Environment

King tides: preparing Canada’s coastline for a future of flooding

King tides are the tipping point at which storms can become devastation — as well as a glimpse of Canada’s coastline 100 years from now. Can green infrastructure help weather the danger?

  • Oct 10, 2022
  • 1,523 words
  • 7 minutes
Photo: Matt Hardy/Unsplash
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Winds whipping, waves crashing, seawalls surmounted; parks flooded, piers demolished, escaped logs hurled. The massive damage caused to Vancouver’s coastline in early January was born from what one Vancouver park board director described a “spectacular confluence of events.”  In circumstances where just a few centimetres of water can prove a tipping point with devastating consequences, one phenomenon surges forward: king tide. 

Non-scientific in origin, the phrase emerged from Australia in 2009 as the country faced its highest seasonal tides in over 20 years. Now, the name is gaining popularity with the public, the media and — slowly, grudgingly — the scientific community.

King tides are both naturally occurring and entirely predictable. Simply put, they are the highest of high tides. How they come about, however, involves a conjunction of cosmic proportions — one befitting their regal title. 

Gravity dictates tides — the Moon, Sun and Earth’s rotation all get a say — manifesting in the local rise and fall of sea levels. In a lunar month, the highest tides occur every two weeks — the new and full moons. These tides, called spring tides, are around 20 per cent higher than regular tides.

King tides require yet another layer of celestial interference. In this case, a spring tide must occur when the Earth, Moon and Sun are aligned at perigee — the orbital point at which the moon is closest to the Earth — and perihelion — the orbital point at which the Earth is closest to the Sun. This occurs around January 2 each year, boosting tide height even further. These are the highest tides of the year. The kings of tides. 

For the kind of damage bestowed upon Vancouver’s coast in early January to occur, a king tide is just one part of the picture. “At present, a king tide on a calm day is not going to have any effect,” says John Clague, professor emeritus, earth sciences at Simon Fraser University, B.C. “But if you have this coincidence of winds that blow waters across the Salish Sea, then you have a storm surge that is operating on top of the king tide. That’s when you see damage.”

The large swathes of low-lying land in Metro Vancouver makes it vulnerable. The delta plain just south of the city is home to a quarter of a million people and vital infrastructure such as major roads and airports, all protected by a series of sea dikes, humanmade barriers to encroaching water. “Most of the dikes were built close to a hundred years ago now,” says Clague. “They were last upgraded in 1948. When they built them, they didn’t really think of sea level rise.”

A barge that ran aground on Sunset Beach, Vancouver, after a 2021 storm surge. (Photo: Ted McGrath/Flickr [CC BY-NC-SA 2.0]
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Sea level rise — predicted to be up to two metres by the year 2100 and accelerating thereafter — is one issue; the price of replacing the dikes is another. A  2011 study estimated the cost of replacing dikes along 250 kilometres of Vancouver coastline and Fraser River shoreline by 2100 at nearly $10 billion. A kingly sum. “And we’ve had a lot of population growth since then,” adds Clague.

As sea levels rise and waves increase in strength, growing levels of damage are expected. With such expensive estimates and more pressing demands on public funds, repairing sea defences fast enough to keep up with rising tides may be out of reach. 

There are other options, however, when it comes to planning for a higher sea level. King tides give Canada a glimpse of what it will face every day by the end of this century, showing what land will be most vulnerable. Andreanne Doyon, assistant professor, School of Resource & Environmental Management at SFU, says B.C. has made some good steps in climate mitigation  — but more attention should be placed on adaptation.

“We know these things [rising sea levels, flooding, storm surge damage] are happening, so how do we make sure that when they happen, they’re not as detrimental?” says Doyon. “One thing we’re seeing is the incorporation of green infrastructure to help respond to all the water.”

