SW3210302_Design Calculations_20220823

COOKE RENTALS
Maiden, NC
TABLE 1 - PROJECT AREAS
sf
ac
Total Project Area
443,291
10.18
On -site Drainage Area
338,879
7.78
Off -site Drainage Area
5,058
0.12
Drainage Area (Total)
343,937
7.90
Proposed Impervious Area
290,479
6.67
% Impervious Area of Project Area
66%
Impervious of Drainage Area
84%
TABLE 2 - IMPERVIOUS AREAS
Location
Area (sf)
Buildings:
Bldg 1 (Main)
13,000
Bldg 2
12,000
Bldq 3
2,000
Total
27,000
On -site Streets
18,384
On -site Sidewalks
-
On -site Parking
6,822
Other (Equip. Storage/Access):
Equip. Storage-1
61,420
Equip. Storage-2
52,708
Equip. Storage-3
124,146
Other (Equip. Storage/Access) - Total
238,273
Total (sf)
290,479
Total (ac)
6.67
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File: Cooke Calcs 2022-08-22.xlsx !,7;1
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Date: 8/22/2022 Page 1 Ethics • Integrity • Engineering

COOKE RENTALS
Maiden, NC
Table 3 - Treatment Volume Calculation using Simple Method
Rv = 0.05 +0.9 * IA
Where: Rv = Runoff coefficient [storm runoff (in)/storm rainfall (in)], unitless
IA = Impervious fraction [impervious portion of drainage area (ac)/drainage area (ac)], unitless.
IA = (Imprev. Area)/(Total Area)
Dv = 3630 * Rp * Rv * A
Where:
Dv = Design Volume of runoff that must be controlled for the design storm (ft3)
Rc = Design storm rainfall depth (in) (1.0")
A = Watershed area (ac)
Parameter Wet Detention Basin
Total Drainage Area (ac.)
7.90
Impervious Area (ac.)
6.67
I�
0.84
Rv (Runoff Coefficient)
0.81
Rp (Design Storm; 1")
1.0
A (Watershed Area; ac.)
7.90
Req'd Treatment Vol. (Vol. betwn Perm. & Temp pools; ft3)
23,219
Design Treatment Vol. (ft)
24,246
Ref.: BMP Design Manual Sec. 3.3.1
Table 4 - Piedmont and Mountain SA/DA Table
% Imprevious Cover SA/DA Table
4.0
5.0
6.0
80%
2.41
2.07
1.82
85%
2.53
2.19
1.93
90%
2.64
2.31
2.04
Table 5 - Permanent Pool
(PP) Surface Area
Drainage Area (ac.)
(ac)
7.90
(sf)
343,937
Impervious Area (ac.)
(ac)
6.67
(sf)
290,479
Percent Impervious Cover
84.5%
Depth (ft)
5.10
SA/DA Ratio (Interpolated)
2.15
Req'd PP SA (sf)
7,395
Desi n PP SA sf
7,526
Cooke Calcs 2022-08-22.xlsx
Date: 8/22/2022
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COOKE RENTALS
Maiden, NC
able 6 - Eauation 2 A
✓erage Depth (Da g)
Da„g = Average Depth (ft)
PP (Avg. Area Method)
VPP = Volume of Permanent Pool (co
Top Area (APP; Permanent Pool Surface Area)
Vol. (% of Perm. Pool Vol.)
Design PP Vol. (co
Min. Forebay Vol. (co
Design Vol.
Percent of VPP
Davg = VPP/APP
5.1
VPP (based on Stage -Storage Volume)
38,008
7,526 EL.940.00
15% to 20%
24,246
15% 3,637
5,713
23.6%
Table 8 - Discharge Rate for 2-5 day drawdown
Q = Cd x A x (2gHo)10.5
Cd
0.6
Orifice Diameter (in.)
2.50
Area (so
0.034
g
32.2
Permanent Pool SA Elev.
940.00
Treatment Vol. SA Elev.
942.00
H (Top of Treat. Elev. - Perm.Pool)
2.00
Use H/3
0.67
Q (cfs) per orifice
0.13
No. of orifices
1
Total Q (cfs)
0.13
Treatment Vol. Design (co 24,246
Drawdown (sec.) = V/Q 181,010
Drawdown (days) 2.10
Note:
Ref.: BMP Design Manual Sec. 3.5.2
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COOKE RENTALS
Maiden, NC
Table 7a - Wet Pond Stage -Storage
Incremental
Incremental
Depth (ft)
Elevation
Area (so
Storage (co
0
940.00
7,526
1
939.00
6,834
7,180
2
938.00
6,174
6,504
3
937.00
5,546
5,860
4
936.00
4,950
5,248
5
935.00
4,386
4,668
6
934.00
3,854
4,120
7
933.00
3,354
3,604
7.25
932.75
3,234
824
Total Volume
38,008
Table 7b - Forebay Stage -Storage
Cummulative
Incremental
Depth (ft)
Elevation
Area (so
Storage (co
0
940.00
2,059
1
939.00
1,675
1,867
2
938.00
1,323
1,499
3
937.00
1,003
1,163
4
936.00
715
859
4.5
935.50
583
325
Total Volume
5,713
Table 7c - Treatment Volume Stage -Storage
Cummulative
Incremental
Depth (ft) Elevation
Area (so
Storage (co
0 940.00
9,810
1 941.00
12,429
11,120
2 942.00
13,823
13,126
Total Volume
24,246
943 15,274
944 16,781
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File: Cooke Calcs 2022-08-22.xlsx !,7;1
ENGINEERING
Date: 8/22/2022 Page 4 Ethics • Integrity • Engineering