance Manual for State .
Nonpoint Source Program Staff Engineers and Managers. The Terrene Institute. EPA No. 68-C8-0034. 54
PP.
U.S. EPA,;1992. Stormwater Management for Industrial Activities: Developing Pollution Prevention Plans
and Best Management Practices. Office of Watet Government Institutm Inc: Rockville, MD.
Urbonas, B. and LA. Roesner, eds. 1986. Urban Runoff Quality=Impact and Quality Enhancement
Technology. American Society of Civil Engineers. New York, NY. 477 pp.
Whipple, W., N.S. Grigg, T. Grizzard, C. W. Randall. R. P. Shubinski, and L. S. Tucker.1983.
Stormwater Management in Urbanizing Areas. Prentice Hall, Inc. Englewood Cliffs, NJ. 234 pp.
96

Proposed Stormwater Best Management Practices
•
L1
Proposed
Stormwater
BMP Alternatives
Basic Design Requirements
(Conditions or Limitations)
Assumed
TSS Removal
Efficiencies
Typical
Costs
erAcre*
Wet Detention
1.5 in/acre in Permanent Storage
85%
$50042500
1" rainfall drawdown in 2 to 5 days
,
Sand Filters + Detention
1.00 in/Impervious Acre and required Surface Area
85%
$10,000
Peak attenuation of the 1 yr. 24 hr. storm, or 1" drawdown
5 acre max. drainage area per filter
Bioretention
1.00 in/Impervious Acre and required Surface Area
85%
$3000-S5000
Peak attenuation of the 1 yr. 24 hr. storm, or 1" drawdown
5 acre max. drainage area per filter
Wetland/Wetponds
1.25 inlacre in Permanent Storage
85%
$750-S3000
Peak attenuation of the 1 yr. 24 hr. storm or 1"drawdown
'
Percentages of ponded area at givens depths
0.75 in/acre in Permanent Storage
60%
Peak attenuation of the 1 yr. 24 hr. storm or 1" drawdown
Percentages of ponded area at givens depths
Dry Extended. Detention
Detain the 1 yr. 24 hr. storm for a period of-48 hrs
. 50%
$30042000
Grassed Swales
Low slope: <= 4%
35%
$30041000
Low Velocity: <=2.5 fps
Checkdams every l' elevation or as necessary for velocity
Minimum length 100'
Vegetation Requirements
_ .
Higher slope: 4% - 10"o
1590
$200-S1000
Higher Velocity >2.5 fps
No check dams
Minimum Length 100'
Vegetation Requirements
Vegetated Filter Strips
50' length along flow for slopes to 5�o
50' + 4' for every ln0 increase in slope to 15%:
Drainage areas < 5 acres
Velocities limited to < 3 fps
in natural areas with woody vegetation
41040
S30041000
m planted woody vegetation area
3070
in planted grass filter
25 ,o
Infiltration Areas
1.5 inJacre storage volume
85'7,
S1000-SZ000
minimum infiltration rate of 0.27 in./hour
drawdown of the device within 3 days
*Costs: In the experience of those involved with the Chesapeake Bay ini L-Live, total cost of cotnpiiance
ranged from a low of 1% to maximum of 2.5 :-c or the total project cost. Bec •.:se of the si�. s fcci f c nat:,-e

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THE INFORMA TION SHO WN IN THIS
FIGURE WAS REFORMATTED BY UR S
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LOW DENSITY BEACH RESIDENTIAL
BR-2
MEDIUM DENSITY BEACH RESIDENTIAL
BR-3
HIGH DENSITY BEACH RESIDENTIAL
BC-1
GENERAL BEACH COMMERCIAL
BC-2
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COMMUNITY SHOPPING MALL
BH
BEACH HOTEL
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LOW DENSITY VILLAGE RESIDENTIAL
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MEDIUM DENSITY VILLAGE RESIDENTIAL
VR-3
HIGH DENSITY VILLAGE RESIDENTIAL
VC-1
VILLAGE COMMERCIAL
VC-2
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VILLAGE COMMERCIAL
KHW
KITTY HAWK WOODS
PCD
PLANNED COMMERCIAL DEVELOPMENT (OVERLAY)
PUD
PLANNED UNIT DEVELOPMENT (OVERLAY)
ETJ
EXTRATERRITORIAL JURISDICTION
ETJ — RECREATIONAL BEACH AND
SWIMMING DISTRICT
lWe
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WATER DISTRICT
MS-1
MEDICAL EMERGENCY & GOVERNMENTAL SERVICES
OR
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GRAPHIC SCALE
10009 0 10009
1" = 10009
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THE PREPARATION OF THIS FIGURE WAS FINANCED IN PART THROUGH
A GRANT PROVIDED BY THE NORTH CAROLINA COASTAL MANAGEMENT
PROGRAM, THROUGH FUNDS PROVIDED BY THE COASTAL ZONE
MANAGEMENT ACT OF 1972, AS AMENDED, WHICH IS ADMINISTERED BY
THE OFFICE OF OCEAN AND COASTAL RESOURCES MANAGEMENT,
NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION.
