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<br />'""'.... , <br />i0;-:;':' <br /> <br />up to 20 percent of its total body weight. This stored fatty tissue <br />enables the sandhills to endure the rigors of their remaining northward <br />migration and nesting cycle. Typically, cranes eat very little from <br />the time they leave the Platte until incubation is complete. The <br />condition of the birds upon reaching nesting areas influences <br />reproductive success and maintenance of the population (Fish and <br />Wildlife Service, 1976). <br /> <br />Thus, scientists from the Fish and Wildlife Service. the Sandhill <br />Crane Committee. and the International Crane Foundation believe <br />preservation of this Platte River habitat is necessary for survival <br />of the sandhill crane populations (Fish and Wildlife Service, 1976). <br /> <br />Present Situation <br /> <br />River Mechanics <br /> <br />The Platte River channel between Overton and Chapman is in a dynamic <br />state with variations from year to year in the areal extent and <br />location of shallow, submerged sandbars. <br /> <br />Three major factors maintain the present channel width and shallow. <br />submerged, unvegetated sandbars in the 80-mile river reach between <br />Overton and Chapman (USBR. 1977). One is the peak flood discharges <br />that develop the stream channel velocities for a continually shifting <br />streambed. A second factor is ice jams which have a great influence on <br />maintaining the shallow and open. unvegetated sandbars on the Platte <br />River downstream from Overton. Nebraska. The formation of ice jams <br />occurring from December through March forces the water to flow under <br />the ice with velocities that scour the channel bottom. It is this <br />scouring action or movement and continual shifting of the streambed that <br />helps maintain the open channel of unvegetated sandbars. Since the ice <br />jams occur every year there is little or no chance for vegetation to <br />establish. And, a third factor is the movement of streambed material <br />over a much wider width of channel by the breaking up of the ice jam. <br />This may occur more than once each year. <br /> <br />Flows <br /> <br />Streamflow of the Platte River from North Platte, Nebraska. to Chapman, <br />Nebraska. has been greatly modified over time due to the development <br />of irrigation facilities ,and reservoir storage on both the North Platte <br />and South Platte Rivers. Flows of the South Platte River at Julesburg <br /> <br />27 <br />