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<br />. <br /> <br />velocity flash floods which are particularly hazardous to life and <br />property. The foothills regions have flash floods similar to the <br />mountain regions, but generally reflect a greater hazard because. dry <br />washes became raging torrents with. high velocities that erode the <br />normal boundaries of stream flow. As the foothills streams converge <br />to form the main tributaries and tributary streBllls converge on the <br />main stream., the valleys and flood plains become broader. The <br />broader valleys and flatter stream slopes reduce the discharge rate <br />of the flood by combinations of temporary overbank storage and lower <br />energy gradients. The lower velocities increase the duration of <br />flooding and permit the sediment load and debris load carried from <br />upstream areas to be deposited on the more productive lands of the <br />lower valleys. Consequently, the dBlllaging effects in the lower <br />valleys are a combination of destruction by erosion and inundation <br />with reduction in the productive quality of valley lands by flood <br />debris and sediment. The damaging effects of floods are also governed <br />significantly by the nature of storm patterns and tributary runoff. <br />Rainfall concentrated over one tributary watershed generally limits <br />the destructiveness of floods to the tributary stream affected. <br />However, the runoff from larger storm patterns results in flood dis- <br />charges on many tributaries which converge on the main 8trelllll, thereby <br />causing more widespread destruction, prolonged inundation, and greater <br />flood damages over larger areas. <br /> <br />III . EXISTING IMPROVEMENTS <br /> <br />14.. FEDERAL IMPROVEMENTS <br /> <br />a. Corps of Engineers. <br /> <br />(1) The Cherry Creek DlIIIl and Reservoir on Cherry Creek was <br />campleted in 1953 at a cost of $14.7 million. It is situated <br />approximately 1l.5 miles above t!1e mouth of the strelllll at central <br />Denver. It controls 385 square miles of the 409 square mile Cherry <br />Creek watershed. The dlllll is a rolled earth fill structure, with a <br />reservoir storage capacity to the crest of the emergency spillw~ of <br />96,000 acre-feet. This storage capacity consists of 81,000 acre-feet <br />for flood control storage and 15,000 acre-feet for conservation storage. <br />The conservation pool also serves the project's recreation function. <br /> <br />(2) The Kelly Road Detention DlIIIl is a small capacity (380 <br />acre-feet) flood detention project on Westerly Creek situated near the <br />Lowry Air Force Base at Denver, Colorado. It provides flood protection <br />for portions of Aurora and Denver, Colorado. It was completed by the <br />Corps of Engineers in 1954 at a cost of $227,000. <br /> <br />b. Soil Conservation Service. The Soil Conservation Service has <br />constructed three watershed projects in the South Platte River basin <br />which include a total of 106 floodwater retarding structures. The <br /> <br />8 <br /> <br />. <br />