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number, and selection of one of three (3) dimensionless double triangle unit <br />hydrograph shapes. This information is further discussed in the SEDCAD+ User's <br />Manual (Schwab and Warner, 1987) and in the SEDCAD+ Inputs section that <br />follows. Routing of hydrographs is accomplished by Muskingum's methods. <br />Specific hydrologic output values calculated by the SEDCAD+ model are as <br />follows: <br />• Peak Flows (cfs) <br />• Storm Runoff (inches) <br />• Runoff Volume (acre-feet) <br />• Total Storm Hydrograph <br />SEDCAD+ Hydrology Inputs <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 />• Time of Concentration <br />• Curve Number <br />• Routing Parameters <br />Precipitation Distribution. A precipitation distribution is input to model the runoff <br />hydrograph. SEDCAD+ allows the user to choose between the SCS Type I or <br />Type II storms. For the Grassy Creek Mine the SCS Type II storm was selected. <br />Storm Duration. A storm duration of 24 hours was used for design. <br />Return Period/Precipitation. ' A :precipitation amount is required for the <br />appropriate return period. For the Grassy Creek Mine the following precipitation <br />values were used: <br />6-year, 24-hour event: 0.9 inches <br />10-year, 24-hour event: 1.8 inches <br />25-year, 24-hour event: 2.1 inches <br />100-year, 24-hour event: 2.6 inches <br />2 <br />