Quebec floods: Improving flood mapping is first step in future mitigation, expert says
For the second time in three years, Quebec is in the grips of devastating spring floods.
In Sainte-Marthe-sur-le-Lac, Que., one of the hardest-hit communities, thousands were forced to leave their homes last Saturday, when a dike keeping the Lake of Two Mountains out, gave way.
Around 5,000 got out safely, but many say they lost everything in a matter of minutes.
Questions have been swirling as to what’s causing the massive spring floods and how to move forward.
Quebec Premier François Legault promised to do a post-mortem and earlier this week announced the creation of a ministerial committee to come up with a flood action plan.
Professor Pascale Biron, an expert in river dynamics at Concordia University, is calling for a more holistic approach to watersheds.
Biron argued that the provincial government bears some responsibility for the current crisis for allowing control over flood maps to go to municipalities, something she says happened in the early 2000s.
“The responsibility for flood maps was shifted to municipalities, which is not necessarily the best entity to manage this,” she said. “They have sort of a conflict of interest with property taxes and development in potentially risky zones.”
WATCH: Flooding in Ste-Marthe-sur-le-Lac
While the previous Liberal government invested over $20 million to revise flood maps following the 2017 floods, Biron said improvements are needed in how mapping is tackled.
“Right now, all our ways of mapping and managing floods is based on past events that we have known,” she said, adding that with the unpredictability of extreme weather events, it could be wise to plan for things we haven’t seen yet.
That, according to Biron, means mapping beyond the 100-year flood.
“That’s what is done in Europe,” she said. “Following major events they had in the early 2000s, they go and map events that would occur on average every 200 or 500 years, so at least they know that these zones are still at lower risk but nevertheless at risk.”
Biron also demystified the concept of the 100-year flood.
“With a 100-year flood, people think: ‘Oh well I had a 100-year flood, therefore, I have 99 years of peace ahead of me,'” she said. “That’s not how it works. A 100-year flood means you have one over a hundred, so a one per cent chance every year of being flooded or reaching that level.”
“A one per cent chance, when you think of the lottery, it’s quite high,” she said, adding that in other countries the 100-year flood mark is considered a medium risk, whereas here it’s almost considered an act of God.
WATCH: Quick action by soldiers and municipal workers averts flooding disaster in Pierrefonds
She also cautioned against being lulled into a false sense of security when it comes to dikes.
“People feel safe behind a dike and if you talked to people following Katrina, they were very surprised and they were also protected by a dike — a huge dike,” she said. “So it is a problem, that feeling of being safe and realizing it remains a risk zone.”
For Biron, part of the solution, once again comes down to how we map flood risks.
“France for example, when they map flood risk, they consider dikes as being transparent,” she said. “They still map these zones as being high risk, because, as we have seen in Sainte-Marthe-sur-le-Lac, if it goes above the dike or if the dike is breached, then it’s really a disaster. It’s so fast, people have no time really to react.”
In addition to better mapping, Biron said we need to take into account how we build our cities and how the land is managed.
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