SW7970117_HISTORICAL FILE_20200826

STORMWATER DIVISION CODING SHEET
POST -CONSTRUCTION PERMITS
PERMIT NO.
SW
DOC TYPE
❑ CURRENT PERMIT
❑ APPROVED PLANS
HISTORICAL FILE
❑ COMPLIANCE EVALUATION INSPECTION
DOC DATE��C����
YYYYM M D D

ROY COOPER
Governor
NUCHAEL S. REGAN.
Secretary
BRIAN WRENN
Director
NORTH CAROLINA
Environmental Quallry
August 26, 2020
Mr. Charles E. Schulz, Deputy Facilities Officer
MCAS Cherry Point
PSC Box 8006
Cherry Point, NC 28533
Subject: Stormwater Permit Renewal
Stormwater Management Permit SW7970117
MCAS Cherry Point — Commissary Expansion
Craven County
Dear Mr. Schulz:
A Division of Energy, Mineral, and Land Resources file review has determined that
Stormwater Permit SW7970117 for a stormwater treatment system consisting of a
wetland detention system serving the Commissary Expansion expires on February 14,
2021. This is a reminder that permit renewal applications are due 180 days prior to
expiration. We do not•have a record of receiving a renewal application.
Please submit'a completed permit renewal application along with a $505.00 fee for
permit renewal. Application forms for renewal can be found on our website at:
httpsn/4deq.rLc.gov/about/­divisions/energy-mineral-Iand-resources/energy-mineral-land-
rtiles/stormwater-t)rogram/i)ost-constrALcti-m. North Carolina General Statutes and the
Coastal Stormwater rules require that this property be covered under a stormwater
permit. Failure to maintain a permit subjects the owner to assessment.of civil penalties
If you have questions; please feel.free to contact me at [phone]. 1 will be glad to
discuss this by phone or meet with you.;lf you would like, I can e-mail you a copy of the
application form. You can request a copy by e-mailing me at roaer.thorpe(@ncdenr.aov.
Sincerely,
Roger K. Thorpe
Environmental Engineer
North Carolina Department of Environmental Quality I Division of Energy. Mineral and Land Resources
Washington Regional Office 1 943 Washington Square Mall I Washington. North Carolina 27889
®� 252.946.6481

UNITED STATES MARINE CORPS
MARINE CORPS AIR STATION
POSTAL SERVICE CODE BOX 8003
CHERRY POINT, NORTH CAROLINA 28533-0003
Mr. Roger Thorpe -
North Carolina Department of Environment
and Natural Resources
Division of Water Quality
943 Washington Square Mall
Washington, NC 27889
Dear Mr. Thorpe:
5090/29466
LN
February 27, 2007
MAR 0-5 2007
This letter is being sent to formally notify your office of the
Marine Corps Air Station Cherry Point's schedule to address the
compliance issues stated in the Notice of Violation dated February 20,
2007 concerning permit SW7970117. The compliance issues being
addressed include:
-Constructing a check dam 200 yards from the inlet of the
Stormwater canal.to retain one inch of runoff from impervious
surfaces.
-Removing excess vegetation from the canal and along its banks.
-Repairing erosion occurring at the inlet of the canal.
A work order to correct these issues has been sent to our
Facilities Maintenance Department as a top priority work request.
Certification of the work will be done immediately following
completion of the repairs and 'a copy of the design certification will
be forwarded for your records as soon as the work is completed.
Thank -you for bringing this matter to our attention to insure that we
remain in compliance with our Stormwater Management Program.
Please direct any questions or comments to Mr. William Potter of
the Environmental Affairs Department at [phone].
Sincerely,
Bnvi(ro me tal Affairs Officer
By dir ion of the
Commanding Officer

