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• Using the 10-year, 24-hour storm to model postmining conditions, SEDIMOT II predicted a 20-fold increase in peak discharge, and runoff volume increased by a factor of 33. The model predicted a 36-fold increase in sediment yield, but peak sediment concentration increased by less than 1 milligram per liter. The use of the 100-year, 24-hour depth (2.60 inches) resulted in increased runoff under postmining conditions, including a 13-fold increase in peak discharge, and an 8-fold increase in runoff volume. Although sediment yield tripled under postmining conditions, the peak sediment concentration decreased by more than 60 percent. Table 17-27 presents values for SEDIMOT II input parameters determined for each subwatershed established and modeled in the upper 006 Gulch drainage. The entire portion of Subwatershed I lies outside of any proposed mining-related disturbance, and values for input parameters were held constant for both pre- and postmining conditions. In all other subwatersheds, values of curve numbers increased and times of concentrations decreased significantly for postmining model runs. Increases in curve numbers ranged from 11 percent (Subwatershed II) up to 64 percent (subwatershed VIIB). Decreases in time of • concentration ranged between 8 percent (Subwatershed II) and 46 percent (subwatershed VIIB). Values for K factor also significantly increased in all subwatersheds (except Subwatershed 1) under postmining conditions, ranging from 18 percent (Subwatershed II) up to 35 percent (Subwater sheds IV and VIB). Slope length (L factor) both decreased and increased in the modeled subwatersheds under the postmining scenario. The magnitudes of the decreases were more pronounced in the larger subwatersheds (subwatersheds III, IV, and V), ranging from 13 percent (Subwatershed IV) up to 60 percent (subwatershed V). Average watershed slope, or S factor, was lower in all subwatersheds under postmining conditions, with the exception of Subwa to rsheds I, V, and VI B. Although average watershed slope increased by more than 20 percent in the largest subwatershed (V), the postmining slope (17.5 percent) determined for this subwatershed was lower than the weighted average of all postmining slopes calculated for each subwatershed (18.6 percent). The higher runoff rates and volumes predicted for postmining conditions in the 006 drainage resulted from higher curve numbers and lower times of concentration. Increased • sediment yields were largely caused by increases in K factor values, combined with increased runoff volumes and rates. The reduced sediment concentration predicted for 71