20001048 Ver 2_Stormwater Info_20010612

Hobbs, Upchurch & Associates, P.A.
Consulting Engineers
-w 300 S.W. Broad Street • Post Office Box 1737 • Southern Pines, NC 28388
June 12, 2001 / 5
.J
Mr. Todd St. John
NCDENR - Division of Water Quality
4401 Reedy Creek Road
Raleigh, NC 27607
RE: Anson County Correctional Facility
DWQ Project Number 001048
HUA No. DC9902
Dear Mr. St. John:
We are herein responding to your letter of January 18, 2001 with review comments on the
subject Anson County Correctional Facility stormwater management plans.
(1) Vegetated Side Slopes - basin side slopes above the top of dam elevations are
specified to be seeded with a mix of bermuda, bahiagrass and lespedeza grasses,
all in accordance with the seeding specifications and seeding schedule on drawing
sheet C.D.4B. Basin side slopes from the top of dam elevations down to the
bottom of pond elevations are specified to be seeded with a mixture of native
aquatic vegetation and marsh plants as specified in notes on Detail 1 of sheet
C.D.3B. Basin side slopes are indicated both in the grading plans with contours
and on Detail 1 of C.D.3B to have six horizontal to one vertical slopes within the
ponds on three of the four sides, with the forth side being the slope of the earth
and dam embankment with three to one slopes.
(2) Vegetative Shelf - the proposed shelf is a flat slope with six horizontal to one
vertical side slopes, again is indicated on the grading plans with contours and on
the Detail I of C.D.3B. The seeding specifications of native aquatic vegetation
and marsh plants is added to notes of Detail 1 of C.D.3B.
Southern Pines, NC • Telephone [phone] • Fax [phone] • e-mail: [e-mail]
Myrtle Beach • Nags Head • Raleigh • Charlotte
Mr. Todd St. John
June 12, 2001
Page -2-
(3) Draw Down Orifice Diameter-revised detention basin design calculations and
spreadsheets are attached and indicate that two of the three draw down orifices
remain sized as before. Pond No. 1 has a 1/2" orifice with the temporary water
quality pool drawn downtime of 4.65 days. Pond No. 2 has a l" orifice with a
draw down of 2.72 days. Pond No. 3 has a 1" orifice with a draw down of 2.97
days. Orifice calculations and draw down calculations are computed with the
standard orifice equation as indicated on page 2 of the spreadsheet calculations.
The orifices are sized to draw down the temporary water quality pool volume in 2
to 5 days.
We request your review and approval of these responses, with attached revised drawings
and calculations included. Please advise if you have any further questions or comments
in order to complete your technical review process for the proposed stormwater
management plans for the protection of wetlands at the project site.
Sincerely,
HOBBS, UPCHURCH & ASSOCIATES, P.A.
C f
Charles D. Heiser, P.E.
Attachments
cc: Mr. Jim Gates, NC DOC
Pond #1
Detention Basin Design
Determine Surface area and volume required
Drainage Area = 16.61 Acres
Impervious area = 7.07 Acres
% Impervious
From Table I.1 of NCDENR Stormwater Best Management Practices SA/DA =
For Depth = 3 feet Permanent Pool
Depth = 3 ft
BASIN DIMENSIONS
/Length Width L/W Ratio
165 55 3.00 :1
Sideslopes 6 :1---
DETERMINE STAGE-STORAGE FUNCTION
S Z
CONTOUR INCR ACCUM
CONTOT FR ARFA VnI.T ThAp V('1T T TKAP QTn r:P
! A 5 2n01
V!ULMIDS ,,,()UP
42.56 %
1.80 %
Required
Surface Area 13023.57 SF
Basin
Surface Area 18291 SF
y x
I- Q 1-7
FT S Q. FT CU. FT CU. FT FT IT
0 0 0
1 11859 5930 5930 1 8.687695171 0 0.98
2 14931 13395 2 9.869129 0.6931472 2.05
3 18291 16611 5936 3 10.48948094 1.0986123 3.02
4 21939 20115 56 4 10.93400835 862944 3.98
5 25875 23907 79958 5 11.28925052 ±1.
094379 4.96
6 30099 27987, 107945, 6 11.58937249 1.7917595 5.98
From Linear Regression Ks = 6085
b = 1.61
corr. = 0.99976297

Pond #I
Determine Volume to Be controlled by 1" storm
Calculate Rv
Rv = 0.05 + 0.009 * I
Volume to be treated
Volume = Rainfall * Rv * Drainage Area
Rainfall= 1 in
STAGE-STORAGE function
KS = 6085
b = 1.61
Set riser Z
Volume to drain
Orifice Required
Drawdown time
Say
Qo =
Rv =
V =
Say
V =
2-5 Days
Qreq.
3.5 Days
Cd =
Cd * (pi*D^2/4) * (2g * ((Z-0)/2))^(1/2)
D (in) D (ft) Qo(cfs) Drawdown (days) Remark
2 0.17 0.1174 2.62 Too Fast
0.5 0.04 0.0073 41.86 Too Slow
1.5 0.13 0.06611 1 4.65 I OK
0.43 in/in
0.5994583 acre-ft
26112 of
Z= 2.47441718
Z= 2.5
El (riser) = 5.5
26548 of
0.0877903 cfs
0.6

Pond #1
Pipe to Drain Pond
Qo = Cd * (pi*D^2/4) * (2g * ((Z-0)/2))^(1/2)
Riser Depth = 5.5 ft
Riser Depth Volume = 94305.431 cf
D (in) D (ft) Qo(cfs) Drawdown (hrs) Remark
6 0.50 1.5678 16.71 OK
Determine Post Development and Pre Development Runoff Coefficients
Pre Development
Use C Area (ac) % Area % * C

PavemtBld 0.95 0 0.00% 0.00%
Pastureland 0.3 18.43 100.00% 30.00%
Total: 18.43

Use C= 30
Post Development
Use C Area (ac) % Area % * C

Pavemt/Bld 0.95 7.07 42.56% 40.44%
Turf 0.3 9.54 57.44% 17.23%
Total: 16.61

Use C= 58%

Pond #1
Determine Post Development and Pre Development Curve Number
Pre Development
Catchment No. 1
Land Use HSG CN Area Wt. CN
(ACRES)
Open Space B 61 0.00
C 74 0.00
D 80 18.43 80.00
Streets & Roads B 98 0.00
(Pavement & Buildings) C 98 0.00
D 98 0.00
B 98 0.00
C
D 98
98
Totals: 18.43 80.00
Use CN: 80
Post Development
Catchment No. 1
Land Use HSG CN Area Wt. CN
(ACRES)
Turf B 61 0.00
C 74 0.00
D 80 9.54 45.95
Streets & Roads B 98 0.00
C 98 0.00
D 98 7.07 41.71
0.00

Totals: 16.61 87.66
Use CN: 88

Pond #1
Set Crest of Riser at Water Quality Stage
Set riser at water quality stage + Permanent Pool
Stage(WQ): 2.4744172 ft
Say 2.5 Riser Elevation:
Compute Allowable Outflow:
Qpre= 34 cfs See "Peak Inflow" sheet
Qpost = 59 cfs 10 yr flood
Estimate Stormwater Storage Needed:
S = (Qpost - Qpre) * Tp *60 sec/min
S=
If S is neg. (Qpre > Qpost)
S = 1.39 * Qpost * Tp S =
S needed =
Qp =
Determine Total Storage
Total Storage = Flood Storage + Water Quality
Total Storage =
Total Stage =
Configure Outlet
Select Riser by Orifice Equation
Cd = 0.b
h = ((0.159 * Q)/(Cd * D^2))^2
h is to Centerline of barrel
Set uD Trial and Error table
s.
5.5 ft
Tp = 68.29 min.
Tp = 44.86 min.
?67290 of
l
3679 of
67290 of
34 efs
93838 cf
5.48 ft
Z
D (inch) D (ft) h (ft) h + D/2 (ft)

15 1.25 33.25 33.88
24 2 5.07 6.07
18 1.5 16.04 16.79
Try barrel = 18
Route to confirm Riser = 30

