Seepage found at new Colliery dam spillway

NANAIMO – city waiting on advice from engineers to determine whether problem exists.

Leakage at Colliery Dam Park’s new auxiliary spillway isn’t a concern at this point, according to Geoff Goodall, city director of engineering and public works.

Nanaimo’s auxiliary spillway, a solution to potential safety hazards at the lower Colliery dam, has seepage along the concrete and water is trickling out of the rip rap toward Harewood Creek.

The sight prompted Colliery Dam Park Preservation Society representatives to send a letter to the city to get answers. Roblyn Hunter, director at large with the society, said it could be perfectly normal and expected, but she doesn’t know. Jeff Solomon, also with the society, said the major concern is any potential of lower water volume at the lake during its high recreational season.

Goodall told the News Bulletin concrete structures like this one often have leakage and the city has been monitoring it. Leaks have reduced a ‘fair bit’, but some seepage persists, he said, adding often it seals on its own but the city has techniques it can do if it doesn’t. Seepage does not affect the integrity of the structure, according to Goodall.

Groundwater is also seeping underneath the structure, which has drainage to collect water and divert it out the bottom side of the spillway. Goodall said the city has gone back to its engineers Golder Associates with the seepage problem and are waiting for comment on whether it’s unexpected or normal for the structure.

Goodall has his theories. He said the water could be moving sidewalks underneath the structure. On whether the water is from the dam leaking as a result of building the structure, he said it could be.

“When you look at the elevation difference between where the water is coming up and the top surface water in the reservoir, it’s possible that some of the water is coming underneath in the soil layer that’s underneath the dam structure,” he said, although adding it could be groundwater in the area also influenced by the level of water in the reservoir.

The city expects an update from engineers early next week.

Nanaimo News Bulletin