SW6230705_Design Calculations_20230831 (28)

4D Site Solutions, Inc.
DESIGN REQUIREMENTS:
A. Pass the storm event
SCM 15 Pre-Development Runoff-100-yr
Drainage Area,(DA)= 16.13 acres
Intensity,(I)= 7.57 inches/hr
Composite Runoff Coefficient,(C)=> 0.30
Maximum Release Rate,(Qloo)=> 36.63 cfs
SCM 15 Post-Development Runoff-100-yr
Drainage Area,(DA)= 16.13 acres
Intensity,(I)= 9.52 inches/hr
Composite Runoff Coefficient,(C)=> 0.59
Peak Release Rate,(Qloo)=> 90.60 cfs
Detention Pond Stage-Storage Function
Contour Contour Incr. Accum. Stage
Elev. Area Storage Storage(S) (Z)
(ft) (sf) (cf) (cf) (ft) ln(S) ln(Z) Z est
295.5 20,647 - - -
296.0 22,448 10,774 10,774 0.50 9.28 -0.69 0.55
297.0 24,344 23,396 34,170 1.50 10.44 0.41 1.52
298.0 26,317 25,331 59,500 2.50 10.99 0.92 2.48
299.0 28,367 27,342 86,842 3.50 11.37 1.25 3.45
300.0 30,493 29,430 116,272 4.50 11.66 1.50 4.46
300.5 31,585 15,520 131,792 5.00 11.79 1.61 4.98
301.0 32,696 16,070 147,862 5.50 11.90 1.70 5.50
301.5 33,825 16,630 164,492 6.00 12.01 1.79 6.04
302.0 34,975 17,200 181,692 6.50 12.11 1.87 6.60
Regression Output:
b= 1.14 (X Variable Coeff)
Ks= 21,166 (eY-b`te`Cept)
Stage-Storage Equation is of the form:S=(Ks)(Z)b
printed: 7/7/2023 1.25 PM Page 1 of 3

4D Site Solutions, Inc.
Primary Spillway
Barrel
Number of Barrels= 1
Dia.of Barrel= 24 inches
Area of Barrel,(Ab)= 3.14 sf
Pipe Length,(L)= 80 feet
Friction Coeff.,(Kp)= 0.01058
Inv.of Barrel= 295.50 feet
Riser
Elev.of Riser Crest= 299.00 feet
Rectangular
Length Weir= 36 inches Width Weir= 48 inches
Total Weir Length= 14.00 feet
Area of Riser= 12.00 sq.ft.
Orifice in Riser
Dia.of Orifice= 3.00 inches
Number of Orifices= 1
Area of Orifice,(Ab)= 0.05 sf
Orifice Coefficient(CO= 0.60
Inv.of Orifice= 295.50 feet
Length of weir 3.00 feet
Top of weir= 296.79 feet
Weir Coefficient(Cw)= 3.00
Emergency Spillway
Width of Spillway(Approx.)= 25 feet
Weir Coefficient= 3.3
Crest Elevation= 310.00 feet
Summary of Results
Maximum Release Rate,(Qloo)= 36.63 cfs
Release Rate,(Q1oo)= 74.53 cfs
Normal Water Surface Elev.= 295.50 feet
Water Surface Elev.@ Outlet(Q100)= 299.73 feet
printed: 7/7/2023 1.25 PM Page 2 of 3

4D Site Solutions, Inc.
Inflow Hydrograph-100-yr
Peak Inflow,(Qp)_> 90.60 cfs
Time to Peak Calculation: CN= 71 P= 7.91 in. S= 4.08 in.
Q*= 4.50 in. (depth of runoff)
Vol= 263,551 cf (vol.of runoff)
Time to Peak,(Tp)=> 34.9 minutes
(SCS TR-55)
printed: 7/7/2023 1:25 PM Page 3 of 3