20100735 Ver 1_Stormwater Info_20100907

•
20100735
PRE- AND POST-DEVELOPMENT
STORMWATER MANAGEMENT CALCULATIONS
For
FIRST CHOICE EYECARE
PARCEL # 08324002
STALLINGS, NORTH CAROLINA
Prepared For:
First Choice Eye Care
c/o Kevin and Margaret Bigham
7800 Stevens Mill Road
Matthews, North Carolina 28104
Prepared By:
Amicus Engineering, PC
7714 Matthews-Mint Hill Road
Charlotte, North Carolina 28227
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032006 _
IN ..GINS.
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Original Submittal - September 2010
•
Amicus Engineering Project No: 17-10-033
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APPENDIX I CALCULATIONS

•
•
SEDIMENT TRAP CALCULATIONS
•
0
Project No: 17-10-033 Sheet No: of
Date: 06-16-10
Calcs Performed By: JLM
• Calcs Checked By: NRP
Amicus Ingineering Project Name: Proposed Professional Building at Lawyer's Road
Subject: Sediment Traps ST-1
OBJECTIVE:
Design sediment traps ST-1 to detain runoff during Phase III of the construction
process.
REFERENCES:
1. North Carolina Erosion and Sediment Control Handbook, 2008.
2. "Proposed Erosion Control Plan" by Amicus Engineering PC, 06/16/10.
3. Charlotte Mecklenburg Stormwater Design Manual, 1993.
TERMS:
Q10 = 10-year peak flow, (ft3/s)
C = runoff coefficient
i = rainfall intensity, (in)
A = drainage area, (acres)
t, = time of concentration, (min)
GIVEN/REQUIREMENTS:
Minimum design storm = 10-year
Drainage area for sediment trap ST-1 = 1.28 acres
TRAP DIMENSIONS ST-1
Height to spillway = 3.0 ft = 3.0 ft therefore ok.
Height of embankment = 5 ft = 5 ft therefore ok.
111/!
SS16
;a SEAL
032006
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GIN,
91 AS R 9
[Ref: 1]
[Ref: 2]
Exterior embankment side slope = 3:1 > 2:1 therefore ok.
Interior embankment side slope = 3:1 > 2:1 therefore ok.
Weir length = 6 feet > 4 feet therefore ok.
Spillway depth = 2.0 ft > 2.0 ft therefore ok.
Top width of embankment = 5 ft > 5 ft therefore ok.
CALCULATIONS:
[Ref: 1]
[Ref: 1]
[Ref: 1]
[Ref: 1]
[Ref: 1]
[Ref: 1]
[Ref: 1]
1. Determine if trap ST-1 is adequate to handle the 10-year storm during
construction.
Use rational method to determine peak flow based on conservatism and
drainage area being less than 200 acres [Ref: 3]
a. Assume maximum time of concentration is 5 minutes
Total drainage area = 1.28 acres
b. Determine rainfall intensity based on t,.
• - i = 7.03 inches/hour [Ref: 3, Table 2-3]
Amicus Ingineering
Project No: 17-10-033 Sheet No: of
Date: 06-16-10
Calcs Performed By: JLM
Calcs Checked By: NRP
Project Name: Proposed Professional Building at Lawyer's Road
Subject: Sediment Traps ST-1
c. Determine runoff coefficient, C
- 46% Impervious area C = 0.95
- 54% Smooth bare packed soil C = 0.60
- Weighted runoff coefficient C = 0.76
d. Determine peak flow
QO = CiA
Qio = (0.76)(7.03in / hr)(1.28acres) = 6.84cfs
e. Check sediment trap volume
Volume for Sediment Trnn ST-1
to
[Ref: 1, Table 8.03b]
[Ref: 1,-Table 8.03b]
[Ref: 3, Eq. 2-1]
Elevation [Ref. 2] Area [Ref: 2] Height Volume
682 5,674
1 5,179
681 4,683
1 4,216
680 3,749
1 3,316
679 2,883
1 2,486
678 2,089
1 1,729
677 1,368
Total basin volume to spillway (elev. 680.00 ft) = 7,531 ft'
- Minimum required basin volume = 3,600 ft3/acre [Ref: 1]
Total volume required = (3,600 ft3/acre)(1.28 acres) = 4,608 ft3
- 4,608 ft3 < 7,531 ft3 therefore ok.
f. Determine minimum surface area of sediment trap
- Minimum surface area = (435 sq. ft.) x (Q i o )
- (435 sq. ft.) x (6.84 cfs) = 2,976 sq. ft.
- 2,976 sq. ft.< 3,749 sq. ft. therefore ok.
[Ref: 1 ]
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Z:- ILI-r . I J
Practice Standards and Specifications
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Definition A small, temporary ponding basin formed by an embankment or excavation
to capture sediment.
Purpose To detain sediment-laden runoff and trap the sediment to protect receiving
streams, lakes, drainage systems, and protect adjacent property.
Conditions Where Specific criteria for installation of atemporary sediment trap areas follows:
Practice Applies • At the outlets of diversions, channels, slope drains, or other runoff
conveyances that discharge sediment-laden water.
• Below areas that are draining 5 acres or less.
• Where access can be maintained for sediment removal and proper
disposal.
In the approach to a stormwater inlet located below a disturbed area as
part of an inlet protection system.
• Structure life limited to 2 years.
A temporary sediment trap should not be located in an intermittent or
perennial stream.
Planning Select locations for sediment traps during site evaluation. Note natural
Considerations drainage divides and select trap sites so that runoff from potential sediment-
producing areas can easily be diverted into the traps. Ensure the drainage
areas for each trap does not exceed 5 acres. Install temporary sediment traps
before land disturbing takes place within the drainage area
Make traps readily accessible for periodic sediment removal and other
necessary maintenance. Plan locations for sediment disposal as part of trap
site selection. Clearly designate all disposal areas on the plans.
In preparing plans for sediment traps, it is important to consider provisions to
protectthe embankment from failure from storm runoff that exceeds the design
capacity. Locate bypass outlets so that flow will not damage the embankment.
Direct emergency bypasses to undisturbed natural, stable areas. If a bypass is
not possible and failure would have severe consequences, consider alternative
sites.
Sediment trapping is achieved primarily by setdin.g within a pool formed by
an embankment. The sediment pool may also be formed by excavation, or by
a combination of excavation and embankment. Sediment-trapping efficiency
is a function of surface area and inflow rate (Practice 6.61, Sediment Basin).
Therefore, maximize the surface area in the design. Because porous baffles
improve flow distribution across the basin, high length to width ratios are not
necessary to reduce short-circuiting and to optimize efficiency.
Because well planned sediment traps are key measures to preventing off
site sedimentation, they should be installed in the first stages of project
development-
Rev. 6/06
6.60.X
U
Design Criteria Summary TempornrySediment Trap
Primary Spillway: r Sjo?pillway
Maximum Drainage Area: 5 acre
Minimum Volume: 3600 cub feet per acre of disturbed area
Minimum Surface Area: 435 square feet per cfs of Q10 peak inflow
Minimum L/W Ratio: 2:1
Minimum Depth: 3.5 feet, 1.5 feet excavated below grade
Maximum Height: Weir elevation 3.5 feet above grade
Dewatering Mechanism: Stone Spillway
Minimum Dewatering Time: N/A
Baffles Required: 3
Storage capacity Provide a minimum volume of 3600 ft3/acre of disturbed
area draining into the basin. Required storage volume may also be determined
by modeling the soil loss with the Revised Universal Soil Loss Equation or
other acceptable methods. Measure volume to the crest elevation of the stone
spillway outlet.
Trap cleanout Remove sediment from the trap, and restore the capacity
to original trap dimensions when sediment has accumulated to one-half the
design depth.
Trap efficiency-The following design elements must be provided for
adequate trapping efficiency:
• Provide a surface area of 0.01 acres (435 square feet) per cfs based on the
10-year storm;
• Convey runoff into the basin through stable diversions or temporary slope
drains;
• Locate sediment inflow to the basin away from the dam to prevent short
circuits from inlets to the outlet;
• Provide porous baffles (Practice 6.65, Porous Baffles),
• Excavate 1.5 feet of the depth of the basin below grade, and provide
minimum storage depth of 2 feet above grade.
Embankment-Ensure that embankments for temporary sediment traps do
not exceed 5 feet in height. Measure from the center line of the original ground
surface to the top of the embankment- Keep the crest of the spillway outlet
a minimum of 1.5 feet below the settled top of the embankment. Freeboard
may be added to the embankment height to allow flow through a designated
bypass location. Construct embankments with a minimum top width of 5 feet
and side slopes of 2:1 or flatter. Machine compact embankments.
Excavation-Where sediment pools are formed or enlarged by excavation,
keep side slopes at 2:1 or flatter for safety.
Outlet section-Construct the sediment trap outlet using a stone section of
the embankment located at the low point in the basin. The stone section serves
two purposes: (1) the top section serves as a non-erosive spillway outlet for
flood flows; and (2) the bottom section provides a means of dewatering the
basin between runoff events.
Stone size-Construct the outlet using well-graded stones with a d50 size of 9
inches (Class B erosion control stone is recommended,) and a maximum stone
•
6.60.2 Rev. 6106

Practice Standards and Specifications
size of 14 inches. The entire upstream face of the rock structure should be
covered with fine gravel (NCDOT 9.57 or #5 wash stone) a minimum of 1 foot
thick to reduce the drainage rate.
Side slopes-Keep the side slopes of the spillway section at 2:1 or flatter.
To protect the embankment, keep the sides of the spillway at least 21 inches
thick.
Depth-The basin should be excavated 1.5 feet below grade.
Stone spillway height-The sediment storage depth should be a minimum of
2 feet and a maximum of 3.5 feet above grade.
Protection from piping-Place filter cloth on the foundation below the riprap
to prevent piping. An alternative would be to excavate a keyway trench across
the riprap foundation and up the sides to the height of the dam.
Weir lenb b and depth-Keep the spillway weir at least 4 feet long and sized
to pass the peak discharge of the I0-year storm (Figure 6.60a). A maximum
flow depth of six inches, a minimum freeboard of i foot, and maximum side
slopes of 2:1 are recommended. Weir length may be selected from Table 6.60a
shown for most site locations in North Carolina.
Cross-Section 124 min. of NCDOT #5
or #57 washed stone •
• 3600 cu ft/acre
'L
1 ?- filter
'? - a!?mm AEI-
fabric
Design settled
_vtop
214
Plan View
1.5' min.
mix
Overfill 6' for
settlement

_
---- --- Mi. -
a 5.
-
m
f iax
ll
4

2' to 3.5' f
1 .:

fi Iter 3'
fabric min.
Natural
Ground
Figure 6.60a Plan view and cross-section view of a temporary sediment trap.
Rev. 6106
L
?? ,,, ??,?"?¢. r•t,? .?J Emergency by-
4' 6" below
'n g settled top of
dam
6.60.3

• Table 6.60a
Design of Spillways
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Drainage Area Weir Length'
(acres) (ft)
1 4.0
2 6.0
3 8.0
4 10.0
5 12.0
' Dimensions shown are minimum.
Construction 1. Clear, grub, and strip the area under the embankment of all vegetation and
Specifications root mat. Remove all surface soil containing high amounts of organic matter,
and stockpile or dispose of it properly. Haul all objectionable material to the
designated disposal area.
2. Ensure that fill material for the embankment is free of roots, woody
vegetation, organic matter, and other objectionable material. Place the fill in
lifts not to exceed 9 inches, and machine compact it. Over fill the embankment
6 inches to allow for settlement.
3. Construct the outlet section in the embanlonent. Protect the connection
between the riprap and the soil from piping by using filter fabric or a keyway
cutofftrench between the riprap structure and soil.
• Place the filter fabric between the riprap and the soil. Extend the fabric
across the spillway foundation and sides to the top of the dam; or
• Excavate a keyway trench along the center line of the spillway foundation
extending up the sides to the height of the dam. The trench should be at
least 2 feet deep and 2 feet wide with 1:1 side slopes.
4. Clear the pond area below the elevation of the crest of the spillway to
facilitate sediment cleanout.
5. All cut and fill slopes should be 2:1 or flatter
6. Ensure that the stone (drainage) section of the embankment has a
minimum bottom width of 3 feet and maximum side slopes of 1:1 that extend
to the bottom of the spillway section.
7. Construct the minimum finished stone spillway bottom width, as shown
on the plans, with 2:1 side slopes extending to the top of the over filled
embankment. Keep the thickness of the sides of the spillway outlet structure
at a minimum of 21 inches. The weir must be level and constructed to
grade to assure design capacity.
8. Material used in the stone section should be a wel l-graded mixture of stone
with a d. size of 9 inches (class B erosion control stone is recommended) and
a maxirnum stone size of 14 inches. The stone may be machine placed and the
smaller stones worked into the voids of the larger stones. The stone should be
hard, angular, and highly weather-resistant.
9. Discharge inlet water into the basin in a manner to prevent erosion. Use
temporary slope drains or diversions with outlet protection to divert sediment-
laden water to the upper end of the pool area to improve basin trap efficiency
(References: Runoff Control Measures and Outlet Protection)-
6.60.4
Rev. 6106
[,CEF:1]
u
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8.03.6
U
Table 8.031
Value of Runoff Coefficien
(C) for Rational Formula
Land Use C Land Use C
t
Business: Lawns:
I
Downtown areas 0.70-0.95 Sandy soil, flat, 2% 0.05-0.10
Neighborhood areas 0.50-0.70 Sandy soil, ave., 0.10-0.15
2-7%
Residential: Sandy soil, steep, 0.15-0.20
Single-family areas 0.30-0.50 7%
Multi units, detached 0.40-0.60 Heavy soil, flat, 2% 0.13-0.17
Multi units, Attached 0.60-0.75 Heavy soil, ave., 0.18-0.22
Suburban 0.25-0.40 2-7%
Industrial: Heavy soil, steep,
7% 0.25-0.35
Light areas 0.50-0.80
Heavy areas 0.60-0.90 Agricultural land:
Parks, cemeteries 0.10-0.25 Bare packed soil
Smooth 0.3 -0.60
Playgrounds 0.20-0.35 Rough 0.20-0.50
Cultivated rows
Railroad yard areas 0.20-0.40 Heavy soil no crop 0.30-0.60
Heavy soil with
Unimproved areas 0.10-0.30 crop 020-0.50
Streets: Sandy soil no crop 0.20-0.40
Asphalt 0.70-0.95 Sandy soil with
Concrete 0.80-0.95 crop 0.10-0.25
Brick 0.70-0.85 Pasture
Heavy soil 0.15-0.45
Drives and walks 0.75-0.85 Sandy soil 0.05-0.25
Woodlands 0.05-0.25
Roofs 0.75-0.85
NOTE: The designer must use judgement to select the appropriate C
value within the range for the appropriate land use. Generally, larger
areas with permeable s oils, flat slopes, and dense vegetation should
have lowest C values. S maller areas with slowly permeable soils, steep
slopes, and sparse vege tation should be assigned highest C values.
Source: American Society of Civil Engineers
Rev. 6/06
0
IS Design Frequency
Design
Frequencies
3.5.1
Rainfall
Intensity
3.5.2

Table 3-3
Rainfall Intensities - Charlotte, North. Carolina
Storm Duration Rainfall Intensity(in /hr 1
Return Period (Years)
hours minutes 2 3 5 10 25 50 100
0 5 503 560
-0
•
6.30 7.0 8.21 9.00 9.92
6 4.78 5.33 6.02 6. 5 7.89 8.65 9.53
.7 4.55 5.09 5.76 6.49 7.59 8.32 9.17
8 4.34 4.88 5.53 6.26 7.31 8.03 8.84
9 4.16. 4.68 5.32 6.04 7.06 7.75 8-54
10 3.99 4.50 5.12 5.84 6-83 7.50 8.26
.15 3.33 3.79 4.35 5.03 5.87 6.46 7.11
16 3.23 3.67 4.22 4.89 5.72 6.29 6.92
17 3.13 3.57 4.10 4.77 5.57 6.13 6.74
18 .3.04 3.47 3.99 4.65 5.43 5.97 6.57
19 2.96 3.37. 3.89 4.53 .
5.30 5.83 6.41
20 2.88 3.29 3.79 4.43 5.17 5.69 6.26
21 2.80 3.20 3.70 4.32 5.05 5.56 6.12
22 2.73 3.12 3.61 4.23 4.94 5.44 5.98
23 2.66 3.05 3.53 4.14 4.83 5.32 5.85
24 2.60 2.98 3.45 4.05 4.73 '5.21 5.73
25 2.54 2.91 3.37 3.96 .4.63 5.10 5.61
26 2.48 2.85 3.30 3.88 4.54 5.00 5.50
27 2.43 2.79 3.23 3.81 4.45 4.90 5.39
28 2.38 2-73 3.17 3.73 4.36 4.81 5.29-
29 2.33 2.68 3.11. 3.66 4.28 4.72 5-19
30 2.28 .2.62 3.05 3.60 4-20 4.64 5.09

40
.1.90
2.20
2:57
3.05
3.56.
3.93 .
4.32
50 1.64 1.90 2.23 2.66 3.10 3.43 76
3
1 1.45 1.68 1.98 2.36 2:76. 3.05 .
3
34
2 0.88 1.03 1.21
; 1.45 1.70 1.89 .
2
06
3 0.65 - 0.76 ,
0.90 1.07 1.25 1.40 .
1
52
6 0.38' 0.44 0.53 0.62 0.73 0.82 .
0
89
12 0.22 0.26 . 0,31: 0.36 0.42 0.47 .
0
51
24 0.13 0.15 0.18 0.20 0.24 0.27 .
0.29
Taken from equation for IDF curve for Charl otte, N.C.
'Z ,n
.°icrr•im j'C'aCer• Ser-vire..,,
•
•
3.6 Rational Method ?-
Introduction When 'using the ratioral method some precautions should be considered.
3.6.1
• In determining the C value (land use) for the drainage area, hydrologic analysis
should take into account future tend use changes. Drainage facilities should
be designed for future land use c®nditions as specified in the County and City
Ind Use Plans.
• Since the rational method uses a composite C value for the entire drainage
area, if the distribution of land uses within the drainage basin will affect the
results of hydrologic analysis, then the basin should be divided into two or
more sub-drainage basins for analysis.
• The charts, graphs, and tables included in this section are given to assist the
engineer in applying the rational method. The engineer should use good
engineering judgement in applying these design aids and should make
appropriate adjustments when speck site characteristics dictate that these
adjustments are appropriate.
Runoff The' rational formula estimates the peak rate of runoff at any location in a
Equation watershed as a function of the drainage area, runoff coefficient, and mean rainfall
3.6.2 intensity for a duration equal to the time of concentration (the time required for
water to flow from the most remote point of the basin to the location being
analyzed). The rational formula is expressed as follows:
Q = ClA - 13.1)
Where: Q = maximum rate of runoff (cfs)
C = runoff.coefficient representing a ratio of runoff to rainfall
1 = average rainfall intensity for a duration equal to the time of
concentration (in/hr)
Infrequent
Storms
3.6.3
A = drainage area contributing to the' design location (acres)
The coefficients given in Table 3-5 ';are applicable for storms of 2-yr to 10-yr
frequencies. Liss:n.;g?e? ;dens.)i?r:sXrrsj:::gre?:npcffrtron:;z
i?, #e t vj o€f < Fr `°t t- 1 a`uQ?# i`: 6%::: The adjustment of the rational
method for use with major storms'can be made by multiplying the right side of
the rational formula by a frequency factor C;. The rational formula now becomes:
Q = CC,IA 13.2)
3-11

SKIMMER SEDIMENT TRAP
CALCULATIONS
•
0
Project No: 17-10-033 Sheet No: of
Date: 06-16-2010
Calcs Performed By: JLM
Calcs Checked By: NRP
Amicus engineering Project Name: Proposed Professional Building at Lawyer's Road
Subject: Skimmer Sediment Trap
OBJECTIVE:
Design Skimmer Sediment Trap SST-1 to contain 10-year peak runoff. The sediment
basin shall be a skimmer type sediment structure as per the North Carolina Erosion
and Sediment Control Handbook. The sediment basin shall be designed for Phase II
development conditions.
THEORY/DESIGN CONSIDERATIONS:
The structure was designed as a skimmer type sediment trap based on the drainage
area being less than 5 acres.
REFERENCES:
1. North Carolina Erosion and Sediment Control Handbook, 2008.
2. "Phase II Erosion Control Plan; Valencia Subdivision," by Amicus Engineering
PC, 06/16/10.
3. Charlotte Mecklenburg Storm Water Design Manual, 19 93.
4. Faircloth Skimmer Sizing (www.fairclothskimmer.com/skimmer.html)
TERMS: C
Qio_ 10-year peak flow, (ft3/s)
3
QP -minimum flow through principal spillway, (ft /s)
?_ • p ti . ?

