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<br />O~35 <br />FLOOD CONTROL STORAGE REQUIREMENTS FOR NARROWS RESERVOIR <br /> <br />The flood storage space recommended by the Corps of Engineers <br />for Narrows Reserv,oir was based on storing the I-percent proba- <br />bility spring flood (lOa-year flood) on the South Platte River <br />with a maximum release rate of 5,000 c.f.s. The 100-year storage <br />would include 475,000 acre-feet of exclusive flood control space <br />plus 75,000 acre-feet of joint use flood control and conservation <br />space, <br /> <br />BENEFIT ANALYSIS <br /> <br />AVERAGE ANNUAL BENEFITS <br /> <br />Flood control benefits are equivalent to the difference be- <br />tween the average annual damages under existing conditions and <br />the average annual damages with the Narrows Dam operating. <br /> <br />.The Narrows with the recommended operation and flood control <br />storage would provide about a 16 percent reduction in the flood <br />~e potential on the South Platte River between the dam and <br />the city of North Platte, Nebraska considering both existing and <br />future conditions. Benefits downstream of the city of North <br />Platte would be negligible. <br /> <br />The reduction in average annual damages to existing devel- <br />opment that would be provided by the Narrows ranges from $640,000 <br />to $1,400,000. The reduction depends upon the assumed degree of <br />coincidence between peak flows from upstream of the damsite and <br />peak flows generated from areas downstream from the damsite. <br />Records of previous floods indicate that there is a low degree of <br />coincidence. Benefits to existing development of $793,000 is the <br /> <br />23 <br />