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<br /> <br />was modeled using Mr.rCAT since it is capable of handling large homogenous <br /> <br /> <br />areas in B..'l efficient manner. T"ne diversity in land use );Btterns existing <br /> <br /> <br />in the l75-square mile area lying downstream from Golden required a substantial <br /> <br /> <br />degree of detail in area breakdown. The SWMM was therefore used in this <br /> <br /> <br />portion of the basin 3ince it is a considerably more efficient technique in <br />handling small numerous sub-areas. Flood routing along the main stem of <br />Clear Creek was accomplished using a dti'fusion routing technique. <br />b. Rainfall. Rainfall values for the 100-, 50-, and 10-year 6-hour <br />events were obtained from the Precipitation-Frequency Atlas of the Western <br />United States, Atlas 2, Volume III, Colorado, published by the National <br />Oceanic and Atmospheric Administration in 1973. In each case, a 500-year <br />value was estimated by extrapolating the selected Atlas'values on semi- <br />logarithmic paper. Adjustments for depth-area were based on the depth-area <br />relationship presented.in the NOAA publication. Adjustments for length of <br />record were made on logarithmic probability paper using Beard.' s table of <br />expected probability adjustments for various lengths of record. The spatial <br />variation of the rainfall potential shown in the Atlas for the Clear Creek <br />basin was simulated in the models through the introduction of several hyeto- <br />graphs. The time variation of rainfall for each hyetograph was based on a <br />stUlj.y of hOurly precipitation data recorded during major storms in the 30uth <br />Platte River basin and refined to 30-minute values by using Civil Works <br />Bulletin 52-8, Plate No. 11 (1952) as a guide. The distribution is given <br />in Table 1 below. <br /> <br />5 <br /> <br />