Stuck on a Site Plan Approval? Start With Where the Rain Goes
Planning to build, expand, or redevelop a property in the Greater Toronto Area (GTA)? Depending on the project, you may need a stormwater management plan as part of the site plan approval process. This document helps demonstrate how rainwater will be managed on the property and how the proposed development may affect surrounding areas and municipal infrastructure.
Stormwater management requirements can vary depending on the site’s characteristics, the scope of development, and the applicable municipal policies. Understanding these requirements early can help property owners, builders, and developers prepare a coordinated submission and reduce the likelihood of revisions.
This guide outlines the key considerations for preparing a stormwater management plan for Toronto site plan approval.
Why Does Toronto Take Rainwater So Seriously?
Toronto’s location beside Lake Ontario, its network of ravines, and its extensive urban development all influence how stormwater must be managed. During heavy rainfall, roofs, roads, and parking lots generate runoff that can place additional pressure on storm sewers and natural waterways.
Without appropriate controls, stormwater runoff can contribute to basement flooding, streambank erosion, and the transport of pollutants into local waterways and Lake Ontario.
The City of Toronto’s stormwater management requirements are intended to address these risks by managing runoff quantity, improving water quality, and protecting natural systems. Depending on the project, the applicable requirements may also address water balance, erosion control, and the effects of development on downstream infrastructure.
Where Does Stormwater Fit in the Site Plan Process?
Site plan approval involves coordination among several disciplines, including architecture, landscape design, surveying, and civil engineering. Stormwater management affects many aspects of the site design because roof drains, parking areas, grading, landscaping, and underground utilities influence how water moves across and away from the property.
A pre-application consultation, where available or appropriate, can help identify applicable submission requirements and potential site constraints before the design progresses too far.
Early coordination between the project team and municipal staff can also help identify drainage issues, servicing limitations, and other considerations that may affect the proposed development.
What Goes Into a Stormwater Management Plan?
A stormwater management submission commonly includes a technical report supported by engineering calculations and drawings. The report describes existing drainage conditions, evaluates the proposed development, and explains how the design will manage stormwater in accordance with applicable requirements.
Depending on the project, a submission may include:
- Existing and proposed drainage area plans
- Peak flow calculations for applicable design storms
- Stormwater storage calculations for tanks, ponds, underground systems, or rooftop controls
- Water quality treatment measures
- Erosion and sediment control measures for the construction period
- Grading and servicing drawings coordinated with the stormwater report
The scope of the submission depends on the development, site conditions, and requirements established by the reviewing authorities.
Quantity, Quality, and Water Balance: Three Key Considerations
Stormwater management generally addresses three related objectives: controlling runoff quantity, improving runoff quality, and maintaining an appropriate water balance.
Water quantity control regulates the rate and, where required, the volume of runoff leaving a property. Storage systems may temporarily retain stormwater and release it at a controlled rate to help reduce downstream flooding risks.
Water quality control reduces pollutants carried by runoff, including sediment, oils, and other contaminants, before the water enters municipal infrastructure or natural waterways.
Water balance considers how rainfall is distributed among infiltration, evapotranspiration, storage, reuse, and runoff. Depending on site conditions and applicable requirements, measures may be incorporated to help maintain pre-development water balance characteristics.
These considerations help shape a stormwater management plan for site plan approval and determine which control measures are appropriate for a particular property.
Low Impact Development: Managing Runoff on Urban Lots
Space constraints are common across the GTA, particularly on infill and redevelopment sites. Low Impact Development (LID) measures can help manage rainfall closer to where it lands while making efficient use of available space.
Potential measures include:
- Underground stormwater storage systems
- Permeable pavement
- Bioretention gardens and other landscaped infiltration features
- Green roofs
- Rainwater harvesting and reuse systems
The suitability of each measure depends on factors such as soil conditions, groundwater levels, available space, site grading, utility locations, and maintenance requirements.
Incorporating stormwater management measures during the early design stages can help coordinate them with the building layout, landscaping, and servicing infrastructure. A Stormwater Management Plan for Toronto should evaluate the available options against the site’s specific conditions and applicable municipal requirements.
Do Smaller Projects Need a Stormwater Management Plan?
In some cases, yes. Infill housing, townhouse developments, small commercial buildings, fuel stations, and industrial expansions may require stormwater management documentation as part of the approval process.
The requirements depend on factors such as the proposed development, the amount of new or altered impervious area, existing drainage conditions, and the sensitivity of the receiving system.
Smaller projects may require a more limited analysis, while larger or more complex developments may need detailed hydrologic and hydraulic modelling. Confirming the submission requirements with the City and any other relevant reviewing authorities can help establish the appropriate scope of work.
How Conservation Authorities Affect the Approval Process
Properties near ravines, rivers, floodplains, wetlands, and other regulated areas may be subject to review by a conservation authority, such as the Toronto and Region Conservation Authority (TRCA).
Depending on the location and proposed work, conservation authority requirements may address flood hazards, erosion, watercourses, and the protection of natural features. Additional permits or approvals may be required where applicable.
