What is a Tidal Bore?



This is the incoming tidal bore just past Maitland, N.S.

A tidal bore is a rare phenomenon found in only a few places around the world. It occurs when a large amount of water enters a narrow shallow river. The incoming tide's leading edge forms a churning, tumbling, wall of water that travels upriver against the outflowing current.


For a tidal bore to be created, there must be a large rise in tide at the mouth of the river where the initial advance of water is impeded or restricted by a structure such as a sandbar. The river must be shallow and nearly flat. The water cannot fill into the river fast enough to match the quickly rising tide at the mouth creating an advancing front. The resistance from the river bed and the outgoing flow of water causes the incoming front to topple over and churn. You can hear the tidal bore from about 1 km away when it's churning.



There are quite a few tidal bores produced by the tides from the Bay of Fundy; most notable are the Petitcodiac River, Moncton, N.B., the Salmon River, Truro, N.S., and the Shubenacadie River, N.S. (that's where we come in).




Why the Bay of Fundy?


The Bay of Fundy has the largest tides in the world! More water flows into the Bay of Fundy in one tide than the amount of water that flows through all of the freshwater rivers in the whole world at the same time. We are talking about 120 billion tons of water with every tide. This is enough water that Nova Scotia has a small seismic shift every time the tide comes in, tilting Nova Scotia on one of its minor plates.


So why the Bay of Fundy? It all starts in the Gulf of Maine when a tidal bulge enters the bay. This is how the tide goes in and out everywhere except that the Bay of Fundy is a very shallow bay, so the water gets pushed up off the bottom. As the water continues further inland, the bay keeps getting narrower and narrower pushing the tides up even further and making the water move faster.


The bay also has one other unique, very important feature. That is that the amount if time it takes for the water to drain out completely is almost exactly when the tide starts to come in again. This is much like the water sloshing back and forth in a bath tub and greatly enhances the rise and fall in the bay.



Nothing Boring About the Tidal Bore

From afar, the tidal bore may look like just a ripple, and in some places and some tides it is. The best way to see and experience the tidal bore is to go "tidal bore rafting"!


When the tidal bore is "churning" you can hear it from about 1km away. If you can hear and see it, then you better get into a boat! We know how to ride the tidal bore the best! We'll let you hear the bore and see it's real size just before the water slashes over the front of the boat, soaking everyone inside! Then we'll turn around and ride right on top as the wall of water spreads out across the channel. Then it's time for the rapids, but that's a story for another day.


If anyone tells you that the tidal bore is boring, you tell them, "you must be doing it wrong!"