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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 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 Map Thumnail

Flood Plain mapping is currently available for purchase where specified in the Flood Plain Mapping Index (available for download as a PDF -5,799K pdf). 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. Please see the sample flood plain map on this page for more details.
Click here to download a sample as a PDF
 - 683KB pdf.

Flood plain maps are available as hardcopy or PDF ($30+tax) or AutoCAD (dwg) or Microstation (dgn) formats ($125+tax) and can be purchased on-line from the First Base Solutions Map Warehouse. Please click here to be directed to the page on our website with the link to the Map Warehouse.

Contact Mike Todd mtodd@trca.on.ca  for questions regarding flood plain mapping or to purchase a map. 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 or Diana Li at x.5221 to be directed to the Planner for your region.


Hydrology / Hydraulics


TRCA has 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.

Specific modeling information and report references are available for viewing by using the watershed links below:

Etobicoke Creek | Mimico Creek | Humber River | Don River | Highland Creek | Rouge River | Petticoat Creek | Frenchman's Bay | Duffins Creek | Carruthers Creek

 

Etobicoke Creek: Hydrology

Report Reference: "Etobicoke Creek Flood Control Study, Watershed Management Strategy" (Fred Schaeffer & Associates Ltd., Sept. 1996) 
Hydrologic Model: OTTHYMO 89 
Return period peak flows based on the SCS-24 hour design storm.
Land Use Development Scenarios based on information received from the Town of Caledon, City of Brampton, City of Mississauga and City of Etobicoke.
     Existing - land use in the Etobicoke Creek Watershed as of 1992;
     Future - land use conditions based on current and proposed Official Plans and
    draft plans of subdivision information;
 
Future scenario has been used for delineation of Regional Storm Floodlines
Note: an update to this model is currently underway with an expected completion in early 2006

Hydraulics

Report Reference: "Etobicoke Creek Flood Control Study, Watershed Management Strategy" (Fred Schaeffer & Associates Ltd., Sept. 1996)
Hydraulic Model: HEC-2 Model includes 5, 10, 25, 50, 100 year return period peak flows and Regional Storm peak flows. All flows represent the Future Land Use Scenario. Pending TRCA revision/updates.
 
Peak Flow & Water Surface Elevation Data should be obtained directly from TRCA staff
Note: an update to this model is currently underway with an expected completion in early 2006

Mimico Creek:Hydrology

• Report Reference: "Hydrologic Model Study Etobicoke & Mimico Creeks" (James F.MacLaren Ltd., 1978) and the "Mimico Creek: Hydrology Update" (M.M. Dillon Ltd., 1983 )
• Hydrologic Model: HYMO
 
Note: an update to this model is currently underway with an expected completion in summer 2006

Hydraulics

• Report Reference: "Hydrologic Model Study: Etobicoke & Mimico Creeks" (James F.MacLaren Ltd., 1978 )
• Hydraulic Model: HEC-2 Model includes 5, 10, 25, 50, 100 year return period peak flows (existing conditions) and Regional Storm peak flows (Future scenario)
 
Peak Flow & Water Surface Elevation Data should be obtained directly from TRCA staff

Humber River:Hydrology

• The Humber watershed hydrology is currently being updated. Please contact Authority staff to confirm status of website information.
• Report Reference: "Humber River Watershed Hydrology/Hydraulics and Stormwater Management Study " ( Aquafor Beech Ltd., April 1997) and the "West Humber River Subwatershed Study " (Aquafor Beech Ltd., 1996)
• Hydrologic Model INTERHYMO / OTTHYMO 89 Return period peak flows based on 1-, 6-, 12- & 24 hours AES (basin specific - Tributary Based Control Strategy)
• Unit Flow Rates as per the "Humber River Watershed Hydrology/Hydraulics and Stormwater Management Study" (Aquafor Beech Ltd., April 1997)
• Land Use Scenarios based on the "Humber River Watershed Strategy Land Use Planning Study" (Marshall Macklin Monaghan, 1996)
     Existing - land uses in the Humber River watershed current as of 1994;
     Future 1 - committed future land uses as designated by the Official Plans of regional and
     local municipalities in the Humber River watershed, and relevant Official Plan Amendments;
     Future 1 scenario has been used for delineation of the Regional Storm Floodlines.
 
Future Committed scenario has been used for the delineation of Regional Storm Floodlines

Hydraulics

• Report Reference: "Humber River Watershed Hydrology/ Hydraulics and Stormwater Management Study " ( Aquafor Beech Ltd., April 1997) and the "West Humber River Subwatershed Study " (Aquafor Beech Ltd., 1996) HEC-2 model further updated by TRCA staff (1997).
• Hydraulic Model: HEC-2
Model includes: 2, 5, 10, 25, 50, 100 -year return period peak flows as per Tributary Based Control Scenario - to reflect SWM strategy, and the Regional Storm (Future 1 - no control).
 
