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HISTORY OF THE DAMS 9 FIGURE G.-The remains of the outlet valve from Lawn Lake dam. Investigations of this valve led to the conclusion that lead caulking had severely deteriorated. material. Campers in the vicinity of Lawn Lake the night before the failure reported hearing a noise that sounded like strong winds. This sound indicated that the reservoir may have been discharging through the dam for at least 3 to 4 hours before the hole enlarged sufficiently-or embankment failure occurred-above the outlet pipe, causing a total breach of the dam where the outlet works were located (figs. 7A,B). Surveyed breach dimensions are: Depth of 28 ft, top width of 97 ft, and bottom width of 55 ft. Following the complete failure of the dam embankment at about 0530 MDT, the resulting outflow of water reached its peak dis- charge very quickly (estimated to be within 10 minI. The resulting flood peak of 18,000 ftSts (see "Dam-Break Modeling") then proceeded down the Roaring River toward Horseshoe Park and the Cascade Lake dam. CASCADE LAKE DAM Cascade Lake dam, a concrete gravity dam, was located on the Fall River in Rocky Mountain National Park, 5.3 mi west of Estes Park (fig. 1). A diversion dam was originally constructed at the site in 1908 for a pipeline to a hydropower plant downstream. The powerplant supplied electricity to the Stanley Hotel and the town of Estes Park. The site was at the head of a steep drop with numerous rapids and large boul- ders in the Fall River, where the stream eroded through several Pleistocene terminal moraines that dammed the Fall River, creating a glacial lake in Horseshoe Park just upstream. Cascade Lake dam consisted of a con- crete wall several feet thick, reinforced with a masonry rock buttress on the downstream side. The founda- tion and abutments were in glacial terminal-moraine sediments; no bedrock is evident in the foundation. A photograph at Cascade Lake dam is shown in figure 8. The dam was acquired in 1945 by the town of Estes Park, which owned it at the time of failure. Various im- provements were made on the structure. It was enlarged to 17 ft high in 1923. The reservoir behind the dam was dredged at least twice since 1945, most recently in November 1981. Postfailure surveys indicated that the water behind Cascade Lake dam was approximately 12 ft deep, and the dam was 143 ft long prior to failure. Because of the sediment accumulation of 5 ft, a height