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<br />OGJ7 <br /> <br />Types of Flood Damages Considered <br /> <br />Historical and potential future damages reflect only physical or <br />tangible damage to property resulting from floods in the South Platte <br />Basin. They do not reflect intangible damages. The types of damages <br />considered include the categories of urban, transportation, emergency <br />and cleanup, irrigation, and agriculture. <br /> <br />'- <br /> <br />Flood Control Storage Requirements for Narrows Reservoir <br /> <br />The flood storage space recommended by the Corps of Engineers for <br />Narrows Reservoir was based on storing the 1 percent probability <br />spring flood (lOa-year flood) on the South Platte River with a <br />maximum release rate of 5,000 ft3/s. The recommended storage would <br />include 475,000 acre-feet of exclusive flood control space plus <br />75,000 acre-feet of joint use flood control and conservation space. <br /> <br />Benefit Analysis <br /> <br />Average-Annual -Benefits <br /> <br />Flood control benefits are equivalent to the difference between the <br />average annual damages under existing conditions and the average <br />annual damages with the Narrows Dam operating. <br /> <br />The Narrows with the recommended operation and flood control storage <br />wou 1 d prov i de about a 16 Jlercent reduc tion_in_the_flood_damage_potent_i a-1 <br />- -----ontl'ie -South Platte River between the dam and the city of North Platte, <br />Nebraska, considering both existing and future conditions. Benefits <br />downstream of the city of North Platte would be negligible. <br /> <br />The reduction in average annual damages to existing development that <br />would be provided by the Narrows ranges from $640,000 to $1,400,000. <br />The reduction depends upon the assumed degree of coincidence between <br />peak flows from upstream of the damsite and peak flows generated from <br />areas downstream from the damsite. Records of previous floods indicate <br />that there is a low degree of coincidence. Benefits to existing <br />development of $793,000 is the best estimate based on these records. <br />Therefore, average annual equivalent benefits are $793,000 under <br />existing conditions and $836,000 considering future conditions. <br /> <br />15 <br />