As cities become increasingly inundated, some are moving toward other forms of water-sensitive urban design to capture and redistribute the excess. Case in point: the Sea2City Design Challenge, which wrapped up In September looked at how Vancouver could adapt to rising sea levels while also benefiting socially, economically and ecologically. The entries, some of which will be used to inform the city’s overarching coastal adaptation plan, include integrating absorbent wetlands into the landscape, creating flood parks and using shoreline plants and habitats to build riparian zones. (See the above infographic for examples of what this could look like.)

As well as absorbing and redistributing water, the green approach can mitigate issues like the urban heat island effect. “Areas with lots of hard surfaces are hotter than areas with lots of vegetation,” says Doyon. “By incorporating more green and blue spaces in our cities, we can keep the temperature down in the summer — especially during heat waves.”

The west coast isn’t the only coastline dealing with king tides and rising sea levels. A 2021 study by Dalhousie University scientists found that sea-level rise is causing permafrost (ground that remains completely frozen for at least two years straight and is important in stabilizing coastlines) along the Arctic coast to thaw and retreat, threatening northern ecosystems. The vulnerability of coastal communities in the Arctic is heightened as a result, as this loss of permafrost can trigger fast slumps of previously stable earth — land that may provide the bedrock for a community’s infrastructure. One example of the importance of permafrost is its long utilized role as a natural freezer. In Tuktoyaktuk, in the Inuvialuit Settlement Region, N.W.T., the 19-room community freezer is carved deep into the permafrost. Fish and meat, harvested from spring to fall, is stored here to last through winter. Losing this would mean losing the community’s food security. The impact doesn’t stop there. As permafrost thaws, saltwater flows into terrestrial and freshwater environments and tons of previously-locked carbon is released into the atmosphere. 

The east coast faces similar challenges as those faced out west, explains Patricia Manuel, professor at Dalhousie University’s school of planning. They are further compounded, however, by ongoing adjustment to deglaciation 15,000 years ago. Not only is Nova Scotia’s sea level rising — the landmass is sinking.

In Peggy’s Cove, the iconic Nova Scotian community perched picturesquely on wave-washed boulders bordering the Atlantic Ocean, preservation is a must. The area is under threat of flood and sea-level rise, so much so that a multi-million dollar infrastructure improvement plan was put in place by the provincial government. The plan included raising a portion of Peggy’s Point Road (the road that leads to Peggy’s Cove’s famous lighthouse) and a new breakwater built of natural materials to address sea-level rise and “one-in-five-year” storm surge inundation — perhaps those occurring during a king tide. 

“Our tideline is progressing inland, meaning that now-dry land will soon be the landward extent of the highest tide,” says Manuel. And when factoring king tides into the equation, the threat heightens. Buildings currently above the tideline will soon be at risk of flooding — with or without a storm.

Over in Halifax, ongoing development of the waterfront — such as the award-winning, $57.6 million Halifax Central Library — means avoiding flooding all together won’t be possible. When avoiding or scaling back coastal development isn’t an option, accommodating the rising tides is the next approach, says Manuel. As well as redesigning the surrounding coastal area to be greener and more absorbent, important buildings can be designed to be flood-proofed. Options include wet and dry floodproofing. The former involves clearing a space under a structure where flood waters can occupy without corroding the foundation and other essential — or expensive to replace — systems. Materials are required for construction that allow easy cleaning after the waters subside and walls should be easily drainable. Dry floodproofing can be more labor-and parts-intensive. Water-resistant materials are applied along the exterior walls of buildings to keep out all water. This method, however, exposes the structure to substantial hydrostatic pressures, which is not the case with wet floodproofing. “And if you can’t do any of those,” says Manuel, “then [you can] build a wall around it and protect it.”

The message is clear. Whether Arctic, British Columbian or Nova Scotian, all of Canada’s coastline is under threat; flooding that is today caused by a spectacular confluence of events could tomorrow become a regular occurrence. There are solutions at hand. But the stakes are high.

“Around five per cent of humanity lives within five metres of sea level,” says Clague. “We are going to see huge social turmoil as we learn to deal with this problem.”

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This story is from the November/December 2022 Issue

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