Don Mills Channel Flood Reduction Notice of Commencement

A Notice of Commencement for the project was issued on July 27, 2018 and August 2, 2018 in the Markham Economist & Sun.


As part of Markham’s Flood Control Program, a Class Environmental Assessment was initiated on the Don Mills Channel.

The Don Mills Channel is a small man made channel that runs through the commercial / industrial area in the Woodbine Ave and Denison Street area. Several of the private properties and roads in this area are prone to flooding during large storm events.

The environmental assessment aims to:

  • Identify and understand the causes of flooding in the study area
  • Develop a range of alternative solutions to reduce flooding and flood damages from the Don Mills Channel
  • Recommend the preferred solution or suite of solutions to best reduce flooding and flood damage
  • Establish the funding, approvals and other activities needed to implement the recommended solutions.

The Study Objective is to provide flood protection for a Council Approved 5 year Level of Protection for the Don Mills Channel Area, as per the following Council Resolution (February 2013):

That the City's flood control strategy adopt a 5 year level of service target for Don Mills Channel drainage system based on its original design and consider other options, subject to technical feasibility and approval as part of a future Class EA;

The current system of open channels and culverts does not have adequate capacity to handle storm water runoff during large storm events. Businesses surrounding the Don Mills Channel have flooded numerous times since the land was developed in the 1970’s. Major roads in the study area, including Woodbine Avenue, can be impassable during severe storms.

The Don Mills Channel study area was realigned and confined to a relatively narrow channel corridor through urban development. Significant portions of the Don Mills Channel were also piped through some of the older development sites in the study area.

Study Area 

Map is available upon request. Please email your request to Rob Grech, Manager of Stormwater at

Estimated Flooding

This image shows the predicted extents of flooding from the August 19, 2005 storm event within the study area, and pictures taken during and shortly after the storm.

This image shows the predicted extents of flooding from the August 19, 2005 storm event within the study area, and pictures taken during and shortly after the storm.

Project Schedule

  • Winter / Spring 2016
    • Notice of Study Commencement
    • Existing Conditions Inventory and Analysis
  • Fall 2016
    • Liaison committee meeting with key stakeholders to review existing conditions
    • Public Information Centre (PIC) #1
  • Spring / Summer 2017
    • Development of initial flood reduction alternatives
    • City / Agency Technical Consultation Process
  • Spring 2018
    • Liaison committee meeting with key stakeholders to review preliminary preferred alternative
    • Public Information Centre #2
  • Summer 2018
    • Confirmation or Refinement of Preferred Alternative
    • Finalize the Project File Report, post the Notice of Completion and make the final report available for 30 day public review period


The evaluation is based on the following criteria:

evaluation criteria

Natural Environment

  • Potential impact on terrestrial system (vegetation, trees and wildlife)
  • Potential impact on aquatic systems (aquatic life, surface water and groundwater)
  • Potential to improve natural environmental conditions

Social Environment

  • Disruption to existing community during construction (business disturbance, traffic, noise)
  • Impacts to community in the long term (emergency access, land acquisition, aesthetics)
  • Ability to reduce risks to public safety
  • Impacts to Archaeological systems and First Nations
  • Timeless of implementation


  • Effectiveness of solution in reducing flood risk (minimum 5 year level of service target)
  • Impacts on upstream and downstream landowners
  • Long term operations and maintenance
  • Ability to meet regulatory requirements


  • Estimated costs to implement project
  • Estimated costs of long term operations and maintenance
  • Reduction in potential future flood damages
  • Estimated losses in tax revenue

Preliminary Preferred Alternative

The preliminary evaluation of the options identified as part of the EA process can be found on the Evaluation of Alternatives Table.

On February 20, 2018, City staff presented the preliminary preferred alternative depicted below to Council, and received approval to hold public meetings to receive feedback on this alternative. A public meeting will be held on April 4, 2018 to obtain feedback from the public on the evaluation that has been performed by the City and TMIG in recommending this as the Preliminary Preferred Alternative through the Environmental Assessment process.

Map is available upon request. Please email your request to Rob Grech, Manager of Stormwater at

Documents, News & Resources

Process for Project Municipal Class Environmental Assessment

Class EA Phase 1

Identify Problem or Opportunity

  • Identify Need
  • Initiate Consultation with the public and agencies
  • Notice of Commencement

Background Review

  • Obtain and review background documentation and initiate agency contact
  • Identify data gaps to be address during the site inventory/ investigation

Class EA Phase 2

Site Inventory / Investigation

  • Undertake natural heritage investigations
  • Aquatic habitat assessment
  • Incidental wildlife survey
  • Undertake hydrology/hydraulics investigation
  • Archealogical Investigattions
  • Identify opportunities and constraints
  • PIC #1

Evaluation of Alternatives

  • Identify alternatives
  • Complete impact assessments
  • Evaluate alternatives
  • Select preferred alternative
  • Preliminary Design / Project File Report

Preliminary Design / Project File Report

  • Preliminary design of preferred alternative
  • Recommendation for further study, if required
  • PIC# 2
  • Develop a staging and implementation plan
  • Prepare Project File Report
  • Notice of Completion
  • 30-day Public Review


  • Detailed Design / Implementation
  • Detailed design of the proposed works
  • Obtain permits and approvals
  • Prepare contract drawings and tender documents
  • Construction and operation of the worksPost-construction monitoring

Project ifnormation about the Class EA Process for Municipal Infrastructure Projects.

Get Involved

You can get involved in the planning process by attending public information meetings which will take place throughout the process. Sign up for our email list by contacting one of the managers below to stay informed throughout the project.


Robert Grech, P.Eng.,
City Project Manager, City of Markham
8100 Warden Avenue
Markham, Ontario, L6G 1B4
905.477.7000 extension 2357

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