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percentage of each soil type that will be stripped and redistributed for reestablishing <br />• irrigated pasture and rangeland. <br />Watershed slope (6) and slope length (L) were averaged for both conditions by measuring at <br />least ten slopes and slope lengths on both the pre- and postmining 1:400 scale maps. The <br />average watershed slope and Length for premining conditions were calculated to be 8.2 <br />percent and 250.6 feet, respectively. For postmining conditions, an average slope of 6.7 <br />percent and an average slope length of 318.2 feet were calculated. <br />Once all input parameters were determined for both pre- and postmining conditions, two <br />computer files (batch input) were constructed and run using SEDIMOT II. Appendix 17-1 <br />contains both input files used to evaluate the effects of pre- and postmining conditions <br />in the watershed area above the proposed 007 pond on runoff and sediment. Table 17-28 <br />presents the results of both SEDIMOT II runs using the two batch input files. Results <br />include peak discharge (cis), runoff volume (acre-feet), peak sediment concentration <br />(mg/1) and sediment yield (tons). <br />Postmining conditions resulted in reductions of all runoff and sediment parameters <br />• predicted by SEDIMOT II. Peak discharge and runoff volume were reduced by 64 and 47 <br />percent, respectively. Sediment concentration was reduced by 38 percent, and a 66 .percent <br />decrease in sediment yield was predicted for postmining conditions. <br />the predicted decreases in runoff are largely due to the increased time of concentration <br />resulting from lower slopes within the disturbance limits and a slight increase in the <br />hydraulic length of the watershed representative of the postmining topography. Also, the <br />lower curve number selected for postmining conditions reflects the proposed reclamation of <br />the disturbed area, including replacement of adequate depths of suitable topsoil material <br />and a successful stand of reestablished vegetation. <br />Predicted reductions in sediment concentration and yield are largely due to significantly <br />lower slopes (S) under postmining conditions. Although the slope lengths will increase, <br />reduced runoff from the lower slopes will result in lower sediment production. <br />Runoff from postlaw reclaimed areas in the Nucla Mine likely exhibit similarly reduced <br />• runoff and sediment as predicted by SEDIMOT II for the Nucla East mining area. Although <br />reestablished vegetation at the Nucla Mine is largely characterized as rangeland, the <br />17-86 Revised 04/11/88 <br />