Dynamic Coulee Landscape

The coulee environment is more fragile than you might expect, despite it’s ‘timeless’ look.

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Late fall in the coulee environment – dry slopes and wet river valley. Cottonwood Park, along the Oldman River – home of the City’s rattlesnake hibernaculum (Photo: S. Boon)

We had a skiff of snow a week ago (a far cry from the blizzard we had two days ago!), which was perfect for illuminating the topography of the coulee slopes. Particularly this slope failure, which I’ve been watching for a few years now.

Slope failures in action (Photo: S. Boon)

Coulees are notoriously unstable, which is ironic given the amount of development that happens on them around here.

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Housing development in the coulee region. Notice the well-watered greenspace relative to the brown and dry coulees (Photo: Avonlea Homes)

Their instability stems largely from their makeup, which is mainly glacial tills similar to the sediments in the image below.

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A bank failure along the Belly River, in Moon River Estates west of Lethbridge. This is different than the coulee failures, but shows the glacial till that both landforms contain. (Photo: S. Boon)

The biggest driver of coulee instability is water. Whether it’s from a rainy spring or just from homeowners overwatering their yards, water turns the till into a slurry that can’t maintain its structure. It will slump downslope with gravity, leaving a changed landscape in its wake. Many houses in town that back onto the coulees – for the view, of course – lose parts of their backyard every year. Public pathways in the river valley are often covered over by slope failures and slumps. One of our main roads is inundated with eroded coulee material during heavy rainstorms.

It’s ironic that we look forward to rain and snowfall as necessary moisture to drive agriculture in the region, but that same moisture negatively impacts people living and recreating in the river valley. The best way to live within this dynamic landscape requires a major shift in our behaviour and mindset. For one thing, summer watering could be restricted to prevent overwatering, and residents could take on the challenges of xeriscaping and recognize the normalcy of a brown summer lawn – similar to residents in coastal Victoria. Additionally, development setbacks could be created to minimize the direct impact of residential housing on the coulee environment.

But as long as people want their green lawns in a semi-arid climate, and their fabulous views over the river valley, not much will change. Until it’s their house sliding down into the coulee bottom – I predict huge changes then. :)

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