Qe = minimum flow through emergency spillway, (ft3/s) _
SEAL
cfs = cubic feet per second - - 0 3 2 0 0 6 =
C = runoff coefficient •• F ?? 4
i = rainfall intensity, (in/hr)
)
P
tia
A =drainage area,(acres) l AS'R. Y

GIVEN/REQUIREMENTS: ob-16-16
Minimum design storm = 10-year [Ref: 1 ]
CALCULATIONS FOR SKIMMER SEDIMENT TRAP SST-1
1. Basin Dimensions
Height of embankment = 5 ft < 5 ft therefore ok. [Ref: 1 ]
Exterior embankment side slope = 3:1 > 2:1 therefore ok. [Ref: 2]
Interior embankment side slope = 3:1 > 2:1 therefore ok. [Ref: 2]
Length to width ratio > 2:1 therefore ok. [Ref: 1]
Spillway side slope = 3:1 therefore ok. [Ref: 1]
Spillway depth = 2.0 ft > 2.0 ft therefore ok. [Ref: 2]
Top width of embankment = 8 ft therefore ok. [Ref: 1 ]
0
•
Project No: 17-10-033 Sheet No: of
;. ? Date: 06-16-2010
Calcs Performed By: JLM
Calcs Checked By: NRP
Amim Ingineering Project Name: Proposed Professional Building at Lawyer's Road
Subject: Skimmer Sediment Trap
2. Determine peak flow for basin drainage area
- Use rational method to determine peak flow based on conservatism and
drainage area being less than 200 acres [Ref: 3]
a. Determine time of concentration
- t,, = 5 minutes [Ref: 3, Fig. 3-1]
- conservative assumption
b. Determine rainfall intensity based on t,
- do = 7.03 inches/hour [Ref: 3, Table 3-3]
c. Determine runoff coefficient, C
- Total drainage area = 1.58 acres
o Assume smooth bare packed soil, C = 0.60 [Ref: 1, Table 8.03b]
d. Determine 10-year peak flow
Q10 = CiA
•
Q10 = (0.60)(7.03in / hr)(1.58acres) = 6.66 ft3 Is [Ref: 3, Eq. 3. 1]
3. Determine Basin Volume
Vnlrlme fnr gkimmPr QPriimant Tro„ QQT 1
Elevation (ft)
[Ref: 21 Area (ft)
[Ref: 2] Height (ft)v Volume (ft )
679 23,503
1 22,254
678 21,005
1
17,398
677 13,791
1 10,149
676
T 6,507
u. i Vlat vaJUl VV1LL111G LL) pinicipic splnway = 4Y,6u1 n-
b. Determine required basin volume
Minimum required basin volume = 3,600 ft3/acre [Ref: 1]
Total volume required = (3,600 ft3/acre)(1.58 acres) = 5,688 ft3
- 5,688 ft3 < 49,801 ft3 therefore ok.
c. Determine minimum surface area of skimmer sediment trap
- Minimum surface area = (435 sq. ft.) x (Qlo )
_ (435 sq. ft.) x (6.66 cfs) = 2,897 sq. ft.
2,897 sq. ft.< 23,503 sq. ft. therefore ok.
[Ref: 1 ]
•
Project No: 17-10-033 Sheet No: of
Date: 06-16-2010
Calcs Performed By: JLM
Calcs Checked By: NRP
Amicus engineering Project Name: Proposed Professional Building at Lawyer's Road
Subject: Skimmer Sediment Trap
d. Determine if actual surface area of skimmer sediment trap is adequate for the
50-yr storm event
Q, = GA
•
Q50 = (0.60)(9.00in/ hr)(1.58acres) = 8.53 ft3Is
- Minimum surface area = (435 sq. ft.) x (Q50)
- (435 sq. ft.) x (8.53 cfs) = 3,711 sq. ft.
- 3,711 sq. ft.< 23,503 sq. ft. therefore ok.
4. Design emergency spillway
a. Determine required capacity for emergency spillway
- Qe = Qio = 6.66 cfs
- Elevation of bottom of spillway = 679.00 ft
- Assume excavated soil in spillway is erosion resistant
- Bottom width of spillway = 12.0 ft
- Depth of emergency spillway = 2.0 ft
- Stage = 0.69 ft < 2.0 ft therefore ok.
5. Design Skimmer
a. Required water storage volume = 5,688 ft3
b. Desired dewatering time = 1 days
c. A 2.0-inch skimmer is required
d. A 0.9-inch orifice radius is required
e. A 1.8-inch orifice diameter is required
[Ref: 3, Eq. 3.1]
[Ref: 1]
[Ref: 1 ]
[Ref: 1, Table 8.07c]
[Ref: 1, Table 8.07c]
[Ref: 4]
[Ref: 4]
[Ref: 4]
c:

LI
101
Design Criteria Summary:
Temporary Sediment Trap
Primary Spillway: Stone Spillway
Maximum Drainage Area: 5 acres
Minimum Volume: 3600 cubic feet per acre of disturbed area
Minimum Surface Area: 435 square feet per cfs of Q,0 peak inflow
Minimum L/W Ratio: 2:1
Minimum Depth: 3.5 feet, 1.5 feet excavated below grade
Maximum Height: Weir elevation 3.5 feet above grade
Dewatering Mechanism: Stone Spillway
Minimum Dewatering Time: N/A
Baffles Required: 3
Storage capacity-Provide a minimum volume of 3600 ft-/acre of disturbed
area draining into the basin. Required storage volume may also be determined
by modeling the soil loss with the Revised Universal Soil Loss Equation or
other acceptable methods. Measure volume to the crest elevation of the stone
spillway outlet.
Trap cleanout-Remove sediment from the trap, and restore the capacity
to original trap dimensions when sediment has accumulated to one-half the
design depth.
•
Trap efficiency-The following design elements must be provided for
adequate trapping efficiency:
• Provide a surface area of 0.01 acres (435 square feet) per cfs based on the
10-year storm;
• Convey runoff into the basin through stable diversions or temporary slope
drains;
• Locate sediment inflow to the basin away from the dam to prevent short
circuits from inlets to the outlet;
• Provide porous baffles (Practice 6.65, Porous Baffles);
• Excavate 1.5 feet of the depth of the basin below grade, and provide
minimum storage depth of 2 feet above grade.
Embankment-Ensure that embankments for temporary sediment traps do
not exceed 5 feet in height. Measure from the center line of the original ground
surface to the top of the embankment. Keep the crest of the spillway outlet
a minimum of 1.5 feet below the settled top of the embankment. Freeboard
may be added to the embankment height to allow flow through a designated
bypass location. Construct embankments with a minimum top width of 5 feet
and side slopes of 2:1 or flatter. Machine compact embankments.
Excavation-Where sediment pools are formed or enlarged by excavation,
keep side slopes at 2:1 or flatter for safety.
Outlet section--Construct the sediment trap outlet using a stone section of
the embankment located at the low point in the basin. The stone section serves
two purposes: (1) the top section serves as a non-erosive spillway outlet for
flood flows; and (2) the bottom section provides a means of dewatering the
basin between runoff events.
Stone size-Construct the outlet using well-graded stones with a d50 size of 9
inches (Class B erosion control stone is recommended,) and a maximum stone
40 6.60.2 Rev. 6/06

Table 8.07c
Design Table for Vegetated Spillways Excavated in Erosion Resistant Soils
(side slopes-3 horizontal:1 vertical)
9
Discharge Slope Range Bottom
Sta
e
Q
CFS Minimum
Percent Maximum
Percent Width
Feet g
Feet
15 3.3 12.2
3.5 18.2 12 ) 69
3.1 8.9
20 3.2 13.0 12 .81
3.3 17.3 16 .70
2.9 7.1 8 1.09
25 3.2 9.9 12 .91
3.3 13.2 16 .79
3.3 17.2 20 .70
2.9 6.0 8 1.20
30 3.0 8.2 12 1.01
3.0 10.7 16 .88
3.3 13.8 20 .78
2.8 5.1 8 1.30
2.9 6.9 12 1.10
35 3.1 9.0 16 .94
3.1 11.3 20 .85
3.2 14.1 24 .77
2.7 4.5 8 1.40
2.9 6.0 12 1.18
40 2.9 7.6 16 1.03
3.1 9.7 20 .91
3.1 11.9 24 .83
2.6 4.1 8 1.49
2.8 5.3 12 1.25
45 2.9 6.7 16 1.09
3.0 8.4 20 .98
3.0 10.4 24 _89
2.7 3.7 8 1.57
2.8 4.7 12 1.33
50 2.8 6.0 16 1.16
2.9 7.3 20 1.03
3.1 9.0 24 .94
2.6 3.1 8 1.73
2.7 3.9 12 1.47
60 2.7 4.8 16 1.28
2.9 5.9 20 1.15
2.9 7.3 24 1.05
3.0 8.6 28 .97
2.5 2.8 8 1.88
2.6 3.3 12 1.60
70 2.6 4.1 16 1.40
2.7 5.0 20 1.26
2.8 6.1 24 1.15
2.9 7.0 28 1.05
2.5 2.9 12 1.72
80 2.6 3.6 16 1.51
2.7 4.3 20 1.35
Discharge Slope Range Bottom
St
Q

CFS Minimum

Percent Maximum

Percent Width

Feet age
Feet
2.8 5.2 24 1.24
80 2.8 5.9 28 1.14
2.9 7.0 32 1.06
2.5 2.6 12 1.84
2.5 3.1 16 1.61
90 2.6 3.8 20 1.45
2.7 4.5 24 1.32
2.8 5.3 28 1.22
2.8 6.1 32 1.14
2.5 2.8 16 1.71
2.6 3.3 20 1.54
100 2.6 4.0 24 1.41
2.7 4.8 28 1.30
2.7 5.3 32 1.21
2.8 6.1 36 1.13
2.5 2.8 20 1.71
2.6 3.2 24 1.56
120 2.7 3.8 28 1.44
2.7 4.2 32 1.34
2.7 4.8 36 1.26
2.5 2.7 24 1.71
2.5 3.2 28 1.58
140 2.6 3.6 32 1.47
2.6 4.0 36 1.38
2.7 4.5 40 1.30
2.5 2.7 28 1.70
2.5 3.1 32 1.58
160 2.6 3.4 36 1.49
2.6 3.8 40 1.40
2.7 4.3 44 1.33
2.4 2.7 32 1.72
180 2.4 3.0 36 1.60
2.5 3.4 40 1.51
2.6 3.7 44 1.43
2.5 2.7 36 1.70
200 2.5 2.9 40 1.60
2.5 3.3 44 1.52
2.6 3.6 48 1.45
2.4 2.6 40 1.70
220 2.5 2.9 44 1.61
2.5 3.2 48 1.53
2.5 2.6 44 1.70
240 2.5 2.9 48 1.62
2.6 3.2 52 1.54
260 2.4 2.6 48 1.70
2.5 2.9 52 1.62
280 2.4 2.6 52 1.70
300 2.5 2.6 56 1.69
Example of Use
Given: Discharge, Q = 87 c.f.s. Spillway slope, Exit section (from profile) = 4%
Find: Bottom width and Stage in Spillway
Procedure: Enter table from left at 90 c.f.s. Note that Spillway slope (4%) falls within slope ranges corresponding to
bottom widths of 24, 28, and 32 ft. Use bottom width, 32 ft, to minimize velocity. State in Spillway will be
1.14 ft.
Note: Computations based on: Roughness coefficient, n = 0.40. Maximum velocity 5.50 ft. per sec.
8.07.8 Rev. 6/06

•
Calculate Skimmer Size
Basin Volume in Cubic Feet -5,688 Cu.Ft Skimmer Size 2.0 Inch
Days to Drain* 2 Days Orifice Radius 0.9 Inch[es]
`In NC assume 3 days to drain Orifice Diameter 1.8 Inch[es]
0

Practice Standards and Specifications
•

Definition A small, temporary ponding basin formed by an embankment or excavation
to capture sediment-
Purpose To detain sediment-laden runoff and trap the sediment to protect receiving
streams, lakes, drainage systems, and protect adjacent property.
Conditions Where Specific criteria for installation of a temporary sediment trap are as follows:
Practice Applies • At the outlets of diversions, channels, slope drains, or other runoff
conveyances that discharge sediment-laden water.
• Below areas that are draining 5 acres or less.
• Where access can be maintained for sediment removal and proper
disposal.
- In the approach to a stormwater inlet located below a disturbed area as
part of an inlet protection system.
• Structure life limited to 2 years.
A temporary sediment trap sibould not be located in an intermittent or
perennial stream.
is
Planning Select locations for sediment traps during site evaluation- Note natural
Considerations drainage divides and select trap sites so that runoff from potential sediment-
producing areas can easily be diverted into the traps. Ensure the drainage
areas for each trap does not exceed 5 acres. Install temporary sediment traps
before land disturbing takes place within the drainage area
Make traps readily accessible for periodic sediment removal and other
necessary maintenance. Plan locations for sediment disposal as part of trap
site selection. Clearly designate all disposal areas on the plans-
In preparing plans for sediment traps, it is important to consider provisions to
protectthe embankmentfrom failure from storm runoff that exceeds the design
capacity. Locate bypass outlets so that flow will not damage the embankment.
Direct emergency bypasses to undisturbed natural, stable areas. If a bypass is
not possible and failure would have severe consequences, consider alternative
sites.
Sediment trapping is achieved primarily by settling within a pool formed by
an embankment- The sediment pool may also be formed by excavation, or by
a combination of excavation and embankment. Sediment-trapping efficiency
is a function of surface area and inflow rate (Practice 6.61, Sediment ,basin).
Therefore, maximize the surface area in the design. Because porous baffles
improve flow distribution across the basin, high length to width ratios are not
necessary to reduce short-circuiting and to optimize efficiency-
E
Because well planned sediment traps are key measures to preventing ofd
site sedimentation, they should be installed in the first stages of project
development.
Rev. 6106 6.60.1

0
Design Criteria Summary:
Primary Spillway:
Maximum Drainage Area:
Minimum Volume:
Minimum Surface Area:
Minimum L/W Ratio:
Minimum Depth:
Maximum Height:
De.watering Mechanism:
Minimum Dewatering Time:
Baffles Required:
Temporary Sediment Tray)
Spillway
?5 acre
3600 cub feet per acre of disturbed area
435 square feet per cfs of Quo peak inflow
2:1
3.5 feet, 1.5 feet excavated below grade
Weir elevation 3.5 feet above grade
Stone Spillway
N/A
3
Storage capacity Provide a minimum volume of 3600 ft3/acre of disturbed
area draining into the basin. Required storage volume may also be determined
by modeling the soil loss with the Revised Universal Soil Loss Equation or
other acceptable methods. Measure volume to the crest elevation of the stone
spillway outlet.
Trap clean out-Remove sediment from the trap, and restore the capacity
to original trap dimensions when sediment has accumulated to one-half the
design depth.
Trap efficiency-The following design elements must be provided for
adequate trapping efficiency:
- Provide a surface area of 0.01 acres (435 square feet) per cfs based on the
10-year storm;
•
Convey runoff into the basin through stable diversions or temporary slope
drains;
Locate sediment inflow to the basin away from the dam to prevent short
circuits from inlets to the outlet;
- Provide porous babies (Practice 6.65, Porous Bafes);
- Excavate 1.5 feet of the depth of the basin below grade, and provide
minimum storage depth of 2 feet above grade.
Embankment-Ensure that embankments for temporary sediment traps do
not exceed 5 feet in height. Measure from the center line ofthe original ground
surface to the top of the embankment. Keep the crest of the spillway outlet
a minimum of 1.5 feet below the settled top of the embankment. Freeboard
may be added to the embankment height to allow flow through a designated
bypass location- Construct embankments with a minimum top width of 5 feet
and side slopes of 2:1 or flatter. Machine compact embankments-
Excavation-Where sediment pools are formed or enlarged by excavation,
keep side slopes at 2:1 or flatter for safety-
Outlet section-Construct the sediment trap outlet using a stone section of
the embankment located at the low point in the basin. The stone section serves
two purposes: (1) the top section serves as a non-erosive spillway outlet for
flood flows; and (2) the bottom section provides a means of dewatering the
basin between runoff events.
•
6.60.2
Stone size-construct the outlet using well-graded stones with a d50 size of 9
inches (Class B erosion control stone is recommended,) and a maximum stone
RCV. 6106

Practice Standards and Specifications

E
size of 14 inches. The entire upstream face of the rock structure should be.
covered with fine gravel (NCDOT #57 or #5 wash stone) a minim um of 1 foot
thick to reduce the drainage rate.
Side slopes-Keep the side slopes of the spillway section at 2:1 or flatter.
To protect the embankment, keep the sides of the spillway at least 21 inches
thick.
Depth-The basin should be excavated 1.5 feet below grade.
Stone spillway height-The sediment storage depth should be a minimum of
2 feet and a maximum of 3.5 feet above grade.
Protection from piping Place filter cloth on the foundation below the riprap
to prevent piping. An alternative would be to excavate a keyway trench across
the riprap foundation and up the sides to the height of the dam.
Weir length and depth-Keep the spillway weir at least 4 feet long and sized
to pass the peal, discharge of the I0-year storm (Figure 6.60a)_ A maximum
flow depth of six inches, a minimum freeboard of 1 foot, and maximum side
slopes of 2:1 are recommended. Weir length may be selected from Table 6.60a
shown for most site locations in North Carolina.
Cross-Section 12` min. of NMOT #5
or #57 washed stone
3600 cu ft/acre
rl
filter
fabric
Design settled
,gip %
---- -

---
T -- zn 5'

...... s : Max
2' to 3.5' ikT . fi;
.
------ .
------
Plan View
--------A ----------------------
1.5' min.
s?
5'
?'•
-11
Overfill 6° for
r settlement
MEMO-
'r Emergency by-
4',af pass 6 below
w
min.1~5 settled top of
...:: s' 1?j^ dam
filter 31
fabric min.
Figure 6.60a Plan. view and cross-section view of a temporary sediment trap.
Rev. 6106
Natural
Ground
6.60.3
F)Z-,- F>l)

• Table 6.60a
Design of Spillways
Drainage Area Weir Length'
(acres) (ft)
1 4.0
2 6.0
3 8.0
4 10.0
5 12.0
'Dimensions shown are minimum.
Construction 1. Clear, grub, and strip the area under the embankment of all vegetation and
Specifications root mat. Remove all surface soil containing high amounts of organic matter,
and stockpile or dispose of it properly. Haul all objectionable material to the
designated disposal area.
2. Ensure that fill material for the embankment is free of roots, woody
vegetation, organic matter, and other objectionable material. Place the fill in
lifts not to exceed 9 inches, and machine compact it. Over fill the embankment
6 inches to allow for settlement.
3. Construct the outlet section in the embankment. Protect the connection
between the riprap and the soil from piping by using filter fabric or a keyway
cutoff trench between the riprap structure and soil.
• Place the filter fabric between the riprap and the soil. Extend the fabric
across the spillway foundation and sides to the top of the darn; or
. • Excavate a keyway trench along the center line of the spillway foundation
extending up the sides to the height of the dam- The trench should be at
least 2 feet deep and 2 feet wide with 1:1 side slopes.
4. Clear the pond area below the elevation of the crest of the spillway to
facilitate sediment cleanout_
S. All cut and fill slopes should be 2:1 or flatter.
b. Ensure that the stone (drainage) section of the embankment has a
minimum bottom width of 3 feet and maximum side slopes of 1:1 that extend
to the bottom of the spillway section-
7. Construct the minimum finished stone spillway bottom width, as shown
on the plans, with 2:1 side slopes extending to the top of the over filled
embankment. Keep the thickness of the sides of the spillway outlet structure
at a minimum of 21 inches. The weir must be level and constructed to
grade to assure design capacity.
8. Material used in the stone section should be awell-graded mixture of stone
with a d50 size of 9 inches (class B erosion control stone is recommended) and
a maximum stone size of 14 inches. The stone may be machine placed and the
smaller stones worked into the voids of the larger stones. The stone should be
hard, angular, and highly weather-resistant-
9. Discharge inlet water into the basin in a manner to prevent erosion. Use
temporary slope drains or diversions with outlet protection to divert sediment-
laden water to the upper end of the pool area to improve basin trap efficiency
(References: Runoff Control Measures and Outlet Protection).
•
6.60.4
Rev. 6106
[,(EF:11
9

r1
?J
8.03.6

Table 8.0
Value of Runoff Coeffick
(C) for Rational Formi
3b Land Use C Land Use C
ant
ila 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., .
0.10-0.15

Residential: 2-7%

Single-family areas 0
30-0
50 Sandy soil, steep, 0.15-0.20
.
.
Multi units, detached 0.40-0.60 7%
Heavy soil
flat
2%
0
13-0
17
Multi units, Attached 0.60-0.75
Suburb ,
,
Heavy soil, ave-, .
.
0.18-022
an 025-0.40 2-7%
Industrial: Heavy soil, steep,
Light areas 0.50-0.80 7% 0-25-0.35
Heavy areas 0.60-0.90 Agricultural land:
Parks, cemeteries 0.10-0.25 Bare packed soil
Smooth 0.3 -0.60
Playgrounds 0.20-0.35 Rough 0-20-0.50
Cultivated rows
Railroad yard areas 0.20-0.40 Heavy soil no crop 0.30-0.60
Unimproved areas 0-10-0.30 Heavy soil with
crop 0.20-0.50
Streets: Sandy soil no crop 020-0.40
Asphalt 0-70-095 Sandy soil with
Concrete 0.80-0.95 crop 0.10-0.25
Brick 0.70-0.85 Pasture
Heavy soil 0.15-0.45
Drives and walks 0.75-0.85 Sandy soil 0.05-0.25

Roofs Woodlands 0.05-0.25
0.754185
NOTE: The designer must use judgement 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
stee
,
p
slopes, and sparse vegetation should be assigned highest C values-
Source: American Society of Civil Engineers
Rev. 6106
IS Design Frequency .
Design
• Frequencies
3.5.1
Rainfall
Intensity
3.5.2

•

Table 3-3
Rainfa ll lntensiiies - Cha rlotte, North.Carolina
Storm Duration Rainfall Intensity(in /hr )
Re turn Period (Years)
hours minutes 2 3 5 10 25 50 100
0 5 5.03 5.60 6.30 7.0? 8.21 9.00 9
92
6 4.78 5.33 6.02. 6 75 7.89 8.65 .
9
53
.7 4.55 5.09 5.76 6.49 7.59 8.32 _
9
17
8 4.34 4.88 5.53 6.26 7.31 8.03 .
8
84
9 4.16 . 4.68 5.32 6.04 7.06 7.75 .
8
54
10 3.99 4.50 5.12 5.84 6.83 7.50 .
8
26
15 3.33 3.79 4.35' 5.03 5.87 6.46 .
7
11
16 3.23 3.67 4.22 4.89 5.72 6.29 .
6
92
17 3.13 3.57 4.10 4.77 5.57 6.13 .
6
74
18 .3.04 3.47 3.99 4.65 5.43 5.97 .
6
57
19 2.96 3.37 . 3.89 4.53 ,
5.30 5.83 .
6
41
20 2.88 3.29 3.79 4.43 5.17 5.69 .
6
26
21 2.80 3.20 3.7Q 4.32 5.05 5.56 .
6
12
22 2.73 3.12 3.61 4.23 4.94 5.44 .
-5
98
23 2.66 3.05 3.53 4.14 4.83 :5.32 .
5
85
24 2:60 2.98 3.45 4.05 4.73 '5-21 .
5
73
25 2.54 2.91 3.37 3.96 .4.63 5.10 .
5
61
26 2.48 2.85 3.30 3.88 4.54 5.00 .
5
50
27 2.43 2.79 3.23 3.81 4.45 4.90 .
5
39
28 2.38 2.73
. 3.17 3.73 4.36 4.81 .
5
29-
29 2.33 - 2.
68 3.11: 3.66 4.28 4.72 .
5
19
30 2.28 .2.62 3.05 3.60 4.20 4.64 .
5
09

40
.1.90
2.20 .
2:57
3.05
3.56.
3.93 .
.
4
32

1 50 1.64 1.90 2.23 2.66 3.10 3.43 .
3.76

2 1.45 1.68 1.98 2.36 2:76. 3.05 3.34

3 0.88 1.03 1.21; 1.45 1.70 1.89 2.D6

6 0.65
' 0.76 0.90 1.07 1.25 1.40 1.52

12 0.38 0.44 0.53 0.62 . 0.73 0.82 0.89

24 0.22 0.26 . 0,3T 0.36 0.42 0.47 0.51
D.13 0.15 0.18 0.20 0.24 0.27 0.29
Taken from equation for O F curve for Charlotte, N.C.
t

•
3.6 Rational Method
Introduction When 'using the rational method some precautions should be considered.
3.6.1
• In determining the C value (land use) for the drainage area, hydrologic analysis
should take into account future iand use changes. Drainage facilities should
be designed for future land use conditions as specified in the County and City
Land Use Plans.
Since the rational method uses a composite C value for the entire drainage
area, if the distribution of land uses within the drainage basin will affect the
results of hydrologic analysis, then the basin should be divided into two or
more sub-drainage basins for analysis.
• The charts, graphs, and tables included in this section are given to assist the
engineer in applying the rational method. The engineer should use good
engineering judgement in applying these design aids and should make
appropriate adjustments when specific site characteristics dictate that these
adjustments are appropriate.