i Pond #1
Foreba Required Vol Zee 1
Total Storage = 93838 of Total Storage)
Fore Bay Volume = 20 o Total Volume
Fore Bay Volume = 18768 of
Forebay Dimension
Try Length Width
60 55
Depth 4 ft
Sideslopes 3 :1
Volume = (Average Area*Depth)
Area = (Length + (2 *Depth* Sideslope))*(Width + (2 *Depth* Sideslopes)
Area = 6636 sf
Volume =
Sediment Storage
From "Sediment predictions in Eastern United States"
Malcom, H.R. and Smallwood, C., (1977)
19872 CF
Where:
(for Urbanized) V = 2.96 * A^0.67 V = Sed. Volume (acre-ft/year
A = Area (sq. miles)
V = 0.2563296 acre-ft/year
11166 cf/year
Cleanout interval 2 Years
Volume= 22331 of
Total Volume Needed for Pond = (cleanout volume - (0.25 * Forebay volume)) = 17363 of
Pond #1
Peak Inflow
DESIGN STORM:
BACKGROUND:
REFERENCES:
SOLUTION - Qp:
HUA No. DC9902 Anson County Prison Site
Anson County, NC
10-Year, 24-Hour Depth; 10-Year Intensity
Use the Rational Method
(Malcom, 1991; Wanielista, 1990)
Use the Kirpich Equation & the Rational Method
INPUT OUTPUT
L = ft
H = ft
Tc = 10.00 minutes
I = 6.09 in/hr
Pre Development
SOLUTION - Tp:
A = 18.43 acres
C = 0.30
INPUT
P = 4.97 in
CN = 80
TERMINOLOGY:
A = Watershed Area, (acres)
a = Statistical Variable
b = Statistical Variable
C = Runoff Coefficient
CN = Curve Number
H = Vertical Relief, (ft)
I = Rainfall Intensity, (in/hr)
Qp = 34 cfs
OUTPUT
S = 2.50 in
Q* = 2.87 in
Tp = 68.29 minutes
L = Hydraulic Lenth, (ft)
P = Precipitation Depth, (in)
Q* = Runoff Depth, (in)
Qp = Peak Discharge, (cfs)
S = Ultimate Soil Storage, (in)
Tc = Time of Concentration, (minutes)
Tp = Time to Peak, (minutes)
FINAL RESULTS: Qp = 34 CFS
Tp = 68.29 MINUTES
Pond #I
Peak Inflow
HUA No. DC9902 Anson County Prison Site
Anson County, NC
DESIGN STORM: 10-Year, 24-Hour Depth; 10-Year Intensity
BACKGROUND: Use the Rational Method
REFERENCES: (Malcom, 1991; Wanielista, 1990)
SOLUTION - Qp: Use the Kirpich Equation & the Rational Method
INPUT OUTPUT
L = ft
H = ft
Tc = 10.00 minutes
I = 6.09 in/hr
Post Development
SOLUTION - Tp:
A = 16.61 acres
C = 0.58
INPUT
P = 4.97 in
CN = 88
TERMINOLOGY:
A = Watershed Area, (acres)
a = Statistical Variable
b = Statistical Variable
C = Runoff Coefficient
CN = Curve Number
H = Vertical Relief, (ft)
I = Rainfall Intensity, (in/hr)
Qp = 59 cfs
OUTPUT
S = 1.36 in
Q* = 3.64 in
Tp = 44.86 minutes
L = Hydraulic Length, (ft)
P = Precipitation Depth, (in)
Q* = Runoff Depth, (in)
Qp = Peak Discharge, (cfs)
S = Ultimate Soil Storage, (in)
Tc = Time of Concentration, (minutes)
Tp = Time to Peak, (minutes)
FINAL RESULTS: ?Qp = 59 CFS
Tp = 44.86 MINUTES
Pond #I
Peak Inflow
HUA No. DC9902 Anson County Prison Site
Anson County, NC
DESIGN STORM: 25-Year, 24-Hour Depth; 25-Year Intensity
BACKGROUND: Use the Rational Method
REFERENCES: (Malcom, 1991; Wanielisla, 1990)
SOLUTION - Qp: Use the Kirpich Equation & the Rational Method
INPUT
L = ft
H= ft
A = 18.43 acres
Pre Development C = 0.30
SOLUTION - Tp: INPUT
P = 5.82 in
CN = 80
I = 7.30 in/hr
Qp = 40 cfs
OUTPUT
S = 2.50 in
Q* = 3.62 in
Tp = 71.93 minutes
TERMINOLOGY:
A = Watershed Area, (acres)
a = Statistical Variable
b = Statistical Variable
C = Runoff Coefficient
CN = Curve Number
H = Vertical Relief, (ft)
I = Rainfall Intensity, (in/hr)
L = Hydraulic Lenth, (ft)
P = Precipitation Depth, (in)
Q* = Runoff Depth, (in)
Qp = Peak Discharge, (cfs)
S = Ultimate Soil Storage, (in)
Tc = Time of Concentration, (minutes)
Tp = Time to Peak, (minutes)
OUTPUT
Tc = 10.00 minutes
FINAL RESULTS: ?Qp = 40 CFS
Tp = 71.93 MINUTES
Pond #I
DESIGN STORM:
BACKGROUND:
REFERENCES:
SOLUTION - Qp:
Peak Inflow
HUA No. DC9902 Anson County Prison Site
Anson County, NC
25-Year, 24-Hour Depth; 25-Year Intensity
Use the Rational Method
(Malcom, 1991; Wanielista, 1990)
Use the Kirpich Equation & the Rational Method
INPUT
L = ft
H = ft
Tc = 10.00 minutes
I = 7.30 in/hr
A = 16.61 acres
Post Development C = 0.58
SOLUTION - Tp: INPUT
P = 5.82 in
CN = 88
TERMINOLOGY:
A = Watershed Area, (acres)
a = Statistical Variable
b = Statistical Variable
C = Runoff Coefficient
CN = Curve Number
H = Vertical Relief, (ft)
I = Rainfall Intensity, (in/hr)
Qp = 70 cfs
OUTPUT
S = 1.36 in
Q* = 4.45 in
Tp = 45.77 minutes
L = Hydraulic Lenth, (ft)
P = Precipitation Depth, (in)
Q* = Runoff Depth, (in)
Qp = Peak Discharge, (cfs)
S = Ultimate Soil Storage, (in)
Tc = Time of Concentration, (minutes)
Tp = Time to Peak, (minutes)
OUTPUT
FINAL RESULTS: Qp = 70 CFS?
Tp = 45.77 MINUTES
Pond #I
Chainsaw Routing
(REF: Malcom, 1991)
HUA No. DC9902 Anson County Prison Site
Anson County, NC
Design Storm: 10-year
Pond must detain inch of rainfall runoff from all impervious surfaces
RESULTS
Q.T = 22 CFS Z.rsvr = 7.63 FT T-S.nrm = 108,722 CU-FT
Q.pr = 0 CFS Z.s = 0.00 FT WSA.max = 33,829 SQ-FT
FRBD.min = 2.62 FT V.s = 0.0 FPS T-S.max = 160,232 CU-FT
WSEL.nrm = 3.00 FT Qs = 0 CFS WSA.nrm = 19,148 SQ-FT
SEL.max = 7.63 FT 11 IL T-S.det = 80,548 CU-FT

INPUT
Qp = 59 CFS N.r = I Cw.s = 3.00
Tp = 44.86 MIN Cw.r = 3.30 Ct.s = 2.45
dT = 4 MIN Cd.r = 0.60 B.s = 5.00 FT
M= 3 :1
Ks = 6085
b= 1.61 D.r = 2.50 FT
EL.s = 9.00 FT
N.b = 1
EL.dam = 10.25 FT Cd.b = 0.60 EL.r = 5.90 FT
EL.i = 0.00 FT D.b = 18 INCH EL.r = 5.90 FT
OUTPUT
A B C D E F G H I
Time
T Inflow
I Storage
S Elevation
WSEL Outflow
O Riser
O.r-w Riser
O.r-o Barrel
O.b Spillway
O.s
MIN CFS CU-FT FT CFS CFS CFS CFS CFS
0 0 28174 3.00 0 NA NA NA 0.0
4 1 28174 2.59 0.00 0.0 0.0 11.5 0.0
8 5 28450 2.61 0 0.0 0.0 11.6 0.0
12 10 29532 2.67 0 0.0 0.0 11.8 0.0
16 17 31889 2.80 0 0.0 0.0 12.2 0.0
20 25 35887 3.01 0 0.0 0.0 12.8 0.0
24 33 41768 3.31 0 0.0 0.0 13.6 0.0
28 41 49625 3.68 0 0.0 0.0 14.5 0.0
32 48 59397 4.12 0 0.0 0.0 15.6 0.0
36 54 70875 4.59 0 0.0 0.0 16.7 0.0
40 57 83715 5.10 0 0.0 0.0 17.7 0.0
44 59 97469 5.60 0 0.0 0.0 18.7 0.0
48 58 111616 6.09 2 2.2 10.4 19.6 0.0
52 55 125083 6.54 13 13.2 18.9 20.4 0.0
56 50 135203 6.86 21 24.5 23.2 21.0 0.0
Pond #I
60 45 142274 7.08 21 33.3 25.7 21.4 0.0
64 40 147944 7.26 22 41.0 27.5 21.7 0.0
68 36 152361 7.39 22 47.2 28.8 21.9 0.0
72 32 155672 7.49 22 52.0 29.8 22.1 0.0
76 28 158006 7.56 22 55.4 30.4 22.2 0.0
80 25 159479 7.60 22 57.6 30.8 22.2 0.0
84 22 160190 7.62 22 58.7 31.0 22.3 0.0
88 20 160232 7.63 22 58.7 31.0 22.3 0.0
92 18 159683 7.61 22 57.9 30.9 22.2 0.0
96 16 158616 7.58 22 56.3 30.6 22.2 0.0
100 14 157093 7.53 22 54.0 30.2 22.1 0.0
104 13 155172 7.48 22 51.2 29.7 22.0 0.0
108 11 152902 7.41 22 47.9 29.0 21.9 0.0
112 10 150329 7.33 22 44.3 28.2 21.8 0.0
116 9 147492 7.24 22 40.3 27.4 21.6 0.0
120 8 144428 7.15 21 36.2 26.4 21.5 0.0
124 7 141168 7.05 21 31.9 25.3 21.3 0.0
128 6 137741 6.94 21 27.6 24.1 21.1 0.0
132 6 134173 6.83 21 23.2 22.8 20.9 0.0
136 5 130486 6.71 19 19.0 21.3 20.7 0.0
140 4 127125 6.60 15 15.3 19.8 20.6 0.0
144 4 124510 6.52 13 12.6 18.6 20.4 0.0
148 4 122421 6.45 11 10.6 17.5 20.3 0.0
152 3 120715 6.40 9 9.0 16.6 20.2 0.0
156 3 119295 6.35 8 7.8 15.8 20.1 0.0
160 2 118093 6.31 7 6.8 15.1 20.0 0.0
164 2 117061 6.27 6 5.9 14.5 20.0 0.0
168 2 116164 6.25 5 5.2 13.9 19.9 0.0
172 2 115376 6.22 5 4.7 13.3 19.9 0.0
176 2 114678 6.20 4 4.2 12.8 19.8 0.0
180 l 114055 6.17 4 3.7 12.4 19.8 0.0
184 1 113495 6.16 3 3.3 11.9 19.8 0.0
188 1 112989 6.14 3 3.0 11.5 19.7 0.0
192 1 112530 6.12 3 2.7 11.2 19.7 0.0
196 1 112111 6.11 2 2.5 10.8 19.7 0.0
200 1 111727 6.10 2 2.2 10.5 19.6 0.0
204 l 111376 6.08 2 2.0 10.1 19.6 0.0
208 I 111052 6.07 2 1.9 9.8 19.6 0.0
212 1 110753 6.06 2 1.7 9.5 19.6 0.0
216 0 110477 6.05 2 1.6 9.3 19.6 0.0
220 0 110221 6.04 1 1.4 9.0 19.5 0.0
224 0 109984 6.04 1 1.3 8.7 19.5 0.0
228 0 109763 6.03 1 1.2 8.5 19.5 0.0
232 0 109558 6.02 1 1.1 8.3 19.5 0.0
236 0 109367 6.02 1 1.0 8.0 19.5 0.0
240 0 109189 6.01 1 0.9 7.8 19.5 0.0
244 0 109023 6.00 1 0.9 7.6 19.5 0.0
248 0 108867 6.00 1 0.8 7.4 19.5 0.0
252 0 108722 5.99 1 0.7 7.2 19.5 0.0
Pond #I
Chainsaw Routing
(REF: Malcom, 1991)
HUA No. DC9902 Anson County Prison Site
Anson County, NC
Design Storm: 25-year
Pond must detain inch of rainfall runoff from all impervious surfaces
RESULTS
Q."I' = 24 CFS Z.rsvr = 8.44 FT T-S.nrm = 109,408 CU-FT
Q.pr = 0 CFS Z.s = 0.00 FT WSA.max = 35,985 SQ-FT
FRBD.min = 1.81 FT V.s = 0.0 FPS T-S.max = 188,614 CU-FT
WSEL.nrm = 3.00 FT Q.s = 0 CFS WSA.nrm = 19,148 SQ-FT
SEL.max = 8.44 FT T-S.det = 81,234 CU-FT

