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SQEST RIDGE <br />HYDROLOGIC RECONSTRVCTION PLAN <br />• <br />INTRODUCTION <br />The Hydrologic Reconstruction Plan addresses runoff controls within <br />the permanent program lands on the West Ridge mining area which are <br />permitted under Permit C-80-001, and also includes the previously <br />reconstructed, ephemeral watercourse between West Ridge and Center Ridge. <br />The areas covered by the plan are shown on Exhibit 4.6-M1. The plan <br />includes placement and designs of check dams along the watercourse between <br />West Ridge and Center Ridge and placement and designs of terraces along the <br />slope of the West Ridge mining area. This section of the permit <br />application includes the following items: designs of check dams, designs of <br />terraces, a construction schedule and computer modeling documentation which <br />predicts peak storm water runoff. <br />CHECK DAM PLACEMENT AND DESZGN9 <br />• A total of 21 check dams have been designed for placement along the <br />watercourse which lies between the West Ridge mining area and the Center <br />Ridge mining area. The check dams consists of seven types of dam <br />configuration with the smallest dams located in the uppermost reaches of <br />the watercourse and larger dams being used progressively downslope to <br />accommodate increased flow volumes. <br />The placement and design of each type of check dam was based on the <br />watercourse slope, acreage serviced at the location of the most downslope <br />check dam of a given type and the projected flow. The watercourse was <br />divided into eight segments. Segments one through seven end at the <br />confluence of a terrace and the watercourse while segment eight ends at the <br />West Ridge sedimentation pond (see Exhibit 4.6-M2 and Table 4.6-M1). The <br />spacing between individual dams was determined using criteria in Design of <br />Sediment Control Measures for Small Areas in Surface Coal Mining, Simons, <br />Li & Associates, Inc.(1983). From these criteria it was determined that <br />two Type 1 dams are needed, one Type 2 dam, three Type 3 dams, four Type 4 <br />dams, four Type 5 dams, three Type 6 dams, and four Type 7 dams. The <br />projected peak flow for design of each type of dam was determined using the <br />• SEDIMOT II computer model. <br />1 <br />March 31,1994 <br />