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<br />.-..-. <br /> <br />FLOOD CHARACTERISTICS <br /> <br />Because of its particular geographic location, Rangely is subject to <br /> <br />five different types of events that cause flooding. They are ice jams, snow <br /> <br />melt, rain on snow, general rain, and local thunderstorms. Ice jams, rain <br /> <br />on snow and local storms historically have caused the greatest flood damage <br /> <br />in and around Rangely. Ice jams are formed by ice flows piling up at an <br /> <br />obstacle such as an existing ice accumulation, bridge, or bed irregularity. <br /> <br />The ice completely blocks the whole channel section down to the river <br /> <br />I ~ bottom. Streamflow then has to flow by infiltration through the ice plug, <br />. <br /> <br />or, if allowed to increase in depth, it spills out and floods adjacent land. <br /> <br />Often ice jams are unstable enough to break up when upstream water level <br /> <br />increases. Ice jams are usually caused by Chinook winds and temperature <br /> <br />inversions. During a Chinook it is not unusual for a two-foot layer of snow <br /> <br />to disappear in one day. At the same time the temperature may rise as much <br /> <br />as 300 C (540 F) in a few hours. A temperature inversion can cause ice jams <br /> <br />by melting upper elevation snow and ice while maintaining freezing conditions <br /> <br />~ at lower elevations. <br />:1 <br /> <br />Only two years of streamflow data is available at Rangely. Information on <br /> <br />flooding at Rangely came from local residents and newspaper accounts. Data <br /> <br />from precipitation stations. at Rangely and Meeker, and stream flow records <br /> <br />for White River near Watson and White River near Meeker helped to verify <br /> <br />reported events. <br /> <br />3 <br />