Floodplain Mapping


Why Floodplain Mapping?

Conservation Authorities in Ontario have a legal mandate to ensure that development does not occur in areas that are susceptible to flooding and erosion. Building in these areas can result in damage to properties when flooding or erosion occurs, and in extreme cases can result in loss of life.

Conservation Authorities are also required to protect wetlands. Because of the nature of the landscape in much of the CRCA’s jurisdiction many of our wetlands are located adjacent to our rivers, lakes and streams. Wetlands provide important fish and wildlife habitat and act as water storage facilities, holding water back during periods of high water and releasing water during periods of drought.

In order to direct development away from flood and erosion-prone areas, and wetlands we first need to identify where these areas are located. One of the ways that we do this is by preparing floodplain mapping.

This mapping is used by our staff when reviewing development applications. They are also used for our Development, Interference with Wetlands and Alterations to Shorelines and Watercourses Regulations (Ontario Regulation 148/06). Visit our planning and permits page for more information.

Floodplain mapping is also used by municipalities in preparing official plans and zoning by-laws, which guide future development in their municipalities.

How is Floodplain Mapping Prepared?

Preparing mapping involves a combination of field work and computer modelling. Background data such as land use, topography and precipitation is gathered. This is used to build a computer model that calculates flows during storm events at various locations along the creek system. In this part of Ontario the standard of protection is to the 1 in 100 year flood event, also called the regulatory flood. This is the event that has a one per cent chance of occurring in any year or a one per cent probability.

The computer model also uses data that includes information about the size, depth and shape of the creek; culvert sizes along the creek and flows through the creek. The model calculates water levels along the creek based on projected flows through the creek system.

The water level information generated by the model is then applied to mapping of the creek system. The resulting information is a floodplain map showing the regulatory flood level of a 1 in 100 year flood.

Why Update Floodplain Mapping?

  • new data available
  • updated topographic information
  • improved modelling techniques and software
  • new development and construction such as roads, culverts, grading and filling.

All of these changes can affect the size and location of the floodplain area.