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<br />'I <br /> <br />Summary and Conclusions: <br /> <br />(Note figure referenced below are to the Draft Report which is not included with this <br />annual report. The Draft Report can be obtained by calling George Smith at <br />303-236-5322 ex 235) <br /> <br />A draft of the interpretive report was reviewed by two USGS colleague reviewers and a <br />USGS editor. In addition, the draft report was submitted to the U.S. Fish and Wildlife <br />Service for review by members ofthe Upper Colorado River Endangered Fish Recovery <br />Program. Comments from the Recovery Program reviewers and USGS technical and <br />editorial were incorporated into a [mal draft of the interpretive report. Publication of the <br />report is being delayed temporarily pending a decision on whether to incorporate the WY <br />2001 and 2002 sediment data with the previously-collected data, recompute the sediment <br />transport equations, and revise the recommendations based on those amended transport <br />equations. <br /> <br />Large amounts of sediment are stored in the lower Little Snake, lower Yampa, and lower <br />Green rivers in the form of alluvial banks, bars, and islands. These near-channel areas <br />may be important secondary sources of sediment that periodically is~ntrained by the <br />Green River and its larger tributaries. Aerial photographs made in 1988 of the channels <br />of the Little Snake River downstream from the Lily streamflow gage, the Yampa River <br />downstream from Cross Mountain, and the Green River from the Lodore Ranger Station <br />to Jensen were assessed to determine the relative abundance of alluvial materials in the <br />banks and bars. The relative abundance of subaerial alluvial deposits in the photographs <br />varied from river to river in the watershed and fro111 subreach to sub reach along a river. <br />Although the flood-plain width was relatively narrow and the surface area of alluvial <br />deposits was small, the Little Snake River a few miles downstream from streamflow- <br />gaging station 09260000 had a consistently high percentage of alluvial material along its <br />boundaries. <br /> <br />) <br /> <br />The large sediment yield of the Little Snake River is reflected in the increase in relative <br />abundance of alluvial deposits in the Yampa River immediately downstream from the <br />Little Snake River confluence. The relative abundance of alluvial material decreases <br />abruptly from more than 80 percent to less than 20 percent as the Yampa River flows into <br />the steep and narrow Yampa Canyon. Alluvial deposits are relatively scarce in Yampa <br />Canyon between River Miles 45 and 21. The canyon geomorphology in this reach is <br />dominated by the massive limestone of the Morgan Formation; also, the riveris steep and <br />the canyon floor is narrow, providing little area suitable for significant alluvial sediment <br />storage. The Yampa River flows through the massive Weber Sandstone downstream <br />from River Mile 21 and, from here to the mouth, the canyon floor is wider and more <br />conducive to sediment deposition. <br /> <br />85 B:;3 <br />