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A dam failure in the Mekong basin, Laos, 2018: Possible cause of the failure and impacts of flash flood

Authors: Edward Park*, Nanyang Technological University
Topics: Hazards, Risks, and Disasters, Resources, Hazards and Vulnerability
Keywords: human disaster
Session Type: Paper
Presentation File: No File Uploaded

One of the dams holding in the Xe-Namnoy hydroelectric reservoir (Saddle dam D) in Southern Laos failed catastrophically on July 23rd 2018 and caused severe flash flooding and the loss of life, limb and property. First, Our results show that reservoir water level was lower than the dam crest (limit of storage capacity) when the dam collapsed; indicating that reservoir did not fill up and did not overtop the dam, hence indicating structural failure. Second, we estimated that the failure of Saddle dam D released 350 million tons of water that spilled off to the adjacent Vang Ngao basin causing catastrophic flash flood downstream over the next two days, and the reservoir level to fell 20 m. Third, the saddle dam was an “Earth-fill” dam, assumed to be impermeable. However, sediments sampled from a nearby quarry suggest a mixture of a like-loess, oxisols and saprolite was used for the construction. Grain size analysis suggests a significant proportion of silt or silt-size muddy “aggregates” (semi-permeable). We consider that a lack of compaction and a potential overestimation of the clay content by dispersion of mud aggregates while conducting geotechnical analyses, contributed to underestimate the risk of piping and seepage susceptibility. In conclusion, the disaster is caused collectively by lack of assessment of impacts and hazards in the receptive basin in case of failure, poor geomorphological-geotechnical engineering, and efficient emergency plan or aler

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