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<br />. <br /> <br />studies were made in order to become acquainted with the model <br /> <br /> <br />parameters utilized in the program. This resulted in modifying <br /> <br />the program logic to adapt the model to larger areas which <br /> <br />experience overbank flow in addition to channel flow. Reconsti- <br /> <br />tution of the May 1973 flood hydrograph for the uncontrolled <br /> <br />Cherry Creek area lying downstream from Cherry Creek Dam provided <br /> <br /> <br />practical experience in application of the model to other basins. <br /> <br />The results of the Cherry Creek reconstitution are shown on plate 12. <br /> <br />Model Input Parameters. The rainfall and loss parameters <br /> <br />used in the model studies are discussed below. <br /> <br />. Rainfall. A rainfall model was developed for use as needed <br /> <br />in the South Platte River basin. The rainfall-frequency relation- <br /> <br />ships were obtained from NOAA Atlas 2 for Colorado published in <br /> <br /> <br />1973. The NOAA values were adjusted for expected probability. <br /> <br /> <br />The 500-year values were estimated by extrapolating on arithmetic- <br /> <br />probability paper. The various rainfall durations presented in <br /> <br />the NOAA publication were studied at each location to determine <br /> <br /> <br />which duration best represented the specific condition being <br /> <br />analyzed. In each case the 6-hour duration was selected. A <br /> <br />30-minute distribution of this 6-hour storm is shown in the <br /> <br />following table 10. It was developed from a study of hourly <br /> <br />precipitation data recorded for major storms in the South Platte <br /> <br /> <br />River basin and refined to 30-minute values by using Civil Works <br /> <br />Bulletin 52-8, Plate No. 11 (1952) as a guide. <br /> <br />56 <br /> <br />. <br />