Nanaimo’s 10 dams all lie on seismic fault lines.
That tidbit of information drew a nervous chuckle from city council members when a review of local dam safety was presented at a governance and priorities meeting Monday, March 11.
The City of Nanaimo is in the midst of a provincially mandated 10-year dam safety review, and this week’s presentation was a refresher for council on the city’s obligations and responsibilities as a dam owner.
Nanaimo owns 10 dams, the largest of which, Jump Creek and South Fork, are the city’s water supply reservoirs. Old Reservoir No. 1 and Witchcraft Lake are both partially decommissioned and Westwood Lake, old Harewood, McGregor Creek, and Colliery Dam Park’s lower and middle dams form lakes for public recreation.
All dams in B.C. have hazard classifications, ranging from ‘low’ to ‘extreme,’ identifying the impact, should they fail, on infrastructure, the environment and potential loss of life.
Mike Squire, city water resources manager, said a seismic study on the Jump Creek dam, built in 1931, is in the works.
“You’ll see in the capital plan, several years from now we’re going to be looking at a seismic study and an upgrade for that,” Squire said. “It’s on a fault line. Ironically … there’s a minor fault line that runs west to east on Vancouver Island … If you line up all those fault lines, that’s where all our dams are. We’ll be looking at that in the future.”
But of more immediate concern and carrying a high hazard rating is middle colliery dam in Colliery Dam Park.
Dave Bonin, senior hydro-technical engineer with Hatch Ltd. consulting engineering and project implementation firm, said a hydrology analysis on the dam has been performed, a dam safety review is coming, and a seismic analysis will also have to be done on that dam and on several others in Nanaimo.
“We are majorly concerned about that middle colliery dam because it has been found to be susceptible to seismic and has been out of compliance with the regulation for a while,” he said.
Bonin said, as a dam safety engineer “I really like this dam, even from an aesthetic point of view” noting the dam’s recreational, cultural and historic value, but also said the structure has its challenges. Some remediation work to the spillway and dam was carried out in 2016, but Bonin said there is crumbling concrete and exposed rebar under the bridge crossing the spillway, which itself is undersized and in an advanced state of deterioration.
“The regulator also knows this and has been pushing us really had to try and address these issues for a number of years … this, until recently, was identified as the most risky dam in the province and fortunately some of the work we did got it downgraded a little bit, but it’s still not technically in compliance,” he said.
A dam safety review will be complete in the fall which will help form plans to best carry out repairs.
“Fortunately, my structural engineer is pretty optimistic about being able to save most of the dam and just do a lot of repairs to it and basically, hopefully, keep it from looking much different than it is right now,” Bonin said.
Coun. Janice Perrino asked if there was a cost estimate for the repairs, but Bonin said there isn’t because it still hasn’t been decided if the best course of action will be to widen the spillway or raise the dam to increase its capacity. The extent of seismic remediation work needed is also still to be determined. He said he expects cost estimates will be available in the fall.
Bill Sims, the city’s general manager of engineering and public works, said the work currently being done stems from a written order from the government. In an e-mail to the News Bulletin, he said the province is satisfied the city is “pursuing our obligations in a timely manner and so haven’t provided a hard deadline.”
