Quirks & Quarks

Sea levels rising faster in the Maritimes, but science can help communities plan and prepare

Canada has hundreds of thousands of kilometres of coastline potentially vulnerable to sea level rise. But in many Nova Scotia towns built close to the water’s edge, the threat is particularly pronounced making the need for solutions especially urgent.

'This is not something that's going to happen in 25 or 30 years. It's happening right now': local mayor

A storm surge from the Atlantic Ocean hits a break wall in Cow Bay, N.S., on Friday, Jan. 5, 2018. (Darren Calabrese/Reuters)
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This is the second in a series of Quirks & Quarks stories on how science and technology are working in regions and communities across Canada facing unique challenges of climate change. 


David Devene, mayor of Mahone Bay, N.S., takes in the view of his tiny coastal community — numbering about 1,000 residents — with its historic buildings, main thoroughfare and the three waterfront churches that are the town's best-known feature.

It's an iconic view that's been featured on a Canada Post stamp, but what Devene sees are vulnerabilities to climate change.

"High tide'll bring the water up five to six feet and then you get a storm surge. It can be 10, 15, 20 feet," he said.

In these times, the water reaches the foundations of all three churches, and sometimes crosses the highway.

Mahone Bay Mayor David Devene sees his town's vulnerabilities to climate change. (Moira Donovan/CBC)

"And eventually we're going to get up one morning and that road is going to be gone," he said.
 
"This is not something that's going to happen in 25 or 30 years. It's happening right now."

Canada has hundreds of thousands of kilometres of coastline potentially vulnerable to sea level rise. But that threat is particularly pronounced in towns like Mahone Bay.

Many Nova Scotian communities are built close to the water, and the province has one of the most severe rates of sea level rise in the country. That makes the need for solutions — none of them particularly easy or affordable — especially urgent.

Modelling sea level rise

Tim Webster, a research scientist with the Applied Geomatics Research Group at Nova Scotia Community College, has helped model what sea level rise could look like in the province.

His team uses a technology called LiDAR high-resolution topographic mapping, which fires laser pulses at surfaces and maps them by measuring how long it takes for the light to bounce back.

Tim Webster, research scientist with the Applied Geomatics Research Group at the Nova Scotia Community College, helps model what sea level rise could look like in the province. (Moira Donovan/CBC)

"These are high-resolution elevation models of the land surface where we can simulate rising ocean levels and storm surges to look at what's getting flooded," said Webster, who holds a PhD in Earth Science.

"And in recent times, we've moved into a technology called topobathymetric LiDAR, which is similar, in that we are able to produce detailed topographic maps of the land and into the near shore under underwater elevation." 

This kind of technology can help us understand just what's at risk in the future.

According to projections from the Intergovernmental Panel on Climate Change, sea levels could rise by an average of 74 centimetres globally by 2100 at the current rate of emissions.

Unfortunately, Nova Scotia is subject to a particularly star-crossed set of circumstances, geologically speaking. As the water rises, the land is sinking as a consequence of the last ice age.

The area around Hudson's Bay, which was depressed by the thickest part of the Laurentide Ice Sheet thousands of years ago, is now rebounding and moving upward. 

Nova Scotia, which was at the thinner edge of the ice sheet, is headed in the opposite direction.

Essentially, the province is on the downward side of a geological teeter-totter.

This phenomenon — known as glacial isostatic adjustment — means the Maritimes are subsiding at a rate of about 15 centimetres per century, said Webster.

Both these issues combined mean that in parts of Nova Scotia, the sea could rise between one metre and 2.5 metres by 2100. 

Halifax's waterfront

Nova Scotia's biggest city could face tremendous consequences, too.

"We know that our standing level water is going up incrementally year over year and that, in a worst-case scenario, we would experience flooding along our waterfront," said Shannon Miedema, manager of the energy and environment program for Halifax Regional Municipality.

As the water rises in Nova Scotia, the land is sinking as a consequence of the last ice age. (Ben Shannon/CBC)

Big storms such as Hurricane Dorian in the fall of 2019 gave Maritimers a taste of what coastlines could look like if higher sea levels were here to stay. 

