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<br />*"~ ,;.]-.' , <br />0006~3 <br /> <br />DEBRIS FLOW ANNEX <br />GARFIELD COUNTY &IERGENCY OPERATIONS PLAN <br /> <br />I. SITU.'IT!l1, <br /> <br />A. D2.cription of Hazard <br /> <br />), Debrls flows, as deflned by the Colorado Geologlcal Survey (CGS), <br />:::re "slurries of rock, soil, organic matter, ',..,rater and air that <br />flow rapidly do\~n pre-existing drainage channels until they are <br />deposited irl fail-shaped cones ~Ilere the channels enter the nlain <br />valley floor. Debris flow damages result from impacc, burial and <br />floodlng.1I <br /> <br />" <br /> <br />Debris flo'o/s are the <br />landslide threat in <br />unirlcorporated ereas. <br /> <br />IilOSt COrTl~on <br />Glen\%od <br /> <br />ar.d .-nost <br />Sp~ir.gs <br /> <br />serious type of <br />and surroLlnding <br /> <br />3. Due to the large volume of debrls present in the unstable drainage <br />basillS surrour.ding Glenwood Springs. the chreat to people, <br />pro\)erty and essential public services \o/ill be a persistent one. <br />Aggravating the problem IS the 21ter2cion of natu~al debris fans <br />by tIle constructlon of roads. hooes, i~rigation ditches and <br />businesses. <br /> <br />1.2.. .'lajor debris flo\.:s are deep e:lough (Eive feet or iTIore) to <br />traIls port large boulders for long distances at velocities up to 10 <br />to 15 feet per second. Debris flows can produce i~p2c~ pressures <br />on e'posed structures of 400 [0 900 lbs. per square foot, <br />potentially destroying structure5 and causing injurlEs and loss of <br />life. <br /> <br />5. Debris flows can occur in sllrges (due to a cycle of daD formation, <br />bulld up and release of debris and water), ca~sin3 flo'.-Is to bypass <br />established channels and change directions unpredictcbly. <br /> <br />B. Frequency <br /> <br />1. According to newspaper accounts, 18 debris flows haVE occurred in <br />Clem,rood Springs this century, four of ,o/hich inundated the <br />downtown district in only a seven year ?eriod (1936-1943). <br /> <br />2. Following Qn uncommonly heavy thunderstorm on July 24, 1977, the <br />more serious debris flow to hit the city inundated about 200 acres <br />up to 12 feet deep and caused widespread damages. A number of <br />sOlaller debris flo"s occurred in the SWTIf'ler and fall of 1981 and <br />agtli.n in 198~, \,'ith lesser damages. <br /> <br />C. If'lllacts <br /> <br />I. <br /> <br />Estimates <br />mlllion, <br />somewhere <br /> <br />of damages from the lY77 disaster r2nge as high <br />althollgh most reports indic2te total losses <br />between $500,000 and SI million. The 1981 debris <br /> <br />as $2 <br />fall <br />flows <br />