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Combined Sewer Overflow Master Plan

About 1/3 of Winnipeg has old pipes that carry both rain/snowmelt and wastewater in the same sewer. These are called ‘combined sewers.’ In big storms, these pipes are designed to overflow into our rivers. This is called a “combined sewer overflow” (CSO).

The CSO Master Plan is a sewer infrastructure improvement program. It will help us reduce the frequency and volume of combined sewer overflows. Doing this work will:

  • Improve our management of CSOs
  • Reduce the risk of basement flooding
  • Protect the health of our rivers and lakes

The operation of the combined sewer system and implementation of a CSO Master Plan is governed by Environment Act Licence No. 3042 (EA No. 3042), issued by the Province of Manitoba (through Environment and Climate Change) in September of 2013.

CSO Master Plan goals

By 2045, we will capture 85 percent of the combined sewer flow based on a normal (or “representative”) year before it reaches the river. The CSO Master Plan adopted the 1992 year as the “representative year” for annual rainfall and river levels. We use our 2013 sewer system as the baseline from which we measure progress.

The Province also asked us to review what would be required to move to a higher level of capture. That study is due by April 2026. An overall update to the 2019 Master Plan is due by April 2030.

Note: all goals for CSO reduction are based on the ‘representative year.’

How we reduce overflows

To reduce overflows, we use a mixture of grey and green infrastructure. We will choose a specific solution based on what best serves the needs of each combined sewer district.

  • Grey infrastructure uses traditional construction to manage flow:
    • Sewer separation: adds new pipes so rain and wastewater travel in different sewers
    • In-line and latent storage: holds flow back in existing pipes until after the storm event has passed
    • Off-line storage: builds tanks to store extra flow during storms
    • Real-time control: uses technology to optimize flows in our grey infrastructure (e.g. a pump can be set to empty an off-line storage tank when levels in the sewer are low enough for the flow to go to the treatment plant without overflowing).
    • Floatables management: keeps trash and debris out of rivers
  • Green infrastructure uses nature to help manage flow:
    • Projects like rain gardens, trees, and other features that soak up or slow down stormwater so less enters the sewers. These also make streets greener and can help with heat and air quality

Phase I: CSO Control Limits (2013-2015)

  • Gather information and begin technical analysis of CSO control limits
  • Hire consultant to help develop the plan (February 2013)
  • Province issues CSO licence to develop the plan (September 2013)
  • Establish a Stakeholder Advisory Committee (October 2014)
  • Have a CSO Symposium and host public engagement opportunities (March 2015)
  • Submit CSO Master Plan Preliminary Proposal to the Province of Manitoba (December 2015)

Phase II: CSO Master Plan (2016-2019)

  • Receive Provincial decision on CSO Master Plan Preliminary Proposal (November 2017)
  • Develop and submit the CSO Master Plan to the Province of Manitoba (August 2019)
  • Receive approval to begin implementing the CSO Master Plan (November 2019)

Phase III: Implementation (2020-2045)

  • Implement the CSO Master Plan
  • Submit a revised percent capture assessment to the Province of Manitoba (April 2026)
  • Submit an updated CSO Master Plan to the Province of Manitoba (April 2030)
  • Complete the implementation of the CSO Master Plan (2045)

The total cost of the CSO Master Plan will depend on several factors including:

  • Project design choices
  • Construction inflation
  • Tariffs
  • Changes in provincial regulations

The 2019 class 5 cost estimate to implement the CSO program was $1.15 billion. This class estimate gives a range of program costs from $575 million to $2.3 billion. Costs rose from earlier estimates because of:

  • Inflation
  • Changes to how we estimate
  • Addition of a green infrastructure allowance
  • Choosing more sewer separation (which costs more to build but less to operate)

Funding

Our current funding strategy is based on a typical annual investment of $30 million. This value will be escalated annually starting in 2029. Along with an additional $60 million in funding between 2024 and 2027, this is estimated to accumulate nearly sufficient funds to match the class 5 estimate of $1.15 billion by 2045. Funding is adjusted annually as part of the Capital Budget process and is based on anticipated contracts for the coming years. Funds will continue to be adjusted to meet the provincial deadline.

To date, there have been no federal or provincial funding programs available to support on the CSO program. We will continue to seek external funding sources to limit the impact of this critical work on rate payers.

Annual reports

Master plan

Other documents

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