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Ronan's report


Tuesday May 3rd 2011

I'm a member of a small technical group in Alberta that works on major fish passage issues across the province. Most of the issues we look at are related to damn retrofits. I thought I'd share a couple of simple (not) solutions to some of the structures we have here that are blocking trout movements upstream.

First off, I think the best solution would be to get rid of a damn completely. But there are problems with that... you might lose an important tailwater, you might lose over-wintering in the reservoir, and the change in elevation from the new river bed under the reservoir and the river downstream might just be to much to effectively recreate the river ($$$).

One of the ways that we've constructed in Alberta is a simple (not really) rocky bi-pass channel. For this type of fish passage structure you need a lot of adjacent property, enough that you can create a channel long enough to minimize the slope. We also have the added concern of maintaining the channel steep enough that debris doesn't clog it, and flat enough so that we can use a substrate smaller than Volkswagens in it. The key is to create a "river" around the dam so that the reservoir acts like a big pool (the river is still backed up), and the river carries enough flow for fish to get by (gate operated to control in some situations).
A major consideration for this type of structure is ensuring that there is "attraction flow" so fish can find the entrance to the channel. Many of our failed structures don't work only because fish can't find them.

Another way that is much more expensive, but looks damn good, is to back water up over the structure. This only works for low dams and weirs. How this works is that you build additional low dams downstream of the original. These new dams are often built like riffles (or step pools) and have no jump or a very small jump that fish can get over. Enough of these step pools and fish can hop their way up them and over the original dam... kind of like putting a step ladder against a fence.
The struggle here is actually constructing in the river channel, and designing something that will stay during high flows, and that will allow fish to get up. There is a great example of this type of project being constructed in Calgary, right now. The project was more designed for kayak and boater safety, but will be good for the brown and rainbow trout heading upstream.

So the next time you see a dam or weir, take a closer look... there may be a chance for fish to pass.

As an aside, congratulations to our new governing party in Canada. With a majority win (only 40% of the vote) you now have the power to do whatever you want for the next 4 years... use us gently.

Cheers, Harps


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