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• <br />• <br />METHODOLOGY <br />The required hydrology calculations for design of Permanent Diversion #1 <br />and the refuse collection ditches were performed utilizing the SEDCAD+ <br />computer model developed by Civil Software Design. <br />SEDCAD+ is a hydrologic and hydraulic calculation model designed for use <br />on IBM compatible personal computers. The SEDCAD+ model calculates <br />runoff and peak flow via a numerical modeling technique based on user <br />inputs of a design storm, i. e. rainfall amount and duration, selection <br />of rainfall distribution, and convolution increment. Hydrographs are <br />developed on a subwatershed basis with the input of area, time of <br />concentration, SCS curve number, and selection of one of three <br />dimensionless double triangle unit hydrograph shapes. Routing of <br />hydrographs is accomplished by Muskingum's method. In a similar <br />manner, SEDCAD+ performs sedimentology calculations on a subwatershed <br />basis, however, sediment yield values are not required for these <br />particular drainage structures. <br />Inputs to the hydrology component of the SEDCAD+ computer model include: <br />- Precipitation Distribution <br />- Storm Duration <br />- Return Period/Precipitation <br />- Hydrograph Response Shape <br />- Drainage Basin Area <br />- Time of Concentration <br />- Curve Number <br />r1 <br />U <br />Input values used for each structure are shown on the SEDCAD+ printouts <br />contained in Appendix A, Hydrology Calculations, and are described <br />below. <br />-4R- Revised - February, 1990 <br />