floodplain mapping

Why Floodplain Mapping is Important?

In Canada, floods account for the largest portion of disaster recovery costs on an annual basis. The first step to reduce the cost of flood damage within a community is to have mapping that accurately shows flood hazards. These maps help people prepare for and respond to potential flooding and make informed decisions about their own emergency plans and property improvements. The Mattagami Region Conservation Authority (MRCA) has recently updated its floodplain mapping for the City of Timmins. Some of these maps were over 40 years old.

Mattagami Region Conservation Authority’s Role in Floodplain Mapping

The MRCA is a watershed management agency. Our goals include protecting the municipality from natural hazards, conserving our natural environment, and supporting our partners in creating a sustainable community. From a flood management viewpoint, the MRCA, municipal partners, and local stakeholders rely on floodplain mapping for:

  • flood forecasting and warning,
  • emergency planning and response,
  • prioritization and planning for flood mitigation works,
  • community planning and land use decision making, and
  • identifying the extent of the flood hazard.

For more information about floodplain mapping within the City of Timmins, or the MRCA Regulations, contact our office at 705-360-2660.

Frequently Asked Questions

What is a Floodplain?

A floodplain is an area of land near water bodies (rivers, lakes, creeks, etc.) that is often flooded when the water body is too full. Examples of floodplains include low lying lands that are flooded or inundated with water when a river spills over its banks or when lake levels rise due to storm surge, significant precipitation or snowmelt. Floodplains are natural features that allow flow to spread across the landscape, limiting flooding and erosion potential.

What is Floodplain Mapping?

Floodplain mapping is used to identify areas that may be susceptible to riverine flooding during large storm events or annual spring melts (freshet). Floodplain mapping relies on supporting analysis, including hydrologic and hydraulic modelling. Typically, hydrologic modelling predicts how much runoff will be generated by a rainfall event. Flows generated by the hydrologic model are then input into the hydraulic model to predict the peak flood depth, elevation, and velocity of flood flows. The flood elevation is mapped using topographic data (the natural features of the land) to show the limits of the floodplain and other critical information.

There are many different types of information that may be shown with floodplain maps. The most common form of floodplain mapping in Ontario is a Flood Hazard Map, which shows the limit of the regulated flood hazard in conjunction with natural features of the land, and human-made structures such as roads. This type of map is required for land use planning purposes.

What is the Regulated Flood Hazard?

In the MRCA’s jurisdiction, the regulated flood hazard is defined in provincial legislation by either the:

  • 1:100 year floodplain, which is the anticipated limit of flooding that has a 1% chance of occurrence in any given year, or
  • floodplain associated with the Regional Storm. (The Regional Storm for Northern Ontario is a storm that occurred in Timmins, ON in 1961 in which approximately 193 mm of rain fell in 12 hours.)

The MRCA’s Regulatory Policies apply to lands within and immediately adjacent to the Regulated Flood Hazard.

Does Flood Risk Extend Beyond the Regulated Flood Hazard?

While flood hazard mapping identifies the extent of the regulated floodplain associated with riverine, it does not identify the full extent of flood risk. Flooding may be experienced outside of the defined riverine hazard for a variety of reasons, including occurrence of extreme rainfall events (which are greater than the regulatory standard), spring melt, formation of significant ice or debris jams and large beaver dams, major channel adjustments, or due to other flooding mechanisms such as overland flooding caused by rainfall that exceeds the capacity of local drainage systems, seepage, etc.

What Standard was Followed?

Analysis and mapping was undertaken in a manner consistent with the Ontario Ministry of Natural Resources and Forestry’s (MNRF) Technical Guide – River and Stream Systems: Flooding Hazard Limit (2002). This guideline sets out provincial expectations on analysis approaches applied in mapping the regulated flood hazard. The MNRF guideline is used by all Conservation Authorities undertaking flood hazard mapping.