The La Ronge Dam has changed classifications. (submitted photo/Water Security Agency)

By Derek Cornet

news release

La Ronge Dam failure possible: Water Security Agency

Jul 29, 2020 | 2:29 PM

The Water Security Agency (WSA) is advising the public in the La Ronge area of a change to the Dam Safety Emergency Classification of the La Ronge Dam.

According to a news release, the dam has moved from a hazardous condition to a potential dam failure classification. This is a result of the significant amount of rainfall in the area recently, including accumulations ranging from five to 40 millimetres July 25 to 26. The lake level is forecasted to increase by 10 centimetres to 365 metres.

“The dam is not in imminent danger of failing, but the water level is encroaching on the minimum recommended freeboard,” the release states. “When this happens, it changes the Dam Safety Emergency Classification. Freeboard is the distance between the water level and the top of the structure.”

The WSA already has mitigation efforts in place with large sandbags on the top of the dam to raise the level of the freeboard a further 0.5 metres. The La Ronge Dam is 3.5 m in height and, with the current water levels downstream of the dam, a failure would not result in a large wave of water going downstream but rather an increased outflow from the lake into the already flooding Churchill River system. It would also impact being able to manage the lake level as it declines.

The WSA classifies dams as low, significant, high, very high or extreme consequence based on the estimated consequences of dam failure as it relates to loss of life, environmental and cultural impacts, economic damages and restoration costs. La Ronge Dam is classified as significant.

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The WSA is assessing what additional mitigation measures can be invoked such as adding more material or any other measures. Monitoring will be increased from weekly to daily.

At this time, the biggest impact downstream of a failure is thought to be the additional volumes that would be travelling downstream to the Churchill River system, which is already experiencing high water levels. This could increase flood peaks. More analysis is being done to understand what the impact on current downstream water flows would be if the dam were to fail.

The WSA is also going to be working with communities in area the assess low lying areas where the increase in water levels could impact their communities, and any mitigation efforts that may be needed.

–

derek.cornet@jpbg.ca

Twitter: @saskjourno