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' REVISED <br />8/8/85 <br />' ~ Table 4 <br />SEDIMEPITATION POND E <br />RISER PIPE DESIGN CALCULATIONS <br />Required sediment storage = 0.64 ac-ft.'s <br />' From stage - storage table, 0.64 ac-ft = 51_8 ft. 'S ~' 9 <br />- set bottom of dewatering hole @ elevation 51.8 S?, `/ <br />' Weighted Gurve Number = 82 (AMC II) ~` <br />10-year, 24-hour runoff volume is 0.52 in/12 (in/ft) x 35 ac = 1.52 <br />' ac-ft. <br />Peak flow for 10-year, 24-hour event, Type II storm, moderate slope, <br />CN = 82, drainage area = 35 acres is 17.7 cfs corrected - - <br />' Inflow Hydrograph: <br />t Triangular hydrograph w/peak flow of 17.7 cfs, volume of 1.52 ac-ft <br />Time base: 2.7 hours ", <br />_ ~ <br />Time of peak flow = 1.0 hours <br />' ~', Centroid of inflow = 1.1 hours ~~ <br /> Outflow Hydrograph: <br /> Equation for 2-inch orifice: Q = C'a (2 gH)# <br /> C' = orifice coefficient = 0.6 ~' <br />' <br />a = area of orifice = r2 = 0.022 ft2 ~~ <br />' g = gravitational constant = 32.2 r <br /> Peak Outflow: <br /> Runoff volume = 1.52 ac-ft f <br />' Sediment volume = 0_64 ac-ft`s <br /> ~ <br /> 2.16 ac-ft total vo lume ' <br />' From stage-storage table, 2.16 ac-ft = 55.4 ft. ~ <br /> - set top of riser pipe @ 5~t. S'S. `f <br />' Maximum head: 55.0-5~= 3~ S' ~ r S ~,p = ~, S <br /> From orifice equation, peak outlflow is 0.19 cfs ~ 7 <br /> Time required to drain 1.52 ac-ft at <br />hours flow rate of 0.~ cfs is~91,8 <br />'`~ l~3'' 2 <br /> Centroid of~outflow = 96.8 hours/2.85 = 34 hours <br /> <br /> -12- <br /> <br />