Laserfiche WebLink
Drainage Memo <br /> Boeing Flightline, Building 45-005 Swale <br /> March 25, 2020 <br /> Page 2 <br /> A; =Area of contributing area <br /> C = Composite Rational Method coefficient for a watershed <br /> Contributing Areas & Rational C-Values: <br /> Total Area = 2,055 [sq. ft.] <br /> = 0.05 [acre] <br /> Area Runoff <br /> Coef. <br /> Surface Type (sq. ft.) (C) ** <br /> House/Roof Area 750 0.90 <br /> Road /Walk 1,305 0.90 <br /> Landscape 0 0.25 <br /> Total Area = 2,055 <br /> Composite C-value for on-site <br /> project area = 0.90 <br /> TIME OF CONCENTRATION <br /> A time of concentration of 44 minutes will be utilized in this design. <br /> Time of Concentration Velocity Factor, k= 27 ft/s <br /> Slope of Flow Path, s= 0.0017 ft/ft <br /> Average Flow Velocity, V= 0.02295 ft/s <br /> Length of Pipe. L = 60 ft <br /> Time of Concentration, Tc = 43.57 min <br /> INTENSITY AND DESIGN FLOW: <br /> i Q <br /> Return Freq. m n [in/hr] [cfs] <br /> 2 year 3.69 0.556 0.453 0.01921 <br /> 10 year 6.31 0.575 0.720 0.03058 <br /> 25 year 7.83 0.582 0.870 0.03696 <br /> 100 year 10.07 0.586 1.103 0.04682 <br /> www.coffman.com <br />