Two century-old dams at Colliery Dam Park will be removed and existing lakes will be drained within the next year to eliminate a potential flooding hazard in populated areas downstream.
City officials say the Lower and Middle Colliery Dams remain stable under normal conditions, but that a significant seismic or extreme rainfall event could cause the dams to fail, potentially putting hundreds of people in Harewood at risk.
A routine dam assessment performed by the province’s Dam Safety Branch in 2010 raised initial concerns. That assessment was followed up with a more recent study that came with a recommendation to remove the dams. All other dams in the city were deemed safe.
Bill Sims, the city’s manager of water resources, said the city has moved quickly to establish a plan to drain the lakes, remove the dams and establish a community consultation process and an emergency evacuation plan.
On Tuesday morning, city officials were in Harewood visiting more than 400 homes and businesses, including John Barsby Secondary School, that might be affected by a breach.
“We’ve run a few models that indicated the areas that might be affected so we’re in the process of contacting people who fall into those potential areas,” said Sims, adding that forecasting damage would be purely speculative.
According to a city-issued map, a dam failure could affect a large portion of Harewood from Sixth Street to the north to Eighth Street in the south, and bordered by Park Avenue to the east and Howard Avenue to the west. Low-lying areas along Winchester Avenue could also flood, as would the entire channel of the Chase River down to the ocean.
Two open houses have also been scheduled to advise residents on the project. The first will take place Monday (Nov. 5) from 4-8 p.m. at the Nanaimo Aquatic Centre, the second Thursday (Nov. 8) from 4-8 p.m. at the Harewood Activity Centre.
The Lower Dam, a 14.5-metre high structure, and the Middle Dam, at 12 metres, were two of the earliest concrete structures in Nanaimo.
Both were built in 1911 and neither have any reinforcing steel.
“It’s of poor quality,” said Susan Clift, Nanaimo’s director of engineering and public works.
Both dams had upgrading in the late 1970s to comply with provincial standards, shortly after they were taken over by the City of Nanaimo after amalgamation in 1975. The dams have provided recreational opportunities, such as fishing and swimming, since then, and are inspected regularly by city officials.
The expected cost to remove the dams is about $7 million. Some of that money will come from reserves while the balance will come from short-term borrowing, which means a public referendum won’t be required (public approval is required for borrowing for a five-year term or longer).
Sims said other options existed, including further rehabilitating the dams or building new ones.
“We had some cost estimates between $20 million and $30 million for those options,” said Sims.
The council directive to remove the dams came from an in camera meeting on Oct. 22. Nanaimo Mayor John Ruttan defended the decision to go in camera to discuss the issue, saying staff and council needed to not only advise the public of the potential danger but to also announce safety procedures that needed to be established.
“It’s new information and we couldn’t just announce the risk to the public,” said Ruttan. “We also needed to come up with an emergency evacuation plan to go with that. I feel we approached this in the right manner and made the right decisions.”
Officials say the park is still safe to use, though people should avoid it and the Chase River channel in the event of an earthquake or extreme rainfall advisory.
A third dam, the Upper Colliery Dam, is considered secure and will not be removed. None of the Colliery Dams have any relationship with the city’s drinking water supply.
“They were built to service a function that no longer exists,” said Clift.
Draining the lakes will result in a much different Colliery Dam Park, currently one of Nanaimo’s most popular areas for swimming, fishing and hiking. Bridges and trails will remain, and the Chase River will be allowed to re-naturalize, with further opportunities for restoring salmon habitat. Sims said that eventually, forest will reclaim the area that is now the lake bed.
The dams were originally built by the Western Fuel Company for the purpose of storing water for washing coal at Nanaimo’s waterfront.
Initial environmental assessments of the lake beds have revealed no known contaminates.