Canada has the longest coastline in the world. It is, in fact, more than double that of the second longest coastline (held by Norway, with its many fjords). With rising sea levels, the ocean is slowly taking land back, and Canada is especially vulnerable. With its massive coast to protect, the country is looking for help from nature.
Typically, concrete or rock structures are used to protect coastlines, taking the form of seawalls, breakwaters or gabions, which are wire mesh cubes filled with rocks. In recent decades, however, we've learned that natural ecosystems around the world also provide such coastal protection. Coral reefs act similarly to breakwaters: they form off shore and create shallow water barriers so that waves crash over the reef instead of onto the land. Mangroves, the only tree in the world that lives in salt water, have immense and complex root systems in and above the water and create a barrier between ocean storms and the land. And salt marshes, found along Canada's coastlines and in its estuaries, help to protect against shoreline erosion by decreasing the size and strength of waves hitting the coast.
For the people who design coastal protections in Canada, integrating "nature-based solutions" means understanding how much protection they provide, how and where they work best and how they compare with built structures. Canada's National Research Council, supported by the Ocean, Coastal and River Engineering research centre, and partners at the Institut national de la recherche scientifique (INRS) are studying salt marshes to provide that much-needed information.
Speaking about the project's focus, senior research engineer Paul Knox says, "It's been proven that marshes are quite effective in reducing wave energy. How effective they are is the question. It really depends on a lot of environmental conditions, what the slopes are, what the water depths are and what types of plants they contain."
One of the challenges to studying the impact of plants on waves is scaling. Researchers can create a scaled-down model of a ship, coastline and sea floor and then create waves and currents to study things such as ship performance and changes to the coastlines over time. But with live plants, scaled-down models are not possible.
The team at INRS in Quebec City has a facility that overcomes that challenge, the environmental hydraulics laboratory. Researchers recreated a salt marsh at the lab's 120-metre long, 5-metre wide and 5-metre deep outdoor wave tank, known as a flume. This included planting 3 types of salt marsh vegetation (each one grows in a different water depth). "The flume has a very powerful wave generator that can be used to make full-scale waves. This means we can make the kind of waves you'd see out in the ocean," says Knox. "As soon as we start to use live plants, we have to do full-scale testing, which makes the facility at INRS quite unique and quite valuable."
A key role of the NRC in this project is providing guidance based on its decades of experience in coastal research. "We have quite a lot of facilities in Ottawa that have been investigating coastal areas and doing coastal research for decades now," he says. "We've built up a lot of expertise here that INRS has been able to draw upon when designing the testing program for this research."
From late 2023 to 2024, the salt marsh was left intact to overwinter in the INRS flume as an opportunity to collect novel data: no studies had been done before on how the salt marsh and its ability to protect the coast changes with the seasons. Beginning in the spring of 2024, the team resumed testing to answer new questions about whether salt marshes die back over the winter, what the effect of dieback is on their ability to protect the coastline and how long it takes for the salt marsh to regrow and provide its full protection.
"Engineers and practitioners often feel like they're grasping in the dark, trying to find solutions when there's not a lot of data," explains Knox. "One of the most important outcomes of this project will be for practitioners to understand that there are data out there for designing these types of marshes."