HomeMy WebLinkAboutSW6200404_Design Calculations_20230303WATER QUALITY CALCULATIONS
ADDITION OF SOF SSA SITE PERMIT MOD. 03/03/2023
Ft Bragg GSB
Stormwater Pond Volume Comparison
January-2020
Wet Pond
Contour Interval (ft)
NCDEQ Requirements (cf)
EISA Option #2 Requirements (cf)
Pre vs Post Development (10-yr)
Provided in Design (cf)
Volume Main Pool VMr
237 - iw.sB
243 114,602 --
114,972
118,621
Volume of Forebay VFB
240 - 243
17,190 i6 98E}
17,246
17,682
Design Volume Dv
243 - 245.50
47,045
84,681 -aarF,.2-
100,831
Pre -Development = 140,276 cf
Post -Development = 255,248 cf
4 = 114,972 cf
CA
ESS�� q �%
�3/03/2�
= SEAL =
038615
T•
ADDITION OF SOF SSA SITE PERMIT MOD
09/21 /2022
SCurry Ft Bragg GSB TEMF PostDev
Post -Development Basin Qp
Cumberland NOAA-B County, North Carolina
Sub -Area Land Use and Curve Number Details
Sub -Area
Hydrologic
Sub -Area
Curve
Identifier
Land Use
Soil
Area
Number
--------------------------------------------------------------------------------
Group
(ac)
Open space; grass cover 50% to 75%
(fair) B
2.96 2.68
59
GSB
'Paved parking lots, roofs, driveways
B
4.64- 1.04
98
GSB
Paved;. curbs and storm sewers
B
7.2
9a
GSB
Gravel (w/ right-of-way)
B
1.5
85
SOF SSA
Roof Areas
B
0.70
98
SOF SSA
Concrete Surfaces
B
2.08
98
SOF SSA
Perimeter Gravel
B
1.0
85
Total Area / Weighted Curve Number
16.2
'"91
Originally included 3.5 acres of reserve impervious area. Updated area reflects GSB roof area only.
.;Weighted CN remains at 91.
WinTR-55, Version 1.00.10 Page 1 5/29/2019 3:51:24 PM
ADDITION OF SOF SSA SITE PERMIT MOD. 09/21/2022
Project: Ft Bragg GSB TEMF - Wet Basin
Date: 31-Jan-20
Simple Method for Runoff Volume
Rv=0.05 +0.9*IA
Rv - Runoff Coefficient
IA- Impervious fraction
Dv=3630*RD*Rv*A
Dv - Design Volume (cf)
RD - Desing Storm Depth (in)
A - Drainage Area (Ac)
Rv = 0.05 + 0.9 *[A
Where: Rv = Runoff coefficient (unitless)
IA = Impervious fraction (unitless)
DV = 3630*RD*Rv*A
Where: DV = Design volume (cu ft)
RD = Design storm depth (in)
A = Drainage area (ac)
0.28 Ac) Impervious Area (Ac)= 1:24- 13.52
Pervious Area (Ac)= 2.96 2.68
Total Area (Ac)= 16.2
IA= 0.8 0.83
RD, Design Storm Depth (in)= 1.0
Rv= 0.79— 0.80
Dv= n NCDEQ Minimum Design Volume
47,045
ADDITION OF SOF SSA SITE PERMIT MOD. 09/21/2022
Project: Ft Bragg GSB TEMF - Wet Basin - Dv @ 1.8"
Date: 31-Jan-20
Rv=0.05 +0.9*IA
Rv - Runoff Coefficient
IA- Impervious fraction
Dv=3630*RD*Rv*A
Dv - Design Volume (cf)
RD - Desing Storm Depth (in)
A - Drainage Area (Ac)
Simple Method for Runoff Volume
Rv = 0.05 + 0.9 * IA
Where: Rv = Runoff coefficient (unitless)
IA = Impervious fraction (unitless)
DV = 3630*RD*Rv`A
Where: DV = Design volume (cu ft)
Ro = Design storm depth (in)
A = Drainage area (ac)
0.28 Ac) Impervious Area (Ac)= 13.24-- 13.52
Pervious Area (Ac)= 2 96 2.68
Total Area (Ac)= 16.2
IA= 9.82 0.83
RD, Design Storm Depth (in)= 1.8
Rv= 0.79 0.80
Dv= 22, NCDEQ Minimum Design Volume
84,681
ADDITION OF SOF SSA SITE PERMIT MOD. 09/21/2022
Project: Ft Bragg GSB TEMF - Wet Basin
Date: 31-Jan-20
Hydraulic Retention Time (HRT) Method
Dv - Design Volume (cf) From Simple Method @ 1.0"
Dv= 46,195--ef 47,045 cf
VMP = 112,932 s# 114,602 cf
Equation 1: Main Pool Volume, V p
VMp = 0.87 * HRT * DV
s
Where: 0.87 = Factor to adjust for the volume in the forebay
VMP = Main pool volume, not including the forebay (cubic feet)
HRT = Required hydraulic residence time (14 days)
TS = Average time between storm events (5 days)
DV = Design volume (cubic feet)
ADDITION OF SOF SSA SITE PERMIT MOD. 03/03/2023
Wet Pond Drawdown Time
Ft Bragg GSB TEMF
Feb-03-2020
Orifice Diameter 44inches
Q = Cd * A * (2gh)'/2
Cd = 0.6
A = 0.0873 sf
g = 32.2 (ft/s2)
h = (Temp. Pool Elev. - Normal Pool Elev.) / 3
= (245.5 - 243) / 3
= 0.833 ft
Discharge Rate of Orifice (cuft/s) 1 0.384 $�
Volume of Stormwater for Drawdown 1 100,831 +++5�
Incremental Storage (cuft):
Contour Area (sf) Incremental Volume (cf)
245.5
44,278
21,777
245
42,834
41,403
244
39,989
37,650
243
35,359
0.00 3-
Total Storage (cuft)
Drawdown Rate:
Volume of Stormwater / Discharge Rate
CARo
�)F ESS�� q �%
�3/03/2�
= SEAL =
038615
262,869 246368 sec
73.02 fib- h rs
3.04 days
100,831�5,793