Runoff The' rational formula estirnates ths:
E tion peak raze of runoff at any location in a
qua watershed as a function of the drainage area, runoff coefficient, and mean rainfall
3.6.2 intensity for a duration equal to the time of concentration (the time required for
water to flow from the most remote point of the basin to the location being
analyzed). The rational formula is expressed as follows:
Q = CIA - (3.1)
Where: Q = maximum rate of runoff (cfs)
C = runoff.coefficient representing a ratio of runoff to rainfall
1 = average rainfall intensity for a duration equal to the time of
concentration (in/hr)
A = drainage area contribuiing to the" design location (acres)
1]
Infrequent
Storms
3.6.3
The coefficients given in Table 3-5'
frequencies. Liss`#re7>miYf'ar:l
re applicable for storms of 2-yr to 10-yr
............ ..
:: :?,-:~>:-?---t:t: .+?+Axauy??r;;t i ne aaaustment of the rational
method for use with major storms can be made by multiplying the right side of
the rational formula by a frequency factor C;. The rational formula now becomes:
Q = CC,IA (3.2)
3-11
0
HYDROLOGIC
EVALUATION
•
0
U
•
•
Project No: 17-10-033 Sheet No: of
Date: 09-01-10
Calcs Performed By: JLM
Calcs Checked By: NRP
Amicus ingineering Project Name: Proposed Professional Building at Lawyer's Road
Subject: Hydrologic Evaluation
OBJECTIVE:
Determine the overall hydrologic conditions, both pre-developed and post-developed,
for the proposed professional building at Lawyer's Road.
DESIGN CONSIDERATIONS:
This site requires structures to control and maintain water quality and runoff volume.
Because of the lot size and the owner's need to maximize usable space, there will be
two water quality structures to provide the treatment portion of the storm water
system. These structures will be designed to treat and control the 1St inch for water
quality as well as maintain pre-developed flow conditions for the 1-year, 24-hour, 10-
year, 6-hour, the 25-year, 6-hour, and the 50-year, 24-hour storm events. The
structures will also be designed to accommodate and safely pass the 50-year, 24-hour
storm event.
REFERENCES:
1. City of Stallings Post Construction Ordinance for Phase II Stormwater
2. "Manual of Storm Water Best Management Practices," by The North Carolina
Department of Environment and Natural Resources, 2007.
3. "Precipitation-Frequency Atlas of the United States," National Oceanic and
Atmospheric Administration Atlas 14, Volume 2, Version 3.
4. "Pre-Developed Drainage Map," by Amicus Engineering, 06/16/2010.
5. Design Hydrology and Sedimentology for Small Catchments, by C.T. Haan,
1994.
6. HEC-HMS version 3.3 Developed by the Army Corps of Engineers, 2008.
7. Web Soil Survey
8. "Post-Developed Drainage Map," by Amicus Engineering, 09/01/2010.
9. Charlotte Mecklenburg Storm Water Design Manual, 1993.
TERMS:
P,, = x-year 24-hour rainfall, (in)
A = drainage area, (acres)
n = manning's coefficient
L = flow length, (ft)
S = slope, (ft)
v = velocity, (ft/s)
tL = SCS lag time, (hrs)
CN = SCS curve number
QX = x-year flow, (ft3/s)
a = surface flow coefficient
t, = time of concentration, (hrs)
"'
C, A
SEAL
032006 -
4/G1N???"
/??if1111111??\?
07- 01-10
•
E
Amicus engineering
Project No: 17-10-033 Sheet No: of
Date: 07-21-10
Calcs Performed By: JLM
Calcs Checked By: NRP
Project Name: Proposed Professional Building at Lawyer's Road
Subject: Hydrologic Evaluation
GIVEN/REQUIREMENTS:
Treat and control runoff for the 1" inch [Ref: I]
Maintain pre-developed runoff rates for 1-yr, 24-hr storm [Ref: 1]
Maintain pre-developed runoff rates for 10-yr, 6-hr storm [Ref: 1 ]
Maintain pre-developed runoff rates for 25-yr, -hr storm [Ref: 1 ]
Safely pass the 50-year, 24-hour storm [Ref: 2]
Minimum freeboard = 6-inches [Ref: 2]
P 1 = 2.79 inches [Ref 3]
P2 = 3.12 inches [Ref: 9]
Plo = 3.55 inches [Ref: 3]
P25 = 4.20 inches [Ref: 3]
P50 = 6.54 inches [Ref: 3]
Soil type = Bab, ScA [Ref: 7]
Soil Hydrologic Group = B, C [Ref: 7]
I. PRE-DEVELOPED FLOW CALCULATIONS:
1. Calculate composite Curve Number and Time of Concentration for pre-
developed conditions
Subbasin 1
a. Subbasin 1 = 2.44 acres
b. Composite curve number for Subbasin 1
[Ref: 4]
Soil Type
[Ref: 7] Land Cover Area (acres)
[Ref: 4] % Total
Drainage Area Curve Number
[Ref: 2, Table 3-5]
B Wooded 0.30 12 60
C Wooded 0.30 12 73
B Grassed 0.58 24 69
B Impervious 0.04 2 98
B Pond 0.10 4 100
C Pond 1.12 46 100
Pre-developed weighted CN = 84
c. Determine physical properties of various flow segments
Sheet
flow
Coefficient [Ref 5, Tables 3.20, 3.21] 0.24
Slope (ft/ft) [Ref: 4] 0.085
Length (ft) [Ref: 4] 199
•
d. Determine t, associated with sheet flow.
0.007 (nL )0.8
t? = Po.sso.a -
2
0.007 (0.24) (199 ft)]0*8
= 0.23hrs
(3.12in)0" (0.085)o.a
[Ref: 5, Eq. 3.50]
•

b. Composite curve mimher fnr C'rnhhne;n 1
[Ref: 5, Eq. 3.52]
[Ref: 6]
[Ref: 8]
Soil Type Land Cover Area (acres) % Total Curve Number
[Ref: 7] [Ref 81 Drainage Area [Ref: 2, Table 3-5]
B Grassed 0.28 55 69
C Grassed 0.01 2 79
B Impervious 0.20 39 98
C Impervious 0.02 4 98
...,? uv v vivYaJU VV %,16t1L-U -IN - OG
Determine physical properties of various flow segments
Sheet
flow
Coe Ficient [Ref: 5, Tables 3.20, 3.21 ] 0.011
Slope (ft/ft) [Ref: 81 0.043
Length (ft) [Ref: 8] 94
d. Determine tc associated with sheet flow.
0.007(nLf 8 - 0.007 [(0.011)(94ft)]0'
1 - = O.Olhrs
0
P20 5S" (3.12in)"' (0.043)1.4
Amicus engineering
Project No: 17-10-033 Sheet No: of
Date: 07-21-10
Calcs Performed By: JLM
Calcs Checked By: NRP
Project Name: Proposed Professional Building at Lawyer's Road
Subject: Hydrologic Evaluation
e. Determine total pre-developed time of concentration
t, = 0.23 hrs
tL = 0.6(tJ = 0.6(0.23 hrs) = 0.14 hrs
II. PRE-DEVELOPED HYDROLOGIC CONDITIONS:
1. Subbasin 1
Storm Event Peak Outflow
(cfs)
1-yr, 24-hr 4.37
10-yr, 6-hr 6.43
25-yr, 6-hr 8.24
50-yr, 6-hr 14.86
III. POST-DEVELOPED FLOW CALCULATIONS:
1. Calculate composite Curve Number and Time of Concentration for post-
developed conditions
Subbasin I
a. Subbasin 1 = 0.51 acres
c.
[Ref. 5, Eq. 3.50]
Amicus Engineering
•
•
Project No: 17-10-033 Sheet No: of
Date: 07-21-10
Calcs Performed By: JLM
Calcs Checked By: NRP
Project Name: Proposed Professional Building at Lawyer's Road
Subject: Hydrologic Evaluation
e. Determine total post-developed time of concentration
t,? = 0.01 hrs
tL = 0.6(tJ = 0.6(0.01 hrs) = 0.01 hrs
Subbasin 2
a. Subbasin 2 = 1.28 acres
rRef R1
Soil Type
[Ref: 7] Land Cover Area (acres)
[Ref: 8] % Total
Drainage Area Curve Number
[Ref: 2, Table 3-5]
B Grassed 0.36 28 69
C Grassed 0.33 26 79
B Impervious 0.40 31 98
C Impervious 0.19 15 98
Yost -developed weighted UN = 85
b. Determine nhvsical nrcnerties of varions flow ceumentc
Sheet v
flow Shallow
flow
Coefficient [Ref: 5, Tables 3.20, 3.21] 0.011 20.3
Slope (ft/ft) [Ref: 8] 0.029 0.029
Length (ft) [Ref: 8] 100 38
c. Determine t, associated with sheet flow.
0.007(nL)0' 8 0.007[(0.011)(100ft)]08
tl = I o.sSo a = = 0.02hrs [Ref: 5, Eq. 3.50]
(3.12in)0s (0.029) 1.4
d. Determine t, associated with 2nd segment shallow concentrated flow.
v = aS0-5 = (20.3) (0.029)°5 = 3.46 ft l s [Ref: 5, Eq. 3.48]
_ L _ 3 8 ft
t2 3600v 3600 (3.46 ft / s) z O.Ohrs [Ref: 5, Eq. 3.47]
e. Determine total post-developed time of concentration
t,, = t1 + t2 = 0.02hrs + O.Ohrs = 0.02 hrs
tL = 0.6(tc) = 0.6(0.02 hrs) = 0.01 hrs [Ref: 5, Eq. 3.52]
Subbasin 3
a. Subbasin 3 = 0.90 acres
b. Composite curve number for Subbasin 3
[Ref: 8]
Soil Type
[Ref: 7] Land Cover Area (acres)
[Ref: 8] % Total
Drainage Area Curve Number
[Ref: 2, Table 3-5]
C Grassed 0.90 100 79
rost -aeveiopea weigntea L1N = /9
[Ref: 5, Eq. 3.52]
•
Amicus Ingineering
Project No: 17-10-033 Sheet No: of
Date: 07-21-10
Calcs Performed By: JLM
Cales Checked By: NRP
Project Name: Proposed Professional Building at Lawyer's Road
Subject: Hydrologic Evaluation
c. Determine physical properties of various flow segments
Sheet v
flow
Coefficient [Ref: 5, Tables 3.20, 3.21 ] 0.24
Slope (ft/ft) [Ref 8] 0.176
Length (ft) [Ref: 8] 37
d. Determine t,. associated with sheet flow.
•
t _ 0.007(nL)0' _ 0.007[(0.24)(37ft)?08 _0.05hrs
I - PZ .sSo.a (3.12in)1.5 (0. 176)0"
e. Determine total post-developed time of concentration
tc = 0.05 hrs
tL = 0.6(t,) = 0.6(0.05 hrs) = 0.03 hrs
[Ref: 5, Eq. 3.50]
[Ref: 5, Eq. 3.52]
2. Determine storage volume available in the proposed bioretention areas and
landscaped detention area.
a. Bioretention Area BR-1
Elevation (ft)

[Ref: 2] Area (ft)

[Ref: 2] Height (ft) Volume (ft
)
682.00 1,865
1.00 1,586
681.00 1,306
t. otai volume avanaoie in bloretention Area BR-1 (elev. 682.00 ft) = 1,586 ft'
b. Bioretention Area RR-7
Elevation (ft)
[Ref 2] Area (ft)
[Ref: 2] Height (ft) Volume (ft )
681.00 4,683
1.00 4,216
680.00 3,749
mai volume avaiiaoie in t3loretention Area 13K-2 (elev. 681.00 ft) = 4,216 ft'
0
•
Amicus ingineering
Project No: 17-10-033 Sheet No: of
Date: 07-21-10
Calcs Performed By: JLM
Cales Checked By: NRP
Project Name: Proposed Professional Building at Lawyer's Road
Subject: Hydrologic Evaluation
c. Proposed Extended Drv Detention Area DDA-1
C
?I
Elevation (ft)
[Ref: 3] Area (ft)
[Ref: 3] Height (ft) Volume (ft')
679.00 20,465
1 17,874
678.00 15,282
1 12,832
677.00 10,381
1 6,260
676.00 2,138
0.5 535
675.50 0
a. 1 otal volume available in LDA-1 (elev. 679.00 ft) = 37,501 ft'
b. Total pond volume to overflow spillway = (elev. 678.00 ft) = 19,627 ft3
IV. POST-DEVELOPED HYDROLOGIC CONDITIONS:
1. Subbasin 1
Storm Event Peak Outflow
(cfs)
1-yr, 24-hr 1.11
10-yr, 6-hr 1.65
25-yr, 6-hr 2.15
50-yr, 24-hr 3.96
2. Subbasin 2
Storm Event Peak Outflow
(cfs)
1-yr, 24-hr 3.22
10-yr, 6-hr 4.66
25-yr, 6-hr 5.93
50-yr, 24-hr 10.52
3. Subbasin 3
Storm Event Peak Outflow
(cfs)
1-yr, 24-hr 1.61
10-yr, 6-hr 2.51
25-yr, 6-hr 3.32
50-yr, 24-hr 6.37
4. Proposed Bioretention Area RR-1
Storm Event Peak Inflow Peak Outflow Peak Storage Peak Elev.
(cfs) (cfs) (acre-ft) (ft)
1 sc inch 0.08 0.00 0.00 681.13
[Ref 4]
[Ref 4]
[Ref 4]
[Ref: 4]
Amicus Ingineering

Project No: 17-10-033 Sheet No: of
Date: 07-21-10
Calcs Performed By: JLM
Calcs Checked By: NRP
Project Name: Proposed Professional Building at Lawyer's Road
Subject: Hydrologic Evaluation
5. Proposed Bioretention Area BR-2
Storm Event Peak Inflow
(cfs) Peak Outflow
(cfs) Peak Storage
(acre-ft) Peak Elev.
(ft)
1St inch 0.35 0.00 0.02 680.19
6. Proposed Extended Dry Detention Area DDA-1
Storm Event Peak Inflow
(cfs) Peak Outflow
(cfs) Peak Storage
(acre-ft) Peak Elev.
(ft)
1-yr, 24-hr 1.61 0.57 0.02 676.10
10-yr, 6-hr 2.51 0.66 0.04 676.22
25-yr, 6-hr 3.32 0.74 0.05 676.33
50-yr, 24-hr 6.37 1.00 0.12 676.82
7.
Total Post-Devel oped Runoff Flowing
Storm Event Peak Outflow
(cfs)
1-yr, 24-hr 0.57
10-yr, 6-hr 0.66
25-yr, 6-hr 0.74
50-yr, 24-hr 1.00
Off Site
8. Check Regulatory Requirements
For Commercial Site
Q1(post) = 0.57 cfs < Q1(pre) = 4.37 therefore ok.
Q10(post) = 0.66 cfs < Qlo(pre) = 6.43 therefore ok.
Q25(post) = 0.74 cfs < Q25(pre) = 8.24 therefore ok.
Q50(post) = 1.00 cfs < Q50(pre) = 14.86 therefore ok.
For Extended Dry Detention Area DDA-1
Peak elev. For 50 year storm = 676.82 ft < 679.00 ft
Free board = 2.18 feet > 0.50 feet therefore ok.
[Ref: 4]
[Ref: 4]
[Ref: 4]

NCDENR Stormwater BMP Manual
Revised 06-16-09
• The type of ground cover at a given site greatly affects the volume of runoff.
Undisturbed natural areas, such as woods and brush, have high infiltration potentials
whereas impervious surfaces, such as parking lots and roofs, will not infiltrate runoff at
all. The ground surface can vary extensively, particularly in urban areas, and Table 3-5
lists appropriate curve numbers for most urban land use typ es according to hydrol ogic
soil group. Land use maps, site plans, and field reconnaissance are all effective me thods
for determining the ground cover.
Table 3-5
Runoff curve numbers in urban areas for the SCS method (SCS, 1986)
Cover Description Curve Numbers for
Hydrologic Soil Group
Fully developed urban areas A B C D
Open Space (lawns, parks, golf courses, etc.)
Poor condition (< 50% grass cover) 68 79 86 89
Fair condition (50% to 75% grass cover) 49 69 79 84
Good condition (> 75% grass cover) 39 61 74 80
Impervious areas:
Paved parking lots, roofs, driveways, etc. 98 98 98 98
Streets and roads:
Paved; curbs and storm sewers 98 98 98 98
Paved; open ditches 83 89 98 98
Gravel 76 85 89 91
Dirt 72 82 85 88
Developing urban areas
Newly graded areas 77 86 91 94
Pasture (< 50% ground cover or heavily grazed) 68 79 86 89
Pasture (50% to 75% ground cover or not heavily grazed) 49 69 79 84
Pasture (>75% ground cover or lightly grazed) 39 61 74 80
Meadow - continuous grass, protected from grazing and 30 58 71 78
generally mowed for hay
Brush (< 50% ground cover) 48 67 77 83
Brush (50% to 75% ground cover) 35 56 70 77
Brush (>75% ground cover) 30 48 65 73
Woods (Forest litter, small trees, and brush destroyed by 45 66 77 83
heavy grazing or regular burning)
Woods (Woods are grazed but not burned, and some forest 36 60 73 79
litter c(xvers the soil)
Woods (Woods are protected from grazing, and litter and 30 55 70 77
brush adequately cover the soil)
Most drainage areas include a combination of land uses. The SCS Curve Number Model
should be applied separately: once for areas where impervious cover is directly
connected to surface water via a swale or pipe and a second time for the remainder of
the site. The runoff volumes computed from each of these computations should be
added to determine the runoff volume for the entire site.
For the portion of the site that is NOT directly connected impervious surface, a
composite curve number can be determined to apply in the SCS Curve Number Model.
The composite curve number must be area-weighted based on the distribution of land
uses at the site. Runoff from impervious areas that is allowed to flow over pervious
Stormwater Management and Calculations 3-9 July 2007

