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Table 7. SEDCAD Parameters and their Definitions. <br /> Parameter Definition <br /> Design Event Climatic erosivity factor due to <br /> precipitation <br /> CN (Curve Number) Soil erodibility as a function of land <br /> use and hydrologic soil group. <br /> Land Use Slope length and steepness factor <br /> Hydrologic Condition Cover management/land use <br /> Hydrologic Soil Group Soil structure and infiltration rate <br /> CP Factor (Control <br /> Practice Factor) <br /> Time of Concentration Time for runoff in watershed to <br /> reach the watershed outlet. <br /> The parameters reasonably represent the conditions in the field for pre- and post-mining <br /> conditions. <br /> Trapper used SEDCAD 4 to model 20-acre study areas possessing the following sedimentologic <br /> characteristics representative of each bond release parcel: <br /> o Average slope <br /> o Slope lengths <br /> o Soil erodibility factor <br /> o Land use <br /> o Land cover <br /> This methodology allows for applying each block's actual vegetative cover data to the SEDCAD <br /> run for that block. Run for pre- and post-mining conditions, SEDCAD 4 calculated the peak <br /> settleable solids concentration of runoff flowing to a single discharge point at the down-stream <br /> end of each 20-acre study area. The Division finds use of 20-acre study areas a valid approach <br /> for modeling sedimentation in reclaimed drainages in the bond release area. <br /> The total sediment load calculated for the pre-mining block A,F,K,Z and Oak drainage 20-acre study <br /> area was 23.8 tons of sediment and for the same post-mining block, 9.6 tons of sediment. TMI's <br /> SEDCAD 4 modeling concluded that the calculated post-mining peak settleable solids generated from <br /> each block is much less than the calculated pre-mining value. The Division's review of each <br /> parameter is presented in the table below. <br /> Permit Number C 1981010 <br /> SL19 <br />