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<br />2.3 Principal Flood Problems <br /> <br />Because of its particular geographic location, Rangely is subject to <br />five different types of events that cause flooding: ice jams, rapid <br />snowmelt, rain on snow, general rain, and local thunderstorms. The <br />low permeability of the soils in and around Rangely is also a <br />factor in producing flooding in the study area. Historically, ice <br />jams, rain on snow, and local thunderstorms have caused the greatest <br />flood damage in and around Rangely. Ice jams are formed by iceflows <br />piling up at an obstacle, such as an existing ice accumulation, <br />bridge or streambed irregularity. The ice blocks the entire channel <br />section completely down to the river bottom, and water then has to <br />move through the ice plug by infiltration. When infiltration is <br />inadequate, the water-surface elevation increases until spill <br />occurs and adjacent land is flooded. However, ice jams are unstable <br />and often break up when the upstream water level increases. Ice <br />jams are usually caused by Chinook winds and temperature inversions. <br />During a Chinook, air temperature may increase very rapidly (increases <br />of more than 500F in a few hours have been recorded in some areas <br />subject to these winds), and it is not unusual for a 2-foot layer of <br />snow to melt in one day. Temperature inversions cause ice jams by <br />melting upper elevation snow and ice, while freezing conditions <br />remain in the Inwer elevations. The rising water heaves and breaks <br />up river ice and it floats into jams. <br /> <br />.. <br /> <br />. <br /> <br />Twice in the last 85 years, in March 1955 and February 1962, ice <br />jams caused water stages in the White River to reach Main street <br />between Colorow street and Birch Avenue. These floods caused damage <br />to homes, businesses, and public utilities. Ice jam floods have <br />been observed as far back as 1891, when Rangely consisted of a <br />saloon, blacksmith shop, store, and hotel. <br /> <br />In the late summer of 1910 or 1911, a thunderstorm produced flood <br />stages almost to the 1962 level. Another thunderstorm in the 1920s <br />raised the White River to about the location of the Rangely Hotel, <br />but the water was 1.0 foot lower than the 1955 flood. <br /> <br />Two of the largest thunderstorms to produce local flooding occurred <br />in August 194'6 and July 1953. In the 1946 flood, one downtown <br />office building had from 6 to 8 inches of water covering the floor. <br />On July 31, 1953, 1.42 inches of rain was measured in slightly over <br />one hour at the Rangely gage, and resultant local flooding washed <br />out a road and tore away a bridge outside of Rangely. In town, <br />runoff caused drainage ditches to overflow, and damage from the <br />floodwaters was aggravated when the high water picked up oily mud <br />from around a local oil well. <br /> <br />.. <br /> <br />6 <br />