Don River workers went with the flow

As the new river valley filled with water this spring, a leak complicated matters for those overseeing reclamation project

- MAHDIS HABIBINIA

Everything was going according to plan with filling the new Don River valley with water - until workers noticed a leak.

Water was pouring in from one of three massive concrete walls that temporarily separate the new river valley from surrounding bodies of water.

"Imagine you had a full two-litre bottle of pop," said Don Forbes, Waterfront Toronto's project director overseeing remediation and earthworks. "You take a knife and you put a half-inch vertical slice in it."

While the wall will eventually come down and connect the river valley with the lake as part of the $1.35-billion flood protection project in the Port Lands, the riverbed needed to be filled and stabilized first-slowly.

Engineers had to keep the flow rate from water coming through the pumps equal to the rate produced by groundwater welling up from below, balancing the pressure, so things would settle at the same rate along the new riverbed.

"I was concerned about filling the valley too quickly," said Forbes. "If things settle at different rates, then you could end up with river bank slopes collapsing and sloughing off into the river valley."

The Port Lands' massive reclamation project, which includes the renaturalization of the Don River's mouth, has been nearly a decade in the making and dreamt about for far longer.

Earlier this year, the pumps had roared to life and started filling the new river valley with water, marking a critical milestone.

The water gushing out of the leak in the wall that held back Lake Ontario through the Polson Slip threatened to upset the finely calibrated project that was relying on nearby pumps to add water at a carefully controlled rate.