gordon.dewis.ca - Random musings from Gordon


Should they move the houses in Gatineau that were evacuated? No, or at least not before checking for leda clay.

April 25, 2008 @ 00:13 By: gordon Category: Current affairs

There’s a group of houses in Gatineau that were built at the foot of a hill where they shouldn’t have been built.  Somehow the builder(s) obtained permission where it now appears older geologic assessment reports said nothing should be built.  Hydro workers inspecting something at the top of the hill noticed a large crack in the ground and alerted the province who immediately ordered the evacuation of the homes.  Since then it’s been determined that they can’t ever be reoccupied.

Hindsight is 20-20, isn’t it?

So, the home owners who bought the houses in good faith are now faced with the prospect of losing their homes.  The Quebec government is offering up to $100,000 in compensation.  The City of Gatineau is offering an additional $75,000, but only if the owners agree to give up their right to sue.  (For reference, at least one of the homes was reportedly worth almost twice that total amount.)

Basically, the home owners are screwed because someone didn’t pay attention to a map that said “don’t build here” or something similar.

CBC reported on Thursday that the City is looking for lots that the houses can be moved to.  Now, moving a building is a non-trivial task that can costs thousands of dollars.

I haven’t seen an in-depth discussion of the geology in that area in any of the reports, but chances are it’s similar to what’s found on the Ontario side of the Ottawa River: leda clay.

Leda clay is made up of clay- and silt-sized particles that were eroded from bedrock, washed into the Champlain Sea a few thousand years ago and deposited on the bottom.  It retains a fairly high amount of water in it, so it can quickly liquefy if it’s disturbed.  This is nothing new and Natural Resources Canada’s website has a map showing where this has happened in the Ottawa area.  You’ll notice there are a lot of red dots on the Quebec side of the Ottawa River all around where these homes are.

If you’ve lived here for the last 15 years or so, you may recall the Lemieux Landslide east of Ottawa on June 20, 1993.  The town of Lemieux was located on the edge of the South Nation River and as a result of studies of a large landslide that occurred in 1971, the town was abandoned in 1991.  Two years later, another landslide occurred right next to the townsite and 17 hectares of land basically turned to soup and flowed away.

I visited the location of the landslide shortly after it took place while heading to the Eastern Townships with a bunch of geography classmates.  You could walk around on the mud and it would support you.  But stand in one spot while someone tapped the ground next to your feet and you would suddenly sink almost a foot as the clay liquefied.  Very cool to watch, but rather annoying if you were the person trying to extricate your boot.

I mention this because if the houses are located at the foot of a hill of leda clay, the process of removing the houses could be enough to trigger liquefaction.  When it happens there’s usually little warning, so the risk of people being killed could be quite high.

Hopefully they’ll be a little more diligent in their soil assessments before traipsing in and removing the houses, though the City and Province should probably admit that they screwed up and provide these families full compensation as opposed to what they’re offering.

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