The Drimmie Dam on the Grand River in Elora is in such poor shape there is a risk of 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 if the dam suddenly failed, Assistant Chief Administrative Officer Joe Farwell said at a press conference beside the dam on Monday.
The GRCA used computer models and determined that a six foot wave could endanger anglers and kayakers at the foot of the Elora falls. About 300 metres downstream the wave would still be about 2.5 feet high and would be a threat to all river users.
Engineers recommended that the dam be breached, which means placing holes in it to reduce the back water pond above the dam, which is six feet high.
However, the GRCA committee of the whole voted against that option earlier in the day.
Instead, to reduce the risk, the committee recommended the dam be shored by placing rock fill on either side of the structure. Farwell said the work would be done this spring and the cost would be about $100,000.
He said the rocks could be moved into the river from the south side and then placed with heavy machinery.
Farewell told Centre Wellington council at its meeting Monday night the dam simply no longer meets the Ontario dam safety guidelines. It was built over 100 years ago for use as power for the Drimmie Feed Mill. It now provides power for the Elora Mill Inn, and Farwell said that too is a consideration in what to do with the dam. He said it is possible the GRCA may move to rebuild it at some point.
That prompted councillor Fred Morris to ask if the top of the dam could become a pedestrian bridge. That would replace the bridge that was removed for safety reasons several years ago.
Farwell said if that proposal came from the public meetings in the future, “There’s no reason we couldn’t look at that.”
However, he added it might mean a partnership that includes Centre Wellington. The costs for the current dam repairs will be divided between the GRCA and the province.
Farwell said a new dam would cost about $1.2-million, and any cash the municipality could provide would be welcome.
Councillor Shawn Watters, who sits on the GRCA board of directors representing Centre Wellington, asked how soon that work could be “project ready.”
He was thinking of federal and provincial grant programs for infrastructure, but noted that the environmental assessment takes time.
Mayor Joanne Ross-Zuj said Premier Dalton McGuinty has promised to removed some red tape for environmental assessments, some of which have taken years. The province has done nothing on that to date.
Farwell said he hopes that the environmental assessment and work can be done within two years.
He also gave council a safety presentation. He said when there are heavy flows in the river, as they are currently, there is not nearly as much danger to the public as a “sunny day” event. If the dam were to break in the summer during low flows, the six feet of water behind it would sweep downstream and endanger anglers, tubers, and kayakers. Farwell noted that even running through the narrow gorge the water would be about 2.5-feet high until it leveled out in the flats.
He added that removing the backwater would allow the GRCA to control flooding better, and that would protect shops on the Boardwalk on Mill Street, which often get flooded when the water rises too high too quickly.
The long-term future of the dam will be considered by an environmental assessment later this year that would examine alternatives ranging from permanent removal to replacement.
Farwell said the condition of the dam was discovered during normal checks on it by an engineering firm. He said the committee was reluctant to simply breach the dam because there had been no public consultation. The GRCA had planned to meet with business owners on Tuesday to inform them of the situation, and
Farwell said at council there will be further public consultation during the environmental assessment, particularly if there is a chance the dam will be removed.
For Mark Phillips, the manager at the Elora Mill Inn, the decision to stabilize the dam was a good one.
The mill generates its own power, 140 kilowatts per hour, with water from the dam, and also sells some back to the grid, but that depends on the time of year. When water is low, there is little hydro generation.
But Phillips said, “We’re very excited they’ve decided to shore up the dam. He said the issue is not only power for the mill, but an esthetic one. He said people enjoy the pond and he hopes it helps keep people coming back to the community.
“That’s the draw,” he said of the river.
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 March 9. A final decision will be made by the board at a meeting on March 27.
The Drimmie Dam straddles the Grand River in downtown Elora, about 65 metres upstream of the Elora Falls (near the Elora Mill). 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.
Sanchez Engineering Inc. 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.
Farwell also told council that the GRCA is considering placing signs downstream of the dam to warn people of possible hazards this summer.
