Laserfiche WebLink
a <br />Ir,tusTRATrve_ rXAMPf.13 <br />Ared of site 1.37 acres <br />ROC before development 0.15 <br />ROC after development 0.90 e <br />Design storm - predevelopment fret' 1 in 10 years <br />1,ost development freq 1 in 10 years <br />Duration 20 mins <br />Intensity 1.3 ins/hr <br />predevelopment runoff <br />0.15 1.3 x 1 x 1.37 x 435bj cubic fret <br />3 12 <br />= 0.15 x 2155 cubic feet <br />323 cubic feet <br />vost development runoff = 0.90 x 2155 cubic feet <br />1940 cubic feet <br />Runoff differential 1617 cubic feet <br />Additional storage due to lag time equals (time of oincentration)X (w:an rate <br />of discharge over the period). <br />Assume time of concentration = 5 nun. <br />Rate of discharge = 0.27 cubic ft. per sec <br />Mean rate of discharge = 0.135 cfs <br />Additional storage required - n.1 Li x 300 <br />40 cft <br />Detention storage proposed - 1657 cft <br />Orifice opening a 2-1/4 inches <br />discharge :1.15 x 1.3 x 1.3� cfs <br />0.27 cfs <br />head 3.76 feet <br />Outlet pipe <br />Diameter 12 inches <br />slope 1 ft. in 200 <br />Capacity / 3 //.L <br />Q � 0.463 D S <br />N <br />0.463 x 1 x .07 <br />.012 <br />= 2.73 cfs <br />From nomograph Q 2.7 cfs <br />