Dear Mr. Roger Thorpe,
This letter is being sent to notify you of additional
information that has recently been received by our office
concerning Permit SW7970117. Recall that your recent
renewal inspection on February resulted in a Notice of
Violation for the operation of a Stormwater control
structure and raised questions as to the actual structure
covered under Permit SW7970117. During the time of the
inspection there was a lack of specific documentation and
plans for the Stormwater structures. MCAS Cherry Point's
engineering department has recently retrieved additional
construction drawings from the Commissary Expansion Project
which contained the necessary information to correctly
answer the questions raised during the inspection.
During the renewal inspection for SW7970117, a
drainage canal which was thought to have been the permitted
Stormwater structure was inspected and was cited for not
meeting the specifications of the original permit. Now,
due to recent information from the recently retrieved
construction drawings, it is understood that this was the
incorrect structure, and that the actual permitted
structure is located approximately 200 yards north of the
inspected drainage canal.
This canal, which is well maintained and
representative of a proper drainage system, does contain
the required check dam as noted in the permit. However,
there is an additional `vehicle access' berm which was
constructed that is not included in the plans which may
facilitate a modification in the permit. We would like to
request any additional requirements on our part in order to
facilitate a permit modification. It should be noted that
this addition does not negatively impact drainage, and in
fact may be helpful in reducing runoff velocities of the
large amount of rainfall which is directed into the canal,
as well as retain at least 1 inch of rainfall as initially
required in the permit.
Included with this letter are the pictures, plans, and
drawings necessary for better understanding of this
structure's design and function. Any additional
information for modification of the permit will be provided
as required.
Please direct any questions or comments to
Mr. William Potter of the Environmental Affairs Department
at [phone].

Michael F. Easley, Governor
William G. Ross Jr„ Secretary
North Carolina Department of Environment and Natural Resources
Alan W. Klimek, P.E. Director
Division of Water Quality
US MCAS Cherry Point
Environmental Affairs Dept.
Attn: Mr. Doug Nelson
MCAS PSC Box 8066
Cherry Point, NC 28533
Subject:: Stormwater Permit No. SW7970117
MCAS — Commissary Expansion
Craven County,
Dear Mr. Nelson:
The Division of Water Quality issued a Coastal Stormwater Management Permit, Number SW7970117
to USMCAS Cherry Point for US MCAS Cherry Point — MCAS — Commissary Expansion on May 5,
1997. This permit expires on May 5, 2007. Section .1003(h) of 15 A NCAC 2H .1000 (the stormwater
rules) requires that applications for permit renewals shall be submitted 180 days prior to the expiration
of a permit and must be accompanied by a processing fee, which is currently set at $420.00. If this is
still an active project please complete and submit the enclosed renewal application in a timely manner.
If this project has not been constructed and a permit is no longer needed, please submit a request to
have the permit rescinded. If you have sold the project, or are no longer the permittee, please provide
the name, mailing address and phone number of the person or entity that is now responsible for this
permit. Enclosed is a form for change of ownership, which should be completed and submitted if the
property has changed hands.
Your permit requires that upon completion of construction and prior to operation of the permitted
treatment units a certification of completion be submitted to the Division from an appropriate designer
for the system installed. This is to certify that the permitted facility has been installed in accordance with
the permit, the approved plans, specifications and supporting documentation. Please include a copy of
the certification with your permit renewal request and processing fee. Enclosed is a copy of a sample
certification. Also enclosed is a new Operation and Maintenance agreement that should be completed
and submitted along with your renewal application.
You should be aware that failure to provide the Designer's Certification and the operation of a
stormwater treatment facility without a valid permit, are violations of NC General Statute 143-215.1 and
may result in appropriate enforcement action including the assessment of civil penalties of up to
$10,000 per day.
If you have any questions, please feel free to contact us at 252-946-6481.
erely, I
Al Hodge, Re iupervisor
Surface Water Protection Section
Washington Regional Office
Enclosures
cc: Quible & Associates, Inc.
Washington Regional Office/
North Carolina Division of Water Quality Internet: www.ncwaterqualirv.ore t��One
943 Washington Square Mall Phone [phone]Vo Carolina
Washington, NC 27889 Fax [phone] �%)/� lly
An Equal Opportunity/Affrmafive Action Employer -50%Recycled110% Post Consumer Paper [-{L K �/

