Reversing Falls of Saint John

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The Reversing Falls are a series of rapids on the Saint John River located just west of downtown of Saint John, in New Brunswick, in Canada. Here the river runs through a narrow gorge before emptying into the Bay of Fundy. The tremendous rise and fall of the tides of the Bay of Fundy causes the “falls” to reverse direction of flow with each incoming tide.

The Bay of Fundy is subjected to one of the highest tides in the world where the difference in water level between high tide and low tide can reach up to 48 feet (14 meters). In Saint John, the bay tides rise 28 feet. When the tide is low, the full flow of the river thunders through a narrow gorge and empties into the bay. An underwater ledge, 36 feet below the surface causes the water in the river to tumble downward in a series of rapids and whirlpools.


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As the bay tides begin to rise, they slow the course of the river and finally stop the river's flow completely. This short period of complete calm is called slack tide and is the only time that boats are able to navigate the Falls. Shortly after this slack tide the bay tides become higher than the river begins to flow upstream. As the bay tides continue to rise, the reverse flow gradually increases and the rapids begin to form, reaching their peak at high tide. The effect of this reversal is felt upstream as far as Fredericton, more than 80 miles inland. At this point the tidal waters reach 14 feet higher than the river.

After high tide the bay tides begin to fall and the upstream flow of the river gradually lowers until the bay tides fall to the level of the river - once again resulting in another slack tide. The river then resumes its normal course and begins to flow back out of the bay. The bay tides continue to fall below the level of the river until at low tide the rapids are again at their peak, flowing down stream.

The tide of Bay of Fundy are semidiurnal, rising and falling once about every 12 and a half hours. So the river reverses twice each day. There are several ways to observe the falls, but the best vantage point is from Fallsview Park, not far from the Reversing Falls Information Centre.

Also see: Horizontal Falls and Tidal Bore: When Rivers Flow Against The Current


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Sources: Wikipedia /  via AtlasObscura

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