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<br />tributaries have a confluence approximately five miles upstream of the <br />Monument and drain geologically different basins. On an average, the Yampa <br />River annually contributes approximately 72 percent of the water entering <br />Dinosaur at Deerl odge Park but only 23 percent of the annual average <br />sediment load. Conversely, the Little Snake carries 77 percent of the total <br />sediment load with only 28 percent of the average annual water volume <br />(Table 1) that flows into the Yampa Canyon. The average annual sediment <br />load for each river shown on Table 1 is computed by summing the daily <br />measured sediment loads from each gaging station for each water year. See. <br />O'Brien (1984) for a more complete description of the watersheds and the <br />Yampa Canyon geomorphology. <br />Physical attributes of the f ive mil a river reach downstream of the <br />conf I uence and upstream of the canyon in the Deerl odge Park area 1 ndi cate <br />that thl s al I uv lal reach of river 1 s sti 1 I very active. The channel has <br />migrated nearl y 40 feet at the Deerl odge campground duri ng recent h i gh f I ow <br />years, with substantial loss of bank on one side and channel bar growth and <br />attachment on the opposite shore. Generally, the channel is slightly <br />incised in this reach. At the confluence of the two rivers channel shifting <br />and abandonment has occurred. The growth and aggradation of the Little <br />Snake delta is the cause of this local channel migration. This confluence. <br />area and the Deerlodge Park reach wil I be sensitive to changes In the water <br />and sediment discharge ratio. <br />The Deerl odge Park reach upstream of the canyon has a mild slope and an <br />al I uv ial bed of sand whereas the canyon channel is steep w ith a substrate <br />consisting primarily of cobbles, boulders and bedrock. In this alluvial <br />reach, the r aver w 1 I I scour sand f rom the bed or deposi t sand on the bed <br />depending on its ability to transport the sediment (sediment transport <br />capacity) and quantity of sediment supplied fran the upstream tributaries. <br />Essentially, the sediment transport capacity of this reach constitutes the <br />sediment supply to the canyon. As there are no similar major areas of sand <br />storage (al I uv ial channel) in the canyon upstream of Mathers Hole, the <br />sediment load entering the canyon at Deerl odge Park Is sediment load that <br />has been transported through the canyon historically. There are reaches in <br />the canyon, however, which respond to the sediment load with a scour and <br />f111 cycle reflecting the rising and fal I ing nature of the seasonal <br />by drogr aph. <br />The unique nature of the Yampa Canyon channel morphology not only <br />supports important habitat for endangered species of fish (USFWS, 1982) but <br />also creates substrate conditions which are sensitive to variations in <br />sediment load. The Colorado squawfish spawning areas in the laver Yampa <br />Canyon are cobble bar reaches which can be effected by sediment deposition <br />during flows with large sediment loads (O'Brien, 1984). Although spawning <br />sites are mostly located in riffles, areas not generally associated with <br />sediment deposition, spawning does occur in the areas of adverse bed slope <br />which is upstream of riffles and just downstream of deep pool s. These <br />areas are sensitive to sediment deposition. It Is important, therefore, to <br />understand the nature of the sediment load in the cobble reaches of the <br />lower Yampa Canyon. <br />The potential for water resource development In the upper basins of the <br />Little Snake and Yampa Rivers must be carefully evaluated because of the <br />complex Interdependence of the sediment load and water discharge In both <br />2