Tidal Changes in the Bay of Fundy

 

Low tide at Alma in New Brunswick.

The Bay of Fundy in New Brunswick, Canada has the highest tides of any place on Earth. There are two high tides and two low tides every 24-hour period in the Bay. Twice every day the Bay fills and empties of a billion tons of water during each tide cycle. That is more than the flow of all the world’s freshwater rivers combined. 

The Earth's average tide-driven variation in sea level is three feet, but the water level near Wolfville, in Nova Scotia's Minas Basin, can be as much as 53 feet (16 meters) higher than at low tide.

At Fundy National Park, the difference between high and low tide can be as much as 12 meters or 39 feet. At the head of the bay, the tide can rise 16 meters or 53 feet, the height of a four-story building.

When the tides recede, they leave behind beaches of cobbles, shale, pebbles, sand, or mud flats, and strand small boats such as shown above at the village of Alma.

Ocean tides are caused by the gravitational pull of the moon and sun on Earth. Tides are a type of wave motion that affect water levels. Along the coasts, the tides typically reach high tide and ebb tide twice a day, about six hours apart (called a semi-diurnal tide). Tidal actions are more evident when the bodies of water are large or connect to oceans.

Even lakes have tides, though the effects are less obvious. One can note changes in the waves by the sloshing back and forth. On smaller bodies of water, the more significant geostrophic forces are the winds and barometric pressure.

When a bay is open to the ocean, such the Bay of Fundy, the rise and fall of the tide feeds energy into the enclosure periodically and cyclically. Tidal effects depend a great deal on the configuration and location of the shoreline. It is possible for tides to cause water systems to flow in the opposite direction than they normally flow. For example, at low tide the St. John River surges over the rapids at Reversing Falls. At high tide, the tide of the Bay of Fundy forces the Falls to flow backwards. 

Related reading: What are tides? (noaa.gov); Tides | National Oceanic and Atmospheric Administration (noaa.gov); Bay of Fundy: The Highest Tides in the World | National Oceanic and Atmospheric Administration (noaa.gov)