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<br />under the assumption that the reservoir would be at minimum power <br />pool level (200,000 acre-feet) for 60 days prior to the main 30 <br />days of flow. It was found that this prior 60-day inflow could be <br />routed through the reservoir and drawn back. down to 200,000 acre- <br />feet again by June 1, the start of the maximum 30-day inflow. <br />Releases were made so as not to exceed channel capacities whenever <br />possible (17,000 cfs on the Gunnison River at Grand Junction and <br />48,000 cfs on the Colorado River below Grand Junction). <br /> <br />Water is diverted from numerous sites in the upper portions of the <br />Colorado River basin for exportation to the basins of the South <br />Platte and Arkansas Rivers. However, diversions are commonly <br />decreased during high runoff periods mak.ing any reduction in flood <br />peak.s unlik.ely. Irrigation uses also reduce flows, but not <br />significantly, during times of peak. flows. Various Federal <br />agencies have been studying the water resources development aspects <br />of the upper Colorado River basin for many years. A report <br />published in 1971 (Reference 7) contains a reconnaissance plan that <br />identifies, for future detailed study, eight potential storage <br />projects that would provide flood control benefits for Mesa County <br />and three areas for possible future watershed treatment measures.. <br />A publication of the Colorado Water Conservation Board and the U.S. <br />Department of Agriculture (Reference 8) includes information from a <br />reconnaissance study that identifies a number of Roan and Book <br />Cliffs streams that are potentially subject to development of <br />storage projects for flood control. <br /> <br />Since the devastating 1958 flood, a number of flood protection <br />improvements have been made on Indian Wash. The primary flood <br />protection measure is the U.S. Soil Conservation Service IW-l <br />retention structure. The structure, shown in Figure 5, is located <br />northeast of the airport and was completed in the early 1960s. The <br />structure drains an area of 6.2 square miles and was designed for a <br />total storage capacity of 2,140 acre-feet, including 570 acre-feet <br />of sediment storage. Recent measurements indicate that sediment <br />accumulation has accounted for approximately 20 acre-feet since <br />completion of the structure. This value is much less than <br />anticipated because a number of small upstream reservoirs, which do <br />not provide flood protection, do trap sediment. It is estimated <br />that the structure will provide protection for the 6.2 square miles <br />of watershed for floods greater than the 100-year frequency event <br />(Reference 9). <br /> <br />Other flood protection measures include Government Highline Canal <br />and a 1979 channelization project on Indian Wash from North Avenue <br />to Texas Avenue along 28th Street. <br /> <br />Government Highline Canal, as discussed in the U.S. Soil <br />Conservation Service Indian Wash Watershed Work. Plan (Reference 9), <br />has a high spoil bank. and roadway along the south side. Therefore, <br />a capacity, in addition to normal irrigation flow, is provided to <br />intercept runoff from approximately 3.4 square miles of upstream <br />unreservoired drainage area. This additional intercepted flow is <br /> <br />11 <br />