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<br />002879 <br /> <br />GARFIELD COUNTY LANDSLIDE/DEBRIS FLOW PLAN <br />(Annex to Garfield County Emergency Operations Plan) <br /> <br />I SITUATION <br />A. Definitions <br />1. Landslides - the movement of a rigid body of soil or rock along <br />an identifiable surface called a rupture zone. Landslide <br />velocities can range from ten (10) meters per second to one (1) <br />meter per year. <br />2. Debris Flows - as defined by the Colorado Geological Survey <br />(CGS) are "slurries of rock, soil, organic matter, water, and <br />air that flow rapidly down pre-existing drainage channels until <br />they are deposited in fan shaped cones where the channels enter <br />the main valley floor. Debris flow damages result from impact, <br />burial and flooding." <br /> <br />B. Frequency <br />1. According to newspaper accounts, 18 debris flows have occurred <br />in Glenwood Springs this century, four of which inundated the <br />downtown district in only a seven year period (1936-1943). <br />2. Following an uncommonly heavy thunderstorm on July 24, 1977, the <br />most serious debris flow to hit the city inundated about 200 <br />acres up to 12 feet deep and caused widespread damages. A <br />number of smaller debris flows occurred in the summer and fall <br />of 1981 and again in 1984, with lesser damages. <br />3. Mu.d and debris flows are a part of the history of Glenwood <br />Springs. In fact, the central business and residential district <br />is built on the debris fan of Cemetery Hill Gulch and the <br />majority of West Glenwood Springs is also built on an outwash. <br />4. In the winter of 1984/1985, unusually heavy early snowfalls <br />resulted in an increase in slide activity throughout the <br />county. On May 13, 19S5, the Garfield County Commissioners <br />declared a financial disaster due to damages caused by <br />landslides. <br /> <br />C. Impacts <br />1. Estimates of damages from the 1977 debris flow disaster range as <br />high as $2 million, although most reports indicate total losses <br /> <br />- 94 - <br />