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C~ <br /> <br />PEAK FLOW CALCULATIONS <br />Calculations made using the methodology described in Procedures <br />for Determininq Peak Flows in Colorado (SCS, 1980). <br />10-year, 24 hr precipitation event = 1.5 inches <br />Soils - Evanston Series <br />Turret Series <br />Hydrologic Soil Group B <br />Hydrologic Soil Group B <br />Antecedent Moisture II <br />Assuming that a successfully reclaimed area would compare to the <br />pasture or range landuse (fair condition), a curve number of 69 is <br />selected for peak flow calculations. This compares to a curve <br />number of 74 which was used to calculate peak flows for Empire <br />Energy's sediment and runoff control system. <br />1. Watershed with collection ditches in place. <br />Area = 95 acres <br />Average Watershed Slope - <br />S = 0.25Z(LC25 + LC50 + LC75) <br />where: S =Average watershed slope, <br />DA = Watershed Area, <br />Z = Elevation difference between high and <br />• <br />low point, and <br />LC 25, LC50 LC75= Length of contours located at <br />8 <br />