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• monitored tributaries to the main channel have gradients from 4 up to 16 times as great as the <br />main channel reach. The gradient for the reach adjacent to and north of the permit area for Tuttle <br />Draw is 0.0015 ftlft, (see Table 7-37 of Volume B New Horizon 1 Reclamation Plan). <br />Predicted Peak Flows <br />The annual mean and peak discharges were predicted for both Tuttle Draw and Calamity Draw <br />using techniques outlined in the USGS Water Resources Investigations Report 85-4086 titled <br />Estimation of Natural Streamflow Characteristics in Western Colorado (Kircher et al. 1985). The <br />techniques used to predict discharge characteristics ofTuttle Drawand Calamity Draw involved the <br />use of regression relationships determined from historical streamflow records in Western Colorado. <br />Basin parameters and precipitation records were used to correlate discharge characteristics offour <br />different regions of Western Colorado: 1) Mountain; 2) Rio Grande: 3) Southwest and; 4) <br />Northwest. <br />• Using the regression model for the southwestern region, the mean annual discharge and peak <br />discharges from the 2-, 5-, 20-, 25-, 50-, 100- and 500-year recurrence intervals were predicted at <br />two locations each in both Tuttle and Calamity draw. For both draws, discharge characteristics <br />were calculated for the entire drainage (at the mouths), and at the most downstream surface water <br />monitoring site in each Draw (SW-N3, Tuttle Draw and SW-N103, Calamity Draw, see Map 2.04.7- <br />1A). See also Table 7-38, Volume B of New Horizon 1 Reclamation Plan. <br />Streams -Flow <br />This section preserits discussions of flow data collected at surface water monitoring sites <br />established at the New Horizon 2 mining area. All historic data (prior to December,1987) for each <br />site has been compiled and is presented in Attachment 2.04.7-8 (Peabody Appendix 7-5}. The <br />reader should refer to Map 2.04.7-1 to find stream monitoring site locations. <br />Calamity Draw. Flow variability in Calamity Draw is artificially controlled by irrigation water for <br />most of the year. From about mid-April torrid-October, the West Lateral irrigation ditch (managed <br />. by the CCC) is in continuous operation. Exact dates for turning this ditch on and off varies from <br />REVISED JULY 2006 2.04.7-30 <br />