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<br />I <br /> <br />. <br /> <br />BASIN MODEL STUDIES - SOUTH PLATTE RIVER <br /> <br /> <br />In addition to the discharge-probability curves developed for <br /> <br /> <br />the six South Platte River gaging station locations, it was also <br /> <br />necessary to develop peak flow probability values for locations be- <br /> <br />tween the gaging stations. A simple interpolation between values <br /> <br />obtained at the gaging stations would not be valid for most flood <br /> <br /> <br />events since the discontinuities in the probability profiles would <br /> <br /> <br />likely occur at the points where larger tributary streams empty into <br /> <br />the South Platte. In order to estimate the probability values for <br /> <br /> <br />the South Platte at the mouths of the tributaries and other points <br /> <br />between gaging stations, a basin model of the entire South Platte <br /> <br /> <br />River between Chatfield and the Colorado-Nebraska State line was <br /> <br />developed. Tributary inflow used in the model was based on unit <br /> <br /> <br />hydrographs developed for the tributary areas or, where available, on <br /> <br />detailed model studies using the EPA Storm Water Management Model <br /> <br /> <br />(SWMM). The flood routing portion of the model along the main stem of <br /> <br /> <br />the South Platte was developed using the Missouri River Division <br /> <br /> <br />adaptation of Harder's diffusion routing technique. The procedures <br /> <br /> <br />used in estimating discharge-probability profiles through use of the <br /> <br /> <br />model are described in the following paragraphs. A detailed description <br /> <br />of model development and the modeling parameters used is presented on <br /> <br /> <br />pages 54 through 59. <br /> <br />Chatfield to Sand Creek - Dischar~e-Probability Profiles. The <br /> <br />discharge-probability profiles for this reach were developed using <br /> <br />the SWMM procedures for determining tributary inflow and the diffusion <br /> <br /> <br />routing technique for routing of flows down the South Platte River. <br /> <br />These studies were detailed in nature and included both the effects of <br /> <br /> <br />future urbanization and the South Platte channel improvement proposed <br /> <br /> <br />for the reach from Chatfield Dam to Hampden Avenue. The discharge- <br /> <br /> <br />probability profiles developed for this reach of the South Platte are <br /> <br /> <br />presented on plates 33 and 34. The probability values developed from <br /> <br />. <br /> <br />35 <br /> <br />--~~._- <br />