February 19, 2020


  • Toronto has embarked on the largest and most significant storm water management program in the city’s history.
  • Over the next 25 years, the City of Toronto’s Wet Weather Flow Master Plan (WWFMP) projects will virtually eliminate the release of combined sewer overflows and polluted water to Lake Ontario along with key infrastructure upgrades at Ashbridges Bay Treatment Plant to improve system capacity.
  • The program consists of five substantial infrastructure projects that, working together, will significantly improve the water quality in the Lower Don River, Taylor-Massey Creek and along Toronto’s Inner Harbour. This will be done by keeping combined sewer overflows (a mix of rainwater and sewage) and stormwater run-off out of waterways while upgrading the technology and capacity in a number of critical areas.
  • The five projects are:
    • Don River and Central Waterfront Wet Weather Flow System
    • Ashbridges Bay Landform Project/Site of Future High-Rate Treatment Facility
    • New Integrated Pumping System
    • New Outfall
    • New UV (ultraviolet) Disinfection Wastewater Treatment System.
  • The overall program budget is more than $3 billion.
  • When fully implemented, this program will deliver substantial benefits including:
    • Greatly improving water quality in the Lower Don River, Taylor-Massey Creek and along Toronto’s Inner Harbour
    • virtually eliminating the release of combined sewer overflows and stormwater run-off being released into our waterways
    • enhancing recreational uses, such as swimming, boating and fishing
    • improving aquatic habitat for fish and other wildlife
    • reducing nutrient levels that cause excessive algae growth
    • supporting revitalization efforts along the Central Waterfront
    • controlling erosion and sediment in Ashbridges Bay.
  • See Don River and Central Waterfront & Connected Projects for details of each project and a video explaining the program.

Coxwell Bypass Tunnel

  • This tunnel is the first of three phases for the 22-kilometre Don River and Central Waterfront Wet Weather Flow System, which will keep combined sewer overflows (CSOs) out of our waterways by:
    • capturing them within the tunnel system
    • storing them during extreme rainstorms until the system capacity is restored and the water can be transported for treatment
    • transporting the flows to a new and dedicated high-rate treatment facility at the Ashbridges Bay Treatment Plant (ABTP)
    • treating the flows through a new ultra-violet disinfection system
    • discharging them through a new 7-metre diameter, 3.5-km long outfall into Lake Ontario.
  • This phase is a 10.5-km long and 6.3-m diameter tunnel.
  • There are five major shafts, including the one at the Ashbridges Bay Treatment Plant site, which are between 20 and 22 m in diameter and 50 m deep.
  • There are 12 drop shafts which vary between two and four metres in diameter and are also 50 m deep which connect the existing CSOs to the new tunnel system.
  • Construction began in 2018 and is expected to be completed in 2024.
  • Current status:
    • Project overall is approximately 30 per cent complete
    • Construction of two of the five major shafts is complete and excavation is well underway at the remaining three major shafts
    • Four of the 12 drop shafts are underway with one completed.

Tunnel boring machine – “Donnie”

  • The tunnel boring machine named Donnie arrived in Toronto in sections on Thursday, November 28 and was transported by barge and truck to the Ashbridges Bay Treatment Plant shaft site over a three-day period.
  • Donnie was lowered into the 50-m deep and 20-m diameter shaft at the Ashbridges Bay Treatment Plant in sections and then assembled.
  • Fully assembled, Donnie is approximately seven m in diameter, 115 m in length and weighs almost 1,000 tonnes.
  • Once the remainder of the preparations are completed during December 2019 and January 2020, Donnie will be moved into the hand-mined starter tunnel, which is 120 m long.
  • The tunnel boring machine works by breaking up the shale bedrock material with a rotating cutter head, creating the tunnel. The machine transfers the broken-up material to a conveyer-belt system at the back of the machine to be removed.
  • As the machine bores, it erects rings of pre-cast concrete segments to line the tunnel.
  • The tunnel boring machine will take the following route, digging and installing at least 20 m of tunnel per day:
    • Starting from the Ashbridges Bay Treatment Plant site, tunneling west along Lake Shore Boulevard East to Don Roadway
    • North up the Don River valley to the North Toronto Treatment Plant
    • East to the Coxwell Ravine Park shaft site where the tunnel ends.
  • It is anticipated that Donnie’s work will be complete by 2024.