Issue of building on Leda clay in Chelsea, Quebec falls under grounds for concern

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by admin on October 20, 2010

The Editor,

Would you build your house in a landslide zone?

Given the choice, would you build your house on fragile foundations? On soil susceptible to a potentially devastating landslide? What about 50 homes, 100, more?

In Chelsea, Quebec much of our soil is Leda clay, a marine deposit left behind when the Champlain Sea receded thousands of years ago. Leda clay is a soil subtype that is inherently unstable, can suddenly liquefy and, according to Natural resources Canada, is “vulnerable to catastrophic landslides.”

It was following such a catastrophic and tragic landslide in Saint-Jude, Que., in May 2010 that I instigated my own research and discussions with experts at Carleton University into the nature of Leda clay. What I discovered is far from reassuring.

There are four factors that can specifically precipitate a landslide: riverbank erosion, heavy rainfall or snowmelt, earthquakes, and “human activities such as excavation and construction.”

The first three factors are largely beyond our control; the fourth is a matter of choice. Construction of hundreds of homes on this highly sensitive soil in the proposed Chelsea Creek and Common Ground developments is a choice.

Chelsea council seems to be making the choice to endorse these developments. In fact, it may be going one step further. At a municipal meeting scheduled for Thursday, Oct. 21, it is planning to alter a zoning bylaw that affects construction in landslide zones, the nature of which will be discussed at the meeting.

By significantly increasing housing development on Leda clay deposits, the proponents will alter the natural water drainage, disturb the stability of the soil and add mass and weight stress to the clay.

This, in turn, has the potential to dramatically increase the vulnerability of the soil to landslides on and surrounding the proposed Chelsea Creek and Common Ground developments.

Over the past 100 years there have been numerous landslides in this and the Ottawa area. Researchers say a recent increase in frequency may be due to climate changes increasing spring water levels and runoff. I would urge you to look at the research and the pictures of these local landslides and consider the consequences of disturbing this unpredictable soil.

We have a choice. Why take the risk?

Jill Burns

Chelsea, Quebec