SW6230705_Design Calculations_20230831 (35)

4D Site Solutions, Inc.
DESIGN REQUIREMENTS:
A. Post development discharge<or=Predevelopment discharge
SCM 16 Pre-Development Runoff-10-yr
Drainage Area,(DA)= 12.60 acres
Intensity,(I)= 5.99 inches/hr
Composite Runoff Coefficient,(C)=> 0.30
Maximum Release Rate,(Q10)=> 22.64 cfs
SCM 16 Post-Development Runoff-10-yr
Drainage Area,(DA)= 12.60 acres
Intensity,(I)= 7.49 inches/hr
Composite Runoff Coefficient,(C)=> 0.64
Peak Release Rate,(Qio)=> 60.40 cfs
Detention Pond Stage-Storage Function
Contour Contour Incr. Accum. Stage
Elev. Area Storage Storage(S) (Z)
(ft) (sf) (cf) (cf) (ft) In(S) In(Z) Z est
279.5 15,446 - - -
280.0 16,933 8,095 8,095 0.50 9.00 -0.69 0.53
280.5 17,492 8,606 16,701 1.00 9.72 0.00 1.02
281.0 18,061 8,888 25,589 1.50 10.15 0.41 1.50
282.0 19,229 18,645 44,234 2.50 10.70 0.92 2.46
283.0 20,437 19,833 64,067 3.50 11.07 1.25 3.45
284.0 21,687 21,062 85,129 4.50 11.35 1.50 4.46
285.0 22,976 22,332 107,461 5.50 11.58 1.70 5.51
285.5 23,637 11,653 119,114 6.00 11.69 1.79 6.05
286.0 24,533 12,043 131,157 6.50 11.78 1.87 6.60
Regression Output:
b= 1.10 (X Variable Coeff)
Ks= 16,410 (eY"intercept)
Stage-Storage Equation is of the form:S=(Ks)(Z)b
printed: 7/7/2023 131 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= 279.50 feet
Riser
Elev.of Riser Crest= 283.50 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= 2.70 inches
Number of Orifices= 1
Area of Orifice,(Ab)= 0.04 sf
Orifice Coefficient(CO= 0.60
Inv.of Orifice= 279.50 feet
Length of weir= 1.80 feet
Top of weir= 281.01 feet
Weir Coefficient(Cw)= 3.00
Emergency Spillway
Width of Spillway(Approx.)= 25 feet
Weir Coefficient= 3.3
Crest Elevation= 284.50 feet
Summary of Results
Maximum Release Rate,(Qlo)= 22.64 cfs
Release Rate,(Q10)= 22.52 cfs
Normal Water Surface Elev.= 279.50 feet
Water Surface Elev.@ Outlet(Qlo)= 283.54 feet
printed: 7/7/2023 131 PM Page 2 of 3

4D Site Solutions, Inc.
Inflow Hydrograph-10-yr
Peak Inflow,(Qp)_> 60.40 cfs
Time to Peak Calculation: CN= 74 P= 5.24 in. S= 3.51 in.
Q*= 2.56 in. (depth of runoff)
Vol= 116,959 cf (vol.of runoff)
Time to Peak,(Tp)=> 23.2 minutes
(SCS TR-55)
printed: 7/7/2023 1:31 PM Page 3 of 3