1988-04-11_PERMIT FILE - C1981008A

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"triangle area" temporarily fell through, monitoring at SW-N7 continues to take place on a routine basis (see Tab 15, Hydrologic Monitoring Program). Table 7-41 presents means and ranges of the short record of measured discharges collected at SW-N7. During the irrigation season, measured flows range from a low of .006 (April) up to .856 cfs (June). The low flow reported for April of 1986 (.006 cfs) was measured at this site prior to the onset of irrigation. During the non-irrigation season, the limited period of record for discharge measurements indicate that some flow occurs at this site all year long. Flows during the non-irrigation season range from .02 cfs up to .138 cfs. Calamity Draw. Flow variability in Calamity Draw is also artificially controlled by irrigation water for most of the year. From about mid-April to mid-October, the West Lateral irrigation ditch (managed by the CCC) is in continuous operation. Again, exact dates for turning this ditch on and off varies from year to year. Water from the West Lateral is also used primarily for irrigation and secondarily for maintaining water levels in stock ponds and domestic cisterns. Because of the operation of this ditch, the majority of flow in Calamity Draw is irrigation return water. Due to the relatively limited but heavily cultivated and developed watershed area in the upper portion of Calamity Draw, little supplemental flow from precipitation and snowmelt runoff occurs. Surface water monitoring Site SW-N101 is established in Calamity Draw above the eastern boundary of the Nucla East Mining Area (see Exhibit 7-1). SW-N101 has been monitored for flow since July of 1986, as part of the baseline monitoring program established for this mining area. Appendix 7-5 contains instantaneous discharge measurement collected at this site since 1986. Table 7-42 presents means and ranges of measured discharge collected at the surface water sites located along or near Calamity Draw that were monitored for flow on a monthly basis as part ,of the baseline monitoring program (SW-N101, SW-Nl02 and SW-Nl03). During the irrigation season, measured discharge ranged from .605 in April up to 13.4 cfs during July. Measured flows during the non-irrigation season ranged between 1.04 and 2.06 cfs. Interestingly, the short record of discharge measurements may suggest that shallow ground water discharge into Calamity from irrigated lands provides a fairly continuous source of baseflow to Calamity Draw during the non-irrigation season. SW-Nl02 is established on a small tributary of Calamity Draw that returns irrigation tail waters from irrigated fields to the main channel of Calamity Draw (see Exhibit 7-1). Flow at this site is almost entirely influenced by irrigation, although the limited discharge measurements made since July of 1986 (see Table 7-42 and Appendix 7-5) indicate that 7-119 Revised 04/11/88