Flood Plain Management

Learn more about our flood plain maps, our hydrologic and hydraulic models, and our technical criteria.

Flood Plain Management

The Regulatory Flood Plain is the approved standard used in a particular watershed to define the limit of the flood plain for regulatory purposes. Within the TRCA’s jurisdiction, the Regulatory Flood Plain is based on the regional storm, Hurricane Hazel, or the 100 year flood; whichever is greater.

The framework for Flood Plain Management is the TRCA’s Living City Policies (LCP). The LCP sets out development guidelines for properties influenced by valleys and stream corridors. Some of the LCP’s fundamental principles include:

Protection of life and property from flooding and erosion hazards is dependent on natural system protection, restoration and remediation, inclusive of valley landforms, stream corridors, wetlands, watercourses and shorelines.

Development and redevelopment should contribute to the prevention, elimination, and reduction in risk from flooding, erosion, and slope instability.

Adaptive watershed management requires a preventative and proactive approach to address the potential impacts of urbanization and climate change.

Flood Plain Mapping

Flood Plain mapping is currently available for purchase. Each flood plain map displays contours, roads, buildings, etc.; hydraulic data including: the Regional Flood Plain extents, HEC-RAS cross-sections, and the Regional Flood Plain Elevation at specific cross-sections. Download a sample.

Flood plain maps are available as hard copy or PDF ($30+tax), AutoCAD (dwg) or Microstation (dgn) formats ($125+tax), and can be purchased online from the First Base Solutions Map Warehouse.

If you are purchasing flood plain mapping for the purposes of a development application please contact Planning and Development: Grace Conte at 416-661-6600 x 5271 to be directed to the Planner for your region.


TRCA utilizes HYMO based hydrologic and HEC-RAS hydraulic models to aid in enforcing policies and regulations intended to ensure that new developments are located outside of the flood risk area and that existing condition peak flows are maintained through the implementation of stormwater management practices. Regular updates, which typically incorporate technological advancements and additional climate and stream flow monitoring data, ensure that the models are kept current.

With updates to the hydrology models which utilize new computer modeling software, new flow data and updated land use, flood flows for the design and regional storms can be computed at multiple locations within the watershed. These flows are used as inputs to the hydraulic models, which then re-assess and re-produce updated flood line mapping.