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<br /> <br />Figure 3,--Lawn Lake dam and Reservoir, prior to failure (July 11, 1958) <br />(aerial), Photo courtesy of the National Park Service, <br /> <br />Possible Causes of Failure <br /> <br />Six possible causes of the failure of the Lawn Lake dam were investigated <br />by the Office of the State Engineer (1983): (1) Overtopping; (2) earthquake <br />shaking; (3) rodent damage; (4) frost penetration; (5) embankment stability; <br />and (6) piping, <br /> <br />Overtopping and earthquake shaking could be dismissed quickly as possible <br />causes of failure. Weather was not a factor in the failure, Rainfall during <br />July 10-15, 1982, in Estes Park totaled 0,11 in" and no large rainstorms <br />occurred in the area during this period, The sky was clear the morning of the <br />dam failure, Snowpack was about normal and runoff slightly below normal in <br />the surrounding region during the winter of 1981-82. However, based on post- <br />failure surveys of the dam and reservoir, the high-water line in the reservoir <br />at the time of failure was about 2 ft below the crest of the dam. The Nation- <br />al Earthquake Information Center in Golden, Colo., 'indicated that no earth-. <br />quakes were detected at the time. of failure; in fact, no earthquake has ever <br />been measured in the area of the dam (Offi ce of the State Engi neer, 1983). <br /> <br />The possibility of failure from rodent damage and frost penetration was <br />more difficult to dismiss. Marmot burrows were observed along the crest and <br />downstream slope of the remaining dam. Through excavation, personnel of the <br />State Engineer's Office determined that the maximum extent of any burrow was 3 <br />to 4 ft, and that the dam 's i nteri or was not extens i ve ly burrowed enough to <br />cause failure of the dam. <br /> <br />9 <br />