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Regulatory Floodplain Mapping of the Clyde River

Floodplains are low lying areas near a watercourse that are subjected to flooding and unstable slopes due to erosion. In eastern Ontario, the 1:100-year floodplain is the regulatory standard used to identify lands that are vulnerable to flooding. Conservation Authorities in Ontario, including MVCA, are responsible for floodplain management, achieved primarily through the requisition of accurately engineered floodplain mapping data and documentation.

The Clyde River is a major tributary of the Mississippi River and has been identified as one of MVCA’s highest flood risk areas in the recently completed Flood Risk Assessment Study (2022). The Clyde River has seen many recent flood events including flooding in 1998, 2005, 2008, 2014, 2017 and 2019.

MVCA is currently developing regulatory floodplain mapping for the Clyde River that will help us and our municipal partners understand flood hazards and implement effective mitigation strategies to reduce the impacts of flooding in the Clyde River watershed. The mapping will also inform MVCA’s flood forecasting and warning and emergency management programs.

Floodplain mapping involves many components, including data collection, hydrological and hydraulic analyses, public consultations, and floodplain and regulatory limit mapping. The Clyde River floodplain mapping project will also include a climate change analysis to assess how the 100-year flood event is likely to change in the future in response to changing climate. As of March 2023, the climate change analysis and hydrological analysis components of the project have been completed, while bathymetric and hydraulic structure surveys of the Clyde River are planned for spring 2023. MVCA has retained AECOM Canada Ltd. to conduct the hydraulic modelling and floodplain mapping components of the project.

A Public Open House is planned for autumn 2023 when the public will be able to review the draft regulatory floodplain maps. All community members and stakeholders are encouraged to attend – details will be posted on MVCA’s website, social media sites, and local news outlets. The project is being carried out with support from Natural Resources Canada’s Flood Hazard Identification and Mapping Program (FHIMP) and our partners in Lanark County and MNRF with anticipated completion date in March 2024.

Figure 1: Flooding in the Village of Lanark, April 2008