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1.4 HYDROGRAPH RESPONSE SHAPE <br />A unit hydrogxaph is chosen for each drainage area or sub-area modeled to predict the run-off response. <br />The hydrograph responses available in the SEDCAD4 model are slow, medium, and East. A slow response <br />corresponds to a forested area or an area with a number of obstructions. A fast response corresponds to an <br />un-vegetated or poorly protected azea, Medium and fast hydrograph responses were identified as <br />representative fot mine areas. <br />The internal convolution increment is 0.05 hours, and values are saved at the user-specified interval of 0.1 <br />hours or greater. A convolution increment of 0.1 was specified. It should be anted that a rime of <br />concentration less than 0.125 hours bypasses the unit hydxograph technique and instantaneous run-off is <br />assumed. As explained in the SEDCAD4 Users Manual (Schwab and Warner, 1998), the time of <br />concentration restriction of 0.125 hours is dictated by a combination of array size restrictions, minimum <br />internal convolution interval, and the user-specified time increment for saving convolution values. <br />1.5 DRAINAGE BASIN AREA <br />Drainage basin areas were determined for each pond from scaled drawings. The final post-mining <br />topography was used as the worst-case representation for all ponds. Watershed (or sub-watershed) areas <br />were delineated consistent with four general categories representing various stages of reclamation and <br />disturbance. The watershed or sub-watershed delineations reflect anticipated disturbance/reclamation status <br />based on Colowyo's current mining and reclamation plans. <br />1.6 TIME OF CONCENTRATION, Tc <br />The time of concentration was calculated using the SCS upland metl-~od (Soil Conservation Service, 1986). <br />The hydraulic lengths, drainage heights and associated slopes were determined from scaled drawings. The <br />values calculated for each strucrure are shown on asub-watershed basis in the SEDCAD4 prntouts. <br />1.7 MUSKINGUM ROUTING PARAMETERS, K, X <br />The Muskingum Routing Parameters were also calculated using the: SCS upland method. The hydraulic <br />lengths, drainage heights and associated slopes were detemuned from scaled drawings. The values calculated <br />between each structure and/ox sub-watershed are shown in the SEDC:AD4 printouts. <br />1.8 CURVE NUMBER, CN <br />The runoff curve number is a factor relating the amount of rainfall to the amount of runoff for a given area. <br />Curve numbers were jointly developed and agreed upon by the Division of Minerals and Geology and <br />Colowyo. The curve number for the [opsoiled and seeded areas was based on a hydrologic soil group B with <br />no vegetation. Table ] provides a summary of the curve numbers used for the pond design evaluations. <br />Exhibit 7 2 Revision Date 10/23/03 <br />Revision No. TR-56 <br />