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<br />Effects on Missouri River, Fort Randall Dam to Lewis and Clark Lake <br /> <br />Fort Randall Dam is operated as and is expected to remain a peaking <br /> <br /> <br />facility in future years. In general, peaking operations are incompat- <br /> <br /> <br />ible with optimum fishery management downstream from Fort Randall Dam. <br /> <br />This situation exists for all levels of basin development, although it <br /> <br /> <br />will probably be more extreme with increased basin development due to <br /> <br /> <br />the increased value of the peaking capability. The average releases <br /> <br /> <br />during the spawning period would be lower as basin development increases <br /> <br /> <br />and would result in a somewhat smaller spawning area in the downstream <br /> <br /> <br />reach. <br /> <br />Effects on Lewis and Clark Lake <br /> <br /> <br />Fish and game management agencies feel that a relatively long <br /> <br />water-exchange period in Lewis and Clark Lake during the spawning and <br /> <br /> <br />maturation period would benefit resident fisheries. In general, Gavins <br /> <br />Point exchange rates are directly related to the water supply available <br /> <br /> <br />to the main stem system and are inversely proportional to the magnitude <br /> <br /> <br />of upstream depletions. Therefore, the fishery should be enhanced as <br /> <br /> <br />basin development progresses. <br /> <br />Effects on Missouri River, Gavins Point Dam to the Mouth <br /> <br /> <br />Flow depletions resulting from the High Plains diversion will have <br /> <br /> <br />unavoidable adverse ecological effects on the Missouri River. The most <br /> <br />serious ecological effects are likely to occur in the upstream portions <br /> <br />of this reach where the present Missouri River flows make up the <br /> <br /> <br />greatest portion of the normal river flow regime. Ecological effects <br /> <br />from depletions will be less noticeable downstream where incremental <br /> <br /> <br />flows from tributary streams make up a larger proportion of the normal <br /> <br />flow regime. <br /> <br />Ecological effects, both terrestrial and aquatic, will be propor- <br /> <br /> <br />tional to the water depletion. Water depletions at points downstream <br /> <br />from Gavins Point Dam and upstream from the Platte River confluence, <br /> <br />~5 <br />