W f)""
State of North Carolina
Department of Environment,
Health and Natural Resources
Washington Regional Office
James B. Hunt, Jr., Governor
Jonathan B. Howes, Secretary
AF•�•
[DFEE HNR
DIVISION OF WATER QUALITY
May 5, 1997
Environmental Affairs Dept. (LN)
Attn: Mr. Doug.Nelson
MCAS, PSC Box 8066
Cherry Point, NC 28533
Subject: Permit No. SW7970117
MCAS - Commissary Redevelopment
High Density Stormwater Project
Craven County
Dear Mr. Nelson:
The Washington Regional Office received the completed
Stormwater Application for the subject project on March 27, 1997.
Staff review of the plans and specifications has determined that
the project, as proposed, will comply with the Stormwater
Regulations set forth•in Title 15A NCAC 2H.1000. We are forwarding
Permit No. SW7970117 dated May 5, 1997 to MCAS, Cherry Point, NC.
.This permit shall be effective from the date of issuance until
May 5, 2007 and shall be subject to the conditions and limitations
as specified therein. Please pay special attention to the
Operation and Maintenance requirements in this permit. Failure to
establish an adequate system for operation and maintenance of the
stormwater management system will result in future compliance
problems.
If any parts, requirements, or limitations contained in this
permit are unacceptable, you have the right to request an
adjudicatory hearing upon written request within thirty (30) days
following receipt of this permit. This request must be in the form
of a written petition, conforming to Chapter 150B of the North
Carolina General Statutes, and filed with the Office of
Administrative Hearings, P.O. Drawer 27447, Raleigh, NC 27611-7447.
Unless such demands are made this permit shall be final and
binding.
943 Washington Square Mall, Washington, North Carolina 27889 Telephone [phone] FAX [phone]
An Equal Opportunity Affirmative Action Employer

EAD (LN)
May 5, 1997
Page Two
If you have any questions, or need additional information
concerning this matter, please contact Bill Moore at (919) 946-
6481, extension 264.
Sincerely,
"/le
Roger K.. Th pe
Water Quality Supervisor
Washington Regional Office
cc: Quible & Associates
Craven County Inspections
vWashington Regional Office
Central Files

State Stormwater Management Systems
Permit No. SW7970117
STATE OF NORTH CAROLINA
DEPARTMENT OF ENVIRONMENT, HEALTH AND NATURAL
DIVISION OF WATER QUALITY
STATE STORMWATER MANAGEMENT PERMIT
HIGH DENSITY DEVELOPMENT
In accordance with the provisions of Article 21 of Chapter 143,
General Statutes of North Carolina as amended, and other applicable
Laws, Rules, and Regulations
IS HEREBY GRANTED TO
MCAS, Cherry Point
Craven County
FOR THE
construction, operation and maintenance of stormwater management
systems in compliance with the provisions of 15A NCAC 2H.1000
(hereafter referred to as the "stormwater rules") and the approved
stormwater management plans and specifications and other supporting
data as attached and on file with and approved by the Division of
Water Quality and considered a part of this permit for a wetland
detention system to serve the commissary redevelopment project
located at MCAS, Cherry Point, NC.
This permit shall be effective from the date of issuance until May
5, 2007 and shall be subject to the following specified conditions
and limitations:
I. DESIGN
1. This permit is effective only with respect to the nature and
volume of stormwater described in the application and other
supporting data.
2. This stormwater system has been approved for the management of
stormwater runoff as described on page 4 of this permit, the
Project Data Sheet.
3. Approved plans and specifications for this project are
incorporated by reference and are enforceable parts of the
permit.
3

