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<br />0493 <br /> <br />Thus, scientists from the Fish and Wildlife Service, the Sandhill <br /> <br />Crane Committee, and the International Crane Foundation believe <br /> <br />preservation of this Platte River habitat is necessary for survival <br /> <br />of the sandhill crane populations (Fish and Wildlife Service, 1976). <br /> <br />(:;>~. <br /><,> .. <br />. , <br />('-.. ..,,'~ <br /> <br />There are at least three major factors oc~U'rrin~','o,i;;' the Platte River <br />~ ~ 1 <br />in the 80-mile reach still used by cr~~s bet~~n Overton and Chapman <br /><' "., .' ~ <br />. '.I .. . <br />that help maintain the present channel width with the shallow, submerged <br /><' '.:;.' <br /> <br />unvegetated sandbars (pemberton~1977~;One is the peak flood discharges <br /> <br />that develop the stream chann~vel~ties for a continually shifting <br /> <br />~ <br /> <br />River Mechanics <br /> <br />Present Situation <br /> <br />streambed. <br /> <br />Ice jams have a great influence on maintaining the shallow and open, <br />unregulated sandbars on the Platte River downstream from Overton, <br />Nebraska. The formation of ice jams occurring from December through <br />March forces the water to flow under the ice with velocities that scour <br /> <br />the channel bottom. It is this scouring action or movement and continually <br /> <br /> <br />shifting of the streambed that helps maintain the open channel of <br /> <br />, <br />unvegetated sandbars. Since the ice jams occur every year there is <br />, little or no chance for the vegetation to establish itself. Thus, <br />the second factor is the scouring velocities developed under the ice <br />that move the bed material because of the additional head developed <br />'1 <br /> <br />, <br />