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SOUNDVIEW TECHNOLOGY CENTER EVERETT, WA = 2 x 7.97/0.00096 = 4,097 sf=AS This equation results in a surface area of 4,097 SF. The pond was designed with a surface area of 5,000 SF at the top of the sediment storage, which exceeds the minimum requirements for the 70-year flow. The required area of the orifice was calculated using the following equation: Ao =AS(2h)05/0.6 x 3600Tgo.5 =4097 x(2(3.5))0 5/[0.6 x 3600 x 24 x 32.215] = 0.0327 sf Converted to the required diameter using the following calculation: D = 73.54 x Ao0.5 = 73.54 x 0.032705 = 2.45" z 2-7/76" The sediment pond will have a 3.5'minimum depth from top of riser to bottom of live pond along with 7'of free board and 7.5'of sediment storage for a total depth of 6.0'. TESC Pond- Basin B Tributary Area: 11.98 acres (to vault#3 and #5) Flow Frequency Flow Frequency Flow(cfs) 0701 Flow(cfs) 0702 2 Year = 2.8058 2 Year = 0.7787 5 Year = 3.8348 5 Year = 1.0616 10 Year = 4.5932 10 Year = 1.2697 25 Year = 5. 6428 25 Year = 1.5573 50 Year = 6.4935 50 Year = 1.7901 100 Year = 7.4054 100 Year = 2.0394 10-year flowrate: (4.59 + 1.27) = 5.86 CFS The required surface area was calculated using the following equation: SA = 2 x Q 7o/0.00096 = 2 x 5.86/0.00096 = 72,274 sf= AS This equation results in a surface area of 72,274 SF. The pond was designed with a surface area of 73,000 SF at the top of the sediment storage, which exceeds the minimum requirements for the 70-year flow. The required area of the orifice was calculated using the following equation: Ao =AS(2h)05/0.6 x 3600Tgo.5 =72,274x(2(3.5))05/[0.6x3600x24x32.2151 = 0.0974 sf Converted to the required diameter using the following calculation: D = 73.54 x Aoo.s = 73.54 x 0.09740.5 = 4.23" z 4-7/4" The sediment pond will have a 3.5'minimum depth from top of riser to bottom of live pond along with 7'of free board and 7.5'of sediment storage for a total depth of 6.0'. SEPTEMBER 23, 2022 STORMWATER DRAINAGE REPORT PAGE 40