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TOP 50 PROJECT
When It Rains It Pours
Toronto looks to curb sewage over昀氀ows
BY SAUL CHERNOS
EMEMBER THE TORRENTIAL RAINSTORM
of July 8, 2013 which unleashed a record 126 millimetres across much of Toronto in a couple of hours?
Or July 16 of last year, when 98 mm fell in equally
scant time? Images of motorists stranded on normally busy thoroughfares might be etched in our minds because
no one reasonably expects to go swimming while commuting home from work. Less visibly, however, the heavy rainfalls overwhelmed the city’s antiquated combined sewers,
dispatching untreated wastewater and sewage into the city’s
waterways. More than a billion litres bypassed treatment systems and landed in the Don and Humber Rivers and Lake
Ontario during the 2013 event alone, though even overflows
from lesser events all too frequently turn otherwise pleasant
beaches into bacterial hotspots. However, even as climate
change projections promise further chaos, Toronto Water is
engaged in a multi-pronged effort to help curb the flows.
The city has in fact been on the file for decades. In 2003,
Council approved an ambitious 25-year Wet Weather Flow
Master Plan with a view to protecting Toronto waterways
through a literal bucket of measures, including an associated
capital program currently valued at $4.9 billion. Although an
enormous undertaking of this kind takes time to implement,
individual components have been rolled out gradually,
starting with water absorption, downspout disconnection
and basement flooding protection programs. However, it
takes time to fix aging, 1950s and 60s-era infrastructure.
In 2018, after reviewing multiple options and engaging in
lengthy environmental assessments, Council gave the green
light to the Don River and Central Waterfront Wet Weather
Flow System program. Currently pegged at $3.7 billion, it
adds three new tunnels, a pumping station, a high-rate wet
weather flow treatment facility, and other upgrades designed
to improve water quality in the Lower Don River and TaylorMassey Creek and along Toronto’s Inner Harbour.
R
Saul Chernos is a freelance
writer for Water Canada.
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WATER C AN ADA • JULY/AUGUS T 2025
“People didn’t want to be down near the harbour or the Don
because they were so polluted,” says Lou Di Gironimo, general
manager of Toronto Water, which is steering the project. Di
Gironimo compares the management of wastewater overflows
to dealing with a rapidly filling bathtub. “We’re building tunnels
that will capture overflow and store it during a large storm.
Then, after the storm subsides, we can release it and send it
to a treatment facility. The goal is to contain combined sewer
overflows as much as possible and keep it out of our waterways
through the upgrading of technology and capacity to capture,
transport and treat it.”
The Don River and Central Waterfront Wet Weather Flow
System program is particularly driven by the realization that
the city is densifying downtown, close to the lake and the Don.
“We’re building all kinds of residential communities close to
the water because people want to live there,” Di Gironimo says.
“We’ve recently renaturalized the floodplain areas at the Mouth
of the Don and opened a new park, so if we want to be close to
the water we need to make it safer.”
The program’s first shovels came out in December 2018
for the Coxwell Bypass Tunnel, which runs 10.5 kilometres
along the east side of the Don River and is just months from
completion. The tunnel reaches depths of 50 metres and the
WAT E R C A N A D A . N E T
