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segment of Tuttle Draw in the vicinity of the Nucla Mine has the lowest calculated <br /> gradient (.0015 ft/ft) while the reach of Calamity nearest the Nucla East mining area <br /> (SW-N101 to SW-Nl07) is almost six times as steep (.0083 ft/ft). Gradients calculated for <br /> the monitored tributaries to each main channel (West Return Ditch and the Return Ditch <br /> above Site SW-Nl02) have gradients from 4 up to 16 times as great as the main channel <br /> reach. <br /> Predicted Peak Flows. The annual mean and peak discharges were predicted for both Tuttle <br /> and Calamity Draws using techniques outlined in the USGS Water-Resources Investigations <br /> Report 85-4086 titled Estimation of Natural Streamflow Characteristics in Western Colorado <br /> (Kircher et al . 1985). The techniques used to predict discharge characteristics of Tuttle <br /> and Calamity Draws involved the use of regression relationships determined from historical <br /> streamflow records in Western Colorado. Basin parameters and precipitation records were <br /> used to correlate discharge characteristics of four different regions of Western Colorado: <br /> 1) Mountain; 2) Rio Grande; 3) Southwest and; 4) Northwest. <br /> Both Tuttle and Calamity Draws are situated in the southwestern region as outlined by <br /> Kircher et al . (1985). The regression model developed for this region is as follows: <br /> Q = aA(b1)P(b2)EB(b3)SB(b4) <br /> where, <br /> Q = discharge (cfs) <br /> A = drainage area (mi 2) <br /> P = mean annual precipitation minus 10 (in) <br /> EB = mean basin elevation minus 5000 per 1000 feet (ft) <br /> SB = mean basin slope (ft/ft) <br /> and, <br /> a, b1, b2, b3 and b4 are regression coefficients <br /> Using this regression model, the mean annual discharge and peak discharges for the 2-, 5-, <br /> 10-, 25-, 50-, 100- and 500-year recurrence intervals were predicted at two locations each <br /> in both Tuttle and Calamity Draws. For both Draws, discharge characteristics were <br /> calculated for the entire drainage (at each respective mouth), and at the most downstream <br /> surface water monitoring site in each Draw (SW-N3, Tuttle Draw and SW-Nl03, Calamity Draw, <br /> see Exhibit 7-1 ). Table 7-38 presents the regression equations and coefficients applied <br /> 7-110 Revised 04/11/88 <br />