The Bay of Fundy is a large bay located on the Atlantic coast between the Canadian provinces of New Brunswick and Nova Scotia. It is known for large tidal shifts. These shifts are some of the largest and most dramatic in the world. They average 47.5 feet from low to high tide and have set a record of 53.6 feet.
The speed of these changes can also be fast, traveling about eight knots (equivalent to about 10 miles per hour) and raising or falling at a rate of about an inch per minute. The changes are particularly evidenced in different ways, in different places.
The Effect of Tides
Low tide is characterized by huge tidal flats. The sandstone bluffs along the coast have been deeply eroded by the rushing water. One of the best places to see these flats and cliffs are at Burntcoat Head, the site of the world’s highest tides. It serves as visual evidence of the 160 million tons of water than shifts into and out of the bay during each of the bay’s tidal cycles. Just how much water does 160 million tons represent? About the same amount as all the earth’s rivers combined pour into the ocean each day. And remember, the tides shift twice each of these days.
We timed our visit to this location to low tide, where one can see the full extent of the tides by standing down on the mud flats and looking up to the high water marks. While the height is impressive enough, the dramatically carved shapes of the water-scoured sandstone cliffs are even more striking.
We experienced high tide in a different, even more dramatic way—by powering through the tide as it surged at speeds of up to 20 miles per hour up a river that typically flows into the Basin. Nowhere is this surge more dramatic than in the Shubenacadie River, between Maitland and South Maitland. These flows, called “tidal bores”, are what, in open water, are called tidal waves.
Tidal bores occur when water from rapidly rising tides push into the shallow rivers—and especially over sandbars—so rapidly as to create waves. Although most tidal bores are small and barely noticeable, they produce waves here that typically reach 9 to 12 feet. During Harvest Moons, when the moon is closest to the earth and exerting its greatest gravitational pull, waves of 22 feet have been measured. Traditionally lazy rivers are transformed into torrents.
While most people observe these bores from the river bank or observation platforms over the water, we wanted to experience them first hand. So we signed up for a Zodiac trip that would take us through, back over, and then return through the bore many times. They warned us that we would get soaked, and we did. So soaked that by the time we reached an eddy, jumping in for a swim through the tide seemed superfluous. But we did so anyway, floating, uncontrollably, further and further from the Zodiac, which eventually came to retrieve us.
We also had a chance to walk a water-saturated sandbar (easily digging in to over our knees, where we could rock forward without fear of falling into the slop. By the time we returned 60 minutes later, that sandbar was twenty feet below the surface.
Nor were water and mud the only parts of tidal bore experience. We also saw three bald eagles and a nest that was about six feet in diameter.
How does this compare to whitewater river rafting? The waves we experienced were probably equivalent to Class Two, with some approaching Class Three. Good soaking fun but nothing like the sense of terror of Class Five Rapids, which could be possible during a Harvest Moon!
And since these rivers are all sand, you don’t have to worry about hitting submerged rocks that can capsize the craft. Most importantly, white water rafting is done on rafts that float with the current, navigating one rapid after another with paddles. Tidal bores, by contrast, pass a given spot only once every twelve hours. The only way to multiply the experience is to motor back down the river, and continually repeat the process. Repeating, however, does not translate into reliving the same experience, since waves change dramatically depending on the depth, width and contour of the river at different spots.
What does a tidal bore look and feel like? If you’ve reacted or kayaked through whitewater, you know. Unfortunately we did not have a waterproof camera attached to our life vests so that we could show you. But that is a good excuse to go experience it yourselves.
Fundy Tidal Interpretive Center in Maitland
But we still wanted to better understand why tidal variations differ so dramatically in different parts of the world and to better understand the nature of tidal bores and why they only occur in about a dozen places on earth. We learned some of these answers at the Fundy Tidal Interpretive Center in Maitland. The center explained how the size of tidal variations are primarily attributed to a combination of multiple factors:
- The phase of the moon;
- The orbital alignment of the sun, moon, and earth; and
- The Tidal Resonance, which relates to the alignment of the frequency of a wave with the tidal shift and the length and shape of the bay, specifically a length that closely matches the tidal frequency and the bay’s relatively shallow (about 200 feet), V-shaped bottom.
Tidal bores occur when the first incoming wave of an incoming tide meets the fresh water that is flowing from the river into the ocean. This inflowing tide initially rides atop the incoming water—creating a wall of water of 25 to 30 feet that moves up the river at 20 km/hour in Maitland where we rafted the bore. Soon, however, the continuing surge of water overwhelms the outward flow and reverses the direction of the river.
Tidal Shift Effects on the Area’s Economy
The museum also discussed how the Annapolis Valley tidal shifts affected the region’s economy. Among there are:
- The agriculture benefits of building dykes to create new, extremely fertile farmland and the critical role of specialized, one-way sluice gates that allow freshwater to drain from the reclaimed land, but prevent saltwater from invading the land.
- The shipbuilding benefits of having tides that create cost-free dry-docks for several predictable hours each day by “pumping” water from beneath the boats.
- The shipping and trading implications of enforcing schedules in which ships had to arrive at specific times each day and be loaded or unloaded in a defined period so the ship could leave harbor before the tide fell too low.