Peak Flow & Water Surface Elevation Data should be obtained directly from Authority staff.

Don River:Hydrology

• Report Reference: "Don River Hydrology Update" (Marshall Macklin Monaghan Ltd., December 2004)
• Hydrologic Model: VISUAL OTTHYMO.
Return period peak flows based on 12 hour SCS event.
• Unit Flow Rates as per "Unit Flow Rates for Stormwater Control; Upper Don River Watershed" Report (Marshall Macklin Monaghan Ltd., November 1994)
• Land Use Scenarios based on updates of the hydrology study for the Don River watershed and the Official Plans of the municipalities in the watershed current as of 2004 (Marshall Macklin Monaghan Ltd.)
• Existing - land uses in the Don River watershed as of 2002 (Ortho);
• Future - Committed - land use scenario includes all the land committed to development as indicated in the Official Plans
 
Future Committed scenario has been used for the delineation of Regional Storm Floodlines

Hydraulics

• Hydraulic Model: HEC-RAS (MacViro, Earth Tech, 2006), Diffusion Hydraulic Model (DHM) Model (MMM) includes: 2, 5, 10, 25, 50, 100 -yr return period peak flows (existing conditions) and the Regional Storm peak flow (future committed).
• DHM for Lower Don and Richmond Hill (Elgin /Yonge Area only) Peak Flow & Water Surface Elevation Data should be obtained directly from Authority staff

Highland Creek:Hydrology

Lower Highland - South of HWY #401

• Report Reference: "Regional Headwater Hydrology Study" ( MacLaren Plansearch, 1991)
• Hydrologic Model: QUALHYMO
• Return period peak flows based on 4 hour Chicago storm distribution
• Land Use Scenarios
     Existing - land use scenario based on information current to 1986
     Future - committed land use scenario based on future committed development as indicated
    in Official Plans
 
Future committed scenario has been used for delineation of the Regional Storm Floodline

Upper Highland - North of HWY # 401

• Report Reference: "Highland Creek Tributaries Floodline Mapping Extension Study" (EWRG, 1998) - Draft
• Hydrologic Model: Rational Method
• Land Use Scenarios
     Existing - land use scenario based on information current to 1997
     Future - committed land use scenario based on future committed development as indicated
     in Official Plans
 
Future committed scenario has been used for delineation of the Regional Storm Floodlines

Hydraulics

Lower Highland - South of HWY #401

• Report Reference: "Highland Creek Flood Line Mapping - in the City of Toronto" (Marshall Macklin Monaghan, 1999)
• Hydraulic Model: HEC-2
• Model includes: 2, 5, 10, 25, 50, 100 year return period peak flows (existing conditions) and the Regional Storm peak flows (future conditions). 

Upper Highland - North of HWY # 401

• Report Reference: "Highland Creek Tributaries Floodline Mapping Extension Study" (EWRG, 1998) - Draft
• Hydraulic Model: HEC-2
• Pending status information
 
Peak Flow & Water Surface Elevation Data should be obtained directly from TRCA staff

Rouge River:Hydrology

• Report Reference: "Rouge River Watershed Hydrology Update" (Marshall Macklin Monaghan, October 2001)
• Hydrologic Model: Visual OTTHYMO (V2.0)
Return period peak flows based upon 12 AES distribution.
• Regional peak flows based upon Hurricane Hazel
• Land Use Scenarios:
     Existing - land use scenario as of 2000; based upon COMPUSEARCH 1997 land use database and 1999 orthophotography interpretation. Any approved development which was identified as likely to occur within the very near future was also included.
     Future Committed - land use scenario based upon municipal and regional Official Plans and Official Plan Amendments and approved development plans to occur in the distant future. Future Committed scenario has been used to delineate the Regional Storm Flood Lines.
     Future Ultimate - land use scenario assuming full urban development within the watershed based on a 50 % imperviousness for all rural catchments beyond future committed planning. 
 
