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I3.0 HYDROLOGIC ANALYSIS <br />3.1 Existing Data <br />For locations where detailed existing hydrologic analyses were available, those analyses were used <br />to obtain peak 50 -year and 100 -year flows. <br />Published floodplain studies prepared by FEMA for Delta, Colorado provided 50 -year and 100 - <br />year flows at the upstream limit of this study. The floodplain study for Grand Junction provided <br />' 50 -year and 100 -year flows at the downstream limit of the study. <br />3.2 New Hydrologic Information <br />Hydrologic anal ses of the 50-year and 100- ear flood flows for the remainder of the hydrologic <br />y y y <br />points along the study reaches of the Gunnison River were accomplished by interpolation of the <br />known flow values. The peak flows per square mile for the 50 -year and the 100 -year frequencies <br />were virtually the same at both the upstream end of the study and the downstream end of the <br />study. Using the relationship of flow per square mile from the known values, the flow values <br />' for the selected hydrologic locations on the Gunnison which did not already have a detailed <br />floodplain study were calculated. The drainage areas at those points were simply multiplied by <br />the flow per square mile. The flow per square mile selected from the existing data is 3.3 cubic <br />feet per second per square mile (cfs /mil) for the 50 -year flow and 3.7 cfs /mil for the 100 -year <br />flow. Because the flow /drainage area relationship was so constant throughout the study reach, <br />no regression equation had to be computed. <br />3.3 Hydrologic Findings <br />Table 3 shows the results of this analysis in tabular form. <br />1 <br />Fj <br />