INPUT
QP = 70 CFS N.r = 1 Cw.s = 3.00
Tp = 45.77 MIN Cw.r = 3.30 Ct.s = 2.45
dT = 4 MIN Cd.r = 0.60 B.s = 5.00 FT
M= 3 :1
Ks = 6085
b = 1.61 D.r = 2.50 FT
EL.s = 9.00 FT
N.b = 1
EL.dam = 10.25 FT Cd.b = 0.60 EL.r = 5.90 FT
EL.i = 0.00 FT D.b = 18 INCH EL.r = 5.90 FT
OUTPUT
A B C D E F G H I
Time
T Inflow
I Storage
S Elevation
WSEL Outflow
O Riser
O.r-w Riser
O.r-o Barrel
O.b Spillway
O.s
MIN CFS CU-FT FT CFS CFS CFS CFS CFS
V V Z81 /4 s.UU U NA NA NA 0.0
4 1 28174 2.59 0.00 0.0 0.0 11.5 0.0
8 5 28489 2.61 0 0.0 0.0 11.6 0.0
12 11 29724 2.68 0 0.0 0.0 11.8 0.0
16 19 32415 2.83 0 0.0 0.0 12.2 0.0
20 28 36992 3.07 0 0.0 0.0 12.9 0.0
24 38 43739 3.40 0 0.0 0.0 13.8 0.0
28 47 52782 3.83 0 0.0 0.0 14.9 0.0
32 55 64070 4.32 0 0.0 0.0 16.0 0.0
36 62 77390 4.85 0 0.0 0.0 17.2 0.0
40 67 92371 5.42 0 0.0 0.0 18.4 0.0
44 70 108520 5.99 l 0.7 6.9 19.4 0.0
48 70 125100 6.54 13 13.2 18.9 20.4 0.0
52 67 138625 6.97 21 28.7 24.4 21.2 0.0
56 62 149583 7.31 22 43.2 28.0 21.8 0.0
Pond #I
60 55 159175 7.59 22 57.1 30.8 22.2 0.0
64 49 167106 7.83 23 69.3 32.8 22.6 0.0
68 44 173521 8.01 23 79.6 34.3 22.9 0.0
72 39 178595 8.16 23 87.9 35.5 23.1 0.0
76 35 182479 8.27 23 94.4 36.3 23.3 0.0
80 31 185309 8.35 23 99.1 37.0 23.4 0.0
84 28 187206 8.40 23 102.4 37.3 23.5 0.0
88 25 188275 8.43 24 104.2 37.6 23.5 0.0
92 22 188614 8.44 24 104.8 37.6 23.6 0.0
96 20 188305 8.43 24 104.3 37.6 23.5 0.0
100 18 187426 8.41 24 102.8 37.4 23.5 0.0
104 16 186043 8.37 23 100.4 37.1 23.4 0.0
108 14 184217 8.32 23 97.3 36.7 23.4 0.0
112 13 182002 8.25 23 93.6 36.2 23.3 0.0
116 11 179446 8.18 23 89.3 35.7 23.2 0.0
120 10 176591 8.10 23 84.6 35.0 23.0 0.0
124 9 173477 8.01 23 79.5 34.3 22.9 0.0
128 8 170136 7.92 23 74.1 33.5 22.7 0.0
132 7 166601 7.81 23 68.5 32.7 22.6 0.0
136 6 162899 7.70 22 62.8 31.7 22.4 0.0
140 6 159054 7.59 22 57.0 30.7 22.2 0.0
144 5 155089 7.47 22 51.1 29.6 22.0 0.0
148 5 151022 7.35 22 45.3 28.5 21.8 0.0
152 4 146874 7.22 22 39.5 27.2 21.6 0.0
156 4 142658 7.10 21 33.8 25.8 21.4 0.0
160 3 138390 6.96 21 28.4 24.3 21.2 0.0
164 3 134083 6.83 21 23.1 22.7 20.9 0.0
168 3 129749 6.69 18 18.2 21.0 20.7 0.0
172 2 126008 6.57 14 14.2 19.3 20.5 0.0
176 2 123160 6.48 11 11.3 17.9 20.3 0.0
180 2 120933 6.40 9 9.2 16.8 20.2 0.0
184 2 119154 6.34 8 7.7 15.7 20.1 0.0
188 1 117704 6.30 6 6.5 14.9 20.0 0.0
192 l 116502 6.26 6 5.5 14.1 19.9 0.0
196 1 115492 6.22 5 4.7 13.4 19.9 0.0
200 1 114632 6.19 4 4.1 12.8 19.8 0.0
204 1 113891 6.17 4 3.6 12.2 19.8 0.0
208 1 113246 6.15 3 3.2 11.7 19.7 0.0
212 1 112681 6.13 3 2.8 11.3 19.7 0.0
216 l 112180 6.11 3 2.5 10.9 19.7 0.0
220 1 111735 6.10 2 2.2 10.5 19.6 0.0
224 1 111336 6.08 2 2.0 10.1 19.6 0.0
228 0 110977 6.07 2 1.8 9.8 19.6 0.0
232 0 110652 6.06 2 1.6 9.4 19.6 0.0
236 0 110357 6.05 1 1.5 9.1 19.6 0.0
240 0 110088 6.04 1 1.4 8.8 19.5 0.0
244 0 109842 6.03 1 1.2 8.6 19.5 0.0
248 0 109616 6.02 1 1.1 8.3 19.5 0.0
252 0 109408 6.02 1 1.0 8.1 19.5 0.0
Temporary Sediment Trap.
HUA No. DC9902 Anson County Prison Site
Anson County, NC
10-Year Design Storm
OBJECTIVE: Design a Weir for Detention Pond Forebay
Determine the weir length, capacity & freeboard of the forebay
SOLUTION - Qp: Use the calculated Time of Concentration and the Rational Method to determine
the peak inflow from the design storm.
INPUT
L= ft
H= ft
OUTPUT
Tc = 10.00 minutes
I = 6.09 in/hr
A = 16.61 acres
C = 0.58
QP = 59 cfs
SOLUTION - Lw: Use Trial & Error with Weir Length (Lw) & Driving Head (H) to make Qp <= Qw
INPUT OUTPUT
Cw = 3.00
Lw = 20 ft.
H = 1 ft.
DIMENSIONS: A.disturb = 3.30 acres
S-Trap.H = 5.50 ft.
S-Trap.D = 4.00 ft.
S-Trap.W = 55.00 ft.
S-Trap.L = 60.00 ft.
TERMINOLOGY: Cw = Weir Coefficient
Lw = Weir Length, (ft.)
H = Driving Head, (ft.)
Qp = Peak Inflow, (cfs)
Qw = Peak Discharge, (cfs)
A.disturb = Disturbed Area, (acres)
Freeboard = Freeboard of Weir, (ft.)
Cap.-R. = Required Trap Capacity, (cf)
Cap.-D. = Design Trap Capacity, (cf)
S-Trap.H = Sediment Trap Height, (ft.)
S-Trap.D = Sediment Trap Depth, (ft.)
Qp = 58.7 efs
Qw = 60.00 cfs
Freeboard = 0.50 ft.
X 1800 cf / acre
Volume = 5940 of
cf
Capacity = 13200 cf
L = Watershed Hydrailic Length, (ft)
Hv = Watershed Vertical Relief, (ft)
a = Statistical Rainfall Variable
b = Statistical Rainfall Variable
A = Watershed Area, (acres)
C = Rational Runoff Coefficient
Tc = Time of Concentration
I = Rainfall Intensity, (in./hr.)
S-Trap. W = Sediment Trap Width, (ft.)
S-Trap.L = Sediment Trap Length, (ft.)
REFERENCES: (DEHNR, 1988; Malcom, 1991)
AM M\c:\exce1\a1an\C0950ITond1 51181007:58 AM Page 17ot'16
Anti-Flotation Calculations
Riser in Detention Pond #1
HUA No. DC9902 Anson County Prison Site
Anson County, NC
Max. WSEL = 9.71 FT
Riser Invert = 0.00 FT
Riser Diameter = 30.0 INCHES
Riser Volume = 47.7 CF Riser Buoyancy = 2974 LBS
Barrel Diameter = 18.0 INCHES
Barrel Length = 8.0 FT
Barrel Volume = 14.1 CF Barrel Buoyancy = 882 LBS
Slab Length = 5.50 FT
Slab Width = 5.50 FT
Slab Thickness = 2.00 FT Slab Buoyancy = 3775 LBS
Slab Volume = 60.5 CF Slab Weight = 8773 LBS
Unit Wt. of Water = 62.4 LBS/CF
it Wt. of Concrete = 145.0 LBS/CF Total Buoyancy = 7632 LBS
Total Weight = 8773 LBS
Factor of Safety = 1.15 (OK)
NOTE: Factor of Safety must be at least 1.1
P.
Riprap Velocity Dissipator Pad
Outlet of Stormwater Pond No. 1
HUA No. DC9902 - 1000 Cell Close Security Prison
Anson County, NC
Design Storm: 10-year, 10-min.
BACKGROUND: Use the E&S Control Planning & Design Manual, Section 8.06.
At the outlet : flow is 24 cfs , V = 11.7 fps
REFERENCE: (NCDEHNR. 1993)
Step 1. Minimum Tailwater Condition
Step 2. D-o = 18 in.
D-o = 1.5 ft.
Q-10 = 24 cfs
d-50 = 0.8 ft.
Ira = 20 ft.
Step 3. 3*D-o = 4.5 ft.
W = 21.5 ft.
Step 4. d-max 1.2 ft.
d-max 14.4 in.
Step 5. Thickness = 1.2 ft.
Thickness = 14 in.
Figure 8.06 a
Figure 8.06 a
USE: 6 ft.
USE: 22 ft.
Maximum Stone Diameter (1.5*d-50)
USE: Class "2" Rip-Rap
Apron Thickness With Filter Fabric (1.5*d-50)
USE: 15 in.
TERMINOLOGY: Q10 = 10-Year Design Storm, Peak Discharge, (cfs)
D-o = Pipe Diameter, (in. & ft.)
d-50 = Mean Stone Diameter of Rip-Rap, (ft.)
L-a = Length of Rip-Rap Apron, (ft.)
3*D-o = Width of Rip-Rap Apron @ Pipe Outlet, (ft.)
W = Width of Rip-Rap Apron @ End of Apron, (ft.)
d-max = Maximum Stone Diameter of Rip-Rap, (ft. & in.)
Thickness = Thickness of Rip-Rap Apron With Filter Fabric, (ft. &in.)
Pond #2
Detention Basin Design
Determine Surface area and volume required
Drainage Area = 3.93 Acres
Impervious area = 2.91 Acres
% Impervious
From Table I.1 of NCDENR Storm
For Depth = 3 feet Permanent Pool
Depth =
BASIN DIMENSIONS
Length Width
100 30
water Best Management Practices SA/DA =
3 ft Required
Surface Area
L/W Ratio Basin
3.33 Surface Area
Sideslopes 6 :1
DETERMINE STAGE-STORAGE FUNCTION
S Z
CONTOUR INCR ACCUM
CONTOUR AREA VOLUME VOT,UW, STACIE
iinaFi
74.05 %
3.00 %
5135.72 SF
8976 SF
V x
in S In 7 7 Pct
FT S Q. FT CU. FT CU. FT FT FT
0 0 0
1 4704 2352 2352 1 7.763021309 0 1.00
2 6696 5700 8052 2 8.993675787 0.6931472 2.02
3 8976 7836 15888 3 9.673319386 1.0986123 2.98
4 11544 10260 26148 4 10.17152798 1.3862944 3.96
5 14400 12972 39120 5 10.57438912 1.6094379 4.99
6 777T7544 F 15972 55092 6 10.91675979 1.7917595 6.06
From Linear Regression Ks = 2355
b = 1.75
corr. = 0.99991644
Pond #2
Determine Volume to Be controlled by 1" storm
Calculate Rv
Rv = 0.05 + 0.009 * I
Volume to be treated
Volume = Rainfall * Rv * Drainage Area
Rainfall= 1 in
STAGE-STORAGE function
KS = 2355
b = 1.75
Set riser Z
Volume to drain
Orifice Required
Drawdown time
Say
Qo =
Rv =
V =
Say
V =
2-5 Days
Qreq.
3.5 Days
Cd =
Cd * (pi*D^2/4) * (2g * ((Z-0)/2))^(1/2)
D (in) D (ft) Qo(cfs) Drawdown (days) Remark
2 0.17 0.1151 1.10 Too Fast
0.5 0.04 0.0072 17.52 Too Slow
1 0.08 1 0.0288 i 4.38 OK
0.72 in/in
0.234625 acre-ft
10220 cf
Z= 2.3146453
Z = 2.4
El (riser) = 5,4
10888 cf
0.0360069 efs
0.6
Pond #2
Pipe to Drain Pond
Qo = Cd * (pi*D^2/4) * (2g * ((Z-0)/2))^(1/2)
Riser Depth = 5.4 ft
Riser Depth Volume = 44970.657 cf
D (in) D (ft) Qo(cfs) Drawdown (hrs) Remark
4 0.33 0,6904 18.09 OK
Determine Post Development and Pre Development Runoff Coefficients
Pre Development
Use C Area (ac) % Area % * C

