GRCA plans to shore up Drimmie Dam

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GRCA plans to shore up Drimmie Dam to protect river users in Elora Gorge

 

 

March 09, 2009 / GRCA

 

 

The Drimmie Dam on the Grand River in Elora is in such poor shape that there is a risk of a sudden failure, which could send a wave of water roaring through the Elora Gorge.

 

Flows could jump to 12 times normal levels in just 15 minutes. A two-metre (six foot) wave would endanger anglers and kayakers at the foot of the Elora Falls. About 300 metres downstream the wave would still be about 0.8 metres (2.5 feet) high and would be a threat to all river users, including hikers and tubers. To reduce the risk, the Grand River Conservation Authority plans to shore up the dam by placing rock fill on either side of the structure. The work would be done this spring and the cost would be about $100,000. Care would be taken to minimize any impact on the environment.

 

This is an interim measure to protect public safety. The long-term future of the dam would be considered by an Environmental Assessment later this year which would examine alternatives ranging from permanent removal to replacement. An Environmental Assessment is a public process that would involve all levels of government and other agencies, as well as local residents.

 

Tentative approval for the plan was given by the GRCA’s general membership in a committee of the whole meeting on Monday, March 9. A final decision will be made by the board at a meeting on March 27. A staff recommendation that the dam be breached to lower water levels behind the dam was rejected by the board in favor of the plan to shore it up.

 

Drimmie Dam straddles the Grand River in downtown Elora, about 65 metres upstream of the Elora Falls. It is known as a “run of the river” or “low-head” dam. It was built in the late 1800s to power mills. It was acquired by the GRCA in 1984 from the Elora Mill Inn and some remedial work was done at the time to allow the mill to operate a hydroelectric generator using water from the “head pond” created by the dam.

 

However, the dam has significantly deteriorated in recent years, according to a report by Sanchez Engineering Inc. The company was hired by the GRCA in 2007 to do a dam safety assessment.

 

“Visual examination of the dam in the fall of 2007 and June 2008 confirmed that the dam is in very poor condition,” said the Sanchez report. “On the north section, pieces of the concrete have been lost along the top of the dam, which presents a jagged surface. The concrete in the south section is severely broken and water is flowing through the dam itself.”

 

“If nothing is done to repair or replace the dam, its deterioration will continue with time, the dam will fail,” said the report.

 

The report said the dam meets the conditions to be classified as a “significant hazard dam” under the draft Ontario Dam Safety Guidelines.

 

The dam is in such poor condition that there is a risk of what is known as a “sunny day” failure. That would occur when there are no unusual stresses on the dam, such as high flows or pressure from moving ice.

 

In a “sunny day” failure, flows would rise to 65 cubic metres per second (cm/s) compared to 5 cm/s on most summer days.

 

There is also a risk of dam failure associated with the spring melt, but that would not have pose as much of a safety threat because flows are already high.

 

 

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Further information: Cameron Linwood, GRCA Communications Co-ordinator

Phone: (519) 621-2763, Ext. 2251

Fax: (519) 621-4844

E-mail: [email protected]