Stallings Post-Construction Storm Water Ordinance ................... September 18, 2007
0 (1) Storm Water Quality Treatment Volume
Storm water quality treatment systems shall treat the difference in the
storm water runoff from the predevelopment and post-development
conditions for the 1-year, 24-hour storm.
(2) Storm Water Quality Treatment
All structural storm water treatment systems used to meet these
requirements shall be designed to have a minimum of 85% average annual
removal for Total Suspended Solids.
(3) Storm Water Treatment System Design
General engineering design criteria for all projects shall be in accordance
with 15A NCAC 2H.1008(c), as explained in the Design Manual.
(4) Stream Buffers
Perennial streams shall have a 200-foot undisturbed buffer and
intermittent streams shall have a 100-foot undisturbed buffer in the Goose
Creek Watershed. Buffer widths shall be measured horizontally on a line
perpendicular to the surface water, landward from the top of the bank on
each side of the stream.
(5) Storm Water Volume Control
Storm water treatment systems shall be installed to control the difference
in the storm water runoff from the pre-development and post-development
conditions for the 1-year, 24-hour storm. Runoff volume drawdown time
shall be a minimum of 24 hours, but not more than 120 hours.
(6) Storm Water Peak Control
For developments greater than or equal to 10% built upon area, peak
control shall be installed for the 10-yr and 25-yr, 6-hr storms. Controlling
the 1-year, 24-hour volume achieves peak control for the 2-year, 6-hour
storm. The emergency overflow and outlet works for any pond or wetland
constructed as a storm water BMP shall be capable of safely passing a
discharge with a minimum recurrence frequency as specified in the Design
Manual. For detention basins, the temporary storage capacity shall be
restored within 72 hours. Requirements of the Dam Safety Act shall be
met when applicable.
•
20
Precipitation Frequency Data Server C fnF ; 3] Page 1 of 4
POINT PRECIPITATION ' TS
xF FREQUENCY ESTIMATES
FROM NOAA ATLAS 14
CHARLOTTE WB CITY, NORTH CAROLINA (31-1695) 35.2333 N 80.85 W 711 feet
from "Precipitation-Frequency Atlas of the United States" NOAA Atlas 14, Volume 2, Version 3
G.M. Bonnin, D. Martin, B. Lin, T. Parzybok, M.Yekta, and D. Riley
NOAH, National Weather Service, Silver Spring, Maryland, 2004
Extracted: Fri Jan 30 2009
•
Gonfidence Lfrnlts Seasonali Ldcatlon1:Maps Otherllnfo. GIS data Maps [7D 766s "C
Precipitation Frequency Estimates (inches)
ARI* 10 15 30 60 ? MZH [A][j] 30 11 45
?, Fn1X?1 6 r 4 day 77 aav ?
ears) mm mm min mm mm min T da da c
L J 0.40 0.64 0.80 1.09 1.36 1.58 1.69 2.04 2.41 2.79 326 3.66 4.20 4.82 6.47 7.98 10.03 IF]
?? 0.47 0.76 0.95 1.31 1.65 1.91 2.04 2.46 2.91 3.36 3.93 4.39 5 F0115 73 7.63 9.38 11.75
0,55-.0..88 1.11: 1.58 2.03 238 2.54 3;07 3.65 4.22 4.89 5.41 6.10 6.89 9.01 10.91 42] F1
10 0?0 09? 1 2? 1 77 23 32 ? 93 3 55.; 423 4.89 5.65 6.22 6.96 7.80 10.10 12.09 14.71
25 . 0 6 9 1 .{i 2-7,66, 3 181 3 46' 4:20' 5`.04 F8T11 6.68 7.33 8.16 9.02 11.56 13.64 16.37 E
50 " 0 711 1 ` 2a7 293 3S = 3 8? 4:?2;. 5.70 6.54 7.50 8.21
1 -1 9.10 9.98 12.71 14.84 17.64
100 0.75 1.20 1.51 2.32 3.19 3.87 429 5.24 6.37 7.28 8.33 9.10 10.07 10.94 13.86 16.03 18.86 F
200 0.79 1.25 1.58 2.45 3.44 4.21 4.72 5.79 7.07 8.04 9.18 10.02 11.06 11.92 15.02 17.21 20.06 C
500 0.83 1.31 1.65 2.62 3.76 4.65 5.30 6.53 8.05 9.08 10.34 11.28 12.41 13.24 16.59 18.78 21.62 2,
1000 0.85 1.35 1.69 2.74 4.00 4.99 5.76 7.12 8.83 9.89 11.24 12.26 13.46 14.26 17.81 19.97 22.79 C
* These precipitation frequency estimates are based on a partial duration series. AR] is the Average Recurrence Interval.
Please refer to NOAA Atlas 14 Document for more information. NOTE: Formatting forces estimates near zero to appear as zero.
II * Upper bound of the 90% confidence interval
Precipitation Frequency Estimates (inches)
'The upper t>oun i of tfie'confidence interva[ at 90% confidence level is the value which 5"/0 of the Simulated quantile values fa a given fre uency are greaterthan. -
es a
s. AN Ia ?t@ ?tVg%t ?9gNff@ngt IAtRg, - _ , :..,9 _.,. .. -
"?Il a SF IRI gI?A (f9?l nq g artial1-4 ration5gges
Please refer to NOAA Atlas 14 Document for more information. NOTE:: ormatting prevents estimates near zero to appear as zero.
(ye rs) min min min mi39 691 n min lmin hr hr hr hr [24][?41][-4[-7
day day day 11 day day day
0.43 0.69 0.86 1.18 1.47 1.73 1.85 2.24 2.64 3.00 3.51 3.93 .49 5.16 6.87 8.44 10.55
0 0.51 0.82 1.03 1.42 1.78 2.10 2.23 2.70 3.19 3.63 4.24 4.71 5.36 6.13 8.10 9.93 12.33
0.60 0.95 1.21 1.71 2.20 2.61 2.79 3.37 3.99 4.55 5.27 5.81 6.52 7.36 9.56 11.54 14.09 E
10 0.65 1.05 132 2 2.50 2.98 3.21 3.88 4.62 5.28 6.08 6.67 7.44 8.32 10.71 12.79 15.44
11 1.9
2.1
25 0.72 1.15 1.46 6 2.88 3.48 3.79 4.58 5.49 6.25 7.18 7.86 8.72 9.63 12.27 14.43 17.20 E
50 0.77 1.23 1.55 2.34 3.17 3.85 4.24 5.14 6.19 7.03 8.06 8.81 9.74 10.65 13.48 15.71 18.54
E
100 0.81 1.29 1.63 2.50 3.44 423 4.69 5.71 6.91 7.83 8.95 9.78 10.78 11.69 14.71 16.98 19.85 E
200 0.85 1.35 1.70 2.65 3.72 4.61 5.17 6.31 7.66 8.66 9.88 10.77 11.85 12.74 15.95 18.25 21.12 2
F-56-6--]"r0:90 1.42 1.79 2:84 4.08 5.10 6;81 ?.17 8,711K 77 11'1 1313 13,3 14,117 17.64 19.24 32 8 2
JL? 47
`
PM
* Lower bound of the 90% confidence interval
•
u
12.76 F
h"://hdsc.nws.noaa.Rov/cp-i-bin/hdsc/buildout.Derl?tune=Df&units=us&seiies=nd&.tntena... 1 /30/9.000
•
•
•
Precipitation Frequency Data Server
Page 2 of 4.
10 0.56 0.89 1.13 1.63 2.12 2.48 2.67 324 3.87 4.54 525 5.78 6.50 7.28 9.51 11.43 13.97 E
25 0.61 0.98 124 1.83 2.44 2.88 3.13 3.81 4.58 537 6.19 6.78 7.59 839 10.86 12.87 15.53 C
0.65 1.03 1.311.97 2.67 3.18 3.49 426 5.13 6.03 6.93 7.57 8.46 927 11.91 13.97 1
506.70 l(
l(
100 0.68 1.08 137 2.10 2.89 3.47 3.84 4.70 5.68 6.70 7.68 839 933 10.15 12.96 15.05 17.83 E
200 0.71 1.12][12 2 13.10 3.75 4.19 5.13 624 737 8.44 921 1022 11.03 14.00 16.12 18 44 C
500 0.74 1.17 1.47 2.34 3.35 4.10 4.63 5.71 6.99 830 9.47 1033 11.42 1221 15.42 17.54 2036 C
1000 0.76 1.19 1.50 2.42 3.53 435 4.98 6.15 7.56 9.02 1026 1120 1235 13.13 16.52 18.61 21.43 E
The lower bound of the confidence interval at 90% confidence level is the value which 5% of the simulated quantile values for a given frequency are less than.
These precipitation frequency estimates are based on a partial duration maxima series. ARI is the Average Recurrence Interval.
Please refer to NOAA Atlas 14 Document for more information. NOTE: Formatting prevents estimates near zero to appear as zero.
Te.xt,version of tables

S
G
0
a
U
N
L
d
Partial duration based Point Precipitation Frequency Estimates - Version: 3
35.2333 N 80.85 W 711 ft
26
25
24
23
22
21
20
19
18
17
16
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
1 2 3 4 5 6 7 8 910 20 30 40 50 80 100 140 200 300 500 700 1000
Average Recurrence Interval (years)
Fri Jan 30 16:53:36 2009
Duration
5-min 48-hr -x 30-day yi-
10-min -? -hr W 4-day 45-cla
---
15-ruin t 6-hr 6 7-day - y
60-day -W
30-rain 2 12-hr + 10-day -+-
60-rain -( 24-hr -e- 20-day -ci-
httn:Ilhdsc.nws.noaa.2ov/cf?-i-binlhdsclbuildout.nerl?tune=nf&units=us&series=nd&staten,g.___ 111019.009
r
, votion
15-min Unit Hydrograph from S-Curve
r r rve
fs) Smoothed
S-curve Displaced
S-curve, UW
(cfs) UH
smoothed
0 0 0 0 0
9 29 0 58 58
8 68 29 78 78
2 122 68 108 112
8 168 122 92 100
?'-'T Z_M Z `n 7 217 168 98 96
1 251 217 68 85
5 285 251 68 64
5 305 285 40 44
1 331 305 52 36
7 342 331 22 28
9 355 342 26 20
3 360 355 10 14
- 2 368 360 16 12
- - 1 375 368 14 10
9 377 375 4 6
6 378 377 2 4
379 378 2 2
9 382 379 6 0
5 383 382 2 0
- -- n O 383 383 0 0
6 383 383 0 0
s 0 383 383 0 0
6 383 383 0 0
s 0 383 383 0 0
Sum 769
) - S(t-D'))D/D' =1S(t) - S(t-15)130/15.
?e and generally prevent direct derivation of
Taphs for small catchments. Unit hydro-
resent direct stormwater runoff. Baseflow
and water discharges to streams must be
m the flow record before unit hydrographs
i iined from the record. Linsley et al. (1982)
. suited or details- For small catchments,
_ =anit hydrographs are generally used. Syn-
hydrographs are discussed in detail in the
-•• .sections of this chapter. Several synthetic
raph models have been proposed. Gener-
'ovide the ordinates of the unit hydrograph
n of the time to peak, tp, peak flow rate,
mmmmnathernatical or empirical shape description.
75
After presenting procedures for estimating these at-
tributes, several unit hydrograph models are presented.
Estimation of Time Parameters
This section deals with the estimation of the time
parameters D, tL, tp, and tb as shown in Fig- 3.22 and
the time of concentration, t.. Several methods for
estimating these parameters are available. The method
that produces results consistent with good engineering
judgement should be selected for a particular study
area.
The time of concentration is the time it takes for
flow to reach the basin outlet from the hydraulically
most remote point on the watershed. For some areas,
this parameter can be estimated by summing the flow
time for the various flow segments as the water travels
toward the watershed outlet. These segments generally
are overland flow, shallow channel flow toward larger
channels, and flow in open channels, both natural and
improved. The travel time in these various flow seg-
ments depends on the length of travel and the flow
velocity.
Once the velocity in each flow segment is deter-
mined, the time of concentration is determined from
n Li
tc _ - , (3.47)
(-1 vi
where n is the number of flow segments and Li is the
length and vi the flow velocity for the ith segment.
Flow velocity of overland flow and shallow channel
flow can be estimated using results such as those of
Izzard (1946), Regan and Duru (1972), Overton and
Meadows (1976), or from the relationship
v = aS112 (3.48)
based on information in SCS (1975), where S is in ft/ft
and v is in fps. The coefficient a is contained in Table
3.20.
Regan and Duru (1972) present a method for esti-
mating travel time, tt, over a plane surface based on
the kinematic wave equation [Eq. (3.40)]. The equation
is valid for turbulent flow or when the product of the
rainfall excess intensity, ie, in iph and the flow length,
L, in feet is greater than 500. The equation is
t _ 0.0155 (nL)0' (3.49)
t - 0.4s0.3 '
e
where tt is in hours, n is Manning's n, L is in feet, ie
is in iph, and S is the slope in ft/ft. Table 3.21
presents some values for n for overland flow surfaces.
The Soil Conservation Service (1986) presents a rela-
tionship attributed to Overton and Meadows (1976) for

Chapter 3. Rainfall-Runoff Estimation in Storm Water Computations Runoff Estimati
le 3.20 Coefficient a for Eq. (3.48)1 obstacles such as litter, crop residue, ridges, and rocks; time estimatic
and the erosion and transport of sediment. These n
ace a values are for very shallow flow depths of about 0.1 ft
land flow or so. Table 3.21 gives Manning's n values for these The SCS (1
)rest with heavy ground litter 2.5 conditions. The relationship for travel time is on natural wa
ty; meadow 2.5
o.s
L
ash fallow; minimum tillage 5.1 0.007( nL,)D 8 t
L
mtou*; strip cropped 5.1 Tt - Po.5So.4 3.50)
2 1
:)odland 5.1 where t L is tl
ort grass 7.0
where P, is the 2-year, 24-hr rainfall in inches and the of the water
-aight row cultivation 8.6
other terms are as defined for Eq. (3.49). This relation- number by Ec
re; unfilled 10.1 ship is based on shallow, steady, uniform flow; a con- in percentage
vea 20.3 stant rainfall excess intensity; and minor effects from an antecedes
ow concentrated flow infiltration. being used as
luvial fans 10.1 In urban areas, the travel time may have to be based runoff potenti
assed waterways 16.1 on a travel time to a storm drain inlet plus the travel Many local
tall upland gullies 20.3 time through the storm drain itself. Inlet travel time shed physical
can generally be computed as the sum of overland flow example, Putt
.esults in fps; multiply by 0.305 to get m/sec. and shallow channel flow travel times. Flow in storm North Carolir
drains would be considered as open channel flow with
the storm drain pipe flowing full. Often large storms
1Vl*,ing's n for Travel Time Computations for produce runoff rates that exceed the capacity of the
ane Surfaces (Soil Conservation Service, 1986) storm drains and some of the runoff bypasses the where tL is t

i
d
i drains in the form of concentrated surface flow as open
the main wat
pt
on
e
escr channel flow. Such flow should be considered in com-

es (concrete, asphalt,
puting the time of concentration. slope in feet
area
Here t

are soil 0.011
Undersized culverts and bridge openings can cause r
.
of mass of r
idue) 0.05 ponding of flow and a reduction in the average flow an ec
Before,
s velocity. For small ponds and situations where water is exercised to
,er <_20% 0.06 passing through the pond with little or no storage build

er>2o% 0.17
up, the actual travel time through the pond may be equation was
eq

i very small. If significant storage results, the travel time
est.
The durati(
pra
rie 0.15
esb 0.24 is lengthened over that for normal channel flow, and ally associate
Lss 0.41 flow routing as discussed in Chapter 6 must be used. fifth to one-tt
0.13 Flow velocity for open channels can be estimated
' is given by Et
from Manning
s equation, which is treated in detail in
Chapter 4.
sh 0.40
ash 0.80 Other methods are available in the form of empirical
equations for estimating tc. One such relationship that Epsey et t
res are a composite of in compiled by Engman is widely used but based on limited data is expressed by from 41 wate
Kirpich (1940) North Caroli
)ecies such as weeping lovegrass, bluegrass, buffalo grass, j° 2; MISS18Slpp
ss, and native grass mixtures.
sting n, consider cover to a height of about 0.1 ft. This is the
t? = 0,00'78 L0 77 (L /H1 10.385 (3.51) The Watersht
aCIES (3.5 t0
plant cover that will obstruct sheet flow. t10n equatl0)
where t, is in minutes, L is the maximum length of hydrographs

* flow in feet, and H is the difference in elevation in feet jk
f
-et flow over plane surfaces based on between the outlet of the watershed and the hydrauli-
:quation and a kinematic approximation to tally most remote point in the watershed. Obviously,
rations. The equation is for flow lengths of Eq. (3.51) does not consider flow resistance in the form where tP is t.
)0 ft. The friction value or Manning's n is of overland flow and channel roughness. channel leng
roughness coefficient that includes the Several methods for estimating the lag time of a feet, S is the

.indrop impact; drag over plane surfaces-,
watershed are available. One simple method for lag terms of len€
_omputati' Runoff Estimation
and roc time estimation is (Soil Conservation Service, 1973)
it. These tL = 0.6t,. (3.52)
about 0.1
s for the The SCS (1975) has developed a lag equation based
on natural watersheds
is •
- Lo-'(S + 1) 0.7 (50 <CN < 95), (3.53)
(3.50 t L 1900Y0.5
Where tL is the lag in hours, L is the hydraulic length
and the of the watershed in feet, S is related to the curve
relation; number by Eq. (3.22), and Y is the average land slope
'; a con-' in percentage. The S in Eq. (3.53) should be based on
,'ts from' an antecedent condition II curve number, since it is
being used as a measure of surface roughness and not
e based' runoff potential.
travel; Many local studies relating tL or tp or t, to water-
:1 time ' shed physical characteristics have been conducted. For
id flow example, Putnam (1972) in a study of 34 watersheds in
storm North Carolina, presented the relationship
v with L oso
torms tL = 0.490) I-os7 (3.54)
If the
the
Dpen .{ where tL is the basin lag in hours, L is the length of
:om- F the main water course in miles, S is the main stream
slope in feet per mile, and I is fraction of impervious
fuse area. Here tL was defined as the time from the center
low of mass of rainfall to the center of mass of runoff.
T i? Before an equation like (3.54) is used, care must be
exercised to see that the conditions under which the
be equation was developed match the conditions of inter-
ne est.
id The duration, D, of the rainfall excess that is gener-
ally associated with a unit hydrograph should be one-
d fifth to one-third of the time to peak. The time to peak
n is given by Eq. (3.26) as
tp = tL + D/2.
Epsey et al. (1977) studied rainfall-runoff records
from 41 watersheds located in several states (Texas, 16;
North Carolina, 9; Kentucky, 6; Indiana, 4; Colorado,
2; Mississippi, 2; Tennessee, l; and Pennsylvania, 1).
The watersheds ranged in size from about 9 to 9600
acres (3.5 to 3900 hectares). They developed an estima-
tion equation for the time to peak of 10-min unit
hydrographs as
tp = 3.1L0.23S-0.251-0.184)1.57 (3.55)
where tp is the time to peak in minutes, L is the main
channel length from the upper watershed boundary in
feet, S is the slope in feet per foot of the lower 80% (in
terms of length) of the main channel, I is the percent-

Table 3.22 cp Values for Eq. (3.55) (Epsey et al., 1977)
Manning's n
Percentage imp. 0.015 0.03 0.05 0.10 0.15
0 0.82 0.86 0.93 1.15 1.30
20 0.74 0.80 0.88 1.09 1.27
40 0.65 0.72 0.81 1.03 1.22
60 0.60 0.68 0.79 1.00 1.19
age impervious area with an assumed minimum value
of 5% for an undeveloped area, and 4) is a conveyance
factor that depends on the percentage impervious area
and Manning's n for the main channel. Table 3.22
contains some representative values for (D.
The base time of a unit hydrograph is somewhat
arbitrary. Some hydrologists use a base time of five
times the time to peak. Some unit hydrograph models
have a recession limb that asymptotically approaches
q = 0, so that the base time is theoretically infinity.
Estimation of Peak Flow Parameters
The peak flow rate of a unit hydrograph is often
given by an equation of the form
qP = YA/tp. (3.56)
Based on a triangular unit hydrograph with a base
time of 2.67tp, the SCS (1972) estimates the peak flow
of a unit hydrograph from the equation
484A
(3.57)
qp =
tP
where qp is the peak flow in cfs, A is the basin area in
square miles, and tP is the time to peak in hours.
Epsey et al. (1977) recommend that for 10-min unit
hydrographs, the relation
qP = 31620(A0.96/tp.07 1 (3.58)
be used where qP is in cfs, A is the drainage area in
square miles, and tp is the time to peak in minutes-
As was the case for lag time, many studies have been
conducted in an effort to relate qP to watershed physi-
cal conditions. Before any of these empirically derived
equations are used, their applicability should be care-
fully determined.