DIVISION OF WATER QUALITY
PROJECT DATA
Project Name:
Permit Number:
Location:
Applicant:
Mailing Address:
Application Date:
Water Body Receiving Stormwater
Runoff:
Classification of Water Body:
Pond/Basin Depth:
Total Site Area:
MCAS, Commissary Redevelopment
SW7970117
Craven County
1410 I
EAD (LN)
PSC Box 8066
Cherry Point, NC 28533
1/23/97; original
3/27/97; complete
Slocum Creek
SC -NSW
2.0 feet
1.55 acres
Total Impervious Surfaces Allowed: 1.55 acres
Provided Surface Area: 4140 sf
Required
Storage
Volume:
5635
cf
Provided
Storage
Volume:
5650
cf
4

f 4. No homeowner/lot owner/developer shall be allowed to fill in,
alter, or pipe any vegetative practices (such as swales) shown
on the approved plans as part of the stormwater management
system without submitting a revision to the permit and
receiving approval from the Division.
5.• The following items will require a modification to the permit:
a. Any revision to the approved plans, regardless of size
b. Project name change
C. Transfer of ownership
d. Redesign or addition to the approved amount of built -upon
area
e. Further subdivision of the project area.
In addition, the Director may determine that other revisions
to the project should require a modification to the permit.
6. The Director may notify the permittee when the permitted site
does not meet one or more of the minimum requirements of the
permit. Within the time frame specified in the notice, the
permittee shall submit a written time schedule to the Director
for modifying the site to meet minimum requirements. The
permittee shall provide copies of revised plans and
certification in writing to the Director that the changes have
been made.
II. SCHEDULE OF COMPLIANCE
1. The permittee will comply with the following schedule for
construction and maintenance of the stormwater management
system.
a. The stormwater management system shall be constructed in
its entirety, vegetated and operational for its intended
use prior to the construction of any built -upon surfaces
except roads.
b. During construction, erosion shall be kept to a minimum
and any eroded areas of the system will be repaired
immediately.
2. The facilities must be properly maintained and operated at all
times. The approved Operation and Maintenance Plan must be
followed in its entirety and maintenance must occur at the
scheduled intervals.
3. The permittee shall at all times provide the operation and
maintenance necessary to assure the permitted stormwater
system functions at optimum efficiency including, but not
limited to:
I

a. Semiannual scheduled inspections (every 6 months)
b. Sediment removal
C. Mowing and revegetation of side slopes
d. Immediate repair of eroded areas
e. Maintenance of side slopes in accordance with approved
plans and specifications
f. Debris removal and unclogging of outlet structure,
orifice device and catch basins and piping.
4. Records of maintenance activities must be kept and made
available upon request to authorized personnel of DWQ. The
records will indicate the date, activity, name of person
performing the work and what actions were taken.
5. This permit shall become voidable unless the facilities are
constructed in accordance with the conditions of this permit,
the approved plans and specifications, and other supporting
data.
6. Upon completion of construction and prior to operation of this
permitted facility, a certification must be received from an
appropriate designer for the system installed certifying that
the permitted facility has been installed in accordance with
this permit, the approved plans and specifications, and other
supporting documentation. Mail the Certification to the
Washington Regional Office, 943 Washington Square Mall,
Washington, North Carolina, 27889, attention Division of Water
Quality.
7. A copy of the approved plans and specifications shall be
maintained on file,by the Permittee for a minimum of five
years from the date of the completion of construction.
III. GENERAL CONDITIONS
1. This permit is not transferable. In the event there is a
desire for the facilities to change ownership, or there is a
name change of the Permittee, a formal permit request must be
submitted to the Division of Water Quality accompanied by an
application fee, documentation from the parties involved, and
other supporting materials as may be appropriate. The
approval of this request will be considered on its merits and
may or may not be approved.
2. Failure to abide by the conditions and limitations contained
in this permit may subject the Permittee to enforcement action
by the Division of Water Quality, in accordance with North
Carolina General Statute 143-215.6(a) to 143-215.6(c).
3. The issuance of this permit does not preclude the Permittee
from complying with any and all statutes, rules, regulations,
or ordinances which may be imposed by other government
agencies (local, state, and federal) which have jurisdiction.
6

4. In the event that the facilities fail to perform
satisfactorily, including the creation of nuisance conditions,
the Permittee shall take immediate corrective action,
including those as may be required by this Division, such as
the construction of additional or replacement stormwater
management systems.
5. The permit may be modified, revoked and reissued or terminated
for cause. The filing of a request for a permit modification,
revocation and reissuance or termination does not stay any
permit condition.
Permit issued this the 5 th day of May, 1997.
NORTH CAROLINA ENVIRONMENTAL
A. Preston Howard; Jr., P.E., Director
Division of Water Quality
By Authority of the Environmental Management commission
Permit Number SW7970117
7

