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<br />The Granby, Green Mountain, Dillon, Williams Fork, Reudi, and Vega <br />Reservoirs are fill-and-spill-type structures with only incidental <br />flood control storage. <br /> <br />In the Gunnison River drainage basin, regulations for a joint <br />conservation and flood control operation of Paonia Reservoir have <br />been prepared by the CaE and the USBR. The conservation operation <br />of Blue Mesa Reservoir provides substantial flood control benefits, <br />but formal operating regulations for flood control have not been <br />prepared. <br /> <br />Inflow to Blue Mesa Reservoir was routed on the assumption that the <br />reservoir would be at minimum power-pool level (200,000 acre-feet) <br />60 days prior to the main 30 days of flows. It was found that this <br />prior 60-day inflow could be routed through the reservoir and drawn <br />back down to 200,000 acre-feet again by June 1, at the start of the <br />maximum 30-day inflow. Releases were made so as not to exceed <br />channel capacities whenever possible (17,000 cfs on the Gunnison <br />River at Grand Junction and 48,000 cfs on the Colorado River below <br />Grand Junction). <br /> <br />The effects of the Gunnison River basin reservoirs on Fruita are <br />only incidental. <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 often <br />decreased during high runoff periods making any reduction 1n flood <br />peaks unlikely. Irrigation uses reduce flows, but not <br />significantly during times of peak flows. <br /> <br />Various Federal agencies have been studying the water resources <br />development aspects of the upper Colorado River basin for many <br />years. A report published in 1971 contains a reconnaissance-type <br />plan that identifies, for future detailed study, eight potential <br />storage projects that would provide flood control benefits for Mesa <br />County and three areas for possible future watershed treatment <br />measures (Reference 5). A publication of the CWCB and the U.S. <br />Department of Agriculture includes information from a <br />reconnaissance-type 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 (Reference 6). <br /> <br />3.0 ENGINEERING METHODS <br /> <br />For the flooding sources studied by detailed methods 1n the community, <br />standard hydrologic and hydraulic study methods were used to determine <br />the flood hazard data required for this study. Flood events of a <br />magni tude which are expected to be equaled or exceeded once on the <br />average during any 10-, 50-, 100-, or 500-year period (recurrence <br />interval) have been selected as having special significance for <br />floodplain management and for flood insurance rates. These events, <br /> <br />10 <br />