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<br />attenuate in its passage down the Fall River and through the town of Estes <br />Park. <br /> <br />After Cascade Lake dam failed, two campers were swept to their deaths a <br />short distance downstream from the dam. The flood continued down the Fall <br />Ri ver, caus i ng extens i ve damage to homes, mote 1 s, bus i ne5ses, and bri dges, <br />particularly in the town of Estes Park. In Estes Park, the flood entered the <br />Big Thompson River for a short distance before entering Lake Estes, which is <br />formed by the U.S. Bureau of Reclamation's Olympus dam. This reservoir <br />contained all the floodwaters. The peak discharge was 5,500 ftJ/s entering <br />Lake Estes, which is about 12.5 mi downstream from Lawn Lake. Peak discharge <br />into Lake Estes occurred approximately 3 hours and 40 minutes after the <br />failure of Lawn Lake dam. In that brief time, three people were killed and <br />approximately $31 million in private and public damages, cleanup, and economic <br />loss was reported. The flood resulted in a Presidential Disaster Declaration <br />for Larimer County on July 22, 1982. <br /> <br />The purpose of this report is to present the setting, a summary of causes <br />of the dam failures, and the hydrologic data on the flood, and to document <br />geomorphi c effects of the f1 ood. A secondary purpose is to present data <br />obtained from using a dam-break computer model to evaluate that model's <br />capabil it ies on hi gh-gradi ent streams, to enhance and provi de supp I ementa I <br />hydro 1 ogi c i nformat ion, and to eva I uate vari ous hypothet i ca 1 scenari os of <br />dam-breach development and probable impact of the failure of Cascade Lake dam. <br />Documentation and analysis of the flood should provide valuable information on <br />dam-breach floods of small dams on high-gradient streams for future hazard <br />mitigation related to dam failures. <br /> <br />Acknowledgments <br /> <br />Data and data interpretation in this report are based on the combined <br />efforts of many private individuals, and upon local county, Federal, and State <br />agencies. This assistance is gratefully acknowledged. <br /> <br />Many individuals provided valuable eyewitness information that helped in <br />the understanding of the flood characteristics. Local residents also granted <br />access to their property to the field personnel working in the flooded area. <br />Appreciation also is extended to the officials of the town of Estes Park, of <br />Larimer County, and to National Park Service personnel who cooperated and <br />contributed data during the data-collection period. <br /> <br />1; <br /> <br />Jack Truby, Colorado Division of Disaster Emergency Services, provided <br />est i mates of f1 ood damages. A 1 an Pearson, Co I orado Department of Natura I <br />Resources, Division of Water Resources, Office of the State Engineer, provided <br />information on the history and causes of failures of the dams. William <br />Stanton, Colorado Department of Natural Resources, Colorado Water Conservation <br />Board provided historical flood data, flooded area maps, and additional damage <br />data. <br /> <br />! <br /> <br />The U.S. Bureau of Reclamation, through the Western Area Power Adminis- <br />tration, provided hel icopter transportation for the collection of data at <br /> <br />5 <br />