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Substitute Supply Plan /or the <br />L v .rist Apyrapat~nPratinn <br />A study of the exchange potential in the Blue River between Green Mountain Reservoir and the <br />Love Pit operation was conducted to ensure that the decreed Colorado Water Conservation Board <br />(CWCB) in-stream flow requirement in the Blue River segment between Willow and Rock Creeks <br />would not be affected. Because stream gaging data near the operation do not exist, a hydrologic <br />analysis was conducted using available flow data for the area. The mont}tly exchange potential <br />analysis used the hydrologic modeling results of the Metropolitan Denver Water Supply E1S <br />(Denver EIS). That model provided mean monthly flows at several locations on the Blue River <br />under dry year conditions. The dry year used in the model is defined as the average of the mean <br />montlily flows for 1954, 1955, 1963, and 1964. Using modeled flows for the Blue River below <br />Rock Creek, Rock Creek gage records, and an estimated gain in flow from groundwater and minor <br />tributaries for each month, the streamflow in the Blue River below Maryland Creek was <br />approximated. <br />The CWCB in-stream flow for the segment of the river including the L.G. Everist operation is 58 <br />cfs (October 1 to Mazch 31) and 75 cfs (April 1 to September 30). The exchange potential was <br />calculated as the surplus flow in the Blue River above the CWCB flows. The montlily analysis <br />showed that, under dry year conditions, there is sufficient exchange potential to enable the use of <br />Green Mountain Reservoir water in all months except September (see Table 6). As a result, a daily <br />analysis of the exchange potential in September was conducted using a methodology similar to the <br />monthly study. This analysis included the use of Blue River daily flow records for the two driest <br />Septembers on record since the filling of Dillon Reservoir (1978 and 1981). <br />Because the Denver EIS did not provide daily flows, the daily flows from the Blue River below the <br />Dillon gage were used as the starting point. The records from the former gages on Straight and <br />Willow Creeks were adjusted to correspond to 1978 and 1981 conditions. Adding these flows, plus <br />a gain in flow to account for groundwater and minor tributaries, the Blue River flows below <br />Maryland Creek were approximated on a daily basis. The results of the daily exchange potential <br />analysis are shown in Table 7. During September, the total exchange potential is 96 acre-feet and <br />881-025.110 Wright Water Engineers, Inc. Page 10 <br />