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h10V-15-1??1 1~7~28 FFnll ,Er~i,IE~.T GOLUEII <br />• Ms. Kathleen 0. welt <br />November tA, 1991 <br />CALCULATIONS <br />TO 03039290595--1527 P.02r <br />Pege 2 of 3 i <br />Peak discharge was calculated by using methods described in Procedures for Determining Peal< Flows <br />In Colorado, Soil Conservation Service, U.S. Dept. of Agriculture, March, 1980. The equation for peak <br />discharge is: <br />q = gPAQ <br />where; <br />y =Peak Discharge (cts) <br />q, =Peak Discharge (cubic feet per second per square mile per inch of runoff, or csmlinch) <br />A =Drainage Area (square miles) <br />Q =Runoff Depth (inches) <br />7o calculate the peak discharge tar the proposed coal storage pad, the following values were plugflad <br />Into the equation to determine q: <br />q, = 1,000 csmlinch, based on a time of concentration of 0.1 hours, which in turn is based on <br />an elevation difference of 200 feet and a channel length of 2,000 feet. <br />A =Drainage area of the proposed coal storage pad Is 126,000 sq. ft., or 0.0067 sq. mi. <br />0 = 0.65 inches of runoff, based on a 1.8 inch 10-year, 24•hour precipitation event and a rur~oSt <br />curve number' of BG. <br />Since the location of both areas are the same, the drainage area was calulated by subtracting ltre <br />measured area of the existing coal storage.pad from the measured area of the proposed coal storage <br />pad. <br />The increase in storm water volume entering the existing sedimentation pond as the result of a 10-year, <br />24-hour precipitation event was calculated using the following equation: <br />V,,, = AQ <br />.. ~. a ~ticm,n rncuat~n..., i, <br />