Conservation Commission (linked)

Civil Engineers & Land Surveyors, P.C. 
 
BY:    MJO  .   
DATE:   5-1-24  . 
SUBJECT:   Williams School Athletics Team / Maintenance Building .   SHEET No.:    1   OF   1  . 
 
 
 
 
CHECKED:    LJM  .   DATE:   5-1-24  . 
  Water Quality and Required Retention Volume Design Computations   .   PROJECT No.:    23-43  . 
Summer Hill 
1.  Water quality volume and required retention volume computed using the CT Stormwater Quality Manual equation 
 
     WQV = RRV = (1.3)(R)(A)/12, where: 
 
     WQV, Water quality volume (cubic feet) 
     RRV, Required retention volume (cubic feet) 
     P,  Precipitation depth = 1.3 inches 
     R,  Volumetric runoff coefficient = 0.05 + 0.009(I) 
     I,   Post-development impervious area (percent) 
     A   Post-development site drainage area (square feet) 
 
     I = 44.0% 
     R = 0.05 + 0.009(44.0) = 0.45 
     A = 27,030 ft2  
 
     WQV = RRV = (1.3 in)(R)(A)/12 = (1.3 in)(0.45)(27,030 ft2)/12 = 1,318 ft3 
 
 
2.  Stormwater basin storage volume 
Elevation   
ft 
Area            
ft2 
Average Area    
ft2 
Incremental 
Volume 
ft3 
Cummulative 
Volume 
ft3 
Cummulative 
Volume 
Ac-ft 
80.50 
1,010 
1,010 
0 
0 
0 
81.00 
1,035 
1,023 
511 
511 
0.0117 
82.00 
1,405 
1,220 
1,220 
1,731 
0.0397 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
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