Establishing an enhanced emergency warning system to address public safety concerns for the lower and middle Colliery dams over the fall and winter will be the main recommendation in a staff report coming before Nanaimo council on Monday.
The proposal will include active monitoring of water levels at the two dams over the coming months, plus the installation of signage and sirens throughout the city to alert the public in the event that a risk of failure of the dams becomes imminent.
Engineering and public works director Susan Clift said the plan amounts to an enhanced version of a public safety plan launched last October, after the city had originally approved removing the structures entirely. The decision was based off engineering reports that indicated the dams could fail during an earthquake or flood event.
Colliery Dam park users fought against the move, launching the Colliery Dams Preservation Society and a campaign to have the city reverse the decision and examine other options for the historic structures.
The municipality is currently in talks with the Snuneymuxw First Nation and CDPS to find a common path forward. In the short term, however, the province has said the city must implement risk reduction measures if the dams are left standing over the winter.
An inundation study commissioned in 2012, indicated up to 150 people downstream could die if the dams break. The B.C. Dam Safety Section wrote to the Daily News earlier this year and stated that the dams had to be drained in order to stay in place over the winter. But Clift said that doing so would be costly and unfeasible. She also acknowledged the early warning system proposed by city staff would not reduce the risk of a dam failure.
"The chances of the dams breaching are the same, as are the consequences," she said. "It's really just being better prepared."
Development director Toby Seward authored the report, and said the measures would cost between $50,000 and $100,000.
Clift said the Dam Safety Section will be informed of the proposal.
"I don't think it changes a lot from their position," she said. "We are still in a situation where they have concerns and they want us to deal with them."
The city has posted a review of risk mitigation options prepared by consulting firm Klohn Crippen Berger, author of the inundation study.
One of the options includes lowering the dams spillways, which would reduce stored water contained within the structures by 50 per cent. However, KCB estimates the measure would cost in the order of $2 million, and also pointed out that it would involve destroying the original spillway structures, which carry a historic value.
In a separate document posted online, KCB estimated pumping water out of the dams over the winter could cost more than $554,000 per month per dam.
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