?s
Runoff Fsiirncrticn
7oNc- 3.19 35 n)in Lnii Fi?rdre3rra?li i_-or,; 5-Lur.
i:ne
i Tn411 S L;r.-
rc-c< Sr:; vzet
S ?r_z•. D;c NttJ
S_=er, c` IV,
1ci5's t.rH
sr:,r-?eit•
i1 U r; {, o t

"Zi

iii toy fre 1" rq 2 tttil
•t'
25i c7 -
_ fti TM

j 50

. C3 ;5-
ari
a6. ?i--..
2 2:5
240

_;n. _vi
28.
??` :?_ tel.'. t' 37

=-i, fti_ _.= C
S,I: -`9

are C_Xter7sioe grid gcnv_ull? pre\.erti dir ct deri\ation e;
unit h droz,-aphs ?f*r small catchrncn .;_ tr n it li?t'ro-
graphs represent diriCi STOTTm Maier runor% Baseflow
and; or Tound VVattr discharg s-to srrea!ms must be
remt?\;td from the flow record b,,ore unit hvdrzigraphs
can be defined from the record. Linsley ei al. (1982)
can be consulted or deiai.ls. For small catchments-
s?nthetic unit hvdrographs are _generally- used- Srn-
tbetic unit htidrographs we discussed in detail in the
folio rli- sections of this cb; pter. Several sy nthe.tic
unit hydrograph models have been proposed- Gencr-
alh- tiled providt the ordinates of the unit hydregraph
as a function of the: tune to Perak; 1r, peak floc, rate,
qr. and amatheruatical or empirical sliapc description.
75
jizc.r prescntinQ procedure, fn; estimating tf)csc at-
tribute-. several unit hydrograph models ar hied-
Estimalion of Time Parameters
This section deal- with the estimation of the time
parameters D. q, i`, and ry as shown in Fie. 3.22 and
the ifmf. of concentration; r _ 5e\-eral rnothoa- for
estimating t t-St P8Tan.I=IItTS arc a\ suable. Thc; method
.that products results consisicni v."ith good enginccTing
judgcme.m should bt selecied for a pr rticular s5-,Ud V
aria.
1"nc time of concentralinn i:. ihtime it rakes for
flo\r• to reach the basin outlcr from the liydraulicalll:
most remote point or rhe w2iershed_ For some! area:;
this raiam;:tcr can be csiim2zud by summing ih;: o\°:
t)nL for the \ilr)ou- flo\.. segnicnis a- the water travels
10Vja7d ih= v;aicrshed outlei_ TIIt_c stnmcpis cncr^llr
are orvtrLnd how_ sballew. rhanstl rot\• tov..•ard lar.Lr
f?1?nIiel<_ and Pi=1:\- in D7 ,1 both natural i_P_-J
3ln7ro\'ecl. The t_ravcl Time in Blest .=riOLS 0-w St=_-
mtnts demends o- the ltrtt=th o_ tra:.l an-d *hr-- fkl
elocit -
^',nCe n -he 1'ilL)'=i-: iz Lac-- v sEzin:G?ll is t?tt'vr-
h ='
'?
n ined_ th:: 6r!1e ;,_ =onctrii:ceiCD:? )_ =te-,MMCd Uor?
\vz7i-e :i =.5 ih L and L_ r_-
it_,__th _n-d ;}e Bov': for ih%c tile Cr
ni.
i z0\: \?lyCit'_ O i--trlaPi) T_ aid c .lo -I
0
nw C= h= lt:S_1 ___v'? Si C;-i?1%i=
Izzard (39 4-:0- il'L=C a-!d D-?_U tj:i' on a+_ltl
1•t`CPdOtvai=9 ;6 rIro^n he- rtl-iionshi_
bz ad on in oTirnation in SCS (?9 `_?- ?- iere) is in L, ; 21
aid i' IS In fDZZ. Tits co mcieni t k COM3ined in allle
Re.-ar; and Duru 09727 present a method for esii-
matiny rraret_ rini=&, i-_ over a plane surface. based On
the kiaematia• \;zv:c equation [Eq_ (3.40)1. The cquaik)n
is valid for turbrilcni -BOW or ;.hen the product of flit
rainfall ace=_: inLensis;_ i, _ in iph and the ;lox lenar-h,
L. in feet is erca:er than 5.00- The equation is
ac)
s.-he.re r; is in hours, n is Nlanning's n. L is in filer, i_
is in iph; and 1' is the slopc in Rift. Tablu 3.21
nresLnts some value; for n for overland (l.o» surfacc.s.
The Soil Consrrvation Su ice (19S6) presents a rela-
tionship attributer) to Overton and Nkado.vs (1976) f'nr
76
• Table 3.00 C cz- icee.-,i s; ios EG. i ?_"?`
Ci
O; _r_?.<i ;<or

C lip -
Ji(3ri rR?.i. i;

Ham: Lr!iiI_C, 10.!

Tabir 3.21 iZ: -3 _ -F i07 S_ for
-c:-: ove_ Pl_-? -S_,-mac- rSO_ Ccns_ 'z_s' S :: s c . 3 b;,

a7t

Cr___

it2--c_? 7•i -.ice __.
9:7
De rL?e

'L•-i:ttl=?_ _ -z _._ _.;!3 a? '.. ;Di ' ia1'c=ti__'JJL'.._.-?c?iL:.i -
);11L. ? 1??c. =i5. ur= t;ati c? ? o? -_?A,?.
`l. t:Ct: <?i2:4ifi _Cit?$3G?r ccN-c-i -' _
GN: -n of :__" 71 L'rri CL"-'CE ul_: 9: ili
Chcp; er 3_ Rainfall-Runor Esiimalior, in S;orm Vt'Gter
traij•el time for slice, fjc` v cover plane surfaces based On
x annia!?-:-s equation anti a kineniatic approai.malion to
the flcivr equai•ions_ The Cqualion is for 19oU:- lcngth:? of
less than 300 ft_ The i-riction va- ue or Mannin-g's. r is
an. effective roughness coefficient that includes the
cfft:Ci o` raindrop impact; dTaV over plane surfaces:
ob [acles SL]Cfi 2> lJlier. ?rfh ie Citie. r70°_']. Ilili eC
and ilia pro iorl 213d transpo? c+ -edirnzni_ Th
;aloes arc for uerv sha 9c) So;=: dcp.lis of i3}?L1at 0_1
or So. Table 32! . `raeS ???atinir `s r values for the
conditions. The relationship for travel ti riz is
Il.>~lr., ; t 711. j
T_ = i'- Sr

~.?'here P- is the 3-year.'' hr rainfall in inches and
other terns art as deiinect fo: Eq- (3-49). his rclz a
14
shin is based oil shallr?,'r. Stcad?, unift,rrn Tic) - ;:k:
Stunt raiii all c::C°SS illTtjS7P_ and TiLt]L>7 i CC- f:iw
intr'don-
In urban -?Teas. the ;:ra,ral iinf may have to be bay:
on a Travel girt to a S:or drain ir_let plot sri I_a°
air z t]LOuLb the Sto-?1 drain itself- I-anl t i_ar-_ _--
car _-genz_a?l,' be cwnpuicd as aye sun Of o1'erlan fps
`rd i-_ Flo? h =i
Sh'alloi-- ciar.nel t
drain_ -,vould b7 t ciy?ls: -=red a o cn--1ciZcnntl - L) 1St:
.,
Gi^
ins storm drain Ouina fu-11. -LJi{Cn IL-L---c
r oduc,e. rLAi',_r rLii2= rear -::C u Life Cap'ac-i"` 01 t
ciorm r, ra,-l_ any of i._c
ui-ai is in ` - fo-_ Ca Conce.ntrale Sur1?Cc p?i' L-S ctL=
_ _> . =rte _
? Vic.
`?.-:,i d c.o1lcide-?d _i
.rJ - - >J o=: _ Such iio, s ?_]? tr
-h
t:? . ;inn=e io-
-'=GL'.:L __
n3in? t: =o?= azoi i_ -cuL'_a_.o.? lYl -_.c zvt .ag° s
im 1- 1o-07 c-,3' }L'•? = 3 3d S: uaiions v h ` ;::_--
;j_Ss 7i., l•! no J:L'+.c?C
-h
cm l] s'
nc-ncL? L) 'r ila'.'1 fb7 i:L`:7iai cL_T]?21 C -, a
'C ]= 2-1
--yy -er -
-?3T!ln= LAS d=st isz in ?L Cli-aciti-1_ 6 ?uLi L. ?. ]+_z
Flow for o?Crt cnarn-nels can i-- c
ilsoCii_' . '
ioP_? 33i v?3ri=$ cq,S,?i?oi__ rl°h_cel is t-rewl'd ill deta_il
?n27i?r i.
011e; me1h0L s a:z ?L`IlaP ? ?n the forini Of eMID__
equarlons 1L17 °sti aiyil? Onf; such relatioZSlik) is
is 11;ide1y • -d bu bawd on linliied 2daia is cxp:e s°d
3iirpich. ? ] z'' P )
(11 .
is in 1713 XiMum ;>:'.r'_°_til
flow in feet- and H. is the dii:ercncc in elevation u,
bem--zen the outlet of rile +vatershed and -he hydr2
Cady most remote pornl in tn'? wat-CrShtid. Ob-60v
Eq_ {_-d l.) dons nbt COnsider L.),ti- resistance in the f(
of overland tla+ and channct roughne---,s.
Several methods for estimating the laa tirr?e c
watershed are as-ailable. One simplc method for

timic cgimotion 1s (.Sal Con`;::-n-niJon Service, 3973)
0.6
Thy SCrS 0 9-5) has developer] ri lag equ2iion ba e1.]
mg natural watenheds
Li:(S = :
r = (50 S CN < 95); ?=)
1. l oOL? I,- ,.;
OT-- `L 3; the la in boL s. L !, the hydraulic length
of the 1,:aiershed in ftet_ S Ls related do the curve
numuber by Eq. (--,.d, and ?' v the a=:cr;a,*c land slop;;
in tierce 7tane_ The S in Eq. (353,i should be based on
zn, aniecedent conciiilon Il curve number, shic= ,i is
bcnE! uszd as a micasurc of SLrfacL rC3Lghn?=? and not
i_ino poi:.ntial.
Ma--v local S-Ladies relaiinl .', nr r, or ?. 110 i',`r-?ter-
=h°t7 Lsh!'=i'_3! oh'?aci=r! i1CS ha?`i'. l:? -en conducted. For
_amp]e, Putnam `191.21 in "a siudy of 5= WineItTsheds in
?i=`i7 L2TiJ];n?_ r1ri: ?C?I _it ih:. r'l??=10?=1?i?
L
t 3' l
T- s i'h i - l'l1lr5_ - '?3_ ].e :_?i o'
M M ?_c«= L"Co__?['. !ri ?_+ S 1C _?? 7:21_ _„i-c;t]
M =.-tL D=r iie. an 3 L `rd-ciiL t In, l???iuS
arCa_ 1v-rim. = L T: `i j tiles. Lilli'_it
_ a SZZ ? .3iiLa]l it`: iLC Cc?io, { -5 of ' °L'Jrf c ?:J i'_ii,77 like 1_ ic1 c_=e -'_L-1 bt
L 5?= La-. 1'a Cv-., d7i10= umdt= irh -r= ir?
177 tom.--
en lion Y vas dtv-°eio,?_d maich the coocliiic,'ns of
Esi.
i_ie dur?i1o7, 17, of il'-_ rainfall c cts.s 13_I LTe2e_-
Oh' assotiSitd lib a 11-mt h!`&,O-Ifaph Sbould I?_ O 1c-
n
ih io ont-third o tl"ii tiT7C iCo, tr:.a1 The -irn; i0 -3pe3'-
is eiv_n by° -q. (3?6) as -

EDSC of ul_ (197 77.) SLU d7 is raiTlfall-rueloaf r,cord<
irons =1 V:atLYiheds locat,=.d in set eml states M_xa=: 16;
North Carolina, 9. I:eniucky_ 6- Indiana, CoIOTadol
_: Mississippi, Tennessee. L" and Yenns\°Ivania_ 11_
The ,vatershtd,- ranged in size iron abort 9 to 9600
acres U-5 L{ 900 beci m;'j_ They developed an esiinm-
tiC3n equation for the time: io peak of Ill-ruin unit
b;'drograph_ as

•VvherE? !t is the 6me, to peat: in minutes. L is the ruain
channel length from ibe upper Water hod bounclanr in
feet. S is the slope in FCCt per iuut Of 1110 IOWer 90% (in
ierms Of length) of the Inain channel; i'is the percerlt-
Tob]e 122 0'.uue: far F . i3_= ; ?Eo_e_r e: 17i-, 19."e
r, ti n 0.i5

2? D
0.74
CIM 7 l'r i ,{lu
-1? ---
t:
ane imner• L?u:_ a ea ivall till assumed rain IoM t'•alue
r an undE-vtJ =d area, unit 0 I' 8 tOf;:el`fl73Ci
Vi f 10
fauf+T iha_` 6,tiptndS, 051 Thc?lcrC-iliF1__e jynn, 2r\`lOUS FTeii
2nd Manning _s r• for thi! T-laid channt?l_ Ti?l?l
conlalll_z' SOrl3 Tepres°niat?ti'e -dum- t0" ?I?-
T112 bs=c =i1n c of uni_ i'ts` ?o!_'i''-ch is C 73 `-,-:h-a i
a__,LPitr p,. Sonic Ilvdroloni-35 use :: basc- Limit o-
?lmis the lime io pea'L Soi is u7, i_ h'_-ilr'J_==aph rnodti<
-ptOtiCa'a aDproachcS
-ll
ha:c recc-ssivn li;tb filar a?
%i = f3` so trai t?aS jj7njC T_-=, LiiC'a_] ]nen:;
azrimUTSa v ?e Fec k a-=--'. av"•rvMee ?3J
TL,
Z Kt Z7 7
•-- =7_Milo7 O ioaz
g_
B'sCt'. . on 7_ a^_,?1:1r ur!li i',•""Lrl??.ra?5 i'IiLh bas,
Liin Sc S (I? _? .Si 1.n7F'.. -0h c "t3121:1:: zi01':
- ?, - „- .
Ct= 2 unii h_ _,: _aph -:tli! 7-he yy=aiiO

1Yhert [fr is the pczik flov: in Cls_ _=i is 1lic basin aircu L"1
Squzire miics: and :_. 1t? al2 iimt io peaR In hours.
Epsev ei aL 0'9)1) reronunlend that for ](i-min unit
h}droyTaphs. ihu. relation
u? _ l.il. l S)
be used wherr q is in cfs, A is the drainxgc- area in
square trifles; and t€, is the time to peal: in mi.nules_
,As z:aa the cast. for lag time, nanv sludies have bee,,
ro73duacd in an etforL to relate q, io 3ti°uershe.d physi-
cal condiiions. Before Fmv of these empirically dcrivcd
equations arz- ti`cd. their applicability- should be care-
fulii, detern3ined.
Cl*'V'- i-, U'D
•
Project : First Choice Eye Care
.=.r r
Basin Model : Pre-Developed
HEC-HMS Jun 15 15:05:23 EDT 2010
Subbasin-1
? Sink-1
0
r1
U
•
Project: First Choice Eye Care Simulation Run: Pre-Developed 1-yr, 24-hr
Start of Run: 13Apr2009, 00:00 Basin Model: Pre-Developed
End of Run: 14Apr2009, 12:00 Meteorologic Model: 1-yr, 24-hr
Compute Time: 15Jun2010, 12:24:02 Control Specifications: Control Specifications
Volume Units: IN
Hydrologic
Element Drainage Area
(M12) Peak Discharge
(CFS) Time of Peak Volume
(IN)
Sink-1 0.0038125 4.37 13Apr2009, 12:02 1.35
Subbasin-1 0.0038125 4.37 13Apr2009, 12:02 1.35
•
• Project: First Choice Eye Care Simulation Run: Pre-Developed 10-yr, 24-hr
Start of Run: 13Apr2009, 00:00 Basin Model: Pre-Developed
End of Run: 14Apr2009, 12:00 Meteorologic Model: 10-yr, 6-hr
Compute Time: 15Jun2010, 12:24:14 Control Specifications: Control Specifications
Volume Units: IN
Hydrologic
Element Drainage Area
(M12) Peak Discharge
(CFS) Time of Peak Volume
(IN)
Sink-1 0.0038125 6.43 13Apr2009, 12:02 1.98
Fsubba 1n-1 0.0038125 1 6.43 13Apr2009, 12:02 .98

[7
0 Project: First Choice Eye Care Simulation Run: Pre-Developed 25-yr, 6-hr
Start of Run: 13Apr2009, 00:00 Basin Model: Pre-Developed
End of Run: 14Apr2009, 12:00 Meteorologic Model: 25-yr, 6-hr
Compute Time: 15Jun2010, 12:24:24 Control Specifications: Control Specifications
Volume Units: IN
Hydrologic
Element Drainage Area
(M12) Peak Discharge
(CFS) Time of Peak Volume
(IN)
Sink-1 0.0038125 8.24 13Apr2009, 12:02 2.55
Subbasin-1 0.0038125 8.24 13Apr2009, 12:02 2.55
•
,7
• Project: Project 1 Simulation Run: Pre-Developed 50-yr, 24-hr
Start of Run: 13Apr2009, 00:00 Basin Model: Pre-Developed
End of Run: 14Apr2009, 12:00 Meteorologic Model: 50-yr,24-hr
Compute Time: 21Ju12010, 13:17:50 Control Specifications: Control Specifications
Volume Units: IN
Hydrologic
Element Drainage Area
(M12) Peak Discharge
(CFS) Time of Peak Volume
(IN)
Sink-1 0.0038125 14.86 13Apr2009, 12:01 4.70
LS_Ybbasin-l 0.0038125 14.86 13Apr2009, 12:01 4.70
LJ
0
•
Project : First Choice Eye Care
Basin Model : Post-Developed
HEC-HMS Jun 15 15:08:11 EDT 2010
Subbasin-3
Subbasin-2
Subbasin-1
Diversion-2
Diversion-1
BR-2 ` , -- BR-1
LDA-1
?I
4 Sink-1
0
Project: Project 1 Simulation Run: Post Developed 1st inch
Start of Run: 13Apr2009, 00:00 Basin Model: Post-Developed
End of Run: 14Apr2009, 12:00 Meteorologic Model: 1st inch
Compute Time: 21Ju12010, 13:03:13 Control Specifications: Control Specifications
•
Volume Units: IN
Hydrologic
Element Drainage Area
(M12) Peak Discharge
(CFS) Time of Peak Volume
(IN)
BR-1 .000796875 0.00 13Apr2009, 00:00 0.00
BR-2 0.0020000 0.00 13Apr2009, 00:00 0.00
Diversion-1 .000796875 0.08 13Apr2009, 11:56 0.11
Diversion-2 0.0020000 0.35 13Apr2009, 11:55 0.17
LDA-1 0.0042031 0.00 13Apr2009, 00:00 0.00
Sink-1 0.0042031 0.00 13Apr2009, 00:00 0.00
Subbasin-1 .000796875 0.08 13Apr2009, 11:56 0.11
Subbasin-2 0.0020000 0.35 13Apr2009, 11:55 0.17
Subbasin-3 0.0014062 0.05 13Apr2009, 12:00 0.07
r?
L
•

Project:
Simulation Run: Post Devi
Start of Run: 13Apr2009, 00:00
End of Run: 14Apr2009, 12:00
Compute Time: 21 Ju12010, 13:03:13
Volume Units:
Project 1
)loped 1st inch Reservoir: BR-1
Basin Model: Post-Developed
Meteorologic Model: 1 st inch
Control Specifications: Control Specifications
IN
Computed Results ._.._. --- __------ _._
Peak Inflow : 0.08 (CFS) Date/Time of Peak Inflow : 13Apr2009, 11:56
Peak Outflow : 0.00 (CFS) Date/Time of Peak Outflow : 13Apr2009, 00:00
Total Inflow : 0.11 (IN) Peak Storage : 0.00 (AC-FT)
Total Outflow : 0.00 (IN) Peak Elevation : 681.13 (FT)
0
•
•
Project:
Simulation Run: Post Devi
Start of Run: 13Apr2009, 00:00
End of Run: 14Apr2009, 12:00
Compute Time: 21Ju12010, 13:03:13
Volume Units:
Computed Results -
Peak Inflow : 0.35 (CFS)
Peak Outflow : 0.00 (CFS)
Total Inflow : 0.17 (IN)
Total Outflow : 0.00 (IN)
Project 1
,loped 1st inch Reservoir: BR-2
Basin Model: Post-Developed
Meteorologic Model: 1 st inch
Control Specifications: Control Specifications
IN
Date/Time of Peak Inflow : 13Apr2009, 11:55
Date/Time of Peak Outflow : 13Apr2009, 00:00
Peak Storage : 0.02 (AC-FT)
Peak Elevation : 680.19 (FT)
0
Project: Project 1 Simulation Run: Post-Developed 1-yr, 24-hr
Start of Run: 13Apr2009, 00:00 Basin Model: Post-Developed
End of Run: 14Apr2009, 12:00 Meteorologic Model: 1-yr, 24-hr
Compute Time: 21Jul2010, 13:02:19 Control Specifications: Control Specifications
0
Volume Units: IN
Hydrologic
Element Drainage Area
(M12) Peak Discharge
(CFS) Time of Peak Volume
(IN)
BR-1 .000796875 0.00 13Apr2009, 00:00 0.00
BR-2 0.0020000 0.00 13Apr2009, 00:00 0.00
Diversion-1 .000796875 1.11 13Apr2009, 11:54 1.22
Diversion-2 0.0020000 3.22 13Apr2009, 11:53 1.41
LDA-1 0.0042031 0.51 13Apr2009, 12:04 0.30
Sink-1 0.0042031 0.51 13Apr2009, 12:04 0.30
Subbasin-1 .000796875 1.11 13Apr2009, 11:54 1.22
Subbasin-2 0.0020000 3.22 13Apr2009, 11:53 1.41
Subbasin-3 0.0014062 1.61 13Apr2009, 11:55 1.04

