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<br />. <br /> <br />(. <br /> <br />.' <br /> <br />of <br /> <br />. <br /> <br />., <br /> <br />( <br /> <br />.. <br /> <br />.- ( <br /> <br />" <br /> <br />,. <br /> <br />- 27 - <br /> <br />A June 1958 flood on Indian vlash was the most recent flood of <br />record. A depth of 0.53-inch of precipitation in 80 minutes was <br />measured by the Weather Bureau at the airport. An estirrLated 2.2 <br />inches of precipitation uniformly distributed over the watershed <br />would be necessary to produce the est~ated peak flow of 2,700 <br />c.f.s. at the High Line Canal. This indicates that the rainfall <br />was definitely much greater in the watershed area along the Little <br />Book Cliffs than was recorded at the airport. <br /> <br />Runoff characteristics of the watershed above the High Line <br />Canal were compared to the watershed area of-Badger Wash. The Badger <br />Wash study area is a project of the Pacific Southwest Inter-Agency <br />Committee with four Federal agencies as active participants in the <br />study. These include the U. S. D. A. Forest Service Rocky Mountain <br />Forest and Range Experiment Station; and the Department of Interior <br />Geological Survey, Bureau of Land Hanagement, and Bureau of <br />Reclamation. Badger Wash is approximately 30 miles northwest of <br />Grand Junction and has runoff characteristics stmilar to those of <br />Indian Hash. The Bureau of Land Management developed a map of the upper <br />area of Indian Wash showing the range, site, and condition. The <br />result of these studies determined that the soil-complex number for <br />the area above the High Line Canal was 90 for both present and <br />future conditions. The amount of roof tops and paved streets below <br />the High Line Canal resulted in the selection of a soil-cover complex <br />number of 93 for urban areas. . <br /> <br />The floodwater storage of IW-I was based on a storm of greater <br />magnitude than a 100-year frequency with 4.10 inches of precipitation <br />in six hours producing an average of 3.00 inches of runoff fram over <br />the watershed. <br /> <br />Triangular hydrographs were developed and used in flood routing. <br />Time of concentrations for these and other hydrographs were based on <br />bankfull velocity for channels and experiment station results for <br />overland flow. <br /> <br />Stage-discharge relationship for the High Line Canal was based <br />on water surface profiles as developed by use of Leach's method. <br />Flood routing along the High Line Canal was accomplished by use of <br />the stage-storage indication method. <br /> <br />Indian Wash channel and bridge capacities below the High Line <br />Canal were based on stage discharge curves developed by the U. S. <br />Corps of Ar.my Engineers in their preliminary studies. These were <br />checked and found suitable by the Soil Conservation Service for <br />use in detailed planning. <br /> <br />