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WEST SENECA - POST DEVELOPMENT E_App E_Post-Development Model_REV 2 NY-West Seneca 24-hr S1 25-yr Rainfall=3.84" Prepared by Labella Associates Printed 7/26/2026 HydroCAD® 10.20-6a s/n 09581 © 2024 HydroCAD Software Solutions LLC Page 46 Summary for Subcatchment PS-9: OFF-SITE DRAINAGE Runoff = 4.77 cfs @ 12.80 hrs, Volume= 0.764 af, Depth= 1.83" Routed to Reach 9R : East Swale Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-72.00 hrs, dt= 0.01 hrs NY-West Seneca 24-hr S1 25-yr Rainfall=3.84" Area (sf) CN Description 1,089 80 >75% Grass cover, Good, HSG D 1,699 98 Paved parking, HSG D 214,969 79 Woods, Fair, HSG D 217,757 79 Weighted Average 216,058 99.22% Pervious Area 1,699 0.78% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 20.0 600 0.0100 0.50 Shallow Concentrated Flow, Woodland Kv= 5.0 fps 34.2 100 0.0100 0.05 Sheet Flow, 100' Woods: Light underbrush n= 0.400 P2= 2.20" 5.2 157 0.0100 0.50 Shallow Concentrated Flow, Swale Woodland Kv= 5.0 fps 59.4 857 Total Subcatchment PS-9: OFF-SITE DRAINAGE Hydrograph Runoff 5 4.77 cfs NY-West Seneca 24-hr S1 25-yr Rainfall=3.84" 4 Runoff Area=217,757 sf Runoff Volume=0.764 af Runoff Depth=1.83" Flow (cfs) 3 Flow Length=857' Slope=0.0100 '/' Tc=59.4 min 2 CN=79 1 0 0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46 48 50 52 54 56 58 60 62 64 66 68 70 72 Time (hours) Page 513 of 1174