MCAS, Commissary Redevelopment Project
Craven.County
Stormwater Permit No. SW7970117
Designer's Certification
I,
, as a duly
registered Professional Engineer in the State of North Carolina,
having been authorized to observe (periodically/weekly/full time)
the construction of the project,
for
(Project)
(Project Owner)
hereby state that to the best of my abilities, due care and
diligence was used in the observation of the project construction
such that the construction was observed to be built within
substantial compliance and intent of the approved plans and
specifications.
Signature
Registration Number
Date
F]

MCAS Cherry Point, NC, Commissary
Stormwater Management System
Operation and Maintenance Plan
General:
Maintenance of the MCAS Cherry Point, NC, Commissary stormwater system shall be the responsibility of the
Owner. The Owner shall designate an operator familiar with the components of this system. Routine inspections
shall be performed by the operator at regular intervals of approximately one month and at the time of heavy
rainfall events.
Inspections:
Elevations of the ditch shall be maintained as shown on the approved plans. Siltation or erosion
which alters those elevations shall be corrected by adding suitable soil or removing sediment as
necessary. The mean depth of the wet retention pond shall be maintained at depths as shown on
Drawings. Sediment shall be removed and disposed of properly when accumulation at the ditch
bottom reaches one foot in depth.
2. Any vegetation which inhibits proper performance of the ditch and stone berm shall also be
removed and disposed of properly.
3. The embankment of the ditch shall be checked regularly to insure that it is structurally sound and
has not been damaged by erosion or vehicular traffic. Any damage should be repaired
immediately.
4. All catch basins and outlet pipes shall be checked for debris that may clog or inhibit performance.
All debris and litter removed shall be disposed of properly.
tW ORD or nvironmental Engineer
ction of
the Commanding General

Quible
Quible & Associates, P.C.
ENGINEERS • ENVIRONMENTALISTS • PIANNERS
SINCE 1959
March 26, 1997
P.O. Drawer 870
f
...........-. _...._...... _......_.. _.... w, IGtly Hawk. NC 27949
I'" Phone: [phone]
WASH RECEPI OFFICE Fax: 9I9-261-1260
GTONF. Richard Quible. P.E.. R.L.S.
(t
H.W. Bill Gilbod. III, RE
MARII��
/ 7 1997' Joseph S Lassiter, C.E.P
Sean C. Boyle, RE
Mr. Bill Moore 0. E M.
NCDEH&NR,DWQ
943 Washington Square Mall E i
Washington, North Carolina 27889
Re: MICAS Cherry Point, N.C., Commissary Stormwater Management Plan Revisions and Narrative
Havelock, Craven County, NC
Dear Mr. Bill Moore,
As per our recent telephone conversation, additional calculations and revised plans are being submitted.
Included along with this letter is a packet of calculations and a plot of the site mentioned above. This letter
shall act as a narrative to describe the treatment of the stormwater runoff.
The areas draining into the stormwater swale via a series of underground stormwater piping includes die
existing pavement lying to the east of the proposed building to the amount of 25,059 Sq.Ft., the proposed
walk/patio south of the proposed building amounting to 17,390 Sq.Ft., the proposed pavement at 24,566
Sq.Ft. and the concrete dumpster pad amounting to 630 Sq.Ft. The sum of these areas was used to determine
the now, Q, using the Rational Method as demonstrated in the included calculations. It was assumed in this
calculation that all flow from the impervious surfaces flowed into he stormwater piping and to the ditch will
no losses. This allows for a conservative approach to the design of the rip -rap apron at the discharge end of
the stormwater piping. Please review the calculations for flow, velocity and apron sizing.
The stormwater Swale was designed to store the first inch of rain water runoff from the impervious surfaces
listed above. A check dam was placed at the downstream end to hold the first inch of runoff.
The 180 ft. long swale design has been modified by raising the middle 60 feet interval of the swale to an
elevation of 19 feet above M.S.L. This change acts to separate the Swale into three sections. The first section
occupying the first 60 feet of swale length and including the outlet apron has been designed as a sediment
basin. The second section, spanning the next 60 feet, has been designed to be a raised area planted with
suitable wetland plant species and will act as a sediment filter area. The wetland species and spacing have
been specified on the revised plan. These plants should be taken from existing on site stormwater runoff
areas utilizing wetland vegetation for treatment of stormwatcr runoff. The third section encompassing the
last 60 feel of the swale will act as a discharge basin and will be bordered on the south by a rip -rap berm.
The details of this drainage swale rip -rap apron and berm and table of appropriate wetland plant species are
illustrated on the drawing entitled Stromwaler Management Plan, MICAS Cherry Point, N.C. Commissary,
prepared by Quible & Associates, P.C.