"That is something that is a very hard conversation for everybody to have at every level, and you know, we're a working port," said Miedema.

"We have a vibrant waterfront. It's part of our culture, our identity, our community."

Shannon Miedema, energy and environment program manager for the Halifax Regional Municipality. (Moira Donovan/CBC)

"So we don't want to just retreat now and have this big vacant space on our waterfront. But we want to be smart. We want to understand the risk. And we want to understand as best we can when that time may or may not come and how far we might have to go back." 

Halifax is trying to plan for the future, as best it can. The city doesn't own a lot of the land on the waterfront. Much of it is privately held, or owned by other levels of government, so the city can't always decide what goes where.

But it can decide how things are put in place. Since 2014, Halifax has prohibited residential development within roughly 2.5 metres of the harbour's current high water mark. This should protect residences against sea level rise and storm surge. 

With the risks increasing, Miedema said the city is looking at taking measures even further, requiring new commercial buildings to be located a certain elevation above the water, for example. 

Elsewhere in the world, authorities are proposing megaprojects to hold back the sea like Venice's flood barriers or the proposed seawall in New York City.

Liverpool, N.S., is trying to ward off flood waters from rising sea levels while the community is also starting to sink. 3:33

But multibillion-dollar megaprojects aren't likely a practical solution in the Maritimes, so solutions will be a matter of avoiding the danger, or adapting to it. 

The province is currently developing coastal legislation that will regulate how close people can build to the coast.

But that's a big change to the way people have lived around here for hundreds of years, particularly with Nova Scotia's legacy of fishing communities, said Patricia Manuel, professor at Dalhousie University's School of Planning. 

Patricia Manuel, professor in the School of Planning at Dalhousie University in Halifax, has spent the last decade researching the impact of sea level rise and flooding on coastal communities. (Anne De Vries)

"Whenever you drive along the shore here in this province, you're going to see people building too close," she said.

"You will see new buildings going in on an eroding shore that's clearly moving backwards."

But in addition to retreating from or avoiding building at the waterfront, another approach is to protect the shoreline, sometimes with physical infrastructure such as seawalls and dikes, but with nature-based solutions as well, she said.

A process called managed realignment involves moving dikes closer to shore and allowing salt marshes to form on the seaward side. This creates a soft defence against sea level rise and storm surge.

The Converse Marsh managed realignment site in Fort Lawrence, N.S., near Amherst, is one example of a project where a dike is moved closer to shore and wetlands absorb some of the energy impact of waves. (Moira Donovan/CBC)

A similar strategy could help save Mahone Bay, where Mayor David Devene said serious conversations about how to protect the community from climate change began in earnest in 2015 after a particularly high tide.

Initially they thought they could simply pile more rock at the shoreline, the kind of durable quarry rock referred to as armor stone.

"But it was determined that armor stone is not going to really last because you're washing away what's behind the armor stone," said Devene.

The town asked engineering and environmental consulting firm CBCL to come up with an alternative solution.

It proposed infilling part of the Bay to create a foreshore wetland, held together with a dense network of grasses, which would extend out at a downward slope from the current seawall by about five metres.

"So they would be moving to eliminate the energy impact of the waves before it even got to the actual shoreline." 

There are towns, municipalities, properties, coast to coast to coast that are in danger of being flooded by the rising tide. - David Devene

Town council has approved the plan, but now they need a way to pay the $3.5-million bill. Devene said he hopes other levels of government will come to the town's aid, but acknowledges that his isn't the only community that will be looking for help.

"There are towns, municipalities, properties, coast to coast to coast that are in danger of being flooded by the rising tide, the global warming phenomena." 

Mahone Bay Mayor David Devenne points out a compromised road. (Moira Donovan/CBC)

Looking out at Mahone Bay's fragile waterfront, he notes that what might have been the easiest response — curbing climate change — has already slipped from our grasp.
 
"It's an amazing town. We've got folks that are in their 90s that were born here and they've lived here their whole lives. And it's because of the quality of the life here that they do that.

To think that slowing climate change earlier on could have prevented the worst from happening, he said, "is quite daunting and quite unacceptable."


Written by Moira Donovan and Brandie Weikle. Produced by Moira Donovan.

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