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Revised Flood Hazard Map allows Village of Lebret to manage future land development and protect public safety

The Village of Lebret is located 70 kilometres northeast of Regina, along Mission Lake in the picturesque Qu’Appelle Valley. Popular with tourists and cottage owners, Lebret is also home to residents and commercial developments. Heavy spring runoffs present an annual flooding threat to communities in the valley. High water levels and accompanying wave effects (wave setup and run-up) can present a significant flood risk. The most recent flood occurred in 2011 - a 1:100-year flood event. 

Lebret had a flood hazard map in place, developed by the provincial Water Security Agency (WSA) in 2013 to mitigate risk to citizens and property. The map defines and regulates land which cannot be developed (the floodway) and which can be developed, provided that certain measures are taken (the flood fringe). The result was only a relatively small flood fringe area within the Village’s jurisdiction could ever be developed.

Although appropriate methods were used at the time for flood hazard mapping, the Village felt the map needed updating to better delineate the flood fringe, which would protect public safety and property, and could allow for greater land development. In 2021, Lebret engaged Associated Engineering to develop a revised flood hazard plan using today’s advanced analysis and methodologies. 

Using coastal modelling techniques and wave analysis expertise supported developing a reliable flood hazard map

The prime project challenge was the tight timeline. The plan required a detailed bathymetric survey of the lake depths to be completed using a boat in November 2021, before lake freeze-up. All work, which was half funded by the WSA, had to be completed by March 31. The team had to proactively plan, quickly act, acquire information, and identify possible solutions for analysis without delay. The project required a collaborative relationship between the Village of Lebret and the WSA (a key regulatory stakeholder and funding agent). The timeline required that the regulatory approval process be streamlined, so the Associated Engineering team obtained buy-in on the process and results at every project meeting.

To complete the work, we used bathymetric readings, a LiDAR survey, wind and wave analysis, and the 1:100 and 1:500-year flood levels from the WSA. Working in collaboration with WSA, we adapted advanced coastal modelling techniques and leveraged our expertise in wave analysis to develop detailed, reliable flood hazard mapping.

Project Manager, Daryl Brown, shares, “To our knowledge, adoption of coastal technology and models for flood mapping – combining wind and wave action – has not previously been undertaken in the Prairies. This process was key to completing the work on time, with the desired level of accuracy and reliability. This innovative model where wave action is a consideration for public safety and property development can also be applied to other Prairie communities.”

Completed on time and on budget, the new flood hazard map provides Lebret with assurance of the areas that the community can securely develop, while protecting public safety.

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