Friday, December 6, 2013

"Floods come off landscapes, not rivers"

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"Floods come off landscapes, not rivers"

Kevin Van Tighem writes:

I've learned a bit more about this. Calgary: brace yourself for an inundation the likes of which you have never imagined in your worst dreams when (not if) this proposed dam fails.

A dam of this sort has never been placed on a live river before. Even in the seasonal desert streams where they've been tried, there have been many failures. No river hydrologists were involved in the scheme before it was announced. They plan to put the whole river through a culvert (a culvert!!) that will be at least half a km long.

The entire river here is a shifting floodplain of loose gravel. Upstream are forests and slopes that will die and collapse into the floodwaters. In the first or second big flood, the culvert will fill with sediment and be plugged by flotsam.

That's what culverts do during floods - all those track-hoes we've been seeing across southern Alberta this year have been replacing washed-out culverts. Once the culvert plugs, the earth-fill dam will fill, water will spill over the top, and then the floodwaters will wash it away.

The whole temporary reservoir will spill down the river along with most of the dam's gravel and dirt, taking out all of Bragg Creek and the bridges and trophy homes downstream to the Glenmore Reservoir which will (this being a flood event) already be full.

The unprecedented pulse of water and sediment will breach the century-old Glenmore Dam. The resulting flood of water and sediment will likely destroy downtown Calgary.

So - this reckless experiment in flood "mitigation" will not only ruin a beautiful mountain valley and the native fishes and wildlife that rely in that valley, while costing us hundreds of millions of dollars, it will inevitably produce the flood we all fear the most and hope to avoid.

But engineering companies owned by political donors stand to earn windfall public funds and politicians will get re-elected on the boast that they "did something" about flooding, which makes this dam almost politically inevitable....unless Albertans demand the lunacy end and be replaced by more effective solutions (albeit with less ribbon-cutting appeal for politicians).

Those solutions could include restoring beaver populations, reclaiming off-road vehicle damage, replacing clearcut logging with selective cutting, and building small check-dams in coulees and draws that are usually dry except during flood season.

Healthy landscape stuff in other words - because floods come off landscapes, not rivers.

I hate posts that end with "please share." But please share. We don't need to destroy our rivers to reduce flood damage - in fact if we destroy those rivers we will get far worse flooding than ever before.

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