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<br />, <br /> <br />. <br /> <br />be reflected in the discharge-probability profiles along the South <br /> <br />Platte at the confluence of major tributary streams. Discharge <br /> <br />profiles were also developed for the urbanized conditions existing <br /> <br /> <br />in the basin in 1975 and the projected conditions that are <br /> <br />estimated will prevail in 1990. Thia was accomplished by deter- <br /> <br /> <br />mining the effect of the urbanization development on the l-inch <br /> <br /> <br />profile discussed above. Unit hydrographs for areas affected by <br /> <br />urbanization were adjusted to reflect both the estimated increase in <br /> <br />peak discharge and higher runoff that would be associated with the <br /> <br /> <br />increase in impervious area and improved drainage conditions. The <br /> <br /> <br />amount of impervious area was based on applying the land use ratings <br /> <br />presented in table 11 to development projections for 1990. The <br /> <br />discharge profiles developed for these two conditions are also shown <br /> <br /> <br />on plates 24 to 32, As shown on these plates, the effects on peak <br /> <br />discharges along the South Platte as a result of urbanization in the <br /> <br /> <br />Denver metro area become negligible from Kersey downstream. <br /> <br />Sand Creek to State Line - DischarRe-Probability Profiles. <br /> <br />Discharge-probability profiles along the South Platte River for this <br /> <br /> <br />reach for the 500-, 100-, 50-, and lo-year floods with 1975 and 1990 <br /> <br /> <br />urbanized conditions are shown on plates 33 to 44. In general, the <br /> <br />profiles were developed by determining the appropriate runoff to <br /> <br />apply to the South Platte model in order to reproduce the peak dis- <br /> <br />charge-probability values developed from records at the gaging <br /> <br />station locations. In some cases, because of differing slopes in <br /> <br /> <br />probability curves at the gaging stations, inconsistencies developed <br /> <br />in the attenuation of discharge-probability profiles and the attenuation <br /> <br />indicated on the l-inch model discharge profile. ~djustments were <br /> <br /> <br />therefore made in tributary inflows to restore consistency to the <br /> <br />probability profiles. <br /> <br />37 <br /> <br />. <br />