PavemtBld 0.95 0 0.00% 0.00%
Pastureland 0.3 4.5 100.00% 30.00%
Total: 4.5

Use C= 30%
Post Development
Use C Area (ac) % Area % * C

PavemtBld 0.95 2.54 64.63% 61.40%
Turf 0.3 1.39 35.37% 10.61%
Total: 3.93

Use C= 72%
Pond #2
Determine Post Development and Pre Development Curve Number
Pre Development
Catchment No. 1
Land Use HSG CN Area Wt. CN
(ACRES)
Open Space B 61 0.00
C 74 0.00
D 80 4.50 80.00
Streets & Roads B 0.00
(Pavement & Buildings) _
C 98 0.00
_
-- D - - 98 0.00
B 98 0.00
C
D 98
98
Totals: 4.50 80.00
Use CN: 80
Post Development
Catchment No. 1
Land Use HSG CN Area Wt. CN
(ACRES)
Turf B 61 0.00
C 74 0.00
_
D 80 1.39 28.30
Streets & Roads B 98 0.00
C 98 0.00
D 98 2.54 63.34
0.00

Totals: 3.93 91.63
Use CN: 92

Pond 42
Set Crest of Riser at Water Quality Stage
Set riser at water quality stage + Permanent Pool
Stage(WQ): 2.3146453 ft
Say 2.4 Riser Elevation:
Compute Allowable Outflow:
Qpre= 10 cfs See "Peak Inflow" sheet
Qpost = 17 cfs 10 yr flood
Estimate Stormwater Storage Needed:
S = (Qpost - Qpre) * Tp *60 sec/min
If S is neg. (Qpre > Qpost)
S = 1.39 * Qpost * Tp
Determine Total Storage
Total Storage = Flood Storage + Water Quality
Total Storage =
Total Stage =
Confit-`ure Outlet
Select Riser by Orifice Equation
Cd =
h = ((0.159 * Q)/(Cd * D^2))^2
h is to Centerline of barrel
Set un Trial and Error table
S=
S=
S needed =
Qp =
27814 cf
4.10 ft
0.6
Z
D (inch) D (ft) h (ft) h + D/2 (ft)

15 1.25 2.88 3.50
24 2 0.44 1.44
12 1 7.02 7.52
Tp =
Tp =
5.4 ft
16926 cf
952 cf
16926 cf
10 cfs
57.61 min.
40.3 min.
Try barrel = 12
Route to confirm Riser = 18

Pond #2
Forebay Required Volume
Total Storage = 27814 cf ( Total Storage)
Fore Bay Volume = 20% Total Volume
Fore Bay Volume = 5563 cf
Forebay Dimension
Try Len h Width
40 30
Area = (Length + (2 *Depth* Sideslope)) *(Width + (2 *Depth* Sideslopes)
Depth 3 ft
Area = 2784 sf
Sideslopes 3 :l
Volume = (Average Area*Depth)
Volume = 5976 CF
Sediment Storage
From "Sediment predictions in Eastern United States"
Malcom, H.R. and Smallwood, C., (1977)
(for Urbanized ) V = 2.96 * A^0.67
Where:
V = Sed. Volume (acre-ft/year
A = Area (sq. miles)
V = 0.0975875 acre-ft/year
4251 of/year
Cleanout interval 2 Years
Volume= 8502 of
Total Volume Needed for Pond = (cleanout volume - (0.25 * Forebay volume)) = 7008 cf
Pond #2
DESIGN STORM:
BACKGROUND:
REFERENCES:
SOLUTION - Qp:
Peak Inflow
HUA No. DC9902 Anson County Prison Site
Anson County, NC
10-Year, 24-Hour Depth; 10-Year Intensity
Use the Rational Method
(Malcom, 1991; Wanielista, 1990)
Use the Kirpich Equation & the Rational Method
INPUT OUTPJJT
L = ft
H= ft
Tc = 5.00 minutes
I = 7.22 in/hr
Pre Development
SOLUTION - Tp:
TERMINOLOGY:
A = 4.5 acres
C = 0.30
INPUT

P = 4.97 in
CN = 80
A = Watershed Area, (acres)
a = Statistical Variable
b = Statistical Variable
C = Runoff Coefficient
CN = Curve Number
H = Vertical Relief, (ft)
I = Rainfall Intensity, (in/hr)
Qp = 10 cfs
OUTPUT
S = 2.50 in
Q* = 2.87 in
Tp = 57.61 minutes
L = Hydraulic Lenth, (ft)
P = Precipitation Depth, (in)
Q* = Runoff Depth, (in)
Qp = Peak Discharge, (cfs)
S = Ultimate Soil Storage, (in)
Tc = Time of Concentration, (minutes)
Tp = Time to Peak, (minutes)
FINAL RESULTS: Qp 10 CFS
11 Tp = 57.61 MINUTES
Pond #2
Peak Inflow
HUA No. DC9902 Anson County Prison Site
Anson County, NC
DESIGN STORM: 10-Year, 24-Hour Depth; 10-Year Intensity
BACKGROUND: Use the Rational Method
REFERENCES: (Malcom, 1991; Wanielista, 1990)
SOLUTION - Qp: Use the Kirpich Equation & the Rational Method
INPUT OUTPUT
L= ft
H= ft
Te = 10.00 minutes
I = 6.09 in/hr
A = 3.93 acres
Post Development C = 0.72
SOLUTION - Tp: INPUT
P = 4.97 in
CN = 92
Qp = 17 cfs
OUTPUT
S = 0.87 in
Q* = 4.06 in
Tp = 40.30 minutes
TERMINOLOGY:
A = Watershed Area, (acres)
a = Statistical Variable
b = Statistical Variable
C = Runoff Coefficient
CN = Curve Number
H = Vertical Relief, (ft)
I = Rainfall Intensity, (in/hr)
L = Hydraulic Length, (ft)
P = Precipitation Depth, (in)
Q* = Runoff Depth, (in)
Qp = Peak Discharge, (cfs)
S = Ultimate Soil Storage, (in)
Tc = Time of Concentration, (minutes)
Tp = Time to Peak, (minutes)
FINAL RESULTS: p = 17 CFS
11 Tp = 40.30 MINUTES
Pond #2
Peak Inflow
HUA No. DC9902 Anson County Prison Site
Anson County, NC
DESIGN STORM: 25-Year, 24-Hour Depth; 25-Year Intensity
BACKGROUND: Use the Rational Method
REFERENCES: (Malcom, 1991; Wanielista, 1990)
SOLUTION - Qp: Use the Kirpich Equation & the Rational Method
INPUT OUTPUT
L= ft
H= ft
Tc = 5.00 minutes
I = 8.24 in/hr
Pre Development
SOLUTION - Tp:
A = 4.5 acres
C = 0.30
INPUT
Qp = 11 cfs
OUTPUT
P = 5.82 in
CN = 80
TERMINOLOGY:
A = Watershed Area, (acres)
a = Statistical Variable
b = Statistical Variable
C = Runoff Coefficient
CN = Curve Number
H = Vertical Relief, (ft)
I = Rainfall Intensity, (in/hr)
S = 2.50 in
Q* = 3.62 in
Tp = 63.72 minutes
L = Hydraulic Lenth, (ft)
P = Precipitation Depth, (in)
Q* = Runoff Depth, (in)
Qp = Peak Discharge, (cfs)
S = Ultimate Soil Storage, (in)
Tc = Time of Concentration, (minutes)
Tp = Time to Peak, (minutes)
FINAL RESULTS: Qp = I I CFS
11 Tp = 63.72 MINUTES
Pond #2
DESIGN STORM:
BACKGROUND:
REFERENCES:
SOLUTION - Qp:
Peak Inflow
HUA No. DC9902 Anson County Prison Site
Anson County, NC
25-Year, 24-Hour Depth; 25-Year Intensity
Use the Rational Method
(Malcom, 1991; Wanielista, 1990)
Use the Kirpich Equation & the Rational Method
INPUT
L = ft
H = ft
Te = 10.00 minutes
I = 7.30 in/hr
Post Development
SOLUTION - Tp:
TERMINOLOGY:
A = 3.93 acres
C = 0.72
INPUT
P = 5.82 in
CN = 92
A = Watershed Area, (acres)
a = Statistical Variable
b = Statistical Variable
C = Runoff Coefficient
CN = Curve Number
H = Vertical Relief, (ft)
I = Rainfall Intensity, (in/hr)
Qp = 21 cfs
OUTPUT
S = 0.87 in
Q* = 4.89 in
Tp = 40.52 minutes
L = Hydraulic Lenth, (ft)
P = Precipitation Depth, (in)
Q* = Runoff Depth, (in)
Qp = Peak Discharge, (cfs)
S = Ultimate Soil Storage, (in)
Tc = Time of Concentration, (minutes)
Tp = Time to Peak, (minutes)
OUTPUT
FINAL RESULTS: Qp 21 CFS?
Tp = 40.52 MINUTES
Pond #2
Chainsaw Routing
(REF.- Malcom, 1991)
HUA No. DC9902 Anson County Prison Site
Anson County, NC
Design Storm: 10-year
Pond must detain inch of rainfall runoff from all impervious surfaces
RESULTS
Q.T = 4 CFS Z.rsvr = 6.27 FT T-S.nrm = 53,357 CU-FT
Q.pr = 0 US Z.s = 0.00 FT WSA.max = 16,338 SQ-FT
FRBD.min = 1.73 FT V.s = 0.0 FPS T-S.max = 58,579 CU-FT
WSEL.nrm = 3.00 Fl' Q.s = 0 CFS WSA.nrm = 9,394 SQ-FT
SEL.max = 6.27 FT T-S.det = 42,192 CU-FT

