The 1971 landslide near Casselman destroyed about 70 acres of land. (Photo courtesy of South Nation Conservation).

Heavy rain has South Nation Conservation on alert for landslides

Soaked, drenched, dripping: all words that come to mind to describe the continuous barrage of rain in the region.

Some in the weather game are still cheering for a sog-fest. At the time of writing, Ottawah has had 249.8 mm of rain in July. An extra half-millimetre would make this the rainiest July in 140 years.

Potential for serious consequences

While breaking records is admirable—though debatable when it comes to rainfall—all this precipitation has Mathieu Leblanc on alert for landslides. As the head of planning for South Nation Conservation, he and his team are keeping an eye and ear out for any reports of land fissures and cracking near the bank of the Nation River.

At The Nation Municipality’s council meeting on July 24, Leblanc presented a brief history of landslides in the region, most notably the 1971 landslide near Casselman, which occured in a spurt of only 20 minutes and affected about 70 acres of land.

Leblanc highlighted the bank stretching between Casselman and Lemieux is most at-risk due to its sensitive clay. In 1993, Lemieux had a significant landslide as well. According to Leblanc, in 1994 analysts said based on the data, “A major landslide could happen at any moment.”

Since then, using LiDAR technologies, SNC has mapped about 15 other landslide scars in the zone, which counts 26 residences and 41 secondary structures like garages.

An aerial shot of the Lemieux landslide in 1993. (Photo courtesy of South Nation Conservation).

With this year’s rain, Leblanc said he was a little nervous during the spring, and the organization is staying vigilant.

“We want to work more closely with municipalities and residents to reduce the risks associated to (landslides),” he said.

“People sometimes think watercourses are fixed systems,” he said, “but they’re not, they’re always moving.”

Water is constantly carving corners and eating away at banks. Cracks, very soft soil, and depressions in land are all things he said residents near the bank should be on the lookout for regularly. And if they do see something to call SNC right away so it can assess, and hopefully curtail, any serious damage.