1988-04-11_PERMIT FILE - C1981008A

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for each discharge characteristic based on the southwestern region's regression model (Kircher, et al ., 1985). Table 7-39 presents the results of the calculations for each drainage. From Table 7-39, it is evident that Calamity Draw has an annual mean discharge of about one half that predicted for Tuttle Draw. This relationship generally holds true for the remainder of the calculated discharge characteristics. Streams - Flow. The following sections present discussions of flow data collected at surface water monitoring sites established at both the Nucla Mine and Nucla East mining area. The discussions are grouped according to the drainage in which the sites have been located. For instance, discussion of flow data for Sites SW-N1 and SW-N3 will be found under the section titled "Tuttle Draw". All historic data (prior to December, 1987) for each site has been compiled and is presented in Appendix 7-5. The reader should refer to Exhibit 7-1 to find stream monitoring site locations. Tuttle Draw. As is characteristic of all of the surface water sites at both the Nucla Mine and the Nucla East mining area, the flow regime in Tuttle Draw is artifically controlled by irrigation practices for most of the year. From about mid-April through mid-October, the Second Park lateral irrigation ditch (managed by the Colorado Cooperative Company) is in continuous operation. However, exact dates for turning the ditch on and off vary from year to year. During this period, water from the ditch is primarily used for irrigation and secondarily for maintaining water levels in stock ponds and domestic cisterns. Between mid-October and mid-April, the ditch is turned on occasionally in order to maintain levels in stock ponds and cisterns. As a consequence of the operation of this ditch, the majority of flow in Tuttle Draw is irrigation return flow except for occasional supplemental flow from precipitation and snowmelt runoff events. Surface water monitoring Site SW-N1 is located in Tuttle Draw upstream of the Nucla Mine permit boundary. SW-N1 has been monitored for flow routinely since April of 1980. Table 7-40 presents means and ranges of monitored instantaneous discharge at both Sites SW-N1 and SW-N3. Table 7-40 shows that flow measured at SW-N1 varies from zero up to 11 .6 cfs. During the irrigation season (approximately mid-April through mid-October), the means of measured discharge range between .149 and 2.94 cfs, with high flows measured from .275 in April up to 11 .6 cfs in September. During the non-irrigation season, (mid-October through mid-April) flow ranges from .034 up to 1 .03 cfs. 7-112 Revised 04/11/88