Please contact at [phone] with any questions or need any further information.
Sincerely, e�eeeeeennep�
Quible and Associates, P.C. �O��k1 0( jPo
f1�
Sean C. Boyle, P.E.
u
Enc: As slated
CC: Gary McSmith - US Marine Air Corp
Dave Sterling - VIRTEXCO

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UNITED STATES MARINE CORPS
MARINE CORPS AIR STATION
PSC BOX W3
CHERRY POINT, NORTH CAROLINA 28535 3
North Carolina Department of Environment,
Health and Natural Resources
Division of Environmental Management
Washington Regional Office
Water Quality Section
Attn: Mr. William J. Moore
943 Washington Square Mall
Washington, North Carolina 27889
Dear Mr. Moore:
11000/
CE31MP13
LN
l 1 Mar 97
RECEIVED FFICE
WASHINGTON
MAR 13 1997
p,EM.
Enclosed is the stormwater permit application package for Defense Commissary Agency project
CE91MP13, "Commissary Additions and Alterations," at Marine Corps Air Station, Cherry Point.
A check for the permit fee of $385 was forwarded to you with an advance copy of the permit
application package by Quible and Associates, P.C.
If you have any further questions regarding this project, please contact Mr. Gary McSmith of the
Environmental Affairs Department at [phone]. You may also contact Mr. Joe Lassiter of
Quible and Associates, P.C. at [phone] if you wish to discuss the project specifics with the
design firm.
Sincerely,
RD
upervisc ry Environmental Engineer
By direction of
the Commanding General
Encl:
(1) Commissary Additions and Alterations Stormwater
Management Permit Application (2 Copies)
(2) Commissary Additions and Alterations Stormwater
Management Plan (1 Copy)

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? Appendices
M
Riprap (large stones of various sizes) is often used to prevent erosion at the ends
of culverts and other pipe conduits. It converts high -velocity, concentrated pipe
flow into low -velocity, open channel flow. Stone should be sized and the apron
shaped to protect receiving channels from erosion caused by maximum pipe exit
velocities. Riprap outlet structures should meet all requirements in Practice
Standards and Specifications: 6.41, outlet Stabilization Structure.
Several methods are available for designing riprap outlet structures. The method
presented in this section is adapted from procedures used by the USDA Soil
Conservation S ery ice. 0 utlet protection is provided by a level apron of sufficient
length and flare to reduce now velocities to nonerosive levels.
Design Procedure for
Thefollowing procedure uses two sets of design curves: Figure 8.06a is used
condtio sand Figure 8. 6b or maximum tailwater con
Riprap Outlet
for minimum tailwater
Protection
ditios.
the tailwater depth from channel characteristics below the
Step 1. Determine
pipe outlet for the design capacity of the pipe. If the tailwater depth is less than
tailwater condition. If it
half the outlet pipe diameter, it is classified minimum
is than half the pipe diameter, it is classified maximum condition. Pipes
have a
greater
that outlet onto wide flat areas with no defined channel are assumed to
flood stage elevations show
minimum tailwater condition unless reliable
otherwise.
Step 2. Based on the tailwater conditions determined in step 1, enter Figure
d5o size and minimum apron length
8.06a or Figure 8.06b and determine riprap
is median stone size in a well -graded riprap apron.
(La). The d50 size the
Step 3. Determine apron width at the pipe outlet, the apron shape, and the apron
width at the outlet end from the same figure used in Step 2.
Step 4. Determine the maximum stone diameter:
dmax = 1.5 x d50
Step 5. Determine the apron thickness:
Apron thickness = 1.5 x dmax
The apron thickness may be reduced to 1.5 x d5o when an appropriate filter fabric
is used under the apron.
Step 6. Fit the riprap apron to the site by making it level for the minimum length,
Le, from Figure 8.06a or Figure 8.06b. Extend the apron farther downstream
and along channel banks until stability is assured. Keep the apron as straight as
possible and align it with the now of the receiving stream. Make any necessary
alignment bends near the pipe outlet so that the entrance into the. receiving
stream is straight.
8.06.1

