The Lake Simcoe Region Conservation Authority

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Managing Stormwater

A New Way to Manage Stormwater

We’ve been engaged in a ground-breaking research study in an effort to improve stormwater management (SWM), introduce savings, and address the impacts of urbanization, degraded water quality, flooding and climate change.

The project, “Equitable Responsibility for Transformative Design: A systems-based approach to watershed management” demonstrated that improved environmental outcomes can be achieved at lower costs if stormwater is planned at a watershed-scale and considers the use of both publicly and privately owned lands.

summary report can be accessed here​ and the full technical report can be provided by contacting

Now that we have completed the study and it’s shown us the many benefits of changing how we manage our stormwater, we are working with municipalities and other stakeholders on a plan to put these changes in place.

Implementation Blueprint

Municipalities in Ontario and across Canada are grappling with limited budgets for managing stormwater, a legacy of insufficient stormwater control in older underserviced areas, mounting stormwater management infrastructure deficits, and urbanization and intensification of development in the face of an increasing frequency of severe weather resulting from climate change. 

The goal of the system-wide stormwater management study was to determine if an alternative approach to stormwater management would enable municipalities to achieve stormwater quality and quantity control targets at a lower cost.

The study used process-based decision modelling and optimization analysis to test the following three main principles:

  1. Using an optimization methodology for stormwater planning will significantly expand the scope and depth of evaluation of potential sites and measures for stormwater infrastructure, enabling the development more efficient stormwater management strategies.
  2. Siting stormwater control measures on private properties (vs municipal-owned properties only) will provide improved performance at greater cost-efficiency.
  3. Intermunicipal collaboration in planning and managing stormwater using a watershed-scale framework will provide improved performance at greater cost-efficiency as compared with municipal-scale planning.

The notable findings were the impetus for the development of this Implementation Blueprint. To develop the blueprint, all potential options for implementation and screening for what works and in what combination were assessed.  The blueprint is intended as a roadmap to test the collaborative, watershed-wide approach to planning and managing stormwater.

A link to the System-wide Stormwater Management Implementation Blueprint study summarizing outcomes and recommended next steps is below.


Stormwater management is primarily the responsibility of municipalities who plan and execute stormwater management within their jurisdiction, usually with little consideration of impacts to downstream municipalities, or cost savings that could be achieved by working collaboratively. In addition, most municipalities have not been able to allocate the necessary funds to manage stormwater because of competition with other priorities.

These inefficiencies together with inadequate funding has led to a $6.8 billion stormwater infrastructure deficit in Ontario alone.

This pilot project was undertaken in the East Holland River subwatershed to show how stormwater management can be optimized to reduce phosphorus loads and river flow (including flooding) at the lowest cost. In this study it was important to seek optimal use of Low Impact Development (LID) solutions as well as centralized solutions (e.g.hybrid ponds) considering availability of both public and private lands.

What have we learned?

This project tells us what we have known for some time now, ​​that being the need to look at stormwater through a watershed lens. It demonstrates the multiple benefits of undertaking a watershed scale modeling approach. 

Through the study a stormwater methodology was developed for the East Holland River subwatershed that can be further refined and applied to other subwatersheds within the Lake Simcoe watershed and beyond.

Key findings:

  • Identified the most cost-effective stormwater control measures to achieve a 40% reduction in phosphorus load.
  • Achieving a 40% reduction in phosphorus load is only possible if SWM controls are sited on both private and public lands.
  • There is the potential of a 27% cost saving if stormwater management is planned at watershed scale vs jurisdictional scale.
  • Phosphorus reduction strategies also reduced peak flows, leading to a 17- 24% reduction during a 25-year storm event.
  • Optimized solutions will help reduce impacts of climate change. For example, nearly all the projected increase in a 1 in 10-year peak flow event would be mitigated by the optimized SWM solution.  

For more information on this project please ​contact: Don Goodyear at

Project Partners

  • Town of Aurora
  • Credit Valley Conservation Authority
  • Town of East Gwillimbury
  • Fortin Economics
  • Freeman Associates
  • Ministry of Environment, Conservation and Parks
  • Town of Newmarket
  • Paradigm Environmental 
  • Sustainable Technologies Evaluation Program
  • Toronto and Region Conservation Authority
  • Town of Whitchurch-Stouffville
  • York Region

phone icon   Who to Contact 


Integrated Watershed Management 
1-800-465-0437 Toll free

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