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<br />TABLE II <br /> <br />CHANNEL WIDTHS IN THE CRITICAL HABITAT <br /> <br /> River distance <br /> from Nebraska- Channel width (feet) <br />USGS Station Wyoming border 1865 1938 1965 <br />R22W 247 4530 3790 200 <br />Overton 260 5280 4980 1100 <br />Overton (R20W) 261 4800 2890 1100 <br />R18W 272 5450 4380 3720 <br />Odessa 275 4100 3050 1600 <br />R16W 285 4600 3890 3080 <br />R14W 297 3120 2300 1620 <br /> <br />Average <br />Standard Error <br /> <br />4554 <br />295 <br /> <br />3611 <br />349 <br /> <br />1774 <br />461 <br /> <br />Average change from 1865-1938: <br />Average change from 1865-1965: <br />SOURCE: Williams (1978). <br /> <br />-20.7% (-7100 acres). <br />-61.0% (-21 000 acres). <br /> <br />Increased groundwater consumption might affect mean flows in the river (see the <br />Missouri River Basin Commission (1976) Level B study of the Platte River Basin <br />in Nebraska for estimates of this phenomenon), but it is difficult to see how <br />peak flows could be affected. Thus we conclude that the strong association <br />between peak flows and reservoir capacity is a causal relationship. <br />Likewise, the loss of flow is the only reasonable explanation for the <br />decline of channel width. The causal mechanism here is presumably streambed <br />scouring during periods of high flow, especially by ice breaking up. Unfor- <br />tunately, the quantitative relationship between streamflow and channel width <br />is poorly understood. What magnitude of flow is required to maintain a given <br />channel width, and for what duration? Must adequate flows be released annual- <br />ly, or is it sufficient to experience a period of large flow once in several <br />years? What is the time of response between a change of flow conditions and <br />the resul ting change in streambed character? Are losses of channel width <br />reversible? <br /> <br />38 <br />