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. flfJI068 . . An estimate was made of average monthly variations in snowmelt runoff and base flow through use of streamflow estimates for other rivers in the area. For the La Plata River in Colorado downstream of Hesperus, the snowmelt runoff and base flow in March through May was estimated to be 74 percent of the annual total. For the Mancos River downstream of the confluence of the West, Middle, and East Mancos rivers, the flow in March through May was estimated to be 67 percent of the annual total. The La Plata and Mancos drainage areas used as a basis for the monthly streamflow estimates are generally at higher elevations than most of the McElmo Creek drainage basin. Since snowfall contributes less of the total annual flow in the McElmo Creek basin, it is esti- mated that 40 percent of the total snowmelt runoff and base flow occurs in March through May, with the remainder of the flow occuning at a constant rate throughout the year. A summary of estimated snowmelt runoff and base flow for McElmo Creek is provided below: . . (Average values in acre-feet per month) . Location March-May 390 June-February 190 McElmo Creek above Alkali Canyon . "McElmo Creek below Cortez," gage site 680 340 McElmo Creek near State Line 800 400 . Some variation in snowmelt runoff and base flow is estimated to occur depending on whether antecedent precipitation during the year is below average, average, or above average. . . McElmo Creek Virgin Streamflow Summaries of the estimated monthly virgin flow of McElmo Creek are presented in Appendix B. Virgin flows, excluding the component contributed by short-term runoff events, are also presented. -2.1- . ~'i~,:<':