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2.2 Spillway Calculations for Pond "K" <br />Given: Existing 33-inch CMP outlet, length, 100 feet. <br />Inv. Elev. In 6443.8 <br />Inv. Elev. Out 6439.8 <br />Top of Pipe at outlet 6442.55 <br />From Figure 2.1, emergency spillway <br />Inv. Elev. In. 6447.8 <br />if placed at 4~, Inv. Elev, out = 6443.8 <br />From Figure 2.1, maximum water surface elevation for principal <br />spillway during 10-year event is 6447.8 and maximum water <br />surface elevation for both spillways during the 25-year <br />event is 6449, <br />Principal Spillway <br />The orifice plate detailed in Map JFSA-2 was sized to provide detention <br />time of 29 hours (Table 2.2). During the 25-year event (peak flow, 86 cfs), <br />the box inlet set at elevation 6447.6 will allow full pipe flow in the 33- <br />inch principal spillway. The capacity is: <br />H = 6449 - 6442.55 = 6.45 ft <br />H = Ke v2/2g + Kf v2/2g + Ko v2/2g + v2/2g <br />H = (0.5 + 184.8 (.04432100 + 0.5 + 1) v2/2g <br />2.75 <br />V = 9.35 fps <br />A =T(/4 (2.75)2 <br />0= VA= 56cfs <br />Therefore, the emergency spillway must pass <br />88-56 = 32 cfs <br />Weir Length must be L = QH3/2 - 56/2.6(1.2)1'5 = 16 ft <br />Use 4' x 4' concrete box <br />{`J <br /> <br />4 ~ 24` <br />