Coming to grips with the tide

Once you get past Quebec City, the tide plays a part in the day to day of everyone up and down this coast. We’d been looking at tide clocks to see when and where but I’ve never really understood how they work. I knew it had something to do with the pull of the moon and the sun but I always thought that when the tide was low it was because the water was bulging in the middle of the ocean, being pulled by the gravity of these massive celestial bodies. It turns out I only had it partly right. The moon and the sun make it all happen but the sea doesn’t bulge and stretch, it actually just goes around and around.

If you held a round cake pan in your hand and filled it halfway with water and moved it off its axis in a counterclockwise direction, you’d kinda get the idea. The water is the ocean. The sides of the cake pan are the shores. The sides on your right would be the Atlantic coast of Europe and the left hand side would be the Atlantic coast of North America. The swell starts at the bottom right and moves its way up and across and then down the left side and starts over. What it hits on the way — islands, inlets, massive estuaries like the St-Lawrence -- all have an impact, slowing down its path or deviating it but that’s pretty much how it works. If the tide is high on the upper right quadrant, it’s low on the bottom left. All the oceans of the world rotate around these spots called amphidromic points, points which kind of correspond to the middle of the cake pan, or the axis of the water’s rotation and the water level here stays pretty constant. There are five of these points on the planet, one halfway between Madagascar and India, one between the tip of southern Europe and Newfoundland, one southeast of New Zealand, one about halfway between Colombia and the Gold Coast of Australia and the last one is off the coast of Baja. Why the water goes counterclockwise is because of something called the Coriolis Effect. Like if you were a little drunk and the room started spinning to the left (the way the planet does), you’d slam against the wall coming at you on your right. The Coriolis Effect works the same way, on all the big stuff on the planet – water and winds.

As for the super high tides it’s often in places where the water just can’t go any further, like when the tide is swelling up the west coast of the US and then gets trapped under Alaska, the tides get super high. Same goes for the Bay of Fundy where the water doesn’t have anywhere else to go.

When the moon is in line with the earth and the sun you get double pull and the tides are super high (Spring tides). When the moon is at ninety degrees off the earth from the sun, the pull happens in two different directions so you get really small (neap) tides.

Wil and I went on a hike this morning. Wil, with his uncanny instinct for the timing of every single thing, had an idea we would be back for low tide (even though we didn’t actually know how long the hike would take). Off we went, up the cliffs hanging over the floodplain for amazing vistas of the surrounding farmland and back again. As we were coming down toward the river, thousands of snow geese starting landing on the newly exposed mudflats. Like tinsel sparkling in the sky, their bodies caught the sun coming over the cliff in little flashes of light. In their thousands, they settled not far from the water’s edge, digging up roots and getting some calories in on their way from Greenland to Mexico. Groups of a hundred or more welcomed smaller flocks and they all settled in – a broad band of pure white all along the shore. We traipsed through the mud and puddles, marvelling at the colours of the plants and the way the greenery clung to little rocks to anchor itself in the tides. Little coral-coloured samphire popped against a thick blanket of yellow and green seaweed. We wondered what determined how long the birds stayed and how they decided to go. Who decides when? Who decides where? We wandered downriver to the Tête d’Allumette for a beer and watched the birds along the shore, snow geese, mallards, cormorants. We watched as the tide started to come in. The floodplain is very shallow so it wasn’t quick. The water inched its way up the shore, coming ever closer to the birds. The cormorants comically jockeyed for position on the shrinking rocks, the mallards went from pacing to wading. It was as though the snow geese understood that it was just a matter of time and began to lift off. At first it was a few at a time, then it was hundreds at a go. Taking off into the wind, heading toward the Atlantic, a honking mess of elegant white bodies and black wingtips. These birds understand the tides. Tide as mealtime. Tide as shelter. They took to the skies, leaving the shoreline to flood, the advancing water erasing all evidence of their seasonal passage. If it weren’t for those of us who’d seen it, no one would ever have known they were there.