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lip to 20 percent of its total body weight. This stored fatty tissue enables the sandhills to endure the rigors of their remaining northward migration and nesting cycle. Typically, cranes eat very little from the time they leave the Platte until incubation is complete. . The condition of the birds upon reaching nesting areas influences reproductive success and maintenance of the population (Fish and Wildlife Service, 1976). Thus, scientists from the Fish and Wildlife Service, the Sandhill . Crane Committee, and the International Crane Foundation believe preservation of this Platte River habitat is necessary for survival of the sandhill crane populations (Fish and Wildlife Service, 1976). .>" ~ . Present Situation Ri ver Mechani cs The Platte River channel between Overton and Chapman is in a dynamic state with variations from year to year in the areal extent and location of shallow, submerged sandbars. Three major factors maintain the present channel width and shallow; submerged, unvegetated sandbars in the SO-mile river reach between Overton and Chapman (USBR, 1977). One is the peak flood discharges that develop the stream channel velocities for a continually shiftin9 streambed. A second factor is ice jams which have a 9reat influence on maintaining the . shallow and open, unvegetated sandbars on the Platte River downstream from Overton ,Nebraska. The formation of ice jams ... occurring from December through March forces the wat:erto flow under the ice with velocities that scour the channel bottom. It is this scouring action or movement and continual shifting of the streambed that helps maintain the open channel of un vegetated sandbars. Since the ice jams occur every year there is little or no chance for vegetation to establish. And. a third fa.ctor is the movement of streambed material over a much wider width of cliannel by the breaking up of the ice jam. This may occur more than once each year. Flows Streamflow of the Platte River from North Platte. Nebraska, to Chapman, Nebraska, has been greatly 'modified overtime due to the development of irrigation facilities and reservoir storage on both the North Pl atte and South Platte Rivers. Flows of the South Platte River at Julesburg 27 ^. .;- .