Low Impact Development Stormwater Management Guidance Manual

The Ontario government is taking action to protect our waterways, reducing flooding risks and increasing our resiliency to climate change. Improving stormwater management is a key provincial commitment to ensure water resources and ecosystems are safeguarded for future generations.

To help municipalities, property owners, planners, developers and others better manage stormwater runoff and reduce contaminants from entering our waterways, we have developed a new guidance manual that provides information and guidance on innovative stormwater management practices, including green infrastructure (also known as low impact development).

Low impact development uses techniques that mimic the natural environment and allow rainwater to be absorbed where it falls. Examples include rain gardens, green roofs, urban trees, permeable pavement and rainwater harvesting that can minimize the harmful impacts of stormwater runoff.

Input on this proposed draft guidance manual will help ensure that the final manual includes the information municipalities, developers or others need to plan, design and implement innovative stormwater management in their communities. 

The draft Low Impact Development Stormwater Management Guidance Manual aims to:  

• Maintain diversity of aquatic life and opportunities for human uses
• Protect water quality
• Preserve groundwater and stream baseflow characteristics
• Reduce combined sewer overflows
• Reduce the potential for flood damage (e.g., public safety, damage to property and infrastructure)
• Reduce occurrences of stream erosion
• Protect the ecosystem by maintaining the natural hydrologic cycle to the greatest extent possible
• Increase resiliency of communities and associated stormwater infrastructure to climate change and help mitigate climate change

The draft guidance manual does not contain mandatory requirements. The chapters deal with planning, runoff volume control, groundwater considerations, criteria for model selection, climate change considerations, operation and maintenance, erosion and sediment control during construction.

This manual encourages the development and application of innovative practices, designs and technologies for low impact development that are supported by literature, research and field studies. Where the proponent and designer can show that alternate approaches can produce the desired results for treating and managing stormwater, such designs should be considered.

Current regulatory framework 

• The Ontario Water Resources Act and the Environmental Protection Act provide the framework for regulating stormwater management for the protection of the environment. The Ontario Water Resources Act defines sewage works as meaning “any works for the collection, transmission, treatment and disposal of sewage or any part of such works, but does not include plumbing to which the Building Code Act, 1992 applies”, and the definition of “sewage” under the Ontario Water Resources Act includes stormwater. The Ontario Water Resources Act (section 53) requires an Environmental Compliance Approval (ECA) to be in place before using, operating, establishing, altering, extending or replacing, new or existing sewage works.  Sewage works ECAs may be issued to applicants by appointed Directors under Part II.1 of the Environmental Protection Act.   Examples of sewage works that treat storm water include storm sewers, ponds and LID such as rain gardens.