Some locations may require lining of the entire channel cross section to assure
stability.
It may be necessary to increase the size of riprap where protection of the channel
side slopes is necessary (Appendix 8.05). Where overfalls exist at pipe outlets
or flows are excessive, a lined stilling basin should be considered. Acceptable
design procedures for stilling basins are included in the list of references.
5.06.2

Appendices
99
N_
d
Co
a
Cr
0
v
Discharge (ft°Isec)
Curves may not be extrapolated.
Figure 8.06a Design of outlet protection protection from a round pipe flowing full, minimum tailwater condition (Tw < 0.5 diameter).
8.06.3

ez
50 1uu
Discharge (ft3/sec)
Curves may not be extrapolated.
Figure 8.06b Design of outlet protection from a round pipe flowing full, maximum tailwater condition (Tw 2 0.5 diameter).
8.06.4

Appendices
ESTIMATING RUNOFF
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.
The rational formula is:
Q = CiA
Rational Method
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, Tc, 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

El
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, 7%
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
Multi 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, TC. 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, Q (0/sec), by multiplying the previously
determined factors using the rational formula (Sample Problem 8.03a).
8.03.2

Appendices
Sample Problem 8.03a
Determination of peak runoff
rate using the rational
method.
Q=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 i 0-yr frequency storm
Solution:
(1) Drainage area: 20 acres (given)
(2) Determine runoff coefficient, C.
Calculate Weighted Average
Area C from Table 8.03a
Graded' 12 x 0.45 = 5.4
Woodland -a x 0.15 = J-2
20 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)0 = C(i)(A)
Q = 0.33(8.0)(20) = 52.8 cis; Use 53 cfs
'For graded areas use C value range for smooth, bare packed soil
(Table 8.03a).
8.03.3

a)
M
0
m
0
a
m
c
0
a
am
0
E
m
0 0
E
0
t
rn
H (ft)
Note:
Use nomograph Tc for natural basins with well-defined channels, for overland
flow on bare earth, and for mowed -grass roadside channels.
For overland flow, grassed surfaces, multiply Tc by 2.
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.
nin)
200
100
50
10
E
8.03.4

Appendices
ONE
�II� `� \; '\ .• SIN
IIIII��NII\�::.ME
NI�1
MORON
5 10 20
Minutes
Figure 8.03b Rainfall intensity duration curves —Wilmington.
2
u
0..
5 10 20
'Minutes
Figure 8.03c Rainfall intensity duration curves —Hatteras.
Hours
Duration
40 60 2 3 4 6 8 IZ 18 Z4
Hours
Duration
8.03.5

0
L
N
N
L
C
C
T
CC
N
C
f6
C
lL
5 10 20 40 60 2 3 4 6 8 12 18 24
Minutes Hours
Figure 8.03d Rainfall intensity duration curves —Greensboro.
20
15
10
8
0 6
0
L 4
y
N
L
C
C
2
T
y.
C
N I
0.8
m 0.6
C_
Ca 0.4
Cr
0.2
0.1 L
5
Duration
Fi
10 20 40 60 2 3 4 6 8 12 18 24
Minutes Hours
Duration
Figure 8.03e Rainfall intensity duration curves —Raleigh.
8.03.6