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<br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />I: <br />I. <br />. <br />. <br />. <br />. <br />. <br />I. <br />. <br />I. <br />. <br />. <br />. <br />. <br />I. <br />. <br />. <br />. <br /> <br />ENGINEERING METHODS <br /> <br />Hvdrolol!:ic Analvsis <br />The Eagle County PIS presents both detailed and approximate floodplain delineations. Detailed <br />delineations were developed using standard hydrology methods and are mostly well documented. <br />Hydrologic information used for the FEMA approximate floodplain delineations are not available <br />or were not documented by FEMA. However, the Colorado Water Conservation Board <br />(CWCB), using regional regression methodologies for computing lOO-year flood-flow values, <br />has developed acceptable hydrologic information for undeveloped basins. <br /> <br />The CWCB regional regression equation methodology is fully described in a publication by the <br />CWCB entitled "Guidelines for Determining lOO-year Flood Flows for Approximate Floodplains <br />in Colorado". The CWCB regression equation is shown in Table 2. <br /> <br />Table 2. <br /> <br /> <br />Drainage Basin <br />Limitations (s .mi.) <br /> <br />1 to 950 <br /> <br />Sub- <br />Re 'on ID Sub-Re ion Name <br /> <br />COL-l Upper Colorado River <br /> <br />For the equation in Table 2, the QIOO is the lOO-year peak flow in cubic feet per second, and A is <br />the upstream (contributing) drainage area in square miles. The regression equations are only valid <br />for the range of drainage areas as shown. Calculation worksheets are shown in the appendix. <br />The lOO-year peak discharge for each of the undeveloped approximate floodplains is shown in <br />Table 3. <br /> <br />7 <br />