The International Lake Champlain-Richelieu River Study Board was created in 2017 to respond to a request by the Canadian and US governments to explore the causes, impacts and risks of flooding in the Lake Champlain-Richelieu River basin and recommend solutions.
As the study board prepares to present its findings and recommendations to the International Joint Commission (IJC) in 2022, experts are working to complete research into flood control and management in the system.
The board is tasked with investigating solutions to flooding focused around four key themes:
- Examining moderate structural options to reduce high water levels
- Investigating ways to impede flows of waterways during floods
- Developing tools to improve flood response and emergency preparedness
- Considering methods of improving floodplain management.
In early December, the study board plans to release its report, “Flood water storage using active and passive approaches: Assessing flood control attributes of wetlands and riparian agricultural land in the Lake Champlain-Richelieu River watershed,” which addresses Theme 2 of the study.
The report investigates the role of wetlands in slowing flows during flood events and assesses the notion of using increased wetland storage and agricultural land to decelerate flow rates in streams and rivers flowing into Lake Champlain.
Wetlands are natural landscape features within a watershed that can help slow floodwaters and reduce the intensity of floods downstream. Storing floodwaters upland of Lake Champlain in wetlands is considered a nature-based approach to flood mitigation.
Study experts developed models to understand the role of existing wetlands on inflows to Lake Champlain and flows in the Richelieu River, and to assess how adding wetland area to the basin and/or temporarily flooding farmland could create additional flood mitigation benefits.
The researchers then used these models to determine the flood mitigation benefits of existing wetlands, the effect of adding wetlands to the basin and the effect of temporarily using agricultural lands for water storage during flooding.
To determine the effect of existing wetlands, study experts set out to quantify the area of existing wetlands in the basin.
Wetlands cover roughly 7 percent of the basin and have a total area of about 1,684 square kilometers (650 square miles), more than the surface area of Lake Champlain, which is about 1,270 square km (490 square miles).
In addition to their effectiveness at storing water in the basin, wetlands also provide environmental services such as habitat for fish, birds and wildlife, and filter out chemicals and nutrients entering the water system.
Experts used basin-specific models to assess the significance of existing wetlands in mitigating the effects of flooding.
Results demonstrated that existing wetlands significantly reduced the highest flow rates of Lake Champlain tributaries by a range of 9 to 52 percent, as observed in the 20 tributaries examined. Modelling also showed that existing wetlands reduce on average the Lake Champlain annual high water level by 12 centimeters (4.7 inches) and the Richelieu River annual high water level by 9 cm (3.5 inches). Existing wetlands also reduce on average the annual Richelieu River flow rate by 6 percent and the annual Lake Champlain net basin supply by 22 percent.
These results illustrate the key hydrological services provided by existing wetlands. The results also demonstrate that without the presence of wetlands in the basin, the peak water level during the 2011 flood would have been 15 cm (6 inches) higher on Lake Champlain and 12 cm (4.7 inches) higher at Saint-Jean-sur-Richelieu.
Experts further examined the effect of adding wetland area to the basin and temporarily flooding farmland for additional water storage benefits. Although the modeling of these scenarios demonstrated some flood reduction benefits, adding wetlands and/or flooding farmland would involve extensive surface area requirements in the basin and is unlikely to be implementable at a scale required to create significant benefits on the Lake Champlain and Richelieu River.
Given existing policies, programs and regulations in Canada and the United States, fostering restoration and construction of wetlands instead of flooding farmland might provide a socially acceptable framework to build resilience over time in the Champlain-Richelieu basin, the report notes.
The amount of land required to make a substantial impact on flows and water levels of the Lake Champlain and Richelieu River might be cost-prohibitive, and this may not be a viable solution. However, it is important to note that a detailed cost-benefit analysis was beyond the scope of the study and underlying mandate.
Nevertheless, it is important to note that outcomes of this hydrological modelling exercise provide valuable guidance to policymakers. Once the study is complete in 2022, the modelling tool developed will be available to interested parties to identify potential water storage areas and assess multiple scenarios for each sub-watershed within the basin.
For more information on how the study is looking at the effect of wetland storage on mitigating flooding, you can view a technical webinar on the topic presented in November 2020.
Christina Chiasson is a policy analyst for the Canadian Section of the IJC in Ottawa, Ontario.