Checking the relevant mapping and regulatory requirements early in the project can help identify potential constraints and inform the site design. Coordination between the stormwater report, grading plan, and other engineering drawings can also help maintain consistency across submissions.
Climate-Ready Design and Stormwater Resilience
Climate resilience, green infrastructure, and sustainable development are increasingly important considerations in urban planning and site design. Changes in rainfall patterns and the potential for intense storms make effective stormwater management relevant to both new construction and redevelopment.
Municipal policies and standards, including the Toronto Green Standard where applicable, may establish requirements or targets for stormwater retention, water quality, and related environmental performance.
Depending on the site, measures that capture, treat, infiltrate, or reuse rainfall can help manage runoff and support broader environmental objectives. The appropriate design approach depends on the applicable standards, site constraints, and technical feasibility.
Five Common Issues That Can Lead to Additional Review Comments
Stormwater management submissions may require revisions when important design details are incomplete or inconsistent. Common issues include:
- Civil engineering drawings that do not match the latest architectural site plan.
- Storage calculations that do not reflect the applicable design storm or control criteria.
- Downstream sewer capacity that has not been adequately assessed.
- Missing or insufficient soil and groundwater information.
- Inconsistencies between the stormwater management report and the grading plan.
Engaging stormwater management engineering services during the concept design stage can help identify these issues before a formal submission. Coordinating the technical report and engineering drawings throughout the design process can also reduce the need for revisions.
How to Choose an Engineer for Your Project
When selecting an engineer for a stormwater management project in Toronto, consider their qualifications, relevant experience, and familiarity with municipal approval requirements.
Look for a Professional Engineer licensed in Ontario who has experience with projects of a similar type and scale. Ask about previous project experience, the anticipated scope of work, and the coordination of stormwater management with grading and servicing design.
It is also helpful to understand how the engineering team will address review comments, communicate design options, and coordinate with other project consultants.
A clear explanation of technical requirements, design constraints, and potential alternatives can help property owners and developers make informed decisions throughout the approval process.
Quick Checklist Before You Submit
Before submitting a stormwater management package for site plan approval, review the applicable requirements for your property and confirm that:
- The topographic survey and geotechnical information are current and adequate for the design.
- The architectural site plan reflects the latest proposed layout.
- The proposed storm sewer outlet and discharge requirements have been reviewed with the City, where applicable.
- Relevant conservation authority regulation limits and approval requirements have been checked.
- The stormwater report, calculations, grading plan, and servicing drawings are consistent.
The specific submission requirements will depend on the site and the reviewing authorities involved.
Planning a Stormwater Management Submission in Toronto?
Stormwater management requirements vary by property, project type, and approval conditions. Preparing the necessary reports and engineering drawings involves assessing existing drainage conditions, selecting appropriate control measures, and coordinating the design with the overall site plan.
n Engineering Inc. provides civil engineering services, including stormwater management reports, grading plans, and servicing drawings for development projects. Property owners, builders, and developers seeking assistance with a Stormwater Management Plan for Toronto site plan approval can contact the company to discuss their project requirements.
To learn more, call (416) 256 – 9741, email info@nengineering.com, or visit nengineering.com to request a quote.
Frequently Asked Questions
1. What is a stormwater management plan, and why is it required?
A stormwater management plan is a technical report, usually supported by engineering drawings and calculations, that explains how rainfall and surface runoff will be managed on a property.
For site plan approval, the plan helps the municipality assess whether the proposed development addresses applicable requirements for runoff quantity, water quality, drainage, and related environmental considerations.
2. Who can prepare a stormwater management report?
Stormwater management reports involving professional engineering generally need to be prepared, reviewed, or authenticated by a Professional Engineer licensed in Ontario, as required by the nature of the work and applicable regulations.
The engineer’s seal or other required authentication indicates professional responsibility for the engineering work within the scope of their involvement.
3. What is the difference between stormwater quantity control and quality control?
Quantity control manages how much runoff leaves a property and how quickly it is discharged. This may involve temporary storage and controlled release.
Quality control focuses on reducing pollutants in runoff, such as sediment, oils, and other contaminants, before discharge. The specific requirements for each depend on the project and the applicable standards.
4. Do I need conservation authority approval in addition to City approval?
Not every project requires a separate conservation authority permit or approval. Additional requirements may apply if the property or proposed work falls within a regulated area or affects features under the authority’s jurisdiction.
The applicable requirements should be confirmed with the relevant conservation authority and the City early in the project.
5. What is Low Impact Development, and does Toronto encourage it?
Low Impact Development uses measures such as permeable pavement, green roofs, bioretention features, and rainwater harvesting to manage rainfall closer to where it falls.
Toronto’s applicable policies and standards may establish requirements or targets for LID measures, stormwater retention, and water balance. The specific measures required or suitable for a project depend on its location, design, and site conditions.
6. What happens if the downstream sewer cannot accommodate runoff from my site?
The proposed design may need to be revised to address the available downstream capacity and applicable discharge criteria. Potential approaches include additional on-site storage, a reduced discharge rate, or an alternative drainage arrangement where permitted.
The available options depend on site conditions, municipal requirements, and the feasibility of the proposed outlet. Assessing downstream capacity early can help identify potential design constraints.