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<br />. <br /> <br />in Colorado" dated 2000 and prepared by J.E. Vail! in cooperation with the Colorado Department <br />of Transportation and the Bureau of Land Management. <br /> <br />The regional regression equations are based on flood frequency analyses of streamflow data from <br />USGS gaging stations located within Colorado and adjacent states. The equations relate flood <br />magnitude (the dependent variable) to drainage basin and climatic characteristics (the <br />independent variables). Colorado was divided into five distinct hydrologic regions because of <br />widely ranging basin physiography and climate. The five hydrologic regions include the <br />mountain region, Rio Grande region, southwest region, northwest region, and the plains region. <br /> <br />The study area for this report is within the plains region as defined by the USGS. The <br />independent variable for the plains region flood-frequency equations is the contributing drainage <br />area of the basin of interest. For the purpose of this study, the drainage area for the watershed of <br />interest was measured from the USGS 1:50,000 scale County Series mapping for Prowers, Bent, <br />and Kiowa Counties, <br /> <br />. <br /> <br />Study Results <br />Hydrology information for the Wiley Drainage Ditch has been estimated in accordance with the <br />USGS hydrology publication "Analysis of the Magnitude and Frequency of Floods in Colorado" <br />(reference 1). The USGS regression equations for estimating peak discharges in the eastern plains <br />require the watershed's drainage area as the independent parameter. It was assumed that all of the <br />drainage area above the Kicking Bird canal contributes to the peak flow. The drainage areas used <br />in the regression equations were 71.5 square miles at the upstream end of town, and 74.2 square <br />miles at the downstream end of town. Results of the hydrologic analysis are presented in Table 1. <br /> <br />TABLE 1 <br />Summary of Discharges <br />Wiley Drainage Ditch <br /> <br /> D.A. lOO-Year 500- Year <br />Stream and Location (SQ. mi.) Flow (cfs) Flow (cfs) <br />Wiley Drainage Ditch at Hwy 196 71.5 8,600 17,900 <br />Wiley Drainage Ditch at AT&SF Railroad 74.2 8,700 18,200 <br />confluence with South Clear Creek <br /> <br />. <br /> <br />Hydraulic Analysis <br />Hydraulic methods used for the approximate floodplain delineations shown on the Town of Wiley <br />FIRM panel are not available or have not been documented by FEMA. However, more detailed <br />hydraulic studies have been conducted by the CWCB and by the Sear Brown Group on behalf of <br />the Colorado Department of Transportation (CDOT). Computer backwater simulation models <br />(HEC-2 and HEC-RAS) were developed to compute water surface profiles for the Wiley Drainage <br />Ditch through Wiley. The CDOT study developed peak flow values for the Wiley Drainage Ditch <br />that are not consistent with the values listed in Table 1. The detailed floodplain analyses have not <br /> <br />4 <br />