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<br />MINE 3 <br />' Riser Pipe Design <br />Required sediment storage = 0.64 ac-ft. <br />From stage -storage table, 0.64 ac-ft = 95.7 ft. <br />' -set bottom of dewatering hole @ 95.7 <br />Weighted Curve Number = 82 (AMC II) <br />' 10-yr, 24 hr runoff voume is 0.52 in / 12 x 35 ac = 1.52 ac-ft. <br />Peak flow for Type II storm, moderate slope, CN = 82, drainage area = 35 acres is <br />' 17.7 cfs <br />i ' lnflow Hydrograph: <br />Triangular hydrograph w/ peak flow of 17.7 cfs, volume of 1.52 ac-ft <br />' Time base: 2.7 hrs. <br />Time of peak flow = 1.0 hrs. <br />Centroid of inflow = 1.1 hrs. <br />1 <br />I <br /> <br />1 <br /> <br /> <br />1 <br /> <br />i <br />Outflow Hydrograph: <br />Equation for 2-inch orifice: Q = C'a 2 gH <br />C' =orifice coefficient = 0.6 <br />a =area of orifice = r2 = 0.022 ft2 <br />g =gravitational constant = 32.2 <br />Peak Outflow: <br />Runoff volume = 1.52 <br />Sediment volume = 0.68 <br />2.20 ac-ft total volume <br />From stage-storage table, 2.20 ac-ft = 100,0 ft. <br />-set top of riser pipe @ 100.0 ft. <br />Maximum head: 100.0-94.9 ft. = S.l ft. <br />From orifice equation, peak outflow is 0.23 cfs <br />Time required to drain 1.52 ac-ft at flow rate of 0.23 cfs is 80.0 hrs. <br />Centroid of outflow = 80 hrs / 2.85 = 28 hrs. <br />7 <br />