The description of Panchet and Khadakwasla dam failures reminds of the case study of Lawn Lake Dam located in Rocky Mountain National Park upstream of Estes Park, Colorado.
Due to man-made causes, failure of an upstream earthen dam happens and which in turn causes failure of a concrete dam downstream, further compounding the losses.
Lawn Lake dam was an embankment dam and constructed in 1903 and owned by an irrigation company. It fell within the National Park boundary when the Park was established in 1915. The reservoir was at almost 11,000 foot elevation and the dam enlarged a natural glacially-formed lake. The dam was raised in 1931 to 24 feet high and stored a maximum of 817 acre feet of water. A 3-foot diameter, riveted steel outlet pipe was used for releases. A direct-buried gate valve was located in this pipe directly under the crest of the dam. The dam was assigned a “moderate” downstream hazard potential.
Due to its remote location with challenging access, inspections of the facility were relatively infrequent. A number of issues were identified at the dam and documented in inspection reports in 1951, 1975, 1977 and 1978. Between 5:00 and 6:00 AM on July 15, 1982, the dam failed suddenly, releasing 674 acre-feet of water. There was no warning. The peak flow was approximately 20,000 cfs.
The flood spread and then went out the east end of Horseshoe Park, filled and then overtopped a 17-foot-high concrete dam called Cascade Dam. The maximum overtopping was 4 feet. After 17 minutes of overtopping, Cascade Dam gave way and a new flood surge of 16,000 cfs poured through the breach.
The flood swept motels, residential structures, and mobile homes off their foundations. In the town of Estes Park, debris-laden, muddy water up to five feet deep (6,000 cfs) poured through the business district. It damaged 177 businesses (over 90% of the businesses). Damages totaled $31 million and a total of three lives were lost.
The State Engineer performed an investigation and issued a report 8 months following the failure. The report concluded that “… the failure occurred due to leakage under high pressure from the leaded connection of the outlet pipe and valve, causing progressive piping of the dam embankment in the vicinity of the outlet pipe during periods of high reservoir levels and gate closure and sudden collapse of the embankment allowing rapid evacuation of the reservoir.”