Hydraulics

Note: The Rouge watershed flood plain mapping is currently being updated. Please contact Authority staff to confirm status of website information.
• Report Reference: n/a
• Hydraulic Model: HEC-RAS (Clarifica Inc., 2002)
 
Peak Flow & Water Surface Elevation Data should be obtained directly from TRCA staff

Petticoat Creek:Hydrology

• Report Reference: "Petticoat Creek Watershed Hydrology Update" (Greenland Consulting Engineers, 2005)
• Hydrologic Model: Visual OTTHYMO (Version 2.0)
• Return period peak flows based upon 12 AES distribution.
• Regional peak flows based upon Hurricane Hazel
• Land Use Development Scenarios:
      Existing - land use scenario as of 2005; based upon 2002 orthophotography interpretation and any approved development that occurred after 2002 or which was identified as likely to occur within the very near future.
      Future Committed - land use scenario based upon municipal and regional Official Plans and Official Plan Amendments and approved development plans to occur in the distant future. Future Committed scenario has been used to delineate the Regional Storm Flood Lines.
      Future Ultimate - land use scenario assuming full urban development within the watershed based on a 50 % imperviousness for all rural catchments beyond future committed planning.
 
Future Committed scenario has been used for the delineation of Regional Storm Floodlines

Hydraulics

• The Petticoat Creek Watershed flood plain mapping is currently being updated. Please contact Authority staff to confirm status of website information.
• Hydraulic Model: HEC-RAS
Model includes 2, 5, 10, 25, 50, 100 year return period peak flows (existing conditions) and the Regional Storm peak flow (future conditions)
 
Peak Flow & Water Surface Elevation Data should be obtained directly from TRCA staff.

Frenchman's Bay:Dunbarton Creek

Hydrology

• Report Reference: "Pine Creek and Dunbarton Creeks Hydrologic and Hydraulic Study" (Greenland, May 2006)
• Hydrologic Model: OTTHYMO Vo2.0
Return period peak flows based on SCS 12 Hour Type 2 storm distribution
• Land Use Development Scenarios
      Existing - land uses current to 1996
      Future - land use scenario based on municipal OP, draft plan of subdivisions and potential developable lands within watershed
 
Future scenario has been used for delineation of Regional Storm Floodlines.

Hydraulics

• Report Reference: "Pine Creek and Dunbarton Creeks Hydrologic and Hydraulic Study" (Greenland, May 2006)
• Hydraulic Model: HEC-Ras 3.1.3
• Model includes: 2, 5, 10, 25, 50 and 100 year return period flows (existing and future conditions) and Regional
• Storm peak flows (future conditions)
 
Peak Flow & Water Surface Elevation Data should be obtained directly from TRCA staff

Duffins Creek:Hydrology

• Report Reference: "Duffins Creek Hydrology Update" (Aquafor Engineering Ltd., May 2002)
• Hydrologic Model: OTTHYMO 89 Return period peak flows based on 12 hour AES storm.
• Land Use Scenarios based upon "Duffins Creek Watershed Land Use Planning Study" (Walker, Wright, Young Associates Ltd., 1990)
      Existing - land uses in the Duffins Creek Watershed as of 1990;
      Future - committed municipal lands and the north Pickering community of Seaton;
 
Future committed scenario has been used for delineation of the Regional Storm Floodlines

Hydraulics

• Report Reference: "Duffins Creek Watershed Study, Phase 1: Hydrology" (Aquafor Engineering Ltd., July 1991); HEC-2 model updated further by TRCA staff (1997).
• Hydraulic Model: HEC-2
Model includes: 2, 5, 10, 25, 50, 100 year return period peak flows (existing conditions) and the Regional Storm peak flows (future conditions).
 
Peak Flow & Water Surface Elevation Data should be obtained directly from TRCA staff.

Carruthers Creek:Hydrology

• Report Reference: "Carruthers Creek Stormwater Management Strategy - Synopsis Report" (Totten Sims Hubicki Associates, Nov. 1995)
• Hydrologic Model: OTTHYMO 89 Model (Totten Sims Hubicki Associates, 1995) updated by M.M. Dillon and Cosburn Patterson Mather (1997)
• Return period peak flows based on 12 hour AES storm distribution
• Land Use Development Scenarios based on the Region of Durham Official Plan (1994)
      Existing - land uses in the Carruthers Creek Watershed as of 1994 with existing SWM ponds
      Future - committed municipal lands
 
Future scenario has been used for delineation of Regional Storm Floodlines

Hydraulics

• Report Reference: "Carruthers Creek Stormwater Management Strategy - Synopsis Report" (Totten Sims Hubicki Associates, Nov. 1995)
• Hydraulic Model: HEC-2
• Model (Totten Sims Hubicki Associates, 1995) updated by M.M.Dillon and Cosburn Patterson Mather (1997)
• Model includes 2, 5, 10, 25, 50, 100 year return period peak flows (existing conditions) and the Regional Storm peak flow (future scenario)
 
Peak Flow & Water Surface Elevation Data should be obtained directly from TRCA staff