Experts in landslides asked more than ever

In the early hours of July 16, Thomas Fournier woke up to answer an emergency call. An imposing landslide had occurred in Saint-Thuribe in Portneuf, and public security needed its recommendations.

The idea is that we may have a situation that is dangerous for people and it is necessary to decide quickly if there are measures to be taken to ensure the safety of the premisesexplains the Coordinator of Emergency Expertise Requests within the team of field movements of the Ministry of Transport and Sustainable Mobility (MTMD).

He observed some photos, collected the information from the first respondents, and consulted the vast database held by the Ministry of Transport. Note: the problem is major. A team is deployed on the field a few hours later.

When a landslide occurs, it remains a site that can remain dangerous for a few hours, a few days and even a few weekshe illustrates.

His team, which has 15 people in the MTMDis called upon to answer during large shifts, but also smaller. They assess the potential impact of soil movements.

Twice as many requests

Between 2005 and 2016, the team dealt an average of 125 requests for technical assistance linked to field movements per year. Since 2017, they have been processing 268 files per year, on average. Following the passage of the remains of the Debby storm in August 2024, the team processed 250 requests.

According to the team’s coordinator, the engineer Catherine Thibault, it is very rare that two big shifts occur the same year, especially in a inhabited environment. The frequent periods of heavy rain largely explain this increase.

Typically, the landslides are more numerous in the spring, because it rains, the melting of the snow cover brings water to the soils, so typically we had more requests, but now we have a little distributed peaks in the year.

The geological history of Quebec, with its clay soils deposited by old seas and then faded with their salt by rainwater, makes certain parts of the territory conducive to landslides. The events of Saint-Thuribe and Sainte-Monique this year, or the deadly shifts of Saint-Jude in 2010 and Saint-Jean-de-Vianney in 1971 are proof.

The work of the team in risk management risk management is recognized across the country. In Canada, Quebec is the province or it is the most developed, then I would even add that the practices we do in Quebec, it is internationally recognizedshe welcomes herself.

The team’s work goes far beyond responding to emergencies. It proceeds to the cartography of the territory to identify the sites conducive to landslides and, in certain cases, offers prevention work. The team also does research and offers training related to soil movements.

Half of the shifts caused by humans

A landslide occurs when the balance of an embankment is broken, explains Catherine Thibault. For example, when the top is overloaded with a backfill or an outstanding swimming pool, or that you dig your base.

To avoid such situations, his team develops, in close collaboration with geomaticians, cards which it provides to municipalities and MRC so that they can erect a normative framework. The team also performs inspections to ensure that the most conducive sites do not show warning signs of landslides.

People think that because they are in an area of constraint relating to landslides, there will be a landslide, inevitably, with them. But this is not the case! Specifies Rémi Mompin, engineer and the coordinator of these activities within the team. He adds that geotechnical analyzes allow you to have the right time compared to the activities that are safe.

Since 2006, Quebec has carried out around thirty prevention work representing around $ 100 million.

Revolutionary technology

For ten years, technology Lidar revolutionized cartography, explains Rémi Mompin. Planes with this tool sweep the territory as a scanner. The relief under vegetation and buildings is detected and old landslides, including those that could have occurred hundreds of years ago, are identified.

The past is the guarantor of the futurehe said.

Move the slide to see the cartography made from data Lidar.

The Saint-Thuribe region was known to be conducive to large shifts. At the end of the 19th century, one of 4 km² occurred in Saint-Alban. The sector was the subject of a cartography about forty years ago, but the team intends to redo it with modern tools.

The mapping of the 80s was good with the tools of the time, but they did not have Lidar, so it means that the sloping grounds that had been identified [ à risque] at the time were more or less precise.

A more modern cartography would not have made it possible to prevent the shift of Saint-Thuribe, however, says Rémi Mompin.

Still unstable

Several weeks after the shift which took a house (but no life) in Saint-Thuribe, the floors are still unstable, believes Thomas Fournier. In the days following the shifts, it was too dangerous for specialists to approach the crevasse. They then robbed drones to take information.

Even we, when we send teams on the ground, we know a little better the danger, we know what we are dealing with, but in the case of Saint-Thuribe, our team did not approach the unstable walls. This is where the use of the drone is very useful.

Like the Lidar did it for cartography, the drone has revolutionized the field approachhe explains. Previously, the team could put a full day to walk the circumference and get an idea Large shifts. Now in a few minutes the extent of a crevasse can be observed from the air, and even the walls can be inspected safely.

For him, his work is very rewarding. It is satisfactory to know that our impact, our recommendations, our interventions have made it possible to protect goods, infrastructure, and people toohe said.

His team has work to do, because the shifts of Saint-Thuribe and Saint-Monique give them material to study to continue to deepen their knowledge and expertise.