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<br />21 <br /> <br /> <br />These computations were based upon channel and flood plain condi- <br />tions as represented by surveys conducted in the spring of 1974 <br />and data collected from the South Platte River flood of May 1973. <br />The location of each cross section is shown on the flooded area <br />plates. <br />Water surface profiles for the IO-year, 50-year, lOO-year, <br />and 500-year floods were developed for reaches of the South Platte <br />River located in the vicinity of Brighton, Fort Lupton, Plattevil Ie, <br />Evans, Gree ley, La Sa II e, Kersey, and Orchard. These prof i I es a I so <br />show high water marks for the May 1973 flood and a computed water <br />surface profile which represents that flood. This computed 1973 <br />flood profile is based upon the observed high water marks shown <br />and is a "best fit" profile. Elevation-discharge curves showing <br />the IO-year, 50-year, IOO-year, and 500-year floods are also pre- <br />sented. These curves are located at the surveyed cross sections <br />which were not used in computing water surface profiles. The data <br />presented by these curves is based upon relationships developed <br />from physical characteristics of the respective cross section and <br />1973 flood data. A detailed study may show significantly differ- <br />ent results. <br />The flooded area plates show photographs of the flood of May <br />1973 and an outline of that flood. The location of observed high <br />water marks from that flood are also shown. These plates also <br />show the limits of the IOO-year and 500-year floods at each cross <br />section as determined from the water surface profiles or elevation- <br />discharge curves. The location of these flood limits at points <br />between the cross sections where water surface profiles are pre- <br />sented can be determined by selecting the proper water surface <br />elevation from the water surface profiles and establish that point <br />on the flood plain by survey. Similarly, flood characteristics at <br />points between cross sections where water surface profiles are not <br />presented can be estimated by noting the elevation differences <br />between the desired flood and the 1973 flood on the elevation- <br />