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Table 5. SEDCAD Parameters and their Definitions <br /> Parameter Definition <br /> Design Event Climatic erosivity factor due to precipitation <br /> CN (Curve Number) Soil erodibility as a function of land use and hydrologic soil <br /> 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 Practice <br /> Factor) <br /> Time of Concentration Time for runoff in watershed to reach the watershed outlet. <br /> The parameters reasonably represent the conditions in the field for pre and postmining 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 /> • Average slope <br /> • Slope lengths <br /> • Soil erodibility factor <br /> • Land use <br /> • Land cover <br /> This methodology allows for applying each block's actual vegetative cover data of the SEDCAD run <br /> for that block. Run for pre- and post-mining conditions, SEDCAD 4 calculated the peak settleable <br /> solids concentration of runoff flowing to a single discharge point at the down-stream end of each 20 <br /> acre study area. The Division finds use of 20 acre study areas a valid approach for modeling <br /> sedimentation in reclaimed drainages in the bond release area. <br /> The total sediment load calculated for the pre mining block A,F, K and Z-AB 20 acre study area was 33.1 <br /> tons of sediment and for the same postmining block, 28.0 tons of sediment. TMI's SEDCAD 4 modeling <br /> concluded that the calculated postmining peak settleable solids generated from each block is less than the <br /> calculated premining value. The Division's review of each parameter is presented in the table below. <br /> Permit Number C1981010 <br /> SL22 Page 14 of 18 <br />