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1 3.0 HYDROLOGIC ANALYSIS <br />3.1 Existing Data <br />For locations where existing detailed hydrologic analyses were available, those analyses were used <br />to obtain peak 50 -year and 100 -year flows. For some other locations, statistical analyses of <br />stream gages provided by the USGS were available. <br />Published floodplain studies prepared by Merrick and Company for Meeker, Colorado provided <br />50 -year and 100 -year flows above the upstream limit of this study. Floodplain studies prepared <br />by FEMA for Rangely and unincorporated Rio Blanco County provided 50 -year and 100 -year <br />flows near the downstream limit of this study. In addition, USGS gage analyses were available <br />for two tributary streams. <br />3.2 New Hydrologic Information <br />Hydrologic analyses of the 50 -year and 100 -year flood flows for the remainder of the hydrologic <br />points along the study reaches of the White River were accomplished by interpolation of the <br />known flow values. The frequency analysis of the USGS gage for the White River near Rangely <br />was not included in the hydrologic analyses due to the limited number of years of data available <br />at that site and the inconsistency between flow versus drainage area values for the gage and the <br />published values at Meeker and Rangely. The three known values and the corresponding <br />drainage areas were entered into a curve fitting computer program which selects an equation that <br />provides a close description of the plotted curve. The curve fitting program computed the flows <br />at the other hydrologic points on the White River locations by using the drainage areas at each <br />dr location for which flows needed to be calculated. <br />The equation for the White River below Rio Blanco Reservoir is: <br />IQ= 10k +c/LogA <br />where: Q = 50 -year or 100 -year flow; <br />A = drainage area; <br />k = a constant; and <br />c = an exponent <br />The form of the equation is the same for the entire study reach, but the coefficients are different <br />for the two frequencies. <br />White River <br />Downstream of Rio Blanco Lake for 50 -year frequency: k= 6.271, c= -7.486 <br />for 100 -year frequency: k= 7.157, c= - 10.002 <br />1 10 <br />