About tides and currents
Learn about tides and currents, including their causes and how we use their data.
On this page
- Tides and currents in Canada
- Tides in the Great Lakes
- World's largest tides: Bay of Fundy and Ungava Bay
- How we use tide data
- Related links
Tides and currents in Canada
Canada has more than 240,000 kilometres of seacoast with some of the most interesting and peculiar tides. Tides are the periodic rise and fall of the water along ocean coasts that follows a rhythmic daily pattern.
Tides occur in oceans, but to a much smaller extent they also occur in:
- large lakes
- the atmosphere
- the solid crust of the earth
Tides are caused by the gravitational attraction of the sun and moon, which causes waters of the ocean to raise and lower at different parts of the earth. Tidal range varies during the month according to phase of the moon. They are largest at the new and full moons, and smallest at the quarter phases.
There are also non-astronomical factors that affect tides, such as:
- local water depth
- coastline configurations
- ocean-floor topography
Canada began to study the tides along the eastern and western coasts in the 1800s to help ship captains and fisherman. This Canadian Hydrographic Service expanded and refined by this task over the years while charting the navigable waters of Canada.
Tides in the Great Lakes
Most inland waters are too small and shallow to be affected by the tidal forces of the moon and sun. However, we've recorded a very small tidal range of about 0.03 m on the Great Lakes.
We can't easily observe the Great Lakes tide, as the water responds to barometric pressure and wind changes. The tide also isn't large enough to affect navigation or harbour installations.
World's largest tides: Bay of Fundy and Ungava Bay
The world's largest tidal ranges is 16 metres and occurs on the East Coast of Canