Charlevoix | A dam bursts, the lake empties

When we arrive at the edge of Lake Monique, north of La Malbaie, we see two overturned rowboats, and a gaping hole in the middle of the forest, where old moldy stumps adjoin pools of mud.

Almost a month ago, a dam burst. The water from the lake rushed into the breach and dug an impressive furrow several meters deep. Below, a section of forest road was destroyed.

The retention structure has been under the responsibility of the Ministry of the Environment since 2021. It was previously orphaned, built to transform what was a wetland into a body of water to develop the land and fish for trout.

« Ce n’était probablement pas un ingénieur qui a construit ça », lance en boutade Jean Côté, professeur de génie civil à l’Université Laval et spécialiste du cycle de vie des barrages en remblai.

Par une journée froide de novembre, il accompagne – avec une classe d’étudiants – une équipe du ministère de l’Environnement venue constater les dégâts. Il a les deux pieds au bord d’un immense trou dans le sol, là où se trouvait une digue en terre d’environ 2 mètres de haut sur 20 mètres de large.

Le lac n’était ni très grand ni très profond. Et pourtant, la force de l’eau a tout emporté. « Ça montre la force de l’érosion. Ça s’est probablement vidé très rapidement », laisse-t-il tomber.

Un des aspects qui préoccupent M. Côté dans ses recherches, c’est la résilience des barrages en remblai dans un contexte de changements climatiques.

Dans le cas du lac Monique, c’est ce qui s’est produit. « Le ministère est d’avis que [la rupture] is due to significant precipitation in this area. In fact, the data […] report significant precipitation, that is to say more than 135 mm of rain in two days in the Charlevoix sector,” notes Josée Guimond, communications advisor at the Ministry of the Environment.

The work was built in 1970. During its inspection in 2021, the Ministry observed that it was covered in “debris”, and noted a “general disorder of the structure”. The condition of the section was “poor”, and the reliability of the evacuation devices was “inadequate”.

The dam was probably already weakened. Met nearby, Christophe Dandurand is the owner of the Spa Canada chalets, located between Mont Grand-Fonds and Lake Monique. He remembers that in “2016 or 2017,” “the water went over the dam,” which had to be repaired because it also served as a passage for a regional snowmobile route. This was before the Ministry took possession. “It was done in a hurry, as is often the case in Quebec,” lamented Mr. Dandurand.

Another particularity: the type of soil which fills the region, weakening the base of the dams. “When it failed, the foundation was over-dug. This is a known phenomenon in the region, whose soil is composed of easily erodible glacial deposits,” notes Michel Dolbec, Energy project director at WSP Canada.

He emphasizes that all dam owners have a duty to maintain their work in good condition. In this case, however, the risk was “low”. “The biggest loss is the outfitter who lost his lake,” he says.

Martin Dufour, owner of the Domaine Comporté outfitter since the end of 2020, where Lake Monique was located, was still scared and questioned the Ministry’s standards. “Whether it’s low capacity, or high capacity, it’s dangerous. I’m not an engineer, but I have a lesson in life. No need to be a doctor in hydrology: when you see the damage, it’s certain that if I was on the road at the wrong time, I would have been killed. And yet, it is judged to have low capacity,” he said.

He points out that his employees use this forest road every day, and he, two to three times a day.

There are hundreds, even thousands, of dams like Lake Monique all over Quebec. Whether in an urban environment or in the great outdoors. The Ministry of the Environment alone owns 930 government dams, including 391 high capacity, 263 low capacity and 276 small dams.

Even today, the Quebec government continues to “find” some. He inherits works built in the past by developers, vacationers or outfitter owners. The government has already strengthened the law to force owners to better maintain this infrastructure, but the challenge remains very great.

This year, a dam burst in Sainte-Émélie-de-l’Énergie and a protective wall failed in Baie-Saint-Paul, causing very significant damage. A few years ago, residents of Grenville-sur-la-Rouge were scared because of the risk of the Chute-Bell dam breaking. It is impossible to know if the phenomenon is increasing, since “the Ministry does not keep a list of dams that are breaking or suffering damage”.

Will Lake Monique ever be reborn? The Ministry has not yet decided the question. “A cost-benefit analysis will be carried out based on technical feasibility, the nature of the foundations, environmental impacts, environmental needs and safety issues,” notes M^me Guimond.

As for Martin Dufour, he is preparing for the worst. If the lake is abandoned, he projects losses of nearly more than $1 million. He canceled all reservations for his two cabins which now have a view of a swamp. “Since spring, it was the third bout of water. I’m confused,” he says.