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METHODOLOGY AND ASSUMPTIONS <br />• SCS METHOD <br />The required hydrology and sedimentology calculations for [he permanent watershed diversion <br />and permanent diversion culvert were calculated according to procedures set forth in <br />"Procedures for Determining Peak Floa•s in Colorado,' published by the USDA Soil <br />Conserva[ion Service. The culvert was sized utilizing the "National Engineering Handbook, <br />Section 4 Hydrology." The design calculations are detailed in the following sections of this <br />report. <br />SEDCAD+ <br />The required hydrology calculations for the Sediment Pond, Watershed Diversion Ditches 1 <br />through 5, yard ditches, culverts, and the refuse sediment collection ditches were performed <br />utilizing the SEDCAD+ computer model developed by Civil Software Design. <br />SEDCAD+ is a hydrologic and hydraulic calculation model designed for use on IBM compatible <br />personal computers. The SEDCAD+model calculates runoff and peak flow via a numerial <br />modeling technique based on user inputs of a design storm, i.e. rainfall amount and duration, <br />selection of rainfall distribution, and com~olution increment. Hydrographs are developed on a <br />subwatershed basis with the input of area, time of concentration, SCS curve number, and <br />selection of one of three dimensionless double triangle unit hydrograph shapes. Routing of <br />hydrographs is accomplished by Muskingum's method. In a similar manner, SEDCAD+ <br />performs sedimentology calculations on a subwa[ershed basis. <br />Hydrology <br />Inputs to the hydrology component of the SEDCAD+ computer model include: <br />• Precipitation Distribution <br />• Storm Duration <br /> <br />A:~S56ATR1J.REV 358Rc Revised -June 1993 <br />miaveo u.,,. <br />