Project: Project 1
Simulation Run: Post-Developed 1-yr, 24-hr Reservoir: LDA-1
Start of Run: 13Apr2009, 00:00 Basin Model: Post-Developed
End of Run: 14Apr2009, 12:00 Meteorologic Model: 1-yr, 24-hr
Compute Time: 21 Ju12010, 13:02:19 Control Specifications: Control Specifications
Volume Units: IN
Computed Results
Peak Inflow : 1.61 (CFS)
Peak Outflow : 0.51 (CFS)
Total Inflow : 0.35 (IN)
Total Outflow : 0.30 (IN)
- -------------
Date/Time of Peak Inflow :
Date/Time of Peak Outflow
Peak Storage :
Peak Elevation
13Apr2009, 11:55
13Apr2009, 12:04
0.03 (AC-FT)
677.03 (FT)
•
r- 7
l?
• Project: Project 1 Simulation Run: Post-Developed 10-yr, 24-hr
Start of Run: 13Apr2009, 00:00 Basin Model: Post-Developed
End of Run: 14Apr2009, 12:00 Meteorologic Model: 10-yr, 6-hr
Compute Time: 21Ju12010, 13:01:14 Control Specifications: Control Specifications
•
Volume Units: IN
Hydrologic
Element Drainage Area
(M12) Peak Discharge
(CFS) Time of Peak Volume
(IN)
BR-1 .000796875 0.00 13Apr2009, 00:00 0.00
BR-2 0.0020000 0.00 13Apr2009, 00:00 0.00
Diversion-1 .000796875 1.65 13Apr2009, 11:53 1.82
Diversion-2 0.0020000 4.66 13Apr2009, 11:53 2.06
LDA-1 0.0042031 0.58 13Apr2009, 12:04 0.49
Sink-1 0.0042031 0.58 13Apr2009, 12:04 0.49
Subbasin-1 .000796875 1.65 13Apr2009, 11:53 1.82
Subbasin-2 0.0020000 4.66 13Apr2009, 11:53 2.06
Subbasin-3 0.0014062 2.51 13Apr2009, 11:55 1.60
•
•
Project: Project 1
Simulation Run: Post-Developed 10-yr, 24-hr Reservoir: LDA-1
Start of Run: 13Apr2009, 00:00 Basin Model: Post-Developed
End of Run: 14Apr2009, 12:00 Meteorologic Model: 10-yr, 6-hr
Compute Time: 21 Ju12010, 13:01:14 Control Specifications: Control Specifications
Volume Units: IN
•
Computed Results - - .. _ _... __
Peak Inflow : 2.51 (CFS)
Peak Outflow : 0.58 (CFS)
Total Inflow : 0.54 (IN)
Total Outflow : 0.49 (IN)
Date/Time of Peak Inflow :
Date/Time of Peak Outflow :
Peak Storage :
Peak Elevation
13Apr2009, 11:55
13Apr2009, 12:04
0.04 (AC-FT)
677.11 (FT)
0
r-1
l?
•
Project: Project 1 Simulation Run: Post Developed 25-yr, 6-hr
Start of Run:
End of Run:
Compute Time
13Apr2009, 00:00
14Apr2009, 12:00
21 Ju12010, 12:59:49
Basin Model:
Meteorologic Model:
Control Specifications
Post-Developed
25-yr, 6-hr
Control Specifications
Volume Units: IN
Hydrologic
Element Drainage Area
(M12) Peak Discharge
(CFS) Time of Peak Volume
(IN)
BR-1 .000796875 0.00 13Apr2009, 00:00 0.00'
BR-2 0.0020000 0.00 13Apr2009, 00:00 0.00
Diversion-1 .000796875 2.15 13Apr2009, 11:53 2.37
Diversion-2 0.0020000 5.93 13Apr2009, 11:53 2.64
LDA-1 0.0042031 0.64 13Apr2009, 12:05 0.67
Sink-1 0.0042031 0.64 13Apr2009, 12:05 0.67
Subbasin-1 .000796875 2.15 13Apr2009, 11:53 2.37
Subbasin-2 0.0020000 5.93 13Apr2009, 11:53 2.64
Subbasin-3 0.0014062 3.32 13Apr2009, 11:55 2.13
•
• Project: Project 1
Simulation Run: Post Developed 25-yr, 6-hr Reservoir: LDA-1
Start of Run: 13Apr2009, 00:00 Basin Model: Post-Developed
End of Run: 14Apr2009, 12:00 Meteorologic Model: 25-yr, 6-hr
Compute Time: 21Ju12010, 12:59:49 Control Specifications: Control Specifications
Volume Units: IN
Corrputed Results _...._. _. __... , ..._ .._
Peak Inflow : 3.32 (CFS) Date/Time of Peak Inflow : 13Apr2009, 11:55
Peak Outflow : 0.64 (CFS) Date/Time of Peak Outflow : 13Apr2009, 12:05
Total Inflow : 0.71 (IN) Peak Storage : 0.06 (AC-FT)
Total Outflow : 0.67 (IN) Peak Elevation : 677.19 (FT)
•
0
Project: Project 1 Simulation Run: Post-Developed 50-yr, 24-hr
Start of Run: 13Apr2009, 00:00 Basin Model: Post-Developed
End of Run: 14Apr2009, 12:00 Meteorologic Model: 50-yr,24-hr
Compute Time: 21 Ju12010, 13:19:30 Control Specifications: Control Specifications
•
Volume Units: IN
Hydrologic
Element Drainage Area
(M12) Peak Discharge
(CFS) Time of Peak Volume
(IN)
BR-1 .000796875 0.31 13Apr2009, 12:26 2.00
BR-2 0.0020000 0.00 13Apr2009, 00:00 0.00
Diversion-1 .000796875 3.96 13Apr2009, 11:53 4.49
Diversion-2 0.0020000 10.52 13Apr2009, 11:53 4.81
LDA-1 0.0042031 0.84 13Apr2009, 12:28 1.73
Sink-1 0.0042031 0.84 13Apr2009, 12:28 1.73
Subbasin-1 .000796875 3.96 13Apr2009, 11:53 4.49
Subbasin-2 0.0020000 10.52 13Apr2009, 11:53 4.81
Subbasin-3 0.0014062 6.37 13Apr2009, 11:55 4.17
•
•
0
Project: Project 1
Simulation Run: Post-Developed 50-yr, 24-hr Reservoir: LDA-1
Start of Run: 13Apr2009, 00:00 Basin Model: Post-Developed
End of Run: 14Apr2009, 12:00 Meteorologic Model: 50-yr,24-hr
Compute Time: 21Ju12010, 12:58:14 Control Specifications: Control Specifications
Corrputed Results
Peak Inflow :
Peak Outflow :
Total Inflow :
Total Outflow :
Volume Units: IN
6.37 (CFS) Date/Time of Peak Inflow :
0.84 (CFS) Date/Time of Peak Outflow
1.77 (IN) Peak Storage :
1.73 (IN) Peak Elevation
13Apr2009, 11:55
13Apr2009, 12:28
0. 13 (AC-FT)
677.50 (FT)

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Web Soil Survey
Page 1 of 2
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Search Map - Hydrologic Soil Group
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Properties and Qualities Ratings --
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Description of F Q
Rating Tables - Hydrologic Soil Group - Summary By Map Unit

Rating Options !? Summary by Map Unit Union County, North Carolina &'
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BaB Badin channery silt B 13.8 49.6%
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Yiew'Descrption ".View Rating. Totals for Area of Interest 27.8 100.0%
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Representative Slope storms.
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Unified Soil Classification (Surface) classes (A/D, B/D, and C/D). The groups are defined as follows:

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http://websoilsurvey.nrcs.usda.gov/app/WebSoilSurvey.aspx
6/3/2010
Soil Map-Union County, North Carolina
40 Map Unit Legend
Union County, North Carolina (NC179)
Map Unit Symbol Map Unit Name Acres in AOI Percent of A01
BaB Badin channery silt loam, 2 to 8 percent
slopes 13.8 49.6%
BaC Badin channery silt loam, 8 to 15
percent slopes 0.3 1.0%
ScA Secrest-Cid complex, 0 to 3 percent
slopes 13.7 49.3%
Totals for Area of Interest 27.8 100.0%a
•
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USDA ? Natural Resources Web Soil Survey 6/312010
Conservation Service National Cooperative Soil Survey Page 3 of 3
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BIORETENTION-WATER QUALITY
CALCULATIONS
•
r-?
•
Amicus engineering
Project No: 17-10-033 Sheet No: of
Date: 06-16-10
Calcs Performed By: JLM
Calcs Checked By: NRP
Project Name: Proposed Professional Building at Lawyer's Road
Subject: Bioretention -Water Quality
OBJECTIVE:
Determine required water quality volume for the proposed bioretention area.
DESIGN CONSIDERATIONS:
The Manual of Storm water Best Management Practices requires the design volume
of the bioretention structure be based on treating the first inch of runoff using the
Simple Method. Per a previous draft of the manual, a general rule of thumb states
that the surface area of the bioretention area should be between 3% and 8% of the
total drainage area. This rule of thumb was used as a starting point for the design.
REFERENCES:
1. "Manual of Storm Water Best Management Practices," by The North Carolina
Department of Environment and Natural Resources, 2007.
2. "Bioretention Drainage Map," by Amicus Engineering PC, 06/16/10.
CALCULATIONS
1. Bioretention Area BR-1
•
Elevation (ft)
[Ref: 2] Area (ft-)
[Ref: 2] Height (ft) Volume (ft)
682.00 1,865
1.00 1,586
681.00 1,306
i. Total volume available in Bioretention Area BR-1 (elev. 682.00 ft) = 1,586 ftj
Determine surface area required
a. Total drainage area = 0.51 acres [Ref: 2]
b. Surface area of BR-1 = 1,306 ft2 = 0.03 acres [Ref: 2]
c. Percent of area = (0.03 ac./0.51 ac.) = 0.06 or 6% therefore ok
2. Determine water quality volume required for area draining to BR-1
The runoff volume calculations in the "Simple Method" as described
by Schueler (1987) will be used. [Ref: 1]
a. Rv = 0.05 + 0.009(I)
Rv = runoff coefficient = storm runoff (inches) / storm rain faS10 y
r'
I = percent impervious portion of the drainage area = 44% • `L S EA L
032006 ;
Rv = 0.05 + 0.009(44) FN :
Rv = 0.45 (in. / in.) 0 .G N p
i??? AS

Amicus engineering
Project No: 17-10-033 Sheet No: of
Date: 06-16-10
Calcs Performed By: JLM
Calcs Checked By: NRP
Project Name: Proposed Professional Building at Lawyer's Road
Subject: Bioretention - Water Quality
b. For the volume that must be controlled:
Volume = (design rainfall) (Rv) (drainage area)
Volume = 1.00 inch rainfall * 0.45 (in. / in.) * 1/12 (feet / inch) * 22,327 ft2
Volume = 837 ft3
Volume available in BR-1 = 1,586 ft3
837 ft3 < 1,586 ft3 therefore ok.
3. Bioretention Area BR-2
Elevation (ft)
[Ref: 2] Area (ft)
[Ref: 2] Height (ft) Volume (W)
681.00 4,683
1.00 4,216
680.00 3,749
i. Total volume available in Bioretention Area BR-2 (elev. 681.00 ft) = 4,216 ft'

Determine surface area required
a. Total drainage area = 1.28 acres [Ref: 2]
b. Surface area of BR-2 = 3,749 ft2 = 0.11 acres [Ref: 2]
d. Percent of area = (0.09 ac./1.28 ac.) = 0.07 or 7% therefore ok
4. Determine water quality volume required for area draining to BR-2
The runoff volume calculations in the "Simple Method" as described
by Schueler (1987) will be used. [Ref: 1]
c. Rv = 0.05 + 0.009(I)
Rv = runoff coefficient = storm runoff (inches) / storm rainfall (inches)
I = percent impervious portion of the drainage area = 66%
Rv = 0.05 + 0.009(66)
Rv = 0.64 (in. / in.)
•

Project No: 17-10-033 Sheet No: of
tr Date: 06-16-10
Calcs Performed By: JLM
Calcs Checked By: NRP
Amicus ingineering Project Name: Proposed Professional Building at Lawyer's Road
Subject: Bioretention - Water Quality
d. For the volume that must be controlled:
Volume = (design rainfall) (Rv) (drainage area)
Volume = 1.00 inch rainfall * 0.64 (in. / in.) * 1/12 (feet / inch) * 55,626 ft2
Volume = 2,967 ft3
Volume available in BR-2 = 4,216 ft3
2,967 ft3 < 4,216 ft3 therefore ok.
•
LJ

NCDENR Store-twater KT Manua]
Revised 09-28-07
allows the user to select from one of NOAA's numerous data stations throughout the
state. Then, the user can ask for precipitation intensity and view a table that displays
precipitation intensity estimates for various annual return intervals (ARTS) (1 year
through 10DO years) and various storm durations (5 minutes through 60 days)-
The requirements' of the applicable stormwater program will determine the appropriate
values for ARI and storm duration. If the design is for a level spreader that is receiving
runoff directly from the drainage area, then the value for I should simply be one inch
per hour (more information on level spreader design in Chapter 8).
3-3. Runoff Volume
Many stormwater programs have a volume control requirement; that is, capturing the
first 1 or 1.5 inches of stormwater and retaining it for 2 to 5 days. There are two primary
methods that can be used to determine the volume of runoff from a given design storm:
the Simple Method (Schueler,1987) and the discrete SCS Curve Number Method (MRCS,
198M). Both of these methods are intended for use at the scale of a single drainage area-
Stormwater BN1 S shall be designed to treat a volume that is at least as large as the
volume calculated using the Simple-Method. H the SC5 Method yields a greater volume,
then it can also be used.
3-3.1. Simple Method
The Simple Met?nod uses a mir,7rnal amount of information such as Watershed drainage
• area, impervious area, and design storm depth to estimate the volume of runoff- The
Simple Method was developed by measuring the runoff from many watersheds with
l mown imply-vious areas and curve-fit`uz; a relationship betwezn percent
impen oushess and the f r ac ion of rainfall converted to ru_no=_ (the runoff Coefficient).
This relationship is presented bell ow:
Rv = 0.05 +0.9 '.Ti
Where: Rv = Runoff coefficient {storm runoff (in)/storm rainfall (in)], unitless
IA = Impervious fraction [impervious portion of drainage area (ac)/
drainage area (ac)], unitless.
Once the runoff coefficient is determined, the volume of runoff that must be controlled is
given by the equation below:
V=3630*RD*Rz,*A
Where: V = Volume of runoff that must be controlled for the design storm (ft3)
RD = Design storm rainfall depth (in) ffy7ncaliy, 1.0" or 1.5")
A = Watershed area (ac) '

Stormwater Management and Calca ations 3-3 July 2007

E
NCDENTR Storm)vater BMP Manual
12 Bioretention
Descripfi.on
Bioretention is the use of plants and soils for removal of pollutants from stormwater runoff via
adsorption, filtration, sedimentation, volatilization, ion exchange, and biological decomposition.
In addition, bioretention provides landscaping and habitat enhancement benefits.
ReKulatory Credits Feasibility Considerations
Pollutoit Re7ncval
85% Total Suspended Solids High Land Requirement
35% Total Nitrogen Med-High Cost of Construction
45% Total Phosphorus Med-High Maintenance Burden
Water Quantin Small Treatable Basin Size
yes Peak Runoff Attenuation Med Possible Site Constraints
Possible Runoff Volume Reduction Med-High Community Acceptance
Advantages
- Efiiaent removal method for suspended
solids, heavy metals, adsorbed pollutants,
nitrogen, phosphorus, pathoge--is, and
ten- erature_
- Lf providing;riniTation in appropriate soil
conditions it can effeciivzy reduce pealk
runoff rates foi i-dativeiy frequent storms,
reduce runoff volumes, and rezhaiTge
b ound-water.
- flexible adaptation to urban retrofits.
- Individual u_n:it are well suited for use in
small areas, and multiple, distributed units
can provide treatnnent in large drainage
Natural integration into landscaping for
urban landscape enhancement.
Revised 09-28-07
Disadvantages
- Surface soil layer may clog over time
(though it can be restored)-
- Frequent trash removal may be required,
espeaally in high traffic areas.
-te 1V ID°LLznce Sri protecting tl bioretantion
area during construction is essential.
Single unit can only serve a small
drainage area
Requires frequent maintenaance of -plant
matey and mulch layer.
Bioretention
12-1
July 2007
NCDENR Stormwater PIvIl' Manual
0 Major Design Elements
0
Revised 09-28-07
f?eyzxsr?irl b3s?he `" ? Aclniinxstra?ire ,?x?'?es p£??he ?ns? ! , ? ?? P?taf ?Ma a , ? a?ent?
Gnrnrxixssxoia ?3?ief ?e?cat?ons ?a??e necwessa??-t? el= the,sta'tecd?o?l.u2tan'rf?enn?va i
'?' A h 1 1 S C'7} K..ajYY ? X J ? ? v 1 w t `1 ? ? ?, t? r1 J.. ?+`? ? t 4 <'? 1 f rJ. V ''?S.}+ i' ? k r ?, f H-rv 4 :1
;`er(,n;en#? ?7? +S" Jr ?? ? >.. ? ? 'f2i LI k ?? _il Li 1 $L ,T7 4i { •j {? Y ? ? z0 ? x !? C:
.a7._ .5 __u'= K•...u..x.. .. .s: .. .+..fm6 ,rl':. <t_i ..r.
Mingo shall take into account all runoff at ultimate build-out including off-site
drainage-
ide slopes stabilized •c-+rith veetation shall be no steeper than 3:1-
C,
EMP shall be located in a recorded drainage easement with a recorded access
J
asement to a public right of way (ROW).
olume in excess of the design volume, as determined from the design storm, shall
bypass the bioretention cell.
olume in excess of the design volume, as determined from the design storm, shall be
venly distributed across a minimum 30 feet long vegetated filter strip. (_A 50 ft filter
required in some locations.) If this can not.be attained, alternate desigrs will be
onsidered on a case by case basis.
>ioretention facilities shall not be used where the seasonally high water table less than
? feet below bottom of _MP_
Media permeability of 0.52-6"per hour is required, 1-2 in per hour is preferred-
1 e design sha?T be located a =Lu imum of 30 feet from su1ace waters, and 50 feet from-
s S_-'? waters
The design shall be located a minimum of 100 feet from water supply wells.
uudT , Qoae?r?asdn avaab?eril rarseuaat?
7
coos recessA a -Offi
ary
0 ioretention facilities shall not be used -here slopes greater than 20%, or in non-
anently stabilized drainage areas--
ow must be sheet flow (1 ft/sec) or utilize energy dissipating devices.
2 ? onding depth shall be 12 inches or less. Nine inches is preferred
13 edia depth shall be specified for the vegetation used- For grassed cells, use 2 feet
um. For shrubs or trees use 3 feet minimum_
14 e geometry of the cell shall be such that no dimension is less than 10 feet (width,
ength, or radius).
15 edia should be specified as listed in this section.
e phosphorus index (P-index) for the soil must be low, between 10 and 30. This is
6 hough phosphorus to support plant growth without exporting phosphorus from the
ell.
Ponded water shall completely drain into the soil within 12 hours. It shall drain to a
17 level of 24 inches below the soil surface in a maximum of 48 hours.
0 -
Bioretention
12-2
July 2007
NCDENR Sto=water BAQ1-' Manual
Revised 09-29-07
• An underdrain shall be typically installed if in-situ soil drainage is less than 2 in/hr or
is if there is in situ loamy soil (-12% or more of fines). This is usually the case for soil
tighter than sandy Ioam.or if there has been significant soil compaction from
construction.
? 9'Clean-out pipes must be provided if underdrains are required- .
12.1. General Characteristics and Purpose
A bioretention cell consists of a depression in the ground filled with a soil media
mixture that supports various types of water-tolerant vegetation- The surface of the BMP
is depressed in bioretention facilities to allow for ponding of runoff that filters through
the BMI' media-Mater emits the bioretention area via exfiltration into the surrounding
soil, flow out an underdrain, and evapotranspiration. The surface of the cell is protected
from weeds, mechanical erosion, and desiccation by a layer of mulch. Bioretention is an
efficient method for removing a wide variety of pollutants, such as suspended solids,
heavy metals, nutrients, pathogens, and temperature (NC Cooperative Exterisibn, 2©06)_
Bioretention areas provide some nutrient uptake in addition to physical filtration. If
located at a site -ivith appropriate soil conditions to provide infiltration, bioretention can
also be effective in reducing peak runoff rates, reducing runoff volumes, and recharging
groundwater-
Many development projects present a challenge to 4e designer of conventional
stormwater BIN s because of physical site constraints. Bioretention areas are intended to
address the spatial constraints that can be found in densely developed urban areas .
where the drainage areas are highly impervious (see Figure 22-1). They can be used on
small urban sites that wool d not normally support the hydrology of a wet detention
pond and where the soils would not allow for an infiltration device. Median strips,
ramp loops, traffic circles, and parking lot islands are good examples of typical locations
for bioretention areas. See Section 22.3.1 for more illustrated examples of the versatility
of bioretention facilities.
Bioretention units are ideal for distributing several units throughout a site to provide
treatment of larger areas- Developments that incorporate this decentralized approach to
stormwater management can achieve savings by eliminating stormwater management
ponds; reducing pipes, inlet structures, curbs and gutters; and having less grading and
clearing. Depending on the type of development and site constraints, the costs for using
decentralized bioretention stormwater 3cnanagement methods can be reduced by 10 to
25 percent compared to stormwater and site development using other BMPs (Coffman et
al-, 1998).
Bioretention facilities are generally most effective if they receive runoff as close as
possible to the source- Reasons for this include. minimizing the concentration of flow to
reduce entry velocity, reducing the need for inlets, pipes, and downstream.controls,' and
allowing for blending of the facilities with the site (e.g., parking median facilities)- For
sites where infiltration is being utilized, it also avoids excessive groundwater mounding.
Where bioretention takes the place of required green space, the landscaping expenses
•
12-3
July 2JX7
Bioretention
•
NCDENR Sto-=vater BMP Manual
that would be required in the absence of bioretention should be subtractedwhen
determining the actual cost (Low Impact Development Center, 2003). Bioretention cells
may also address landscaping/green space requirements of some local governments
(Wossink and Hunt, 2003)_
Figure 12-1
Bioretention in Parking Lot Island

•
12.2. Meeting Reggulat©ry P,- einents
To obtain a permit to construct a bioretention cell in North Carolina, the biorete_-ntion cell
must meet all of the Requirements specified in the Major Da:--I---Ti elements located at the
b`??nnuig OSef tius cLOn_
PoZluto_nt Removal Czlculations
The pollutant removal calculations for bioretention facilities are as described in Section
3-4, and use the pollutant removal rates provided in Table 4-2 in Section 4.0_
Construction of a bioretention cell also passively lowers nutrient loading since it is
counted as pervious surface when calculating nutrient loading.
Volume Control Calculations
Chapter Revised 09-28-07
A bioretention cell can sometimes be designed with enough storage to provide active
storage control (calculations for which are provided in Section 3.4), however, some may
not have enough water storage to meet the volume control requirements of the
particular stormwater program (since its storage potential is limited because the
ponding depth is limited) so they may need to be used in series with another BMP with
volume control capabilities. All bioretention facilities provide some passive volume
control capabilities by providing pervious surface and therefore reducing the total
runoff volume to be controlled.
Bioretentiion
12-4
July 2007
•
PIPE HYDRAULICS AND
GRATE CAPACITY
CALCULATIONS
0
•
Project No: 17-10-033 Sheet No: of
Date: 09-01-10
Calcs Performed By: JLM
10 Calcs Checked By: NRP
Amicus Engineering Project Name: Proposed Professional Building at Lawyer's Road
Subject: Pipe Hydraulics & Grate Capacity
OBJECTIVE:
Design a series of storm drainage pipes to adequately convey runoff during and after
construction. Verify the grate capacity of all catch basins.
REFERENCES:
1. Charlotte Mecklenburg Stormwater Design Manual
2. "Proposed Grading Plan," by Amicus Engineering PC, 09/01/10.
3. FHWA Urban Drainage Design Program, HY - 22.
4. "Water Resources Engineering," by Mays, Larry W., 2001.
5. Charlotte Mecklenburg Land Development Standards
6. "Hydrologic Evaluation," by Amicus Engineering PC, 09/01/10.
TERMS:
Q i o = 10-year peak flow, (ft3/s)
Qi = 1St-inch peak flow, (ft3/s)
Q f = first flush peak flow, (ft3/s)

C?
Qi = inlet capacity, (ft3/s) S S
ti ?