INPUT
Qp = 17 CFS N.r = I Cw.s = 3.00
Tp = 40.30 MIN Cw.r = 3.30 Ct.s = 2.45
dT = 4 MIN Cd.r = 0.60 B.s = 5.00 FT
M= 3 :1
Ks = 2355
b = 1.75 D.r = 1.50 FT
EL.s = 7.00 FT
N.b = I
EL.dam = 8.00 FT Cd.b = 0.60 EL.r = 5.90 FT
EL.i = 0.00 FT D.b = 12 INCH EL.r = 5.90 FT
OUTPUT
A B C D E F G H I
Time
T Inflow
I Storage
S Elevation
WSEL Outflow
O Riser
O.r-w Riser
O.r-o Barrel
O.b Spillway
O.s
MIN CFS CU-FT FT CFS CFS CFS CFS CFS
0 0 11165 3.00 U NA NA NA U.U
4 0 11165 2.43 0.00 0.0 0.0 5.2 0.0
8 2 11263 2.45 0 0.0 0.0 5.3 0.0
12 3 11647 2.49 0 0.0 0.0 5.3 0.0
16 6 12477 2.59 0 0.0 0.0 5.5 0.0
20 8 13868 2.75 0 0.0 0.0 5.7 0.0
24 Il 15884 2.98 0 0.0 0.0 5.9 0.0
28 13 18527 3.25 0 0.0 0.0 6.3 0.0
32 15 21739 3.56 0 0.0 0.0 6.6 0.0
36 17 25407 3.89 0 0.0 0.0 7.0 0.0
40 17 29374 4.23 0 0.0 0.0 7.3 0.0
44 17 33453 4.56 0 0.0 0.0 7.6 0.0
48 16 37449 4.86 0 0.0 0.0 7.9 0.0
52 14 41172 5.13 0 0.0 0.0 8.1 0.0
56 12 44481 5.36 0 0.0 0.0 8.3 0.0
Pond #2
60 11 47389 5.56 0 0.0 0.0 8.5 0.0
64 9 49945 5.73 0 0.0 0.0 8.6 0.0
68 8 52192 5.87 0 0.0 0.0 8.8 0.0
72 7 54166 6.00 0 0.5 2.7 8.9 0.0
76 6 55785 6.10 1 1.4 3.8 8.9 0.0
80 6 56972 6.18 2 2.2 4.5 9.0 0.0
84 5 57774 6.22 3 2.9 4.8 9.0 0.0
88 4 58261 6.25 3 3.3 5.1 9.1 0.0
92 4 58509 6.27 3 3.5 5.2 9.1 0.0
96 3 58579 6.27 4 3.6 5.2 9.1 0.0
100 3 58525 6.27 4 3.5 5.2 9.1 0.0
104 3 58385 6.26 3 3.4 5.1 9.1 0.0
108 2 58189 6.25 3 3.2 5.0 9.1 0.0
112 2 57958 6.24 3 3.0 4.9 9.0 0.0
116 2 57708 6.22 3 2.8 4.8 9.0 0.0
120 2 57450 6.21 3 2.6 4.7 9.0 0.0
124 1 57191 6.19 2 2.4 4.6 9.0 0.0
128 1 56935 6.17 2 2.2 4.4 9.0 0.0
132 1 56688 6.16 2 2.0 4.3 9.0 0.0
136 1 56450 6.14 2 1.9 4.2 9.0 0.0
140 1 56223 6.13 2 1.7 4.1 9.0 0.0
144 1 56008 6.12 2 1.6 3.9 8.9 0.0
148 1 55805 6.10 1 1.4 3.8 8.9 0.0
152 1 55614 6.09 1 1.3 3.7 8.9 0.0
156 0 55434 6.08 1 1.2 3.6 8.9 0.0
160 0 55266 6.07 1 1.1 3.5 8.9 0.0
164 0 55108 6.06 1 1.0 3.4 8.9 0.0
168 0 54960 6.05 1 0.9 3.3 8.9 0.0
172 0 54822 6.04 1 0.8 3.2 8.9 0.0
176 0 54693 6.03 1 0.8 3.1 8.9 0.0
180 0 54573 6.03 1 0.7 3.0 8.9 0.0
184 0 54460 6.02 1 0.6 2.9 8.9 0.0
188 0 54355 6.01 1 0.6 2.8 8.9 0.0
192 0 54257 6.01 1 0.5 2.8 8.9 0.0
196 0 54165 6.00 0 0.5 2.7 8.9 0.0
200 0 54080 5.99 0 0.5 2.6 8.9 0.0
204 0 53999 5.99 0 0.4 2.5 8.8 0.0
208 0 53925 5.98 0 0.4 2.5 8.8 0.0
212 0 53855 5.98 0 0.4 2.4 8.8 0.0
216 0 53789 5.98 0 0.3 2.3 8.8 0.0
220 0 53728 5.97 0 0.3 2.3 8.8 0.0
224 0 53670 5.97 0 0.3 2.2 8.8 0.0
228 0 53617 5.96 0 0.3 2.2 8.8 0.0
232 0 53566 5.96 0 0.2 2.1 8.8 0.0
236 0 53519 5.96 0 0.2 2.1 8.8 0.0
240 0 53475 5.96 0 0.2 2.0 8.8 0.0
244 0 53433 5.95 0 0.2 2.0 8.8 0.0
248 0 53394 5.95 0 0.2 1.9 8.8 0.0
252 0 53357 5.95 0 0.2 1.9 8.8 0.0
Pond #2
Chainsaw Routing
(REF.- Malcom, 1991)
HUA No. DC9902 Anson County Prison Site
Anson County, NC
Design Storm: 25-year
Pond must detain inch of rainfall runoff from all impervious surfaces
RESULTS
Q.T = 7 CFS Z.rsvr = 6.53 FT T-S.nrm = 53,435 CU-FT
Q.pr = 0 CFS Z.s = 0.00 FT W SA.max = 16,834 SQ-FT
FRBD.min = 1.97 FT V.s = 0.0 FPS T-S.max = 62,813 CU-FT
WSEL.nrm = 3.00 FT Q.s = 0 CFS WSA.nrm = 9,394 SQ-FT
SEL.max = 6.53 FT T-S.det = 42,270 CU-FT

INPUT
Qp = 21 CFS N.r = 1 Cw.s = 3.00
Tp = 40.52 MIN Cw.r = 3.30 Ct.s = 2.45
dT = 4 MIN Cd.r = 0.60 B.s = 5.00 FT
M= 3 :1
Ks= 2355
b = 1.75 D.r = 1.50 FT
EL.s = 7.50 FT
N.b = 1
EL.dam = 8.50 FT Cd.b = 0.60 EL.r = 5.90 FT
EL.i = 0.00 FT D.b = 12 INCH EL.r = 5.90 FT
OUTPUT
A B C D E F G H I
Time
T Inflow
I Storage
S Elevation
WSEL Outflow
O Riser
O.r-w Riser
O.r-o Barrel
O.b Spillway
O.s
MIN CFS CU-FT FT CFS CFS CFS CFS CFS
0 0 11165 3.00 0 NA NA NA 0.0
4 1 11165 2.43 0.00 0.0 0.0 5.2 0.0
8 2 11285 2.45 0 0.0 0.0 5.3 0.0
12 4 11755 2.51 0 0.0 0.0 5.3 0.0
16 7 12769 2.63 0 0.0 0.0 5.5 0.0
20 10 14472 2.82 0 0.0 0.0 5.8 0.0
24 l4 16941 3.09 0 0.0 0.0 6.1 0.0
28 l6 20181 3.41 0 0.0 0.0 6.4 0.0
32 l9 24124 3.78 0 0.0 0.0 6.8 0.0
36 20 28634 4.17 0 0.0 0.0 7.2 0.0
40 21 33521 4.56 0 0.0 0.0 7.6 0.0
44 2l 38559 4.94 0 0.0 0.0 8.0 0.0
48 l9 43508 5.29 0 0.0 0.0 8.3 0.0
52 17 48136 5.61 0 0.0 0.0 8.5 0.0
56 15 52260 5.88 0 0.0 0.0 8.8 0.0
Pond #2
60 13 55888 6.11 1 1.5 3.9 8.9 0.0
64 12 58725 6.28 4 3.7 5.3 9.1 0.0
68 10 60646 6.40 5 5.5 6.0 9.2 0.0
72 9 61796 6.47 6 6.7 6.4 9.2 0.0
76 8 62428 6.51 7 7.3 6.6 9.3 0.0
80 7 62748 6.53 7 7.7 6.7 9.3 0.0
84 6 62813 6.53 7 7.8 6.7 9.3 0.0
88 5 62671 6.52 7 7.6 6.7 9.3 0.0
92 5 62361 6.50 7 7.3 6.6 9.3 0.0
96 4 61920 6.48 6 6.8 6.5 9.2 0.0
100 4 61375 6.44 6 6.2 6.3 9.2 0.0
104 3 60764 6.41 6 5.6 6.1 9.2 0.0
108 3 60194 6.37 5 5.1 5.8 9.1 0.0
112 3 59666 6.34 5 4.5 5.6 9.1 0.0
116 2 59177 6.31 4 4.1 5.5 9.1 0.0
120 2 58723 6.28 4 3.7 5.3 9.1 0.0
124 2 58304 6.26 3 3.3 5.1 9.1 0.0
128 2 57916 6.23 3 3.0 4.9 9.0 0.0
132 1 57557 6.21 3 2.7 4.7 9.0 0.0
136 1 57225 6.19 2 2.4 4.6 9.0 0.0
140 1 56917 6.17 2 2.2 4.4 9.0 0.0
144 l 56633 6.15 2 2.0 4.3 9.0 0.0
148 l 56370 6.14 2 1.8 4.1 9.0 0.0
152 1 56126 6.12 2 1.6 4.0 9.0 0.0
156 I 55900 6.11 1 1.5 3.9 8.9 0.0
160 1 55691 6.10 1 1.3 3.8 8.9 0.0
164 0 55497 6.08 1 1.2 3.6 8.9 0.0
168 0 55317 6.07 1 1.1 3.5 8.9 0.0
172 0 55150 6.06 1 1.0 3.4 8.9 0.0
176 0 54995 6.05 l 0.9 3.3 8.9 0.0
180 0 54851 6.04 1 0.8 3.2 8.9 0.0
184 0 54717 6.03 1 0.8 3.1 8.9 0.0
188 0 54593 6.03 1 0.7 3.0 8.9 0.0
192 0 54477 6.02 1 0.6 2.9 8.9 0.0
196 0 54369 6.01 1 0.6 2.9 8.9 0.0
200 0 54269 6.01 1 0.5 2.8 8.9 0.0
204 0 54175 6.00 0 0.5 2.7 8.9 0.0
208 0 54088 5.99 0 0.5 2.6 8.9 0.0
212 0 54007 599 0 0.4 2.5 8.8 0.0
216 0 53931 5.98 0 0.4 2.5 8.8 0.0
220 0 53860 5.98 0 0.4 2.4 8.8 0.0
224 0 53794 5.98 0 0.3 2.3 8.8 0.0
228 0 53732 5.97 0 0.3 2.3 8.8 0.0
232 0 53674 5.97 0 0.3 2.2 8.8 0.0
236 0 53620 5.97 0 0.3 2.2 8.8 0.0
240 0 53569 5.96 0 0.2 2.1 8.8 0.0
244 0 53522 5.96 0 0.2 2.1 8.8 0.0
248 0 53477 5.96 0 0.2 2.0 8.8 0.0
252 0 53435 5.95 0 0.2 2.0 8.8 0.0
Temporary Sediment Trap.
HUA No. DC9902 Anson County Prison Site
Anson County, NC
10-Year Design Storm
OBJECTIVE: Design a Weir for Detention Pond Forebay
Determine the weir length, capacity & freeboard of the forebay
SOLUTION - Qp: Use the calculated Time of Concentration and the Rational Method to determine
the peak inflow from the design storm.
INPUT OUTPUT
L= ft
H= ft
Tc = 10.00 minutes
I = 6.09 in/hr
A = 3.93 acres
C = 0.72 Qp = 17
SOLUTION - Lw: Use Trial & Error with Weir Length (Lw) & Driving Head (H) to make Qp <= Qw
INPUT OUTPUT
DIMENSIONS:
TERMINOLOGY:
Cw = 3.00
Lw = 15 ft.
H = 1 ft.
A.disturb = 3.93 acres
S-Trap.H = 4.50 ft.
S-Trap.D = 3.00 ft.
S-Trap.W = 30.00 ft.
S-Trap.L = 40.00 ft.
Cw = Weir Coefficient
Lw = Weir Length, (ft.)
H = Driving Head, (ft.)
Qp = Peak Inflow, (cfs)
Qw = Peak Discharge, (cfs)
A.disturb = Disturbed Area, (acres)
Freeboard = Freeboard of Weir, (ft.)
Cap.-R. = Required Trap Capacity, (cf)
Cap.-D. = Design Trap Capacity, (cf)
S-Trap.H = Sediment Trap Height, (ft.)
S-Trap.D = Sediment Trap Depth, (ft.)
Qp = 17.2 cfs
Qw = 45.00 cfs
Freeboard = 0.50 ft.
X 1800 cf / acre
Volume = 7074 of
cf
Capacity = 3600 cf
L = Watershed Hydrailic Length, (ft)
Hv = Watershed Vertical Relief, (ft)
a = Statistical Rainfall Variable
b = Statistical Rainfall Variable
A = Watershed Area, (acres)
C = Rational Runoff Coefficient
Tc = Time of Concentration
1 = Rainfall Intensity, (in./hr.)
S-Trap.W = Sediment Trap Width, (ft.)
S-Trap.L = Sediment Trap Length, (ft.)
cfs
REFERENCES: (DEHNR, 1988; Malcom, 1991)
Anti-Flotation Calculations
Riser in Detention Pond #2
HUA No. DC9902 Anson County Prison Site
Anson County, NC
Max. WSEL = 7.60 FT
Riser Invert = 0.00 FT
Riser Diameter = 18.0 INCHES
Riser Volume = 13.4 CF Riser Buoyancy = 838 LBS
Barrel Diameter = 12.0 INCHES
Barrel Length = 8.0 FT
Barrel Volume = 6.3 CF Barrel Buoyancy = 392 LBS
Slab Length = 4.00 FT
Slab Width = 4.00 FT
Slab Thickness = 1.50 FT Slab Buoyancy = 1498 LBS
Slab Volume = 24.0 CF Slab Weight = 3480 LBS
Unit Wt. of Water = 62.4 LBS/CF
it Wt. of Concrete = 145.0 LBS/CF Total Buoyancy = 2728 LBS
Total Weight = 3480 LBS
Factor of Safety = 1.28 (OK)
NOTE: Factor of Safety must be at least 1.1

