In accepting this project, Acres International and its partners Acres and Associated Environmental Limited (A&A) knew that there would be widespread concern in the surrounding communities at the idea of change on the Big East River, which is situated in a widely used waterway park. They therefore adopted a well-structured process which would generate no surprises for the community, and would consider every possible alternative.
A precedent-setting procedure
| Taking a draft of new MNR dam commissioning guidelines as a starting point, Acres and A&A set about applying the MNR's Class Environmental Assessment process to the project. In addition to social concerns, over 60 different environmental indicators were examined. The complex evaluation process was simplified by developing a scoring system.
The final result was a separate solution for each of the two dams. The release of sediment from behind the Distress Dam was avoided by converting the 5-metre |
 Left to right: Nick Paroschy,MNR, C. Richard Donnelly and Paul Holmes of Acres, Bob Bergman, MNR, Larry King, Acres and Mike Phillips, MNR |
high structure into an overflow weir. This solution retained the upstream reservoir, a favorite location for canoeing, fishing, and observation of wildlife. Water levels would be maintained during the dry season, while spring flooding would be allowed to rejuvenate adjoining wetland habitats.
At Finlayson Dam, hydrostatic studies revealed that although removal of the dam, the preferred solution, would release large quantities of sediment, it would quickly be settled by the river itself. Analysis of flows, in combination with assessment of aerial photos of the river taken before the dams were built, established the fact that a natural silt trap existed downstream from the dam. Hydraulic modeling supported the belief that even under flood conditions silt would not be transported beyond this natural basin; a trial drawdown of the reservoir confirmed that this prediction was correct.
Construction - which included many procedures to protect and stabilize side slopes - began in June 2000 and was completed on schedule in October of the same year. Environmental monitoring by A&A confirmed Acres assessments of the sediment transport scenario, and that one major objective was already in process of achievement - the brook trout and other cool water species were returning to the former Finlayson reservoir.
At the Annual General Meeting of Consulting Engineers of Ontario held in Alliston on May 23, 2003, Acres received the Willis Chipman Award, the highest distinction in Ontario's consulting engineering industry, for decommissioning of the Distress and Finlayson dams.
For further information please contact:
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Rick Donnelly, Division Manager, Hydropower Ontario/Quebec Acres International 905-374-5200 rdonnelly@acres.com
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For a detailed four-page description of this project, downloadable in Adobe Acrobat format, click here.