2025 Lower Conestogo Floodplain Mapping Update

The Grand River Conservation Authority is undertaking a project to update floodplain mapping for the Conestogo River between the Conestogo Dam and the Grand River. GRCA is currently seeking feedback on proposed mapping changes, which will result in amendments to our regulated area mapping under Ontario Regulation 41/24.

Background:

As outlined in a staff report titled “Lower Conestogo Floodplain Mapping Update ”, a project was carried out under the federal National Damage Mitigation Program (NDMP) to complete work necessary to update floodplain mapping for the Lower Conestogo River between Conestogo Dam near Glen Allan to where it meets the Grand River near the Village of Conestogo. The study area is shown in Figure 1 and includes the Townships of Mapleton, Wellesley and Woolwich.

The work completed for the floodplain mapping updates included the collection of detailed measurements of all bridge crossings in this section of the Conestogo River, as well as surveying the shape of the river channel below the water surface. This new data was used to create a hydraulic model, which simulates how flood waters will move through the river and over land to determine what areas will flood based on a given flow. An existing hydrologic model generates the amount of water (flow) anticipated during a storm event. Output from the new hydraulic model was combined with modern topographical data and flows to update the extent of the Regulatory Floodplain in the lower Conestogo River.  

How you can participate:

Until October 24, 2025, feedback is welcome through the “Reviewer” tool below, at a public information meeting, or via mail as outlined below.

1) Send us your feedback through the online “Reviewer” tool:

Using the map below, you can view the existing floodplain (blue) along with the proposed floodplain (green). Click and move your mouse to change the area shown.  The “+” and “-“ icons in the bottom right can be used to zoom in or out. Clicking on the “Basemap” icon in the upper right will toggle the base map between a simplified road map and detailed aerial imagery. Enter a street address in the search box to zoom into a specific property of interest. Moving the slider between “Existing” and “Proposed” will change the transparency of the layers. Comments can be added by zooming the map into an area of interest, clicking on the map and following the link to “Submit a Comment Here”. All comments submitted through this application may be made public.

Please note this study does not include a review of the floodplain mapping for watercourses that drain into the Conestogo River and does not include a review of the Grand River floodplain mapping where it meets the Conestogo River. You will see a red line which marks the Study Limit in these areas.  Please be aware that the floodplain beyond the red line/Study Limit is not shown in the “Reviewer” tool. To see the full extent of the mapped floodplain and other regulated hazards, please use our “Map your Property” tool. While we strive to keep our regulatory mapping as accurate as possible, please note that Ontario Regulation 41/24 applies to all regulated areas whether or not they are currently shown on our mapping.

2) Attend a public information meeting:

A virtual public meeting will be held on Monday, September 22, 2025, at 7:00 pm. An in-person public meeting will be held on Thursday, September 25, 2025 at the Woolwich Memorial Centre (24 Snyder Avenue South, Elmira N2B 1Y9) from 5:00 pm to 7:30 pm, with a presentation at 6:00 pm. If you wish to attend the virtual public meeting, please register by sending an email to Kimiko Chhapyan at kchhapyan@grandriver.ca and a link to the meeting will be sent to you closer to the date.

3) If you wish to provide written comments, please direct them to:

400 Clyde Road, PO Box 729
Cambridge, ON N1R 5W6
Attention: Beth Brown

If you have questions or need help accessing the materials, please contact Beth Brown at 519-621-2763 extension 2307 (bbrown@grandriver.ca)).

Figure 1- Study Area of Lower Conestogo River Floodplain Mapping Update