Riprap Velocity Dissipator Pad
Outlet of Stormwater Pond No. 2
HUA No. DC9902 - 1000 Cell Close Security Prison
Anson County, NC
Design Storm: 10-year, 10-min-
BACKGROUND: Use the E&S Control Planning & Design Manual, Section 8.06.
At the outlet : flow is 9 cfs , V = 10.6 fps
REFERENCE: (NCDEHNR, 1993)
Step 1. Minimum Tailwater Condition
Step 2. D-o = 12 in.
D-o = I ft.
Q-10 = 9 cfs
d-50 = 0.5 ft.
L-a = 16 ft.
Step 3. 3*D-o = 3 ft.
W = 17 ft.
Step 4. d-max 0.75 ft.
d-max 9 in.
Step 5. Thickness = 0.8 ft.
Thickness = 9 in.
Figure 8.06 a
Figure 8.06 a
USE: 4 ft.
USE: 18 ft.
Maximum Stone Diameter (1.5*d-50)
USE: Class "1" Rip-Rap
Apron Thickness With Filter Fabric (1.5*d-50)
USE: 12 in.
TERMINOLOGY: Q10 = 10-Year Design Storm, Peak Discharge, (cfs)
D-o = Pipe Diameter, (in. & ft.)
d-50 = Mean Stone Diameter of Rip-Rap, (ft.)
L-a = Length of Rip-Rap Apron, (ft.)
3*D-o = Width of Rip-Rap Apron @ Pipe Outlet, (ft.)
W = Width of Rip-Rap Apron @ End of Apron, (ft.)
d-max = Maximum Stone Diameter of Rip-Rap, (ft. & in.)
Thickness = Thickness of Rip-Rap Apron With Filter Fabric, (ft. &in.)

Pond #3
Detention Basin Design
-G?o? N 5 ?'li?il
Determine Surface area and volume required
Drainage Area = 3.74 Acres
Impervious area = 1.87 Acres
% Impervious 50.00 %
From Table I.1 of NCDENR Stormwater Best Management Practices SA/DA = 2.00 %
For Depth = 3 feet Permanent Pool
Depth = 3 ft
BASIN DIMENSIONS
Length Width L/W Ratio
75 25 3.00 :1
Sideslopes 6 :1
DETERMINE STAGE-STORAGE FUNCTION
S Z
CONTOUR INCR ACCUM
CONTOUR AREA VOLUME VOLUME STAGE
Required
Surface Area 3258.29 SF
Basin
Surface Area 6771 SF
Y x
In S In Z Z est
FT S Q. FT CU. FT CU. FT FT FT
0 0 0
1 3 219 1610 1610 1 7.3 83 678851 0 1.01
2 4851 4035 5645 2 8.638436899 0.6931472 2.01
3 6771, 5811 11456 3 9.346225243 1.0986123 2.96
4 8979 7875 19331 4 9.869439438 1.3862944 3.95
5 11475 10227 29558 5 10.2940928 1.6094379 5.00
6 14259 12867 42425 6 10.6554813 1.7917595 6.10
From Linear Regression Ks = 1594
b = 1.82
corr. = 0.99986856
Pond #3
Determine Volume to Be controlled by 1" storm
Calculate Rv
Rv = 0.05 + 0.009 * I
Volume to be treated
Volume = Rainfall * Rv * Drainage Area
Rainfall= 1 in
STAGE-STORAGE function
KS = 1594
b = 1.82
Rv =
V =
Say
Set riser Z
Volume to drain V =
Orifice Required
Drawdown time
Say
Qo =
2-5 Days
Qreq.
3.5 Days
Cd =
Cd * (pi*D^2/4) * (2g * ((Z-0)/2))^(1/2)
D (in) D (ft) Qo(cfs) Drawdown (days) Remark
2 0.17 0.1126 0.74 Too Fast
0.5 0.04 0.0070 11.89 Too Slow
1 0.08 0.0282 1 1 2.97 O0.50 in/in

0.1558333 acre-ft
6788 cf
Z= 2.22148265
Z= 2.3
El (riser) = 5.3
7230 cf
0.0239084 cfs
0.6
Pond #3
Pipe to Drain Pond
Qo = Cd * (pi*D^2/4) * (2g * ((Z-0)/2))^(1/2)
Riser Depth = 5.3 ft
Riser Depth Volume = 32905.935 cf
D (in) D (ft) Qo(cfs) Drawdown ( Remark
4 0.33 0.6840 13.36
!% K
Dete
rmine Post Development and Pre Development Runoff Coefficients
Pre Development
Use C Area (ac) % Area % * C

Pavemt/Bld 0.95 0 0.00% 0.00%
Pastureland 0.3 6.88 100.00% 30.00%
Total: 6.88

Use C= 30%
Post Development
Use C Area (ac) % Area % * C

Pavemt/Bld 0.95 1.87 50.00% 47.50%
Turf 0.3 1.87 50.00% 15.00%
Total: 3.74

Use C= 63
Pond #3
Determine Post Development and Pre Development Curve Number
Pre Development
Catchment No. 1
Land Use HSG CN Area Wt. CN
(4 CRES)
Open Space B 61 0.00
C 74 _ 0.00
D 80 6.88 80.00
Streets & Roads B 98 0.00
(Pavement & Buildings) C 98 0.00
D 98 0.00
B 98 0.00
C
D 98
98
Totals: 6.88 80.00
Use CN: 80
Post Development
Catchment No. 1
Land Use HSG CN Area Wt. CN
(ACRES)
Turf B 61 0.00
C 74 0.00
D 80 1.87 40.00
Streets & Roads B 98 0.00
C 98 0.00
D 98 1.87 49.00
0.00

Totals: 3.74 89.00
Use CN: 89
Pond #3
Set Crest of Riser at Water Quality Stage
Set riser at water quality stage + Permanent Pool
Stage(WQ): 2.2214826 ft
Say 2.3 Riser Elevation
Compute Allowable Outflow:
Qpre= 13 cfs See "Peak Inflow" sheet
Qpost = 14 cfs 10 yr flood
Estimate Stormwater Storage Needed:
S = (Qpost - Qpre) * Tp *60 sec/min
If S is neg. (Qpre > Qpost)
S = 1.39 * Qpost * Tp
Determine Total Storage
Total Storage = Flood Storage + Water Quality
Total Storage =
Total Stage =
Configure Outlet
Select Riser by Orifice Equation
Cd =
h = ((0.159 * Q)/(Cd * D^2))^2
h is to Centerline of barrel
Set un Trial and Error table
S=
S=
S needed =
Qp =
9774 cf
2.72 ft
0.6
Z
D (inch) D (ft) h (ft) h + D/2 (ft)

