German Mills Creek Geomorphic Systems Master Plan

The City of Toronto has initiated a study to identify sewer and watermain infrastructure within German Mills Creek that is at risk of erosion from high flows due to storms and snow melt.

This study looks at how the City’s sewer and watermain infrastructure can be protected within the creek using recommended solutions to help reduce or prevent future impact. This will ensure the City’s infrastructure continues to operate and service residents and businesses. The solutions will be part of a Geomorphic Systems Master Plan (GSMP) for the creek that is implemented over a multi-year period.

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, rainwater 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 slides.

 

The map below shows the location of the German Mills Creek area under study.

Map of study area along German Mills Creek from Steeles Avenue East and Leslie Street to the Don River.

The study area is the two-kilometer length of German Mills Creek from Steeles Avenue East to where it meets the East Don River in the west.

While we aim to provide fully accessible content, there is no text alternative available for some of the content on this page. If you require alternate formats or need assistance understanding our maps, drawings or any other content, please contact us at 416-338-2985 or email germanmills@toronto.ca.

 

Study Purpose

  • To identify locations within the study area where City infrastructure is at risk due to erosion
  • To develop, evaluate and recommend solutions that protect the City’s water and stormwater infrastructure from excessive erosion processes within the stream
  • To 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. This study will carry out the following key steps:

  1. Identify the problem or opportunity to be studied
  2. Collect data
  3. Identify and evaluate alternative solutions
  4. Consult public on evaluation results and study recommendations
  5. Complete study report and make available for public review

Once a GSMP is approved, recommended solutions will be included in the City’s Stream Restoration and Erosion Control Program which will prioritize and allocate budget for detail engineering design and construction. Residents will be notified prior to any construction occurring.

Infrastructure Risk Assessment

The study area includes 56 City of Toronto water, stormwater and sanitary sewer infrastructure sites. The level of risk due to erosion was assessed for 43 water and stormwater sites. Based on the risk assessment, 11 priority project sites were identified for further evaluation as part of the study.

The level of risk caused by erosion is based on a technical assessment characterizing risk probability (time to exposure), existing bank protection, and risk severity, should damage occur.

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 is expected within 5 years
  • Regular monitoring required

Imminent risk sites

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

The map below shows the 11 sites with at-risk infrastructure identified as priority projects.

Map image of 11 priority risk-sites.

Alternative Solutions

The following alternative solutions for natural channel design were evaluated for infrastructure at-risk of erosion throughout the study area:

Alternative 1: Do nothing, no improvements

Alternative 2: Improvements through local works less than 200 metres

Alternative 3: Improvements through local works less that 200 metres and floodplain connections

Alternative 4: Improvements in a segment of the creek greater than 200 metres

Evaluation Framework

Alternative solutions are evaluated per project, based on a range of criteria:

  • 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
  • Evaluation of total capital costs against recurring costs for maximum improvements and outcomes over a span of 30 years
  • Protects built and cultural heritage as we as landscape and archaeological resources, long term benefits for the community, minimum or short term negative impacts, and consideration for impacts on private property
  • Evaluation of regulatory agency standards, availability of staff and technical resources, maximum improvement for ecosystem and infrastructure

Recommended Solutions

The following recommended solutions were made based on a risk assessment and evaluation of Alternative Solutions:

  • Six projects are recommended for local works less than 200 metres.
  • Five projects are recommended for local works less than 200 metres with floodplain connections.

Future implementation of the recommended projects would require tree removal, followed by restoration and replanting with native trees and shrubs.

Project 1, 2, 3

Recommended solution: Local work less than 200 metres, with floodplain connections

The recommended solution for these projects:

  • Addresses erosion and risk to City’s water and sewer infrastructure
  • Balances in-stream erosion reduction and tree removals
  • Provides multiple improvements with greater efficiency, reducing costs
  • Improves aquatic habitat

Project 1 may require realignment of the pedestrian bridge located 500 metres west of Leslie Street to allow the stream to follow a natural course.

Projects 4, 5, 6, 7

Recommended solution: Local work less than 200 metres.

The recommended solution for these projects:

  • Addresses erosion risk within existing footprint without major corridor realignment and grading
  • Floodplain connection not as essential in these areas as it is generally well connected
  • Erosion issues are less severe in these locations

Projects 8, 9

Recommended solution: Local works less than 200 metres and floodplain connections

The recommended solution for these projects:

  • Projects in close proximity to each other – addresses multiple erosion risks to infrastructure at once within one construction period as well as provides efficiencies in design costs
  • Balances in-stream erosion reduction and tree removals

Project 10, 11

Recommended solution: Local works less than 200 metres

The recommended solution for these projects:

  • Addresses multiple erosion risks to several infrastructure in close proximity to each other, at once, within one construction period as well as provides efficiencies in design costs
  • Balances in-stream erosion reduction and tree removals

A public site walk and drop-in information was hosted on August 18, 2023.  Members of the public were provided an overview of the study, had the opportunity to review recommended solutions and respond to questions and comments.

Consultation Materials

 

Next Steps

The Environmental Assessment study report will be posted on the project webpage for a 30-day public comment period. Once approved, the recommended solutions will be included in the City’s Stream Restoration and Erosion Control Program and implementation will be prioritized across all GSMPs City-wide.
The public will be notified prior to any construction occurring.

To receive study updates by email, please contact germanmills@toronto.ca and indicate that you would like to be added to the mailing list.