C = runoff coefficient E
/
%
a
T-
Co = orifice coefficient S E A L
= :
d = depth of water ponded over grate, (ft) 0 3 2 0 0 6
g = acceleration due to gravity, (ft/s2) c° GIN ---
'
°
?
ti
i = rainfall intensity, (in/hr) ii
0?
• - ° pp
??
A = drainage area, (acres) /00111W\
a = clear opening area of a grate, (ft)
t, = time of concentration, (min)
GIVEN/REQUIREMENTS:
Minimum design storm = 10-year [Ref: 1 ]
CALCULATIONS:
1. Determine grate capacity for catch basins
a. Determine maximum inflow for 10-yr storm for catch basins
0
Amicus Ingineering
Project No: 17-10-033 Sheet No: of
Date: 09-01-10
Calcs Performed By: JLM
Calcs Checked By: NRP
Project Name: Proposed Professional Building at Lawyer's Road
Subject: Pipe Hydraulics & Grate Capacity
Catch Total 10-yr Rainfall Weighted 10-yr
Basin/ Drainage Intensity, i, Runoff Flow,
Inlet Area (in/hr) Coefficient, C Qio
(Acres), A [Ref: 1, [Ref: 1, (cfs)
[Ref: 2] Table 3-3] Table 3-5]
CB-1 0.32 7.03 0.95 2.14
CB-2 0.71 7.03 0.95 4.74
b. Determine grate capacity for catch basin CB-1 and CB-2
- Since inlets are in sag locations, assume orifice control and 50% clogging by
debris. The maximum ponding depth will be evaluated as 0.5 foot.
- Q; = COA(2gd)0-5 [Ref: 4, Eq. 16.1.33]
- Opening ratio = 0.46 [Ref: 5, CLDS 20.02B]
- Co = 0.67 [Ref: 4]
- Grate capacity for aforementioned structures
Q; =(0.67)[(0.46)x(6sq.ft)][(2)x(32.2 ftIs2)x(0.5ft)]0.5 =10.49 ft3Is
0
(50%) Qi =(0.50)x(10.49 ft3Is)=5.25 ft3Is
o The grate capacity far exceeds the calculated ten year flows
2. Determine pipe sizes for pipes P1- P8, Temp. CPP, and Roof Drain
Collection Pipes [Ref: 3]
Drain
Pipe Contributing
Flow
[Re£2] Flow,
Q
(cfs)
Temp. CPP CB-2 4.74
RD I Roof Drain 0.86
RD2 Roof Drain 0.86
Pi LDA-1 1.000
P2 CB-2 4.74
P3 CB-1 2.14
P4 Existing 36" Pipe 32.31
P5 Existing 36" Pipe 32.31
P6 I"-inch to BR-1 0.085
P7 1St-inch to BR-2 0.355
P8 Roof Drain 0.86
a. Based on hydrologic evaluation
b. Existing flow based on analysis from FHWA Urban
Drainage Design Program
c. 50-year outflow from Landscaped Detention System
[Ref: 6]
[Ref: 3]
[Ref: 6]
•
E
Amicus ingineering
Project No: 17-10-033 Sheet No: of
Date: 09-01-10
Calcs Performed By: JLM
Calcs Checked By: NRP
Project Name: Proposed Professional Building at Lawyer's Road
Subject: Pipe Hydraulics & Grate Capacity
Drain
Pipe Flow,
Q
(cfs) Slope, S
(ft/ft) Manning's
Coefficient, C Required
Diameter (in)
[Ref: 3] Actual
Diameter
(in) Velocity
(ft/s)a
[Ref: 3]
Temp. CPP 4.74 0.169 0.020 12 12 11.92
RD1 0.86 0.007 0.012 12 12 3.42
RD2 0.86 0.007 0.012 12 12 3.42
P1 1.00 0.004 0.012 12 12 2.87
P2 4.74 0.008 0.012 15 15 5.53
P3 2.14 0.012 0.012 12 12 5.38
P4 32.31 0.007 0.012 30 36 8.52
P5 32.31 0.002 0.012 36 36 5.20
P6 0.08 0.005 0.012 12 12 1.52
P7 0.35 0.005 0.012 12 12 2.31
P8 0.86 0.007 0.012 12 12 3.42

clzu,, 0
Iripensi-Ly
?Ct?e;,^iirier??
3-6-B
113E .r2lr3iall iriiEr3s1Y l 5 i'lt: aVrtdQE 3 'in'1211 rate. Rr, IriC•hes/Tiour
4or ca J t3f7
!eOU2i. fl the DIME G COF)CER-a-,arlpi3 fora selected re-Wim penrod_ Or-ti a m IC 3iai
r eru fl p?r6od has -been sefecaed i GT t1eSigi i ariC? c ?i13ic OT CDnCe 7'u 3jiCT3 a 3ICI31ctea
X { T I?7 di rr1aiE arch, The ralnidll in- Le can .ire ete- iflyd TToi3"'i P.2inT211-
tfizIrfl tip- 11i"c'r7CTI 2i2 give in Tab ? - :SI'Ia[C ie-fine interpoil-cia .Can be used
to p rri_ -ramFai[ tm s'? vaiu>?'ar s?i?rm, ur?Vq t bertwee .. the values
:given
in Table 3-3.. -
I h rurlof ppe-I `tier j. JQ ls th Vadable t . the rc-i1onaI ..rgmo d last sus.cep iJiE
It3 precise :a IErnMa iun. grid requires JUG arri.-..nt end clr3darsi?r?diri.g. Vin.' 1ze.:parT
of the design engineer. VNrnilr engmee qg ju'Op--.-Ieni w?,ra? alv?aavs tea .:::;?riir.?c
.tic saleczlc I OT ru-10T3 CC)e iclenu, plcal Cbe icjerks repPE-S it 3E I€-tiE r2iu:?
;•.7 _, _?. _..?,basin ammeters T??
3:e...??r3?iy'E?? ' ?' f?+' uII???3?.? 2133`?.,z? ?1G?iiF:?'3?.''•ti'?7.vti
able - °-omm, ded gi. oil C IiE_::.C',.QriL /ailleS

Des Cfi 0ri -Tl {'i.i A r
Rurom OE, jc?leriz -C)
Lawns
n i?-
woqded C,
5
Ga'°cmE!
creaS: r r

Parks & ceme-re-es 0.30
Resider#fal_ :Cncludi1?_g. s -u ae- ),
Si P91 Farrgily 101 < 9 '000 -IZ
Single--Farnil.' LrC >. .000 ,
7 CAv ll Si?T3c$: .
areas
FH avy -eas
*0- ffice Park-'s
:S:Bi3. pirig. °CenEers
.3-1-4
_ 0 i?0
Ot 70
0
•
•
1.5 Desian Frequerlc.
Design
Fraquenme,s
Aas??I€
? 73,i? ?tSi
C?
RISr
..J
fable. 343
-

. F,dr?a1l ??aL?:1Sf?°5 CrarI????,. ?0'F:h _C:z?Dl ii?c
`
5'o=l b' Cdr Cycii?f Gll 3.?'iLC ?J i?t S_l't?i:.

i70L175 talTiLae$ L .2
.5
?1
;ll
10
5--03
-Z--60
FEL 0
6 -b Y-5
39
;8 .5
4 r.: Lam` 5
5 A:9 J ,{
6-2 7.31
5. 3 2
450 --ri 1. 2

2,S -6; a 2
17
6!3 I.z;. 44 3
f3b
.17
.21 0 `-70

r. '.3 ..3
14 2 BW : 2-S8 3_ S- 4--7 _ -2 5:73
2-5 Z w 7. "3:7 -40
130 8
27 --43 2..7 3,2 3 _ A5 4-9-0 6.3fl.
33 '2-7-3- I::r 47

3
. 2-2B 2-62 n, fl5 E 4 L
4-:37:
.59 1. 64 7.90 2-23 66 : 34
67
j 2.1 4,

03 '82 mEQ

T.Q .e . rr eQ>? i3 , -Ir aID.Fe:t?( e gar f arsOtte
-
, .

C?
v-
FHWA Urban Drainage Design Program, HY-22
HYDRAULIC PARAMETERS OF OPEN CHANNELS
Circular X-Section
Date: 06/09/2010
Project No. .
Project Name.:
Computed by .
INPUT PARAMETERS
1. Pipe Slope (ft/ft) 0.0020
2. Pipe Diameter (in) 36.0
3. Manning's Coefficient 0.012
4. Discharge (cfs) 32.314
OUTPUT RESULTS
Full Flow Conditions
Depth of Flow (ft) 3.00
Velocity (ft/sec) 4.57
L?
0
FHWA Urban Drainage Design Program, HY-22
HYDRAULIC PARAMETERS OF OPEN CHANNELS
Circular X-Section
Date: 09/02/2010
Project No. .
Project Name.:
Computed by .
INPUT PARAMETERS
1. Pipe Slope (ft/ft) 0.1690
2. Pipe Diameter (in) 12.0
3. Manning's Coefficient 0.020
4. Discharge (cfs) 4.740
OUTPUT RESULTS
Partial Flow Conditions
Depth of Flow (ft) 0.50
Velocity (ft/sec) 11.92
Y
E

FHWA Urban Drainage Design Program, HY-22
HYDRAULIC PARAMETERS OF OPEN CHANNELS
Circular X-Section
Date: 09/02/2010
Project No. .
Project Name.:
Computed by .
INPUT PARAMETERS
1. Pipe Slope (ft/ft) 0.0070
2. Pipe Diameter (in) 12.0
3. Manning's Coefficient 0.012
4. Discharge (cfs) 0.860
OUTPUT RESULTS
Partial Flow Conditions
Depth of Flow (ft) 0.35
Velocity (ft/sec) 3.42
•
0

•
FHWA Urban Drainage Design Program, HY-22
HYDRAULIC PARAMETERS OF OPEN CHANNELS
Circular X-Section
Date: 09/02/2010
Project No. .
Project Name.:
Computed by .
INPUT PARAMETERS
1. Pipe Slope (ft/ft) 0.0070
2. Pipe Diameter (in) 12.0
3. Manning's Coefficient 0.012
4. Discharge (cfs) 0.860
OUTPUT RESULTS
Partial Flow Conditions
Depth of Flow (ft) 0.35
Velocity (ft/sec) 3.42
•
•
7xG - 3
FHWA Urban Drainage Design Program, HY-22
HYDRAULIC PARAMETERS OF OPEN CHANNELS
Circular X-Section
Date: 09/02/2010
Project No. .
Project Name.:
Computed by .
INPUT PARAMETERS
1. Pipe Slope (ft/ft) 0.0040
2. Pipe Diameter (in) 12.0
3. Manning's Coefficient 0.012
4. Discharge (cfs) 1.000
OUTPUT RESULTS
Partial Flow Conditions
Depth of Flow (ft) 0.45
Velocity (ft/sec) 2.87
0

FHWA Urban Drainage Design Program, HY-22
HYDRAULIC PARAMETERS OF OPEN CHANNELS
Circular X-Section
Date: 09/02/2010
Project No. _
Project Name.:
Computed by .
INPUT PARAMETERS
1. Pipe Slope (ft/ft) 0.0080
2. Pipe Diameter (in) 15.0
3. Manning's Coefficient 0.012
4. Discharge (cfs) 4.740
OUTPUT RESULTS
Partial Flow Conditions
Depth of Flow (ft) 0.81
Velocity (ft/sec) 5.53
0
11

FHWA Urban Drainage Design Program, HY-22
HYDRAULIC PARAMETERS OF OPEN CHANNELS
Circular X-Section
Date: 09/02/2010
Project No. .
Project Name.:
Computed by .
INPUT PARAMETERS
1. Pipe Slope (ft/ft) 0.012
2. Pipe Diameter (in) 12.0
3. Manning's Coefficient 0.012
4. Discharge (cfs) 2.140
OUTPUT RESULTS
Partial Flow Conditions
Depth of Flow (ft) 0.50
Velocity (ft/sec) 5.38
•
0
?? ??,,Dc- -F>q
FHWA Urban Drainage Design Program, HY-22
HYDRAULIC PARAMETERS OF OPEN CHANNELS
Circular X-Section
41 Date: 09/02/2010
Project No. .
Project Name.:
Computed by .
INPUT PARAMETERS
1. Pipe Slope (ft/ft) 0.0070
2. Pipe Diameter (in) 30.0
3. Manning's Coefficient 0.012
4. Discharge (cfs) 32.310
OUTPUT RESULTS
Partial Flow Conditions
Depth of Flow (ft) 1.79
Velocity (ft/sec) 8.52
is
0

FHWA Urban Drainage Design Program, HY-22
HYDRAULIC PARAMETERS OF OPEN CHANNELS
Circular X-Section
Date: 09/02/2010
Project No. .
Project Name.:
Computed by .
INPUT PARAMETERS
1. Pipe Slope (ft/ft) 0.002
2. Pipe Diameter (in) 36.0
3. Manning's Coefficient 0.012
4. Discharge (cfs) 32.310
OUTPUT RESULTS
Partial Flow Conditions
Depth of Flow (ft) 2.46
Velocity (ft/sec) 5.20
0

69
FHWA Urban Drainage Design Program, HY-22
HYDRAULIC PARAMETERS OF OPEN CHANNELS
Circular X-Section
Date: 09/02/2010
Project No. _
Project Name.:
Computed by .
INPUT PARAMETERS
1. Pipe Slope (ft/ft) 0.0050
2. Pipe Diameter (in) 12.0
3. Manning's Coefficient 0.012
4. Discharge (cfs) 0.080
OUTPUT RESULTS
Partial Flow Conditions
Depth of Flow (ft) 0.11
velocity (ft/sec) 1.52
3 ? ? -7
FHWA Urban Drainage Design Program, HY-22
HYDRAULIC PARAMETERS OF OPEN CHANNELS
Circular X-Section
Date: 09/02/2010
Project No. .
Project Name.:
Computed by .
INPUT PARAMETERS
1. Pipe Slope (ft/ft) 0.005
2. Pipe Diameter (in) 12.0
3. Manning's Coefficient 0.012
4. Discharge (cfs) 0.350
OUTPUT RESULTS
Partial Flow Conditions
Depth of Flow (ft) 0.24
Velocity (ft/sec) 2.31
E

FHWA Urban Drainage Design Program, HY-22
HYDRAULIC PARAMETERS OF OPEN CHANNELS
Circular X-Section
Date: 09/02/2010
Project No. .
Project Name.:
Computed by .
INPUT PARAMETERS
1. Pipe Slope (ft/ft) 0.007
2. Pipe Diameter (in) 12.0
3. Manning's Coefficient 0.012
4. Discharge (cfs) 0.860
OUTPUT RESULTS
Partial Flow Conditions
Depth of Flow (ft) 0.35
Velocity (ft/sec) 3.42
•
0
642 Chapter 16 Stormi:ater.Control: Street and I-Egbway Drainage and Culverts
The.mterczption capacky of the curb-opening inlet is then
Or E?0 = (0.4'.1)(8) = 328 ,cfs
To.co npute ihe:intereeption capacity of the gratain]et,•.egnation (?b-i 27).is used ,
The dome at the vrate is - ien 0.= 8 -.3-29 =.a.7_ . 2 ;
cam: Usine this Dow rate. the.spread'T .:can
puted with equation (16.1.8a):
0 = O_5b e2sif3Tv r
.. 472 = . 00 fi (0 01)1f' (Q 025)513 2sr
T, = 11.22A
Next the velocity can;be.computed for usein.dttermininofrom Figs 16A.8, so Sol
V= Q14 _ o = 4_72 = 3.00 ft/s
(1122)2(
12x Ss .0.025)
From Figure 16.1.8, T = 1.0. The side-foci J tercepd6n efficiencyds co p T.°d:t_inQ.w? 't?c -
16-1 44):
18 . _ ; =0.10
BsZ 0:023(2)'-'
--?
_ The'fipn-1-flow ratio 3s computed using.equanon (16.121)_
117
=1- i =1- 3- =.0.41
Sbe'aitterception .°Ta^i:' is tltea,
fl- fl(I; a _RJ1 - i =.4-72(lY:0,4 _1 = 0:1(1 -I):-^_1))??1 cf,
n`7
?
Ile vital int° hon is tJ. _. O 2 2°
I6:15 .Interception Capacity- and.Efficiencv of inlets iu"Sag.:L-©rations y?
'f
Inlets that- plac5l in. sa= .Iocations o
prate as :u°etr nuder:low heads -anii:as;-ori,7cas io t
heads- The transitionbetwum weir flow, and orifice flow cannot be acctuaiely.denaed, as &- A
ma3 fluctuate-back and forth letween the two.conrro7s.All runoff that eaters sa.?s _mi.st lkr?
#hrmghthe.iWa Asa conseiluence, the 4i ficiency of inlets ;in•sa_Qs inpassing '•debns is so?w?
critical. Comlituation inlets and cud)--op. iing inlets are rcommended,for.saj :Iocations,'as
itilets have c1oU g tendencif-
j -? :I:63_53 Gratelrriefsin'tzLoagion
`3'he:calkacii?r.of.?xateinicis..Q?under:weir,control?.is l ?
u,.'
N`
C'--Pdi? (Lb 1 ?.
& ,
} A rz
A} .
CIL f `?J
16.1 Drainage of Street and Highway Pavements 643
where C, is the weir coefficient; 3.0 for U.S. customary units (1.66 for SI units), P is th-,g1ate
perimeter disregarding bars and the curb side in ft (m), and d is the depth of water over the.inlez
in ft .(m)- The.capacity of grate inlets under office.. control is
-t `O =CO A(2gd)os (16.1.33)
where;+Qo is 0.67, A is the clear opening area of the.gate, ft' (hi-), and g.is `the.acceleration due to
gravity, 32.16 ft/s'- •(9:81 m/s). ,Fig re :16.1-9 provides a design solution for equations .(1.6.1.32)
and (16;1.33)_
Consider a symmetrical
sawQ vertical curve (with a c¢rb) w3xh equal b)j)ass. frnm:in.T:ts npgade of:.#he •'
low point.Determine,the.gr~at :size for a design ;Q o> .6.it3/s and he-cinb depTb Allow .for 30 percent
clowgng of fire.grate- The design'sP-d is Tom. = 12 fi S = 0:0i: S = 0.025.ft_ and n = 0.016. What ?
happens when the flow rate is 8 ft3ls? .
?t3LU17?Ar Accorctingto Fig- 16:1.:9, a grate mnst have a pea*neter:of 12 ft usitig d ? _ - . (
12 0.025
x _ - .) =.03
-crud L =.S .t"': A-'-k!z 50 P---t c1owt"ng by debtis, .ire effeG?e prrimeY' as leduc i by 50
pvrcenc 9ssume the use of a grate would meet the pey ter requirzmew with a double 1.fi X 5 ft gmle.
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0
RIPRAP APRON
CALCULATIONS
0
0
•
•
Project No: 17-10-033 Sheet No: of
U Date: 09-01-2010
.
Calcs Performed By: JLM
Calcs Checked By: NRP
Amim Engineering Project Name: Proposed Professional Building at Lawyer's Road
Subject: RipRap Apron
OBJECTIVE:
Design Riprap Apron (RA-1) to dissipate the 50-year flow discharging from pipe P 1.
REFERENCES:
1. North Carolina Erosion and Sediment Control Handbook, 2008.
2. "Pipe Hydraulics and Grate Capacity," by Amicus Engineering PC, 09/01/10.
TERMS:
Qso = 50-year peak flow, (ft3/s)
do = diameter of discharge pipe, (in)
d50 = median stone size in a well-graded riprap apron, (in)
dmax = maximum stone diameter in riprap apron, (in)
La = length of riprap apron, (ft)
W = downstream width of riprap apron, (ft)
cfs = cubic feet per second
V50 = 50-year peak velocity, (ft/s)
GIVEN/REQUIREMENTS:
Minimum design storm = 50-year
Pipe P1
Qso = 1.00 cfs
V50 = 2.87 ft/s
do = 12"
Assume minimum tailwater conditions
S /
_ SEAL T_:
032006 _
G//18.R
CALCULATIONS:
1. Determine median and maximum stone diameter
a. Determine median stone diameter
- d50 = 4,7
b. Determine maximum stone size
- dmax = 1.5 x d50 = 1.5(4") = 6.0"
2. Determine dimensions of riprap apron
a. Determine minimum length of riprap apron
La=8ft
b. Determine width of riprap apron
- Upstream width = 3 do = 3(1.0 ft) = 3.0 ft
- Downstream width of apron
• o W=do+L,a=1.0+8.0ft=9.0ft
[Ref: 1 ]
[Ref: 2]
[Ref 2]
[Ref: 2]
[Ref: 1, Fig. 8.06a]
[Ref: 1 ]
[Ref: 1, Fig. 8.06a]
[Ref: 1, Fig. 8.06a]
AmIcus Ingineering
Project No: 17-10-033 Sheet No: of
Date: 09-01-2010
Calcs Performed By: JLM
Calcs Checked By: NRP
Project Name: Proposed Professional Building at Lawyer's Road
Subject: RipRap Apron
c. Determine thickness of apron
T = 1.5(dmax) = 1.5(6.0") = 9.0"
- Use T = 11.25"
- Use appropriate filter fabric underneath apron
•
[Ref: I]
0