15 1.25 4.86 5.49
24 2 0.74 1.74
12 1 11.87 12.37
Tp =
Tp =
5.3 ft
2544 cf
825 of
2544 of
13 cfs
68.29 min.
42.4 min.
Try barrel = 12
Route to confirm Riser = 18
.t
Pond #3
Forebay Required Volume
Total Storage = 9774 cf ( Total Storage)
Fore Bay Volume = 20% Total Volume
Fore Bay Volume = 1955 of
Forebay Dimension
Try Length Width
15 25
Area = (Length + (2 *Depth* Sideslope)) *(Width + (2 *Depth* Sideslopes)
Depth 3 ft
Area = 1419 sf
Sideslopes 3 :1
Volume = (Average Area*Depth)
Volume = 2691 CF
Sediment Storage
From "Sediment predictions in Eastern United States"
Malcom, H.R. and Smallwood, C., (1977)
Where:
(for Urbanized) V = 2.96 * A^0.67 V = Sed. Volume (acre-ft/year
A = Area (sq. miles)
V = 0.0944007 acre-ft/year
4112 cf/year
Cleanout interval 2 Years
Volume= 8224 of
Total Volume Needed for Pond = (cleanout volume - (0.25 * Forebay volume)) = 7551 cf
Pond #3
Peak Inflow
DESIGN STORM:
BACKGROUND:
REFERENCES:
SOLUTION - Qp:
HUA No. DC9902 Anson County Prison Site
Anson County, NC
10-Year, 24-Hour Depth; 10-Year Intensity
Use the Rational Method
(Malcom, 1991; Wanielista, 1990)
Use the Kirpich Equation & the Rational Method
INPUT OUTPUT
L = ft
H = ft
Tc = 10.00 minutes
I = 6.09 in/hr
Pre Development
SOLUTION - Tp:
TERMINOLOGY:
A = 6.88 acres
C = 0.30
INPUT
P = 4.97 in
CN = 80
A = Watershed Area, (acres)
a = Statistical Variable
b = Statistical Variable
C = Runoff Coefficient
CN = Curve Number
H = Vertical Relief, (ft)
I = Rainfall Intensity, (in/hr)
Qp = 13 cfs
OUTPUT
S = 2.50 in
Q* = 2.87 in
Tp = 68.29 minutes
L = Hydraulic Lenth, (ft)
P = Precipitation Depth, (in)
Q* = Runoff Depth, (in)
Qp = Peak Discharge, (cfs)
S = Ultimate Soil Storage, (in)
Tc = Time of Concentration, (minutes)
Tp = Time to Peak, (minutes)
FINAL RESULTS: Qp = 13 CFS
11 Tp = 68.29 MINUTES
Pond #3
DESIGN STORM:
BACKGROUND:
REFERENCES:
SOLUTION - Qp:
INPUT OUTPUT
L= ft
H= ft Tc = 10.00 minutes
Peak Inflow
HUA No. DC9902 Anson County Prison Site
Anson County, NC
10-Year, 24-Hour Depth; 10-Year Intensity
Use the Rational Method
(Malcom, 1991; Wanielista, 1990)
Use the Kirpich Equation & the Rational Method
I = 6.09 in/hr
Post Development
SOLUTION - Tp:
A = 3.74 acres
C = 0.63
INPUT
Qp = 14 cfs
OUTPUT
P = 4.97 in
CN = 89
TERMINOLOGY:
A = Watershed Area, (acres)
a = Statistical Variable
b = Statistical Variable
C = Runoff Coefficient
CN = Curve Number
H = Vertical Relief, (ft)
1 = Rainfall Intensity, (in/hr)
S = 1.24 in
Q* = 3.74 in
Tp = 42.46 minutes
L = Hydraulic Length, (ft)
P = Precipitation Depth, (in)
Q* = Runoff Depth, (in)
Qp = Peak Discharge, (cfs)
S = Ultimate Soil Storage, (in)
Tc = Time of Concentration, (minutes)
Tp = Time to Peak, (minutes)
FINAL RESULTS: Qp = 14 CFS
11 Tp = 42.46 MINUTES
Pond #3
Peak Inflow
HUA No. DC9902 Anson County Prison Site
Anson County, NC
DESIGN STORM: 25-Year, 24-Hour Depth; 25-Year Intensity
BACKGROUND: Use the Rational Method
REFERENCES: (Malcom, 1991; Wanielista, 1990)
SOLUTION - Qp: Use the Kirpich Equation & the Rational Method
INPUT OUTPUT
L= ft
H= ft
Te = 10.00 minutes
1 = 7.30 in/hr
A = 6.88 acres
Pre Development C = 0.30
SOLUTION - Tp: INPUT
P = 5.82 in
CN = 80
Qp = 15 cfs
OUTPUT
S = 2.50 in
Q* = 3.62 in
Tp = 71.93 minutes
TERMINOLOGY:
A = Watershed Area, (acres)
a = Statistical Variable
b = Statistical Variable
C = Runoff Coefficient
CN = Curve Number
H = Vertical Relief, (ft)
I = Rainfall Intensity, (in/hr)
L = Hydraulic Lenth, (ft)
P = Precipitation Depth, (in)
Q* = Runoff Depth, (in)
Qp = Peak Discharge, (cfs)
S = Ultimate Soil Storage, (in)
Tc = Time of Concentration, (minutes)
Tp = Time to Peak, (minutes)
FINAL RESULTS: Qp = 15 CFS
11 Tp = 71.93 MINUTES
Pond #3
Peak Inflow
HUA No. DC9902 Anson County Prison Site
Anson County, NC
DESIGN STORM: 25-Year, 24-Hour Depth; 25-Year Intensity
BACKGROUND: Use the Rational Method
REFERENCES: (Malcom, 1991; Wanielista, 1990)
SOLUTION - Qp: Use the Kirpich Equation & the Rational Method
INPUT
L= R
H= ft
OUTPUT
Tc = 10.00 minutes
1 = 7.30 in/hr
Post Development
SOLUTION - Tp:
A = 3.74 acres
C = 0.63
INPUT
P = 5.82 in
CN = 89
TERMINOLOGY:
A = Watershed Area, (acres)
a = Statistical Variable
b = Statistical Variable
C = Runoff Coefficient
CN = Curve Number
H = Vertical Relief, (ft)
I = Rainfall Intensity, (in/hr)
Qp = 17 cfs
OUTPUT
S = 1.24 in
Q* = 4.56 in
Tp = 43.17 minutes
L = Hydraulic Lenth, (ft)
P = Precipitation Depth, (in)
Q* = Runoff Depth, (in)
Qp = Peak Discharge, (cfs)
S = Ultimate Soil Storage, (in)
Tc = Time of Concentration, (minutes)
Tp = Time to Peak, (minutes)
FINAL RESULTS: Qp = 17 CFS
Tp = 43.17 MINUTES
Pond #3
Chainsaw Routing
(REF.• Malcom, 1991)
HUA No. DC9902 Anson County Prison Site
Anson County, NC
Design Storm: 10-year
Pond must detain inch of rainfall runoff from all impervious surfaces
RESULTS
Q.T = 5 CFS Z.rsvr = 6.25 FT T-S.nrm = 39,585 CU-FT
Q.pr = 0 CFS Z.s = 0.00 FT WSA.max = 13,031 SQ-FT
FRBD.min = 1.75 FT V.s = 0.0 FPS T-S.max = 44,722 CU-FT
WSEL.nrm = 3.00 FT Qs = 0 CFS WSA.nrm = 7,142 SQ-FT
SEL.max = 6.25 FT T-S.det = 31,901 CU-FT

INPUT
Qp = 14 CFS N.r = 1 Cw.s = 3.00
Tp = 42.40 MIN Cw.r = 3.30 Ct.s = 2.45
dT = 4 MIN Cd.r = 0.60 B.s = 5.00 FT
M= 3 :1
Ks = 1594
b = 1.82 D.r = 1.50 FT
EL.s = 7.00 FT
N.b = 1
EL.dam = 8.00 FT Cd.b = 0.60 EL.r = 5.80 FT
EL.i = 0.00 FT D.b = 12 INCH EL.r = 5.80 FT
OUTPUT
A B C D E F G H I
Time
T Inflow
I Storage
S Elevation
WSEL Outflow
O Riser
O.r-w Riser
O.r-o Barrel
O.b Spillway
O.s
MIN CFS CU-FT FT CFS CFS CFS CFS CPS
U U 1684 3.UU 0 NA NA NA 0.0
4 0 7684 2.37 0.00 0.0 0.0 5.2 0.0
8 1 7757 2.39 0 0.0 0.0 5.2 0.0
12 3 8044 2.43 0 0.0 0.0 5.3 0.0
16 4 8665 2.54 0 0.0 0.0 5.4 0.0
20 6 9714 2.70 0 0.0 0.0 5.6 0.0
24 8 11245 2.93 0 0.0 0.0 5.9 0.0
28 10 13271 3.20 0 0.0 0.0 6.2 0.0
32 12 15762 3.52 0 0.0 0.0 6.6 0.0
36 13 18647 3.86 0 0.0 0.0 6.9 0.0
40 14 21822 4.21 0 0.0 0.0 7.3 0.0
44 14 25155 4.55 0 0.0 0.0 7.6 0.0
48 13 28504 4.88 0 0.0 0.0 7.9 0.0
52 12 31721 5.17 0 0.0 0.0 8.2 0.0
56 11 34674 5.43 0 0.0 0.0 8.4 0.0
Pond #3
60 10 37293 5.65 0 0.0 0.0 8.6 0.0
64 9 39610 5.84 0 0.1 1.8 8.7 0.0
68 8 41625 6.00 1 1.4 3.8 8.9 0.0
72 7 43093 6.12 3 2.8 4.8 9.0 0.0
76 6 44020 6.19 4 3.8 5.3 9.0 0.0
80 5 44522 6.23 4 4.4 5.6 9.0 0.0
84 5 44722 6.25 5 4.6 5.7 9.1 0.0
88 4 44720 6.25 5 4.6 5.7 9.1 0.0
92 4 44590 6.24 4 4.5 5.6 9.0 0.0
96 3 44384 6.22 4 4.2 5.5 9.0 0.0
100 3 44136 6.20 4 3.9 5.4 9.0 0.0
104 3 43868 6.18 4 3.6 5.2 9.0 0.0
108 2 43593 6.16 3 3.3 5.1 9.0 0.0
112 2 43322 6.14 3 3.1 4.9 9.0 0.0
116 2 43059 6.12 3 2.8 4.8 8.9 0.0
120 2 42808 6.10 3 2.5 4.6 8.9 0.0
124 1 42569 6.08 2 2.3 4.5 8.9 0.0
128 1 42344 6.06 2 2.1 4.3 8.9 0.0
132 1 42133 6.04 2 1.9 4.2 8.9 0.0
136 1 41936 6.03 2 1.7 4.1 8.9 0.0
140 1 41751 6.01 2 1.5 3.9 8.9 0.0
144 1 41579 6.00 1 1.4 3.8 8.9 0.0
148 1 41419 5.99 1 1.3 3.7 8.8 0.0
152 1 41270 5.98 1 1.2 3.6 8.8 0.0
156 1 41131 5.97 1 1.0 3.5 8.8 0.0
160 0 41002 5.96 1 1.0 3.4 8.8 0.0
164 0 40882 5.95 1 0.9 3.2 8.8 0.0
168 0 40770 5.94 1 0.8 3.1 8.8 0.0
172 0 40666 5.93 1 0.7 3.0 8.8 0.0
176 0 40569 5.92 1 0.7 3.0 8.8 0.0
180 0 40479 5.91 1 0.6 2.9 8.8 0.0
184 0 40395 5.91 1 0.5 2.8 8.8 0.0
188 0 40317 5.90 0 0.5 2.7 8.8 0.0
192 0 40244 5.89 0 0.5 2.6 8.8 0.0
196 0 40176 5.89 0 0.4 2.5 8.8 0.0
200 0 40113 5.88 0 0.4 2.5 8.8 0.0
204 0 40054 5.88 0 0.3 2.4 8.8 0.0
208 0 39999 5.87 0 0.3 2.3 8.8 0.0
212 0 39947 5.87 0 0.3 2.3 8.7 0.0
216 0 39899 5.87 0 0.3 2.2 8.7 0.0
220 0 39854 5.86 0 0.2 2.1 8.7 0.0
224 0 39812 5.86 0 0.2 2.1 8.7 0.0
228 0 39773 5.86 0 0.2 2.0 8.7 0.0
232 0 39737 5.85 0 0.2 2.0 8.7 0.0
236 0 39702 5.85 0 0.2 1.9 8.7 0.0
240 0 39670 5.85 0 0.2 1.9 8.7 0.0
244 0 39640 5.85 0 0.2 1.8 8.7 0.0
248 0 39612 5.84 0 0.1 1.8 8.7 0.0
252 0 39585 5.84 0 0.1 1.7 8.7 0.0
Pond #3
Chainsaw Routing
(REF.• Malcom, 1991)
HUA No. DC9902 Anson County Prison Site
Anson County, NC
Design Storm: 25-year
Pond must detain inch of rainfall runoff from all impervious surfaces
RESULTS
Q.T = 7 CFS Z.rsvr = 6.49 FT T-S.nrm = 39,654 CU-FT
Q.pr = 0 CFS Z.s = 0.00 FT W SA.max = 13,447 SQ-FT
FRBD.min = 1.51 FT V.s = 0.0 FPS T-S.max = 47,952 CU-FT
WSEL.nrm = 3.00 FT Q.s = 0 CFS WSA.nrm = 7,142 SQ-FT
SEL.max = 6.49 FT T-S.det = 31,970 CU-FT

