| S.O.S. Improving Levels and Habitat Proposed Riffle Structures Along The Seine River By Harold Thwaites and Jules Legal (SOS Web page 1997) During the past year an SOS sub-committee has been studying the idea of constructing a series of small, "low-tech" riffles along the Seine. It is encouraging that the City's Task Force has independently proposed this idea as a possible strategy for maintaining water levels in their Hydrology Report. The riffles would consist of fieldstone piled across the Seine at selected locations between the floodway and the Red River. Their design would mimic natural riffles, creating a backwater effect that protects upstream banks from erosion while providing important spawning habitat for fish. |
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| Each riffle would be built so it is in the backwater of the next riffle. This would work in harmony with natural sedimentation and erosion by the river, minimizing erosion of the riffle and relying on nature's tendency to build up the river bed at certain points. |
| In the long term, stabilizing the stream bed should help reduce erosion of the riverbank. During high flows, water would simply pass over the top of the low profile riffle. The structures would not worsen or contribute to flooding since maximum flows are controlled by the siphon spillway at the floodway. Nor would they block all flow during low water periods. |
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However, water held back when it is abundant, usually in spring and after heavy rains, would be released at a slower and more sustainable rate. This particular riffle had been build on Sturgeon Creek a few years ago and is functioning well. |
| Benefits from a system of riffles include: Improved fish habitat and associated algae and mosquito control Improved habitat for water fowl, turtles and all aquatic animals Enhanced water quality through increased aeration and decreased fluctuation of levels Promotion of a more diversified fauna Improved recreational qualities for canoeing and walking Reduced erosion and bank failures |
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This riffle below was built on the Wilson River in Manitoba and has shown beneficial effects related to river habitat and bank erosion. |
| There is no question that past interventions have had disastrous consequences for our beautiful little river. Sadly we must face the reality that we can never undo all the damage. However, we believe that at least some of the abuse can be mitigated by the relatively passive, judicious use of weirs. |
| After seven years of planning and obtaining all of the necessary approvals from the civic, provincial and federal governments, S.O.S. is hoping to begin construction in the winter of 2002-2003. |