Hydrology, geomorphology, and dam-break modeling of the July 15, 1982, Lawn Lake Dam and Cascade Lake Dam failures, Larimer County, Colorado

Report summarizes causes for 7/15/1982 failures of Lawn Lake and Cascade Lake dams, in Colorado. At approximately 0530 Mountain Daylight Time on the morning of July 15, 1982, Lawn Lake Dam, a 26-foot-high earthen dam located in Rocky Mountain National Park, Colorado, failed. The dam released 674 acre-feet of water and an estimated peak discharge of 18,000 cubic feet per second down the Roaring River valley. Three people were killed and damages totaled $31 million. The Colorado State Engineer determined that the probable cause of failure was deterioration of lead caulking used for the connection between the outlet pipe and the gate valve. The resulting leak eroded the earthfill, and progressive piping led to failure of the embankment. Floodwaters from Lawn Lake Dam overtopped a second dam, Cascade Lake Dam, located 6.7 miles downstream, which also failed. Cascade Lake Dam, a 17-foot high concrete gravity dam, 12.1 acre-foot capacity dam, failed by toppling with 4.2 feet of water flowing over its crest. The flood continued down the Fall River into the town of Estes Park, which received extensive damage from the overbank flow. This report presents the setting, a summary of the causes of the dam failures, the hydrologic data, and geomorphic effects of the flood. Data on dam-breach floods on high-gradient streams are limited. A dam-break computer model was used to evaluate the model's capabilities on high-gradient streams, to enhance and provide supplemental hydrologic information, and to evaluate various hypothetical scenarios of dam-breach development and probable impact of the failure of Cascade Lake Dam. If Cascade Lake Dam had not failed (or had not been present), peak discharges would have been reduced by 11,300 cubic feet per second immediately downstream from the dam to 500 cubic feet per second less at Estes Park. Maximum flood depths would have averaged 0.6 foot lower, and the flood wave would have reached Lake Estes 0.3 hour later.--(modified author abstract)

Prepared in cooperation with the Colorado Department of Natural resources, Division of Water Resources, Office of the State Engineer. Maps on two folded leaves in pocket. Bibliography: p. 64-65.
GeoRef ID 1985-057182 Citation Jarrett, Robert D. (U. S. Geol. Surv., Lakewood, CO, United States), Costa, John E., Hydrology, geomorphology, and dam-break modeling of the July 15, 1982, Lawn Lake Dam and Cascade Lake Dam failures, Larimer County, Colorado, OF 84-0612, p. 117, illus. incl. 13 tables, sketch map, 33 refs, 1984. 2 over-size sheets. (NC, Da, M, Wb, Db.). Abstract Keywords: Engineering geology, Cascade Lake Dam, channels, Colorado, dams, data processing, discharge, engineering geology, failures, floods, fluvial features, geologic hazards, geomorphology, hydrology, Larimer County , olorado, Lawn Lake Dam, maps, mathematical models, North America, photography, rivers and streams, Rocky Mountain National , ark, Rocky Mountains, surveys, topographic maps, United States, USGS, ISSN , 0196-1497, Miscellaneous .