INPUT
Qp = 17 CFS N.r = 1 Cw.s = 3.00
Tp = 43.17 MIN Cw.r = 3.30 Ct.s = 2.45
dT = 4 MIN Cd.r = 0.60 B.s = 5.00 FT
M= 3 :1
Ks = 1594
b = 1.82 D.r = 1.50 FT
EL.s = 7.00 FT
N.b = 1
EL.dam = 8.00 FT Cd.b = 0.60 EL.r = 5.80 FT
EL.i = 0.00 FT D.b = 12 INCH EL.r = 5.80 FT
OUTPUT
A B C D E F G H I
Time
T Inflow
I Storage
S Elevation
WSEL Outflow
O Riser
O.r-w Riser
O.r-o Barrel
O.b Spillway
O.s
MIN CFS CU-FT FT CFS CFS CFS CFS CFS
U U 7684 3.00 U NA NA NA 0.0
4 0 7684 2.37 0.00 0.0 0.0 5.2 0.0
8 l 7770 2.39 0 0.0 0.0 5.2 0.0
12 3 8106 2.44 0 0.0 0.0 5.3 0.0
16 5 8836 2.56 0 0.0 0.0 5.4 0.0
20 8 10069 2.75 0 0.0 0.0 5.7 0.0
24 10 11874 3.01 0 0.0 0.0 6.0 0.0
28 12 14271 3.33 0 0.0 0.0 6.4 0.0
32 14 17229 3.70 0 0.0 0.0 6.8 0.0
36 16 20671 4.09 0 0.0 0.0 7.2 0.0
40 17 24480 4.49 0 0.0 0.0 7.5 0.0
44 17 28506 4.88 0 0.0 0.0 7.9 0.0
48 16 32582 5.25 0 0.0 0.0 8.2 0.0
52 15 36537 5.59 0 0.0 0.0 8.5 0.0
56 14 40211 5.89 0 0.4 2.6 8.8 0.0
Pond #3
60 12 43386 6.14 3 3.1 5.0 9.0 0.0
64 11 45544 6.31 6 5.6 6.1 9.1 0.0
68 10 46766 6.40 7 7.3 6.6 9.2 0.0
72 8 47468 6.45 7 8.2 6.9 9.2 0.0
76 7 47842 6.48 7 8.8 7.0 9.2 0.0
80 7 47952 6.49 7 8.9 7.1 9.2 0.0
84 6 47848 6.48 7 8.8 7.0 9.2 0.0
88 5 47573 6.46 7 8.4 6.9 9.2 0.0
92 5 47163 6.43 7 7.8 6.8 9.2 0.0
96 4 46651 6.39 7 7.1 6.5 9.2 0.0
100 4 46062 6.35 6 6.3 6.3 9.1 0.0
104 3 45422 6.30 5 5.5 6.0 9.1 0.0
108 3 44877 6.26 5 4.8 5.8 9.1 0.0
112 3 44405 6.22 4 4.3 5.5 9.0 0.0
116 2 43990 6.19 4 3.8 5.3 9.0 0.0
120 2 43620 6.16 3 3.4 5.1 9.0 0.0
124 2 43287 6.14 3 3.0 4.9 9.0 0.0
128 2 42986 6.11 3 2.7 4.7 8.9 0.0
132 1 42711 6.09 2 2.4 4.6 8.9 0.0
136 1 42460 6.07 2 2.2 4.4 8.9 0.0
140 1 42230 6.05 2 2.0 4.3 8.9 0.0
144 1 42017 6.04 2 1.8 4.1 8.9 0.0
148 1 41822 6.02 2 1.6 4.0 8.9 0.0
152 1 41641 6.01 1 1.5 3.9 8.9 0.0
156 1 41474 5.99 1 1.3 3.7 8.8 0.0
160 1 41320 5.98 1 1.2 3.6 8.8 0.0
164 1 41177 5.97 1 1.1 3.5 8.8 0.0
168 0 41044 5.96 1 1.0 3.4 8.8 0.0
172 0 40921 5.95 1 0.9 3.3 8.8 0.0
176 0 40807 5.94 1 0.8 3.2 8.8 0.0
180 0 40700 5.93 1 0.7 3.1 8.8 0.0
184 0 40602 5.92 1 0.7 3.0 8.8 0.0
188 0 40510 5.92 1 0.6 2.9 8.8 0.0
192 0 40424 5.91 1 0.6 2.8 8.8 0.0
196 0 40345 5.90 1 0.5 2.7 8.8 0.0
200 0 40270 5.90 0 0.5 2.6 8.8 0.0
204 0 40201 5.89 0 0.4 2.6 8.8 0.0
208 0 40137 5.89 0 0.4 2.5 8.8 0.0
212 0 40077 5.88 0 0.4 2.4 8.8 0.0
216 0 40021 5.88 0 0.3 2.4 8.8 0.0
220 0 39968 5.87 0 0.3 2.3 8.8 0.0
224 0 39919 5.87 0 0.3 2.2 8.7 0.0
228 0 39873 5.86 0 0.3 2.2 8.7 0.0
232 0 39831 5.86 0 0.2 2.1 8.7 0.0
236 0 39791 5.86 0 0.2 2.0 8.7 0.0
240 0 39753 5.85 0 0.2 2.0 8.7 0.0
244 0 39718 5.85 0 0.2 1.9 8.7 0.0
248 0 39685 5.85 0 0.2 1.9 8.7 0.0
252 0 39654 5.85 0 0.2 1.8 8.7 0.0
Temporary Sediment Trap.
HUA No. DC9902 Anson County Prison Site
Anson County, NC
10-Year Design Storm
OBJECTIVE: Design a Weir for Detention Pond Forebay
Determine the weir length, capacity & freeboard of the forebay
SOLUTION - Qp: Use the calculated Time of Concentration and the Rational Method to determine
the peak inflow from the design storm.
INPUT
L= ft
H= ft
A = 3.74 acres
C = 0.63
OUTPUT
Te = 10.00 minutes
I = 6.09 in/hr
Qp = 14 cfs
SOLUTION - Lw: Use Trial & Error with Weir Length (Lw) & Driving Head (H) to make Qp <= Qw
INPUT OUTPUT
Cw = 3.00
Lw = 6 ft.
H = 1 ft.
DIMENSIONS: A.disturb = 0.50 acres
S-Trap.H = 4.50 ft.
S-Trap.D = 3.00 ft.
S-Trap.W = 25.00 ft.
S-Trap.L = 15.00 ft.
TERMINOLOGY: Cw = Weir Coefficient
Lw = Weir Length, (ft.)
H = Driving Head, (ft.)
Qp = Peak Inflow, (cfs)
Qw = Peak Discharge, (cfs)
A.disturb = Disturbed Area, (acres)
Freeboard = Freeboard of Weir, (ft.)
Cap.-R. = Required Trap Capacity, (cf)
Cap.-D. = Design Trap Capacity, (cf)
S-Trap.H = Sediment Trap Height, (ft.)
S-Trap.D = Sediment Trap Depth, (ft.)
Qp = 14.3 cfs
Qw = 18.00 cfs
Freeboard = 0.50 ft.
X 1800 cf / acre
Volume = 900 cf
cf
Capacity = 1125 cf
L = Watershed Hydraulic Length, (ft)
Hv = Watershed Vertical Relief, (ft)
a = Statistical Rainfall Variable
b = Statistical Rainfall Variable
A = Watershed Area, (acres)
C = Rational Runoff Coefficient
Tc = Time of Concentration
I = Rainfall Intensity, (in./hr.)
S-Trap. W = Sediment Trap Width, (ft.)
S-Trap.L = Sediment Trap Length, (ft.)
REFERENCES: PEHNR, 1988; Malcom, 1991)
Anti-Flotation Calculations
Riser in Detention Pond #3
HUA No. DC9902 Anson County Prison Site
Anson County, NC
Max. WSEL = 7.34 FT
Riser Invert = 0.00 FT
Riser Diameter = 18.0 INCHES
Riser Volume = 13.0 CF Riser Buoyancy = 809 LBS
Barrel Diameter = 12.0 INCHES
Barrel Length = 8.0 FT
Barrel Volume = 6.3 CF Barrel Buoyancy = 392 LBS
Slab Length = 4.00 FT
Slab Width = 4.00 FT
Slab Thickness = 1.50 FT Slab Buoyancy = 1498 LBS
Slab Volume = 24.0 CF Slab Weight = 3480 LBS
Unit Wt. of Water = 62.4 LBS/CF
it Wt. of Concrete = 145.0 LBS/CF Total Buoyancy = 2699 LBS
Total Weight = 3480 LBS
Factor of Safety = 1.29 (OK)
NOTE: Factor of Safety must be at least 1.1
i;
Riprap Velocity Dissipator Pad
Outlet of Stormwater Pond No. 3
HUA No. DC9902 - 1000 Cell Close Security Prison
Anson County, NC
Design Storm: 10-year, 10-min.
BACKGROUND: Use the E&S Control Planning & Design Manual, Section 8.06.
At the outlet : flow is 9 cfs , V = 10.6 fps
REFERENCE: (NCDEHNR. 1993)
Step 1. Minimum Tailwater Condition
Step 2. D-o = 12 in.
D-o = 1 ft.
Q-10 = 9 cfs
d-50 = 0.5 ft.
Ira = 16 ft.
Step 3. 3*D-o = 3 ft.
W = 17 ft.
Step 4. d-max 0.75 ft.
d-max 9 in.
Step 5. Thickness = 0.8 ft.
Thickness = 9 in.
Figure 8.06 a
Figure 8.06 a
USE: 4 ft.
USE: 18 ft.
Maximum Stone Diameter (1.5*d-50)
USE: Class "1" Rip-Rap
Apron Thickness With Filter Fabric (1.5*d-50)
USE: 12 in.
TERMINOLOGY: Q10 = 10-Year Design Storm, Peak Discharge, (cfs)
D-o = Pipe Diameter, (in. & ft.)
d-50 = Mean Stone Diameter of Rip-Rap, (ft.)
L-a = Length of Rip-Rap Apron, (ft.)
3*D-o = Width of Rip-Rap Apron @ Pipe Outlet, (ft.)
W = Width of Rip-Rap Apron @ End of Apron, (ft.)
d-max = Maximum Stone Diameter of Rip-Rap, (ft. & in.)
Thickness = Thickness of Rip-Rap Apron With Filter Fabric, (ft. &in.)