SW6230705_Design Calculations_20230831 (12)

4D Site Solutions, Inc.
DESIGN REQUIREMENTS:
A. Pass the storm event
SCM 13 Pre-Development Runoff-100-yr
Drainage Area,(DA)= 22.47 acres
Intensity,(I)= 7.57 inches/hr
Composite Runoff Coefficient,(C)=> 0.30
Maximum Release Rate,(Qloo)=> 51.03 cfs
SCM 13 Post-Development Runoff-100-yr
Drainage Area,(DA)= 22.47 acres
Intensity,(I)= 9.52 inches/hr
Composite Runoff Coefficient,(C)=> 0.61
Peak Release Rate,(Qloo)=> 130.49 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
307.5 20,932 - - -
308.0 23,019 10,988 10,988 0.50 9.30 -0.69 0.54
308.5 24,084 11,776 22,764 1.00 10.03 0.00 1.03
309.0 25,164 12,312 35,076 1.50 10.47 0.41 1.50
310.0 27,365 26,265 61,340 2.50 11.02 0.92 2.45
311.0 29,622 28,494 89,834 3.50 11.41 1.25 3.42
312.0 31,936 30,779 120,613 4.50 11.70 1.50 4.43
313.0 34,306 33,121 153,734 5.50 11.94 1.70 5.48
314.0 36,733 35,520 189,253 6.50 12.15 1.87 6.58
315.0 39,216 37,975 227,228 7.50 12.33 2.01 7.72
Regression Output:
b= 1.14 (X Variable Coeff)
Ks= 22,121 (eY"mtercePt)
Stage-Storage Equation is of the form:S=(Ks)(Z)b
printed: 7/7/2023 1.09 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= 307.50 feet
Riser
Elev.of Riser Crest= 312.50 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= 307.50 feet
Length of weir 2.50 feet
Top of weir= 309.42 feet
Weir Coefficient(Cw)= 3.00
Emergency Spillway
Width of Spillway(Approx.)= 20 feet
Weir Coefficient= 3.3
Crest Elevation= 314.00 feet
Summary of Results
Maximum Release Rate,(Qloo)= 51.03 cfs
Release Rate,(Q1oo)= 103.67 cfs
Normal Water Surface Elev.= 307.50 feet
Water Surface Elev.@ Outlet(Q100)= 313.45 feet
printed: 7/7/2023 1.09 PM Page 2 of 3

4D Site Solutions, Inc.
Inflow Hydrograph-100-yr
Peak Inflow,(Qp)_> 130.49 cfs
Time to Peak Calculation: CN= 73 P= 7.91 in. S= 3.70 in.
Q*= 4.73 in. (depth of runoff)
Vol= 385,830 cf (vol.of runoff)
Time to Peak,(Tp)=> 35.5 minutes
(SCS TR-55)
printed: 7/7/2023 1:09 PM Page 3 of 3