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• METHODOLOGY AND ASSUMPTIONS <br />The required hydrology, sedimentology, and hydraulic calculations for the <br />Grassy Creek Mine permanent drainage structures were performed utilizing a <br />combination of hand calculations and the SEDCAD+ computer model <br />developed by Civil Software Design. SEDCAD+ is a third generation hydrologic <br />and hydraulic calculation model designed for use on IBM compatible computers. <br />Measurements for premine hydrology and sedimentology parameters were <br />taken from the Reclamation Map in the Rockcastle Permit. This map was <br />developed prior to mining related disturbance and best represents premine <br />configuration. Postmine measurements for Pits 1, 2, 3, 4, 5 and 6 were taken <br />from the Drainage and Sediment Control Map (Map R-1). The Drainage and <br />Sediment Control Map was developed from the Reclaimed Topography (1990) <br />& Bond Release Documentation Map, which reflects aerial photography from a <br />• flight in October of 1990. Postmine topography for Pits 5 and 6, shown on the <br />Drainage and Sediment Control Map was developed by hand. <br />HYDROLOGY <br />Hydrology calculations were performed utilizing the SEDCAD+ computer model. <br />Computer printouts including hydrology inputs and results are contained in <br />Exhibit 1, SEDCAD+ Computer Printouts. <br />SEDCAD+ Hydrology Calculations <br />The SEDCAD+ model calculates runoff and peak flow via a numerical modeling <br />technique based on user inputs of runoff basin information and design storm. <br />Design storm inputs include rainfall amount and duration, selection of a rainfall <br />distribution, and convolution increment. Hydrographs are developed on a <br />subwatershed basis with the input of area, time of concentration, SCS curve <br />number, and selection of one of three (3} dimensionless double triangle unit <br />hydrograph shapes. This information is further discussed in the SEDCAD+ <br />1 <br />