Appendices
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 Service. Outlet protection is provided by a level apron of
sufficient length and flare to reduce flow velocities to nonerosive levels.
Design Procedure for The following procedure uses two sets of design curves: Figure 8.06a is used
R i p ra p Outlet for minimum tailwater conditions, and Figure 8.06b for maximum tailwater
conditions.
Protection
Step 1. Determine the tailwater depth from channel characteristics below the
pipe outlet for the design capacity of the pipe. If the tailwater depth is less
than half the outlet pipe diameter, it is classified minimum tailwater condition.
If it is greater than half the pipe diameter, it is classified maximum condition.
Pipes that outlet onto wide flat areas with no defined channel are assumed
to have a minimum tailwater condition unless reliable flood stage elevations
show otherwise.
Step 2. Based on the tailwater conditions determined in step 1, enter Figure
8.06a or Figure 8.06b, and determine d.0 riprap size and minimum apron length
(L). The dso size is the median stone size in a well-graded riprap apron.
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:
dm.= 1.5xdso
Step S. Determine the apron thickness:
Apron thickness = 1.5 x dmax
Step 6. Fit the riprap apron to the site by making it level for the minimum
length, La, 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 flow of the receiving stream.
Make any necessary alignment bends near the pipe outlet so that the entrance
into the receiving stream is straight.
•
Rev. 12/93
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 plunge pool should be considered, see
page 8.06.8.
8.06.2
L) K'• i
Appendices
3 0
ll?'!
Outlet W = D0 + La 1 i,l'
g pipe I
diameter (Do) I iH
La 80
T ilwater < 0.5D0 ("I !' I' j I fl'' r1l
7 i I
P ?? al I+C ' t. t1I I
60 rk jjl
°k Q?0
? i f 'I I.+I I i I 1.•
50 fI i t 61 ry a
I if t ? i•? hill ,.L.j .. .
:._ [.. ?; L; it I ? !I II ? I? I it II :I?t ; I o a a i
a
20
i z?a'15 is , I- I 3
'' 1 I I
: I ?, i. r l •? I. II I .t I• Ij I I' r ? L 1 II H
?. 10
iz-
-0 if i -k
2 (n
li!= 1` a? I i? ?lii llu i t I I. +. a a
o p t) cu
25,
i vc201 _ t 1 0
I 5 a } t 10
Ili iil! tll `t 1 I'-I u: V, '? 15 1 I I It I ! I j i } t? I .l 1 70
10
lc j:. j• ?, I I
V 5
5 10 20 50 100 200 500 1000
cl?
Discharge (ft3lsec)
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).
?J
Rev. 12/93
8.06.3
Project No: 17-10-033 Sheet No: of
Date: 09-01-2010
Calcs Performed By: JLM
Calcs Checked By: NRP
Amicus engineering Project Name: Proposed Professional Building at Lawyer's Road
Subject: RipRap Apron
OBJECTIVE:
Design Riprap Apron (RA-2) to dissipate the 10-year flow discharging from pipe P-2.
REFERENCES:
1. North Carolina Erosion and Sediment Control Handbook, 2008.
2. "Pipe Hydraulics and Grate Capacity," by Amicus Engineering PC, 09/01/10.
TERMS:
Q 1 o = 10-year peak flow, (ft3/s)
do = diameter of discharge pipe, (in)
d5o = median stone size in a well-graded riprap apron, (in)
dmax = maximum stone diameter in riprap apron, (in)
La = length of riprap apron, (ft)
W = downstream width of riprap apron, (ft)
cfs = cubic feet per second
Vio = 10-year peak velocity, (ft/s)
GIVEN/REQUIREMENTS:
40 Minimum design storm = 10-year [Ref: 1 ]
Pipe P-2
Qio = 4.74 cfs [Ref. 2]
Vio = 5.53 ft/s [Ref: 2]
do = 15" [Ref: 2]
Assume minimum tailwater conditions
CALCULATIONS:
1. Determine median and maximum stone diameter
a. Determine median stone diameter
- d50= 5" [Ref: 1, Fig. 8.06a]
b. Determine maximum stone size
- dmax = 1.5 x d50 = 1.5(5") = 7.5" [Ref: 1]
2. Determine dimensions of riprap apron
a. Determine minimum length of riprap apron
- La = 8 ft [Ref: 1, Fig. 8.06a]
b. Determine width of riprap apron
- Upstream width = 3do = 3(1.25 ft) = 3.75 ft [Ref 1, Fig. 8.06a]
- Downstream width of apron
o W= do + La = 1.25 + 8.0 ft = 9.25 ft
Amicus Ingineering
Project No: 17-10-033 Sheet No: of
Date: 09-01-2010
Calcs Performed By: JLM
Calcs Checked By: NRP
Project Name: Proposed Professional Building at Lawyer's Road
Subject: RipRap Apron
c. Determine thickness of apron
T = 1.5(dma,,) = 1.5(7.5") = 11.25
- Use T = 11.25"
- Use appropriate filter fabric underneath apron
•
[Ref: 1 ]

U
f

jo - 2-
il_water < 0.5Do

Q,aILF??
g?ro??P f?60I'
e \ I, }
I i I
Appendices
ou 1uD 200 Soo to
Discharge (ft3/sec)
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).
Rev. 12/93
3o
Outlet IW = Do + La
diameter (Do)
pipe 1
8.06.3
5`/
Project No: 17-10-033 Sheet No: of
4i'll> Date: 09-01-2010
Calcs Performed By: JLM
"` Calcs Checked By: NRP
Amicus Ingineering Project Name: Proposed Professional Building at Lawyer's Road
Subject: RipRap Apron
OBJECTIVE:
Design Riprap Apron (RA-3) to dissipate the 10-year flow discharging from pipe P-3.
REFERENCES:
1. North Carolina Erosion and Sediment Control Handbook, 2008.
2. "Pipe Hydraulics and Grate Capacity," by Amicus Engineering PC, 09/01/10.
TERMS:
Q10 = 10-year peak flow, (ft3/s)
do = diameter of discharge pipe, (in)
d50 = median stone size in a well-graded riprap apron, (in)
dma, = maximum stone diameter in riprap apron, (in)
La = length of riprap apron, (ft)
W = downstream width of riprap apron, (ft)
cfs = cubic feet per second
V 10 = 10-year peak velocity, (ft/s)
GIVEN/REQUIREMENTS:
Minimum design storm = 10-year [Ref: 1 ]
Pipe P-3
Q10 = 2.14 cfs [Ref: 2]
V10 = 5.38 ft/s [Ref: 2]
do = 12" [Ref: 2]
Assume minimum tailwater conditions
CALCULATIONS:
1. Determine median and maximum stone diameter
a. Determine median stone diameter
- d50= 5" [Ref: 1, Fig. 8.06a]
b. Determine maximum stone size
- dmax = 1.5 x d50 = 1.5(5") = 7.5" [Ref: 1]
2. Determine dimensions of riprap apron
a. Determine minimum length of riprap apron
- La = 8 ft [Ref: 1, Fig. 8.06a]
b. Determine width of riprap apron
- Upstream width = 3do = 3(1.0 ft) = 3.0 ft [Ref 1, Fig. 8.06a]
- Downstream width of apron
o W=do+La=1.0+8.0ft=9.0ft
Amicus engineering
Project No: 17-10-033 Sheet No: of
Date: 09-01-2010
Calcs Performed By: JLM
Calcs Checked By: NRP
Project Name: Proposed Professional Building at Lawyer's Road
Subject: RipRap Apron
c. Determine thickness of apron
- T = 1.5(dmax) = 1.5(7.5") = 11.25"
Use T = 11.25"
- Use appropriate filter fabric underneath apron

[Ref: 1 ]
0

0
I
1c, - ?
Pg _'?
f ?
t??T
Outlet IW = Do + La
diameter (Do)
pipe 1
ilwater < 0.5Do

Discharge (ft3/sec)
2 y t c cYrs
Curves may not be extrapolated.
Figure 8.06a Design of outlet protection protection from a round pipe flowing full, minimum tailwater condition J, < 0.5 diameter).
o? Ppt°6o F
tiX , i
f
N
N
2
C0
0-
W
Q
rr
0
i -0
-7: 1
I. !
a. 0 {?w
5 10 20 50 100 200 500 1000
16
Rev. 12/93
Appendices
8.06.3
C
•
Project No: 17-10-033 Sheet No: of
Date: 09-01-2010
Calcs Performed By: JLM
Calcs Checked By: NRP
Amicus Engineering Project Name: Proposed Professional Building at Lawyer's Road
Subject: RipRap Apron
OBJECTIVE:
Design Riprap Apron (RA-4) to dissipate the 10-year flow discharging from pipe P-5.
REFERENCES:
1. North Carolina Erosion and Sediment Control Handbook, 2008.
2. "Pipe Hydraulics and Grate Capacity," by Amicus Engineering PC, 09/01/10.
TERMS:
Q 1 o = 10-year peak flow, (ft3/s)
do = diameter of discharge pipe, (in)
d50 = median stone size in a well-graded riprap apron, (in)
dmax = maximum stone diameter in riprap apron, (in)
La = length of riprap apron, (ft)
W = downstream width of riprap apron, (ft)
cfs = cubic feet per second
V10 = 10-year peak velocity, (ft/s)
GIVEN/REQUIREMENTS:
Minimum design storm = 10-year
Pipe P-5
Q10 = 32.31 cfs
V 10 = 5.20 ft/s
do = 36"
Assume minimum tailwater conditions
CALCULATIONS:
1. Determine median and maximum stone diameter
a. Determine median stone diameter
- d50 = 7"
b. Determine maximum stone size
- dmax = 1.5 x d50 = 1.5(7) = 10.5"
2. Determine dimensions of riprap apron
a. Determine minimum length of riprap apron
- La = 9.0 ft
b. Determine width of riprap apron
Upstream width = 3do = 3(3.0 ft) = 9.0 ft
- Downstream width of apron
o W= do + La = 3.0 + 9.0 ft = 12.0 ft
[Ref: 1]
[Ref 2]
[Ref: 2]
[Ref: 2]
[Ref: 1, Fig. 8.06a]
[Ref: 1 ]
[Ref: 1, Fig. 8.06a]
[Ref: 1, Fig. 8.06a]
Amicus engineering
Project No: 17-10-033 Sheet No: of
Date: 09-01-2010
Ca1cs Performed By: JLM
Calcs Checked By: NRP
Project Name: Proposed Professional Building at Lawyer's Road
Subject: RipRap Apron
c. Determine thickness of apron
T = 1.5(dinax) = 1.5(10.5") = 15.75"
- Use T = 11.25"
- Use appropriate filter fabric underneath apron

[Ref: 1]
Ir-I
1. Appendices
M'i F
Outlet W = Do + La 9 -
I

pipe
diameter (D

)

1

!'

: L:

''

+
t
;
'

?j

'I
o 4 is
80
La -•1 { I I ?,
ilwater < 0.5Do I I.j . 7 I i j f t

l l ? . t
` W 6o '' I ,,
;
o
??
?e?0 1

i? ,

.{III

,

ll

I

S
i

a i

-

I:.

1

y
e
, 4
?
5 i I r : 3? 1
I' :i t 7- lo
4
i
j ---
-
I
j
I
,
j
?!?
ril
,tI
2
4
3
}
W
J-
1
H

2 f' 5

1 . td ' 11 - 1 f
1
y
_
t -
l
3

j
I
_
i I
I t ?
I Ij
' !I j
?? I {I
I !•j
I
I
I
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f I _ f ? • : I i
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-- -
- , I v

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i.
.
.. t i
11 11
1 iti
Ilj ;
!f' !ll
if
t
I
II1 -F-
,, ,? , 2
ul
`
5
2 ?-
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20

I
.j
I

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I

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5

b

a

I

i

F`rl

I

I

F

?

I t

+

I

1
V 5 i - _ ? '? ?7 w1
I •

3 5 10 20 50 100 200 500 1 000
D ischarge (0 /sec)
Curves may not be extrapolated. P o -- 3? "ZS (c ?
Figure 8.06a Design of outlet protection protection from a round pipe flowing full, minimum tailwater conditio n (Tw < 0.5 diameter).
Rev. 12/93 8.06.3
n
•
0
Project No: 17-10-033 Sheet No: of
Date: 09-01-2010
Calcs Performed By: JLM
Calcs Checked By: NRP
Amicus ingineering Project Name: Proposed Professional Buildin at Lawyer's Road
Subject: RipRap Apron
OBJECTIVE:
Design Riprap Apron (RA-5) to dissipate the 10-year flow discharging from pipe P-6.
REFERENCES:
1. North Carolina Erosion and Sediment Control Handbook, 2008.
2. "Pipe Hydraulics and Grate Capacity," by Amicus Engineering PC, 09/01/10.
TERMS:
Qio = 10-year peak flow, (ft3/s)
do = diameter of discharge pipe, (in)
d5o = median stone size in a well-graded riprap apron, (in)
dimx = maximum stone diameter in riprap apron, (in)
La = length of riprap apron, (ft)
W = downstream width of riprap apron, (ft)
cfs = cubic feet per second
Vi0 = 10-year peak velocity, (ft/s)
GIVEN/REQUIREMENTS:
Minimum design storm = 10-year
Pipe P-6
Qio = 0.08 cfs
V io = 1.52 ft/s
do = 12"
Assume minimum tailwater conditions
CALCULATIONS:
1. Determine median and maximum stone diameter
a. Determine median stone diameter
- d50 = 5"
b. Determine maximum stone size
- dmax = 1.5 x d50 = 1.5(5") = 7.5"
2. Determine dimensions of riprap apron
a. Determine minimum length of riprap apron
- La=8ft
b. Determine width of riprap apron
Upstream width = 3do = 3(1.0 ft) = 3.0 ft
Downstream width of apron
o W= do + La = 1.0 + 8.0 ft = 9.0 ft
[Ref: 1 ]
[Ref: 2]
[Ref: 2]
[Ref: 2]
[Ref 1, Fig. 8.06a]
[Ref: 1]
[Ref 1, Fig. 8.06a]
[Ref: 1, Fig. 8.06a]
Amicus Ingineering
Project No: 17-10-033 Sheet No: of
Date: 09-01-2010
Calcs Performed By: JLM
Calcs Checked By: NRP
Project Name: Proposed Professional Building at Lawyer's Road
Subject: RipRap Apron
c. Determine thickness of apron
T = 1.5(dmax) = 1.5(7.5") = 11.25"
Use T = 11.25"
- Use appropriate filter fabric underneath apron
CJ
[Ref: 1 ]
1?

l?
u

sD 100
2 N
0-
M
Q
Ir-
O
J::.i 0
1000
Discharge (0/sec)
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).
Rev. ]2/93
3 0
Outlet W = Do + La
pipe
diameter (Do) 1
T iIwater < 0.5Do

to?'
r o? Pp 60
;r
e?
51
Y-! I ?` rt -! P - 111 i; 1! f ''1 l
Appendices
8.06.3
CM(k
•

•
Project No: 17-10-033 Sheet No: of
Date: 09-01-2010
Calcs Performed By: JLM
Calcs Checked By: NRP
Amicus Ingineering Project Name: Proposed Professional Building at Lawyer's Road
Subject: RipRap Apron
04, •
OBJECTIVE:
Design Riprap Apron (RA-6) to dissipate the 10-year flow discharging from pipe P-7.
REFERENCES:
1. North Carolina Erosion and Sediment Control Handbook, 2008.
2. "Pipe Hydraulics and Grate Capacity," by Amicus Engineering PC, 09/01/10.
TERMS:
Qio = 10-year peak flow, (ft3/s)
do = diameter of discharge pipe, (in)
d5o = median stone size in a well-graded riprap apron, (in)
dmaX = maximum stone diameter in riprap apron, (in)
La = length of riprap apron, (ft)
W = downstream width of riprap apron, (ft)
cfs = cubic feet per second
V10 = 10-year peak velocity, (ft/s)
GIVEN/REQUIREMENTS:
Minimum design storm = 10-year
Pipe P-7
Qio = 0.35 cfs
Vio = 2.31 ft/s
do = 12"
Assume minimum tailwater conditions
CALCULATIONS:
1. Determine median and maximum stone diameter
a. Determine median stone diameter
- d50 = 5"
b. Determine maximum stone size
- dmaX = 1.5 x d50 = 1.5(5") = 7.5"
2. Determine dimensions of riprap apron
a. Determine minimum length of riprap apron
- La=8ft
b. Determine width of riprap apron
- Upstream width = 3do = 3(1.0 ft) = 3.0 ft
- Downstream width of apron
o W= do + La = 1.0 + 8.0 ft = 9.0 ft
[Ref: 1 ]
[Ref: 2]
[Ref: 2]
[Ref: 2]
[Ref: 1, Fig. 8.06a]
[Ref: 1 ]
[Ref: 1, Fig. 8.06a]
[Ref: 1, Fig. 8.06a]
•
Amicus Ingineering
Project No: 17-10-033 Sheet No: of
Date: 09-01-2010
Calcs Performed By: JLM
Calcs Checked By: NRP
Project Name: Proposed Professional Building at Lawyer's Road
Subject: RipRap Apron
c. Determine thickness of apron
T = 1.5(dmax) = 1.5(7.5") = 11.25"
Use T = 11.25"
- Use appropriate filter fabric underneath apron
C
[Ref: 1 ]
0
•
•
•
U
UI w 7, 'E
. o ?2
Discharge (ft3/sec)
or a C-Pis
D .`
Curves may not be extrapolated.
Figure 8.06a Design of outlet protection protection from a round pipe flowing full, minimum tailwater condition (Tw t 0.5 diameter).
toy`
o? Pp 60
?
???\?J?.?i_I ?? + e
I Si-Qi i?
2 N
0
co
C2
O
1 -0
V $ i I ' II I ?? J? Y.
CM: u,
5 10 20 50 100 200 500 1000
Rev. 12/93
30
Outlet IW = Do + La
pipe 1
diameter (Do)
-;z, SZ T ilwater < 0.5Do
WORM=
l
Appendices
8.06.3
r?
LJ
DRAWDOWN
CALCULATIONS
•
0

Amicus Engineering
OBJECTIVE:
Design a skimmer structure SST-2 that will efficiently drawdown an existing man-
made pond in approximately 7 days.
ASSUMPTIONS/DESIGN CONSIDERATIONS:
It is assumed that the existing man-made pond is spring fed. But until the pond has
been drained and exact spring locations are located, a factor of safety of two will be
used in determining the volume of water that is to be drained by the skimmer
structure.
REFERENCES:
1. "Existing Site Conditions," by Amicus Engineering PC, 06/16/10.
2. Faircloth Skimmer Sizing (www.fairclothskimmer.com/skimmer.html)
CALCULATIONS FOR SHIMMER STRUCTURE DESIGN
Project No: 17-10-033 Sheet No: of
Date: 09-01-2010
Calcs Performed By: JLM
Calcs Checked By: NRP
Project Name: Proposed Professional Building at Lawyer's Road
Subject: Drawdown Calculations
1. Determine Basin Volume
E
Volume of existin man-made and
Elevation (ft)
[Ref: 1 ] Area (ft)
[Ref: 1 ] Height (ft) Volume (ft)
679 49,847
1 46,604
678 43,361
1 39,052
677 34,743
1 30,196
676 25,649
1 15,105
675 4,560
1 3,587
674 2,613
1 1,651
673 689
a. Total basin volume to principle spillway (679.00 ft) = 136,195 ft3
b. Total basin volume to principle spillway (679.00 ft) with
factor of safety included = 272,390 ft3
0
Oti
2. Design Skimmer Structure SST-2
a. Required water storage volume = 272,390 ft3 , SS1 ji 4-
b. Desired dewatering time = 7 days , a SEAL ;
c. A 6.0-inch skimmer is required - 0 3 2 0 0 6 [Ref: 2]
d. A 2.6-inch orifice radius is required
A 5
2 •, .F Ref 2 Q_ .4
G
? •
?
?' ' ?
?
e.
.
-inch orifice diameter is required ;
I N?
,?
?
?? [Ref: 2]
A?
R1
a q- o?-lo
•
•
Calculate Skimmer Size
Basin Volume in Cubic Feet Cu.Ft Skimmer Size 6.0 Inch
Days to Drain* P"7 Days Orifice Radius 2.6 Inch[es]
Orifice Diameter 5.2 Inch[es]
In NC assume 3 days to drain
0
•
APPENDIX II
CONSTRUCTION
DRAWINGS
•
0