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0 <br />• <br />gage at Maybell, Colorado (drainage area - 3410 square miles), the mean <br />annual flow of the Yampa is .42 cfs/mit. The average runoff for the entire <br />Yampa Valley drainage averages 5.7 inches annually. These examples show <br />the extreme variability of annual average water yield at different locations <br />within the drainage basin. <br />Year to year variation in yield may also be great. Historical annual yield <br />has varied from 345.,000 ac -ft in 1977 to 2,135,000 ac -ft for the Yampa <br />River in 1917. Average annual yield amount to 1,116,000 ac -ft. <br />Timing of flows from the valley demonstrates the importance of snowmelt <br />runoff to water yield. Figure 2.7-10shows a graph of the mean monthly <br />discharge of the Yampa River at Maybell (drainage area - 1430 square miles), <br />from 1916 to 1965. About 64 per cent of the flow occurs in May and June <br />with up to 85 per cent occurring from April to July at selected gaging <br />stations within the valley (Steele, et al, 1979). Minimum flows generally <br />occur from August through February. Iorns (1965) reported that summertime <br />flows in streams of the basin from July through October generally include a <br />large component of ground -water discharge. <br />Extremes recorded at the Maybell gaging station are a maximum flow of <br />17,900 cfs on May 19,1917 and a minimum of 2.0 cfs on July 17-19, 1934. <br />Discharge and suspended sediment data of the Yampa River for water year 1979 <br />are given for two sites near the Trapper Mine in Figures 2.7-11 and 2.7-12.. <br />The first site (Craig) is just upstream of.the confluence with Johnson Gulch. <br />2-403 <br />