Stormwater and Drainage

Stormwater and drainage infrastructure in the Region is typically managed at the scale of a development or neighbourhood. However, regional actions can provide common standards for development and coordinate projects of interest, including those in partnership with other organizations.


24-1         Reduce the risks from surface ponding, flooding, and erosion to people and property in the Region

24-2         Minimize the environmental impacts of stormwater quantity and quality on groundwater, surface water, wetlands, and habitat, and encourage the use of stormwater as a resource to improve environmental performance

24-3         Support municipalities in improving stormwater management to minimize local flooding issues and enhance system performance

24-4         Promote innovative solutions to stormwater management that integrate cost-effective natural and engineering solutions


24.01       Integration of Green Network Study Area. Planning for and refinement of the Green Network Study Area shall consider the role of this area for stormwater management and drainage.

24.02       Drainage Plans. Drainage plans shall be required to ensure development is designed and constructed to avoid or mitigate on- and off-site impacts from alteration to drainage to the satisfaction of the municipality. This should incorporate site designs that minimize impervious surfaces and site grading, and provide other on-site controls, and shall be provided at the expense of the developer.

24.03       Existing Watercourses and Wetlands. Existing water courses and wetlands shall be retained in their natural state as much as possible. Inflows should be managed to reduce peak flows and minimize pollutant and sediment loading.

24.04       Pollution Source Control. Municipalities shall endeavor to reduce the pollutants entering surface waters through the stormwater drainage system.

24.05       Emerging Stormwater Management Technologies. Municipalities shall encourage developers and landowners to adopt new, innovative approaches, such as low-impact development (LID) techniques to stormwater management, to address water quality, quantity, and storage in a more efficient, cost-effective, and sustainable way. As part of these efforts, P4G shall encourage the sharing of information between municipalities about these technologies, including performance data and life-cycle costing.

24.06       Alignment of Hydrologic Modeling. Municipalities shall use common hydrological models, assumptions, and standards when developing assessments of local runoff and stormwater management facilities.

24.07       Inventory of Culverts and Drainage Infrastructure. Municipalities should support maintaining a comprehensive inventory of culverts and other drainage infrastructure to allow for accurate hydrological modeling.

24.08       Master Drainage Plans in Concept Plans. Concept Plans shall incorporate a master drainage plan that reviews existing area conditions and provides a preferred strategy for managing stormwater. These plans shall be developed with a sufficient level of detail to support stormwater management plans at the site level, and should identify long-term needs for land dedications and easements to support drainage infrastructure.

24.09       Stormwater Management Plans in Future Urban Growth Areas. Stormwater management plans shall be required as part of Concept Plans or Comprehensive Development Reviews, or at the site development stage, whichever comes first, that detail stormwater control facilities and related improvements, and demonstrate that water quality and quantity impacts from development have been minimized.

24.10       “No Net Impact” Standard Encouraged. On-site stormwater management controls for site development will be encouraged to meet a “no net impact” standard, incorporating sufficient capacity to accommodate surface water runoff for a 1:100-year storm event with no incremental increase in offsite flows in excess of what would have been generated from the property prior to the new development.