Sewage island: $26M flood-proofing aims to protect water-treatment plant

London is building an island fortress of sorts to ensure residents still can flush their toilets as climate change makes Thames River floods more common and dangerous threats.

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Out of sight of most Londoners on the Thames River’s main branch west of the forks, construction crews are circling the city’s largest sewage treatment plant in Greenway Park with massive steel sheets to protect it from floods.

The 750 sheets, averaging almost 10-meters long and 9.5-millimetres thick, are being driven into existing raised dirt berms surrounding the plant in a $26-million project to effectively turn the massive complex into an island when the river floods.

All the plants are in low-lying – and typically flood-prone – areas next to the river, said Kirby Oudekerk, the city’s sewage treatment operations division manager. “(With) the expected increase in the frequency of high-intensity events, that (flood) risk just gets worse and worse over the years.”

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Without the new protection, a flooding Thames could flood the plant, perhaps closing it for a few days with an annoying few centimeters of water, damaging the treatment equipment, or possibly putting the plant out of commission for weeks or months.

The Greenway plant, one of five in the city, processes 60 per cent of the city’s wastewater and processes solid waste for all five plants. Oudekerk estimates the plant treats an average of 120 million liters of sewage a day – and that’s the kicker.

“That’s the amount that would be going in (the Thames), either untreated or only partially treated, until we could get this entire plant back up and running, which would not happen overnight,” he said.

“The potential impact of that far exceeds anything that we’ve seen before in any other aspect of our business.”

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The plants typically discharge treated water by gravity, which is why they’re close to the river despite the flood risk. But that means high flows on the Thames could prevent treated water escaping, flooding the plant from the inside, Oudekerk adds.

To address that, the project will install a pumping station to keep discharge going even during a flood. Construction likely will last into 2027.

Ward 7 Coun. Corrine Rahman chairs council’s infrastructure and corporate services committee, which deals with city roads, sewer, water, and other assets. For her, the project is about protecting one of London’s most precious assets and reducing the risk of major problems, like Calgary’s huge summer water main break that led to weeks of water-use limits.

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“We have to ensure that we have the ability to treat wastewater effectively, and for that reason, we have to look at mitigations,” she said. “What we’re seeing is. . . one-in-250-year storms are happening quite often, and so we want to be prepared for extreme weather and for flooding.”

City staff are working to minimize impacts on local trails and parks as construction continues, she added.

Similar flood-proofing work is slated for the Adelaide Street North sewage plant in the new year. Between the two plants, the cost will be almost $50 million, with Ottawa covering about 40 per cent.

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