Cutting holes in dikes to mitigate the effects of climate change might seem counterintuitive to some.
But that’s exactly the type of measure Danika van Proosdij contemplates as she studies how to best restore salt marshes. Nova Scotia has lost about 80 per cent of these areas of coastal grassland regularly flooded by seawater since the Acadians first settled here in the 17th Century.
“We are cutting holes in dikes and allowing tidal flow to actually come back into a system that was isolated from tidal flow for hundreds of years,” said van Proosdij, a geomorphologist who specializes in how coastal ecosystems respond to human activity.
If the cuts are made properly, they can create conditions that allow plants, fish, and invertebrates to return, she said.
“You’re able to restore a lot of that habitat and kind of offset the habitat that was lost,” said van Proosdij, a professor at Saint Mary’s University’s Department of Geography and Environmental Studies, who describes her work as “almost nature by design.”
“How can we work with the natural processes of salt marshes, for example, to provide protection from coastal erosion or provide habitat mitigation, (or) flood storage protection if we’re restoring a salt marsh,” she said.
Stimulating salt marsh to grow can provide “a buffer from wave energy,” van Proosdij said.
“The key thing is actually having optimum hydrology — so creating conditions where we have regular water tidal flow coming in and out of the system. That tide can bring nutrients. It also brings sediment to allow the marsh to grow up vertically.”
Talk of cutting holes in dikes would likely put the fear into any farmer who owns valuable dike land on the other side.
“That’s why there’s careful planning coming in,” van Proosdij said. “It’s done in very close collaboration with the Department of Agriculture.”
She’s in the initial stages of designing a plan for Truro to help mitigate flooding in the low-lying town by increasing the flood plain.
That work will include figuring out where the best spot is to make a hole in one of the dikes that hold back local rivers.
“We can use software to be able to model predictive effects,” she said. “Before you cut a hole in anything, we know how far the water’s going to come, so there’s no negative impacts on people’s homes or infrastructure in that particular area.”
Over the last decade, van Proosdij has worked closely with the consulting firm CB Wetlands & Environmental Specialists to understand how salt marsh ecosystems, particularly in the Bay of Fundy area, respond to causeways, and dike construction, and how to lessen some of the negative impacts by enhancing their return.
They employ drones to map coastal wetlands and the intertidal zone. Those can be used to build surface models to identify areas where fast-moving water has caused erosion or deposited new sediment, said Jennie Graham, a geomatics specialist who works for CB Wetlands.
“This helps us by telling us where we need to be concerned,” Graham said. “What areas are developing well, what areas we’re seeing erosion, and what that represents for the system at large.”
For example, a causeway built nearly a half century ago near Windsor so a highway could go through resulted in very rapid sedimentation downstream, van Proosdij said.
“By 1992, we started to see the first evidence of colonization by salt marsh vegetation,” she said.
“Over time we’ve had very expansive developments.”
She points to maps of the area made this past July from photos shot by an aerial drone.
“The main surface is completely covered with vegetation,” van Proosdij said. “It’s a very, very productive system. Productive meaning that there’s a lot of biomass. So very tall salt marsh species that serve a very important role for the bottom of the food chain to help feed a lot of fish within that system. And it provides habitat for fish within that particular area.”
She uses hundreds of overlapping images shot by a drone, as well as instruments that allow her to pinpoint the exact location where those photos were taken and what they portray.
From there, she employs software that generates a three-dimensional surface from the aerial photos.
“It is very cool,” said van Proosdij, who started the process using a small blimp about eight years ago, but then shifted to drones after a helium shortage kicked-in a couple of years back.
The multi-rotor copter drone can be instructed to fly over a specific area in a zigzag pattern, said Greg Baker, a geomatics technician at the Maritime Provinces Spatial Analysis Research Centre, located on the SMU campus.
“It takes pictures at the required distance to have the appropriate overlap,” he said. “They key to this process, to create a 3-D model, is to be able to have a sufficient overlap between adjacent photos. And then, when it can see all of those areas, we can build a 3-D model.”
Van Proosdij now has her eye on a camera that can capture infrared images that would allow her to map vegetation more accurately.
“We look for signatures of moistures, for example, changes in chlorophyll content, to help map those differences,” van Proosdij said.
The salt marsh near Windsor is doing quite well, she said.
“It’s a very, very vibrant salt marsh,” she said. The Friends of the Avon River (FAR) group says the downstream salt marsh is too healthy and contributes to what it calls “one of Canada’s biggest man-made disasters” — “The most visible changes are the formation of the huge Windsor-Mudflats immediately below the causeway, the rapid decline of the endangered Atlantic Salmon and American Eel, as well as desecration of their ‘critical habitat’ on the lower and upper reaches of the river.” But FAR also wants to see the dike breached, to recreate the original state of the river above and below the dike.
“When the causeway was constructed, salt marsh upstream was definitely impacted,” said van Proosdij. “When you cut off salt water coming into that system, marshes are no longer able to sustain themselves in that particular area.”
A lot of the land upstream was converted for agricultural use, she said.
“That’s why the Acadians diked many areas for the fertile marshland soils.”
Van Proosdij was on hand at an Atlantic Canada Opportunities Agency funding announcement Thursday that the federal government agency is putting $9.2 million into Springboard Atlantic, a network of 19 academic institutions that aims turn research into new products and services.
“For me it’s been very useful because I don’t produce a widget,” van Proosdij said.
“I don’t produce a particular item. But we have skills and knowledge which we can apply to help companies, to help government, become more efficient and make sure that the decisions that are being made are being made with the most sound scientific basis as possible.”
She can use the three-dimensional models built with the drone pics to predict an optimized design for salt marsh restoration projects, and best practices for managing dike lands.
For the salt marsh near Windsor, van Proosdij’s role is to provide information for environmental impact assessment that will help guide decisions about how and if the highway will be twinned at that particular location.
Salt marsh is lost when tidal flow is cut off in tidal creeks and river systems, she said.
Those are important spawning grounds for many species of fish, including salmon, van Proosdij said.
Part of her work involves making strategic choices about what spots to protect, and where it’s no longer economically viable to do so.
“This is to help make decisions about where we need to hold the line and where we can actually remove some of those dikes and allow that funding that we’ve kept to (go towards topping) up dikes in areas that need it,” van Proosdij said.
This article was a real education for me. More of these please