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<br />The Corps makes periodic inspections of the Project. Inspections have been made in <br />March 1979, May 1981, June 1983, July 1984, April 1985, May 1987, December 1988, <br />September 1989, August 1992, and June 1994. A Colorado Water Conservation Board staff <br />member accompanied the Corps representatives on the June 1994 inspection. Copies of the trip <br />report by the Board representative and the Corps inspection report are on file in the Board office. <br /> <br />HYDROLOGIC AND HYDRAULIC ANALYSES <br /> <br />Topographic Base Mapping <br /> <br />The Corps topographic base maps meet the Board's requirements for detailed floodplain <br />information. The General Plan had a scale of 1 inch ~= 1500 feet and a contour interval of 10 <br />feet. The topographic base map used for Plan and Profile of the levee and related facilities had <br />a scale of I inch = 100 feet and contour interval of 1 foot. <br /> <br />Hvdrologic Analysis <br /> <br />The Corps carried out detailed hydrologic studies in support of the Las Animas Flood <br />Control Project. These studies meet the Board's requirements for dctailed floodplain information, <br />Hydrologic information is summarized in the following paragraphs. <br /> <br />Drainage Area - The drainage area of tlw Arkansas River basin above Las Animas is <br />13,976 square miles. Contributing drainage area below the Pueblo Dam is 9,306 square miles. <br /> <br />Drainage Basin Conditions - Topography of the drainage basin is predominantly gently <br />rolling with an eastward slope. The semiarid conditions result in sparsely vegetated land. <br /> <br />Unit Hydrographs - Synthetic unit hydrographs were used in the hydrologic analysis for <br />the Las Animas Flood Control studies. The Corps developed them by regression analyses during <br />studies of the Purgatorie River at Trinidad, Colorado, and the project document studies of the <br />Arkansas River at Las Animas. <br /> <br />Standard Project Flood (SPF) - The SPF was d,'veloped by the Corps in accordance with <br />their procedures. The June 1921 storm was transposed over the 9,306 square mile drainage area <br />between the Pueblo Reservoir and Las Animas for SPF determination at Las Animas. The SrI' <br />peak was 200,800 c.f.s. <br /> <br />Frequency - Peak flood frequencies were developed by the Corps using now data from <br />1921-1965. Table 1 summarizes the nood frequencies. <br /> <br />Project Design Flood (PDF) - Several steps were involved in determining the PDF. The <br />June 1921 flood peak was estimated at 187,000 c.f.s. at Las Animas. The Pueblo Barrier Dam <br />constructed after the 1921 flood would have reduced the 1921 peak to 140,000 cIs. The Project <br />Design Flood peak was based on the June 1921 peak of 140,000 c.f.s. and was selected as the <br /> <br />7 <br />