Further Work at Middle Colliery Dam Postponed

Additional river flow data will support better analysis of risk

The City of Nanaimo will postpone further work on the Middle Colliery Dam until at least 2023 while more data is collected and analyzed on the Chase River. The completion of the auxiliary spillway at the Lower Colliery Dam in 2016 partially addressed the outstanding requirements from the Provincial Dam Safety Section Order. A second part of the order required the City to address safety risks at the Middle Colliery Dam. The City undertook a review of both flood risk and seismic risk for the Middle Dam. Although not yet definitive, this new study suggests that the extreme flood flows through the Middle Dam are lower than previously estimated.

“This new analysis takes advantage of river level data that wasn't previously available," Poul Rosen, Senior Manager of Engineering said, "The additional data gained by continuing to monitor river levels will provide more certainty of the results and ensure that any future decisions on the Middle Dam can be made with confidence."

The study used several years worth of river level data collected as part of the early warning system installed in 2014 to set a new model and make predictions about extreme flood events. Additionally, a comprehensive review of watersheds in the region and comparison of respective runoff rates was undertaken confirming the findings. Together, this new information provided the basis for deferring further risk assessment until 2023.

"Since this new model only uses a few years worth of data, it is not possible to make definitive predictions about extreme events," added Poul Rosen, "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."

“This doesn't close the book on the Colliery Dams issue, but it does provide a way forward that will rebuild confidence and demonstrates that the City is committed to working with the community," CAO, Tracy Samra explained, "I would like to thank all those dedicated individuals who reached out and worked with us on this file over the years.”

As a result of this study, the City and the Province have agreed the strategy for the Middle Dam going forward will be to collect additional flow data and update the hydrology model in 2022. For more information on the Colliery Dams visit: www.nanaimo.ca/goto/dams



Sheila Gurrie
City Clerk
City of Nanaimo

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