Nanaimo postpones work on dam until 2023 in wake of study

Nanaimo and the province have agreed there’s no need to carry out construction work on the Middle Colliery Dam for at least five years.

In announcing the delay on Tuesday, the City of Nanaimo said a new study indicates that any extreme flood flows through the dam would be lower than previously estimated.

Postponing the work until at least 2023 will allow for more data to be collected from the Chase River, said a statement from the city.

The Lower and Middle Colliery dams, also called the Chase River dams, were built in 1910 and 1911 to store water for washing coal on Nanaimo’s waterfront. The dams are in the Colliery Dam Park.

Past studies found that the aging structures pose a risk to the downstream neighbourhood should they fail due to a major earthquake or rainfall.

An auxiliary spillway was built in 2016 on the Lower Dam, at a cost of about $4.4 million.

The city is now reviewing the flood risk and seismic risk for the Middle Dam.

Poul Rosen, Nanaimo senior manager of engineering, said the new analysis considers river level data that weren’t previously available.

But because it only uses a few years worth of data, it is too early to make solid predictions about the future, he said.

“However, the lower flow results suggest that years of further data collection is warranted before any significant decisions are made or any potential future work at the Middle Dam planned.”

The province and city have agreed to postpone further work on the Middle Dam until 2023, so that more data can be collected.

“The additional data gained by continuing to monitor river levels will provide more certainty of results and ensure that any future decisions on the Middle Dam can be made with confidence,” Rosen said.