TOWN OF KITTY HAWK
DARE COUNTY, NORTH CAROLINA
KITTY HAWK STORMWATER MANAGEMENT PLAN
ZONING DISTRICTS
FIGURE -3
URS Grein e r 5606B VIRGINIA BEACH BOULEVARD
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THE INFORMATION SHOWN IN THIS
FIGURE WAS REFORMATTED BY UR S
GREINER WOOD WARD CLYDE FROM
MAPPING PR 0 VIDED BY OTHERS IN
THE KITTY HAWK OUTREACH PROJECT
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FLOOD ZONES
LEGEND:
ZONE AE _ 100-YEAR STORM EVENT FLOOD
ELEVATION DETERMINED (99)
ZONE AO 100-YEAR STORM EVENT FLOOD DEPTHS OF 1
TO 3 FEET (USUALLY SHEET FLOW ON SLOPING
TERRAIN); AVERAGE DEPTHS DETERMINED (2')
ZONE VE =f, ,; COASTAL FLOOD WITH VELOCITY HAZARD
...:...........:.
(WAVE ACTIONS); 100-YEAR STORM EVENT
FLOOD ELEVATIONS DETERMINED (119 TO 16' )
ZONE X AREAS DETERMINED TO BE OUTSIDE
500-YEAR FLOOD PLAN
THIS IS NOT AN OFFICAL FLOOD INSURANCE RATE MAP (FIRM) AS
DETERMINED BY THE FEDERAL EMERGENCY MANAGEMENT AGENCY (FEMA),
FLOOD INSURANCE RATE MAPS, COMMUNITY - PANEL NUMBERS 378438
00001 D THROUGH 370438 0001-0002, REVISED APRIL 1, 1993, ARE ON
FILE IN THE TOWN OF KITTY HAWK DEPARTMENT OF PLANNING AND
DEVELOPMENT.
THE PREPARATION OF THIS FIGURE WAS FINANCED IN PART THROUGH
A GRANT PROVIDED BY THE NORTH CAROLINA COASTAL MANAGEMENT
PROGRAM, THROUGH FUNDS PROVIDED BY THE COASTAL ZONE
MANAGEMENT ACT OF 1972, AS AMENDED, WHICH IS ADMINISTERED BY
THE OFFICE OF OCEAN AND COASTAL RESOURCES MANAGEMENT,
NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION.
TOWN OF KITTY HAWK
GRAPHIC SCALE DARE COUNTY, NORTH CAROLINA
1000, 0 1000-9 101,KITTY HAWK STORMWATER MANAGEMENT PLAN
FLOOD ZONES
���.
1 = 1000 Ky
-
r FIGURE 5
1981
c- URS Greiner
5606B VIRGINIA BEACH BOULEVARD
Woodword—Clyde VIRGINIA BEACH, VIRGINIA 23462