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Mining at Trapper Mine has not occurred in any of the tributaries to the <br />Yampa upstream of this site. The other site (Hayden) is below an irrigation <br />diversion near Hayden and is approximately 20 river miles upstream of the <br />Craig site. A significant amount of the runoff from early snow melt in <br />April and May was derived from the drainage between Hayden and Craig. <br />Suspended sediment concentration decreased earlier at the upstream site <br />(Hayden) than at the Craig site, which indicates a significant amount of <br />sediment load is added from drainage between these two sites. The base <br />flow conditions between August and March e.re very similar for the two sites. <br />The Williams Fork River is a major tributary to the Yampa River and enters <br />the Yampa downstream of the Trapper Mine. It drains approximately 341 mi2 <br />or ten per cent of the Yampa Valley and shows many of the same character- <br />istics as the Yampa River. Peak flows occur in the month of May, and the <br />majority of runoff occurs from April to June. Figure 2.7-13 gives a bar <br />hydrograph of the mean monthly flow of the Williams Fork River for the <br />period of 1904 to 1927. Water yield per unit drainage area decreased in <br />a downstream direction with higher elevation drainages supplying more <br />snowmelt runoff than the lower areas. Average annual yield at the gaging <br />station above Willow Creek was 1.0 cfs/mi2 (for a drainage area of 108 mi2). <br />For the Williams Fork River at Hamilton (drainage area - 341 mi2), the flow <br />averaged 0.5 cfs/mi2 (7.2 inches of runoff) in the period from 1976-1978. <br />A slightly higher average flow of 0.64 cfs/mi 2. was measured for the period <br />of 1904 to 1927. <br />2-407 <br />