Toronto's once-in-a-lifetime plan to transform the existing mouth of the Don River — known as the Port Lands Flood Protection (PLFP) project — recently encountered a hiccup that could've been catastrophic had it not been for the expertise and quick response of the project's engineers.

When filling the new Don River with water in February, workers encountered a leak, which could've led to river bank slopes collapsing and sloughing off into the river valley. 

According to a new report by the Star, the water was pouring into the valley from one of three concrete walls that currently separate the new river valley from other bodies of water. 

The concrete walls around the river valley were used to keep groundwater out of the new river valley while crews worked to excavate it. Since the Port Lands are so close to the lake, the water table is very high, and without the cutoff walls, water would pool into any holes dug out. The walls also keep the edges of the excavation from collapsing inwards. 

Toronto's human-made river just crossed its biggest milestone yet https://t.co/F7NL8BxmAy

— blogTO (@blogTO) February 17, 2024

As part of the massive $1.35 billion project, the concrete walls will eventually come down and connect the new river valley with Lake Ontario. 

When workers filled the new river valley through the Polson Slip, they had to keep a special eye on the flow rate coming through the pumps, which had to be equal to the rate of the groundwater that welled up from below. 

The leak threatened this critical balance, although the project's engineers quickly came up with a remedy. 

"We left it," Don Forbes, Waterfront Toronto's project director told the Star. "We basically just turned down the flow rate on the pumps we were using to inundate the river and...used the leak to flood the river valley, too."

Although the new Don River valley is now filled, there are still many steps construction crews must take before the Port Lands are officially home to new and sustainable communities. 

The next steps involve connecting surrounding bodies of water to the new river valley by removing three submerged concrete plugs, with much of the work being done underwater. 

The west plug, which is the point where the new Don River will flow into the harbour and the re-naturalized river mouth, will be removed first this summer.