Mimico Creek Restoration and Water Infrastructure Protection Study

The geomorphology of a stream examines how natural and human factors have shaped its form and function over time. Erosion can affect the path a stream follows (form) and the aquatic and terrestrial habitats the stream supports (function). Erosion results in gradual changes to the form and function of the stream and stream bed. Significant changes to water levels contribute to increased erosion.

During storm events, rain water or snow melt runoff enters underground pipes via drains and catch basins on streets and in parks and is discharged from storm sewer outfalls into watercourses that flow to Lake Ontario. At times these flows can be high, resulting in erosion damage. High flows from past storms have caused substantial erosion damage to sewers and watermains located in and near the City’s ravines and watercourses.

This erosion damage can:

• Destabilize the soil near sewers and watermains
• Expose or break buried sewers and watermains
• Damage storm outfalls, erosion control structures, the bottom or banks of the watercourse and aquatic habitats

To learn more about erosion in streams and rivers, view the Understanding Streams  information deck.

The map below shows the location of Mimico Creek and area under study.

The study area includes the 19 km length of Mimico Creek in Toronto from Highway 427 near Disco Road and Attwell Drive to where it meets Lake Ontario.

Study Purpose

The purpose of the study is to develop a Geomorphic Systems Master Plan (GSMP) for Mimico Creek that will include recommendations for stabilizing the creek and protecting water infrastructure from erosion. The study will:

• Identify concerns related to erosion that may damage the City’s water and sewer infrastructure.
• Develop solutions that protect the City’s water and sewer infrastructure from excessive erosion processes within the stream.
• Improve stream functions, such as increasing stream bank stability, reducing erosion, enhancing stormwater conveyance, and improving habitats.

The study will not examine trail conditions or recommend improvements to trails, forestry or ravine amenities.

Study Process

This study will follow the Municipal Class Environmental Assessment process for Master Plans, an approved planning process under the Ontario Environment Assessment Act and includes opportunities for public input.

This study includes the following key steps:

1. Identify the problem or opportunity to be studied
2. Collect data, perform fieldwork and examine existing and future conditions
3. Develop, evaluate and recommend solutions
4. Consult public, review agencies, utilities
5. Complete study report and make available for public review
6. Prioritize infrastructure protection projects

Infrastructure Risk Assessment

As part of the study, 203 water infrastructure sites were assessed, including:

• 93 sanitary sewer crossings or sanitary sewers parallel to the creek
• 112 storm sewer outfalls
• 27 watermain crossings or watermains parallel to the creek

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The level of erosion risk has been assessed at each site:

Very Low-Risk Sites

• Infrastructure and site conditions are very stable

Low-Risk Sites

• Infrastructure and site conditions are stable
• Limited monitoring is required

Medium-Risk Sites

• Infrastructure and site conditions are relatively stable
• Limited/some monitoring may be required

High-Risk Sites

• Infrastructure is not exposed, but exposure is expected within the near future
• Regular monitoring is required

Very High-Risk Sites

• Infrastructure is exposed and/or at risk of failure and requires attention
• Regular monitoring and improvements to the infrastructure are required

Based on the risk assessment of water infrastructure sites, protection for the 25 most at-risk sites is recommended. Following an evaluation of alternative solutions, fourteen projects are being proposed to address the 25 most at-risk sites.

Alternative Solutions

The following alternative solutions to stabilize the creek bed and banks were evaluated for the identified 25 sites in the study area:

Alternative 1: Do nothing (no planned interventions, only ongoing monitoring)

Alternative 2: Improvements through local works less than 100 metres

Alternative 3: Improvements to a segment of the creek greater than 100 metres

Evaluation Framework

Potential solutions were evaluated based on whether the alternative solution achieved the following:

• Addresses erosion and risk to City’s water and sewer infrastructure
• Improves stability of stream and valley walls, flood conveyance, groundwater quality, vegetation, aquatic and terrestrial habitats including habitat for at-risk species, and minimal tree removals
• Sound total capital costs against recurring costs for maximum improvements and outcomes over a span of 30 years
• Protects built and cultural heritage as well as landscape and archaeological resources and assesses long term benefits for the community, minimum or short term negative impacts, and consideration for impacts on private property
• Passes regulatory agency standards, availability of staff and technical resources, maximum improvement for ecosystem and infrastructure

The City is recommending 14 projects to stabilize the bed and banks of the creek through natural channel design:

• Five projects are recommended for work in a segment of the creek less than 100 metres (Alternative 2)
• Nine projects are recommended for work in a segment of the creek greater than 100 metres (Alternative 3)

The 14 projects were assigned priority levels for implementation. Exposed sanitary sewers are the highest priority projects as they pose greater negative impacts if broken as compared to broken storm sewer outfalls or watermains:

• Nine projects are high-priority
• Three projects are medium-priority
• Two projects are low-priority

For more detailed information on the recommended projects, view the Mimico Creek Presentation in the Public Consultation section below.

Potential impacts

Future implementation of the recommended projects requires:

• Tree and vegetation removal, to be followed by habitat restoration and replanting with native trees and shrubs.
• Possible park trail closures to accommodate construction activities. Details will be confirmed as part of a future design phase after the study.
• Some work to occur on private property. Owner of properties affected by the projects have been notified.

Construction impacts will be communicated prior to project implementation.

Public Consultation took place May 27 – June 28,2024. A Virtual Public Meeting was held on Monday June 12, 2024. Members of the public were provided with an overview of the study, had the opportunity to review recommended solutions, ask questions and provide feedback.

Consultation Materials

• Notice of Study Commencement
• Public Consultation Notice
• Mimico Creek Presentation
• Public Consultation Report

Next Steps

Following public consultation, an Environmental Study Report will be prepared with the final study recommendations. The study report will be posted on the project webpage for a 30-day public comment period.
The study results will be shared with the City’s Parks, Forestry and Recreation division and Toronto Region Conservation Authority for coordination and collaboration to advance a long-range plan for Mimico Creek.

In 2021 the City of Toronto carried out emergency work to replace the Van Dusen Boulevard Pedestrian Bridge over Mimico Creek and rehabilitate a portion of Mimico Creek in the area of Van Dusen Boulevard. That work is now complete. Additional needs will be address as part of the Mimico Creek Geomorphic System Master Plan.