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<br />. which is a 1.1 mi2 basin in the Piceance Creek Basin and a gage elevation of 6,335 ft. The largest known <br />rainfall-produced flood of 6,700 ft3/S in northwestern Colorado occurred on Yellow Creek near Rangley <br />(09306255; drainage area is 262 mi2; gage elevation is 5,535 ft) in 1978. Mud was plastered on channel <br />margins and obstructions in the channel (U,S, Geological Survey, unpublished data, 1978). It is likely that <br />the flood was a hyperconcentrated flow or mud flow, thus, the actual water discharge was substantially <br />less. Hence, such floods from sparsely vegetated basins do not reflect flood potential in vegetated basins <br />in northwestern Colorado. For comparison with streams elsewhere in Western Colorado (Jarrett, in <br />review), the maximum unit discharge is 1,640 ft31s1mi2 for Sweetwater Creek near Dotsero (contributing <br />drainage area is about 4.5 mi2 ; elevation is 6,250 ft) at its confluence with the Colorado River. Above <br />about 6,500 ft in northwestem Colorado, the maximum unit discharge is 220 ft3/s1mi2 and was recorded at <br />the USGS streamflow-gaging station located on Long Lake Inlet near Buffalo Pass (092~705; elevation is <br />9,875 ft and the drainage area is 0] mi2), which resulted from record snowmelt in 1957. The Buffalo Pass <br />area is the snowiest in Colorado (Doesken and others, 1984). The maximum unit discharge is 44 ft3/s1mi2 <br />for Elkhead Creek near Elkhead (09244500; period of record is from 1953 to present; gage elevation is <br />7,800 ft and the drainage area is 45A mi2), which corresponds to a peak discharge from snowmelt of 2,850 <br />ft3/s in 1984, For comparison, the maximum unit discharge is about 100 ft31s1mi2 for other small basins <br />above 7,500 ft in Colorado. As drainage-basin size increases, maximum unit discharge decreases. <br />Maximum unit discharge is less than 50 ft3/s1 mi2 for basins larger than about 50 mi2 (figure lOb). For <br />comparative purposes, the unit discharge and elevation relation for basins in westem Colorado in the <br />. Colorado River Basin are shown in figure 11 and for streams east of the Continental Divide in Colorado <br />are shown in figure 12, Streams in northwestem Colorado have fewer rainstorms and smaller floods than <br />the rest of westem Colorado. Clearly, streams in the foothills and eastem Colorado are subject to very <br />large rainfall-produced floods below about 7,500 ft, <br /> <br />The envelope curve (figure lOb) of maximum flooding for northwestern Colorado can be used to <br />estimate the hypothetical maximum flood for Elkhead Creek at Elkhead Reservoir. If the drainage-basin <br />size at the dam (205 mi2) is multiplied by the maximum unit discharge of 35 ft3/s1mi2 for a basin the size of <br />Elkhead Creek at Elkhead Reservoir, the hypothetical maximum flood would be about 7,200 ft3/s, This <br />discharge is comparable to the maximum paleoflood estimate of 5,380 ft3/S determined for Elkhead Creek <br />downstream from Elkhead Reservoir (table 1), <br /> <br />. <br /> <br />22 <br />