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<br />. <br /> <br />. <br /> <br />. <br /> <br />ENGINEERING METHODS <br /> <br />Hvdrolol!ic Analvsis <br />Hydrologic information used for the South Platte River floodplain delineation in Morgan County's <br />PIS was extracted from the 1977 Corps of Engineers study, For the purposes of Floodplain <br />Designation, the flood hydrology values for the South Platte River are summarized in Table 1. <br />Additional information on the South Platte hydrology can be found in the 1977 Corps study, <br /> <br />Table 1 <br />South Platte River - Summary of Discharges <br /> <br />Location 100-year Peak Flow (cfs) <br />At the Weld-Morgan County line 43,000 <br />Upstream from Kiowa Creek 42,500 <br />Downstream from Kiowa Creek 42,500 <br />Upstream from Biiou Creek 42,000 <br />Downstream from Biiou Creek (Fort MOf1(an) 114,000 <br />Upstream from Badger Creek 93,000 <br />Downstream from Badger Creek 104,500 <br />Morgan-Washington County line 94,000 <br /> <br />Hydrology information for the other streams with approximate floodplain delineations in Morgan <br />County's PIS can be estimated in accordance with the CWCB's Guidelines for Determining 100- <br />Year Flood Flows for Approximate Floodplains in Colorado (Guidelines). The lOO-year flow for <br />each of the streams with approximate floodplains (in all of Prowers County) can be estimated by <br />utilizing the regression equation for South Platte River Basin, subregion SPL-l. The equation is <br />QIOO = 707.9(A)o,654 , where QUMJ is the lOO-year peak flow in cubic feet per second, and A is the <br />upstream (contributing) drainage area in square miles, The regression curve for subregion SPL-l is <br />presented in the Appendix, The regression equation is only valid for tributary streams having <br />drainage areas between 2 square miles and 1090 square miles, and is not valid for the South Platte <br />mainstem, <br /> <br />Users should be cautioned that the regression equation may significantly overesimate peak flows for <br />drainage basins that are primarily within "sand hills" areas, The regression equations may not give <br />reasonable results for basins having significant diversions, reservoirs, or other features that would <br />affect flood flows, The table below presents drainage areas and estimated lOO-year flows for <br />selected streams in Morgan County, <br /> <br />4 <br />