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<br />than three feet deep, occasionally occurs in some southern portions <br />of Rangely as a result of rampant thunderstorm runoff from ravines <br />and washes. <br /> <br />Due to a lack of streamflow records for the immediate vicinity of <br />Rangely, data basic to estimating the frequency of past floods are <br />not available. <br /> <br />2.4 Flood Protection Measures <br /> <br />There are no Federal flood control projects affording protection <br />to Rangely, and none are under consideration. Most new development <br />in Rangely is being kept out of potential flood damage areas. <br /> <br />College Canyon Draw has been channelized between South White Avenue <br />and County Highway 2 to increase channel capacity. <br /> <br />A dam has been constructed on the White River at the Taylor Draw <br />Reservoir approximately seven miles upstream of the Town of Rangely. <br />The reservoir was not constructed for flood protection purposes. <br />The reservoir storage volume is 13,800 acre-feet as compared to an <br />average annual runoff of 550,000 acre-feet for the approximately <br />3,000 square mile drainage area, and has no significant affect on <br />the 100-and 500-year floods. Construction of the dam was completed <br />in the spring of 1984. Though not intended to provide flood <br />protection, it is expected that the dam will indirectly serve to <br />lessen or eliminate flooding problems caused by ice jams in the <br />town. It is believed the dam will provide flood protection since <br />it will collect ice flows and fluctuate discharges in the river <br />causing existing ice accumulations to break up thus preventing <br />blockages. <br /> <br />3.0 ENGINEERING METHODS <br /> <br />For the flooding sources studied in detail in the community, standard <br />hydrologic and hydraulic study methods were used to determine the flood <br />hazard data required for this study. Flood events of a magnitude which <br />are expected to be equaled or exceeded once on the average during any <br />10-, 50-, 100-, or 500-year period (recurrence interval) have been selected <br />as having special significance for flood plain management and for flood <br />insurance rates. These events, commonly termed the 10-, 50-, 100-, and <br />500-year floods, have a 10, 2, 1, and 0.2 percent chance, respectively, <br />of being equaled or exceeded during any year. Although the recurrence <br />interval represents the long term average period between floods of a <br />specific magnitude, rare floods could occur at short intervals or even <br />within the same year. The risk of experiencing a rare flood increases <br />when periods greater than 1 year are considered. For example, the risk <br />of having a flood which equals or exceeds the 100-year flood (1 percent <br />chance of annual exceedence) in any 50-year period is approximately 40 <br />percent (4 in 10), and, for any 90-year period, the risk increases to <br />approximately 60 percent (6 in 10). The analyses reported herein reflect <br />flooding potentials based on conditions existing in the community at the <br /> <br />7 <br />