SW6210506_Design Calculations Pond 2_20210528

DESIGN REQUIREMIENTS:
A. Contain the I inch storm
Drainage Area, (DA) - 2.24 acres
Intensity, (1) - 0.13 inches/hr
Composite Runoff Coefficient, (C) 0.30
Maximum Release Rate, (Qj) => 0.09 CIS
Drainage Area, (DA) - 2.24 acres
Intensity, (1) - 0.13 inches/hr
Composite Runoff Coefficient, (C) 0.58
Peak Release Rate, (Qj) - 0. 17 efs
Contour
Contour
Iner.
Accum.
Stage
Elev.
Area
Storage
Storage (S)
(Z)
00
(sf)
(cf)
(cf)
00
In (S)
In (Z)
Z est
289.5
-
-
-
-
-
290.0
3,685
921
921
0.50
6.83
-0.69
0.48
290.5
4,177
1,966
2,887
1.00
........................
7.97
...........................
0.00
1.04
291.0
4,691
2,217
5,104
1.50
8.54
0.41
1.54
291.5
5,226
2,479
7,583
2.00
8.93
0.69
2.02
292.0
5,782
2,752
10,335
2.50
9.24
0.92
2.49
292.5
6,354
3,034
13,369
3.00
9.50
1.10
2.97
293.0
6,940
3,324
16,693
3.50
9.72
1.25
3.46
293.5
7,540
3,620
20,313
4.00
9.92
1.39
3.95
-
-
fifififififififi
fifififififififi
-289.50
#NUM!
#NUM!
#NUM!
Regression Output:
b- 1.47 (X Variable Coeff)
Ks- 2,708 (e Y-iriter-pt )
Stage - Storage Equation is of the form: S - (Ks)(Z) b
printed: 5/20/2021 8 51 AM Page 1 of 3

Barrel
Number of Barrels —
Dia. of Barrel —
Area of Barrel, (Ab) —
Pipe Length, (L) —
Friction Coeff., (Kp) —
Inv. of Barrel —
Riser
Elev. of Riser Crest
Rectangul
Length Weir— 36 inches
Total Weir Length
Area of Riser —
Orifice in Riser
Dia. of Orifice —
Number of Orifices —
Area of Orifice, (Ab) —
Orifice Coefficient (Cd) —
Inv. of Orifice —
Length of weir —
Top of weir —
Weir Coefficient (Cw)—
Width of Spillway (Approx.) —
Weir Coefficient —
Crest Elevation —
Maximum Release Rate, (Qj) —
Release Rate, (Qj) —
Normal Water Surface Elev. —
1
15 inches
1.23 sf
50 feet
0.01980
289.50 feet
292.25 feet
Width Weir— 48 inches
14.00 feet
12.00 sq. ft.
1.25 inches
I
0.01 sf
0.60
289.50 feet
1.00 feet
291.10 feet
3.00
10 feet
3.3
292.50 feet
0.09 efs
0.05 efs
289.50 feet
Water Surface Elev. @ Outlet (Qj) — 291.09 feet
printed: 5/20/2021 8 51 AM
Page 2 of 3

Peak Inflow, (Qp) =>
Time to Peak Calculation: CN
Q*—
vol—
Time to Peak, (Tp)
(SCS TR-55)
0.17 efs
80 p— 2.96 in.
1.22 in. (depth of runoff)
9,921 ef (vol. of runoff)
704.3 minutes
S— 2.50 in.
printed: 5/20/2021 8 51 AM
Page 3 of 3

Cotswold
Pond 42
Antiflotation Calculation
Input Data
Safety Factor:
1.50
Top Width of Riser (ft)
3.00
Top Length of Riser (ft)
4.00
Thickness of Riser (ft)
0.50
Thickness of Bottom of Riser (ft)
0.50
Top of Riser (ft)
292.25
Invert of Riser (ft)
289.50
Volume of Riser (cf)
22.50
Unit Weight Of Concrete (lb/cf)
150.00
Unit Weight of Water (lb/cf)
62.40
Block Height (ft)
0.00
Block Width (ft)
0.00
Block Length (ft),
0.00
Output
Fw (Uplift Force, lb)
2059.20
Fc (Weight of Concrete,lb)
3375.00
Design Volume (cf),
22.50
Design Safety Factorl
1.64
Volume OK
1728-POND 2 Antiflotation.xls 5/20/2021

Cotswold Pond #2
Drawdown Time
Temporary storage volume —
Orifice #I diameter=
Area of orifice
Orifice #2 diameter
Area of orifice
Orifice Coefficient (Cd)
Orifice elevation --
Water elevation ---
Driving head (H) =
Discharge (Q) —
Drawdown time =
5,356 cf
1.25 in
1
0.0085 sf
0 in
0
0.0000 sf
0.60
289.50 ft
291.09 ft
0.53 ft
0.0299 cfs
179269 s
49.8 hr
2.1 days
1728-Drawdown.xlsx Printed 5/20/2021

Cotswold Pond N2
Storm Water Control
SCS curve number
Hydraulic Soil Group: B
Area
SCS CN
Building (sf)
25,350
98
50,295
Driveways (sf)
6,669
98
Pavement (sf)
10,736
98
Pond (sf)
7,540
98
Open space (sf)
47,467
61
Offsite -open space (sf)
0
61
Offsite -impervious (sf)
0
98
Total (sf)
97762
80
Total (ac)
2.24
Rational Coefficient
Predevelopme
Postdevelopme
Area
C
Area
C
Impervious (sf)
0
0.95
Building (sf)
25,350
0.95
Open space (sf)
619,528
0.30
Driveways (sf)
6,669
0.95
Pavement (sf)
10,736
0.95
Pond (sf)
7,540
0.30
Open space (sf)
47,467
0.30
Offsite -open space (sf)
0
0.3
Offsite -impervious (sf)
0
0.95
Total (ac)
619528
0.30
Total (ac)
97762
0.58
Total (ac)
14.22
Total (ac)
2.24
1728-Runoff coefficient calcs.xls Printed 5/20/2021

Cotswold Pond #2 Required Storm Volume
Wet Pond
Drainage Area:
2.24 acres
Impervious Area: 50,295 sf (1.15 ac)
% Impervious: 51.4%
1 inch Storm Event:
Rv = 0.05+0.009 1
Rv = runoff coefficient
I= percent impervious
Rv=0.05+0.009*51.4%
= 0.5126
For volume that must be controlled:
Volume=3,630*Rd*Rv*A
Volume = 3,630*(l inch)*(0.5126)*2.24 acres = 4,168 cf
Temporary volume stored = 5,356 cf
SA/DA ratio is 1.83 for a depth of 3.0 feet
Required surface area = 2.24 ac * (0.0183) = 0.0410 ac or 1,786 sf
Surface area provided (main permanent pool) = 2,779 s
409 Chicago Drive, Suite 112, Fayetteville, NC 28306
office 1910-426-6777 fax [phone] license number I C-2354
On time, every time. I www.4Dsitesolutions.com