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<br />. <br /> <br />The average annual flood damages under existing conditions <br /> <br /> <br />downstream from Kelly Road Dam are $2,390,000; there is an addi- <br /> <br /> <br />tional $9,000 in average annual damages on Lowry Air Force Base <br /> <br /> <br />downstream from the potential Upper Lowry Dam. The Urban <br /> <br /> <br />Drainage and Flood Control District, with financial assistance <br /> <br /> <br />from the State of Colorado, the city and county of Denver, and <br /> <br /> <br />the city of Aurora, is proceeding with the proposed lO-year <br /> <br />channel improvements downstream from Kelly Road Dam. These <br /> <br /> <br />channel improvements would reduce the average annual damages by <br /> <br /> <br />$704,000, leaving a residual of $l,686,OOO in average annual <br /> <br /> <br />damages downstream and $9,000 on Lowry Air Force Base. <br /> <br />Three potential plans of improvement to Kelly Road Dam were <br /> <br /> <br />considered. Two of these plans would not incr~ase the existing <br /> <br /> <br />25-year flood control storage. They would, however, increase the <br /> <br /> <br />surcharge zone and improve the spillway so that the structure <br /> <br /> <br />could pass the probable maximum flood without overtopping the <br /> <br /> <br />embankment. The best of these two plans would involve the devel- <br /> <br /> <br />opment of full site capacity of the existing dam alignment by <br /> <br /> <br />raising the dam about lO feet and extending the east and west <br /> <br /> <br />embankments upstream to 6th Avenue. The other'25-year plan would <br /> <br /> <br />raise the dam only 8 feet. This would result in a savings in <br /> <br /> <br />embankment and land costs, but the increased costs for the wider <br /> <br /> <br />spillway that would be required would more than offset these <br /> <br /> <br />savings. <br /> <br />The third plan would involve raising the embankment about <br /> <br /> <br />lO feet and moving the west embankment about 150 feet west. This <br /> <br /> <br />would increase the flood control storage to the level of a 50-year <br /> <br /> <br />flood and the increased benefits downstream would be more than <br /> <br /> <br />sufficient to offset the increased embankment and land costs. <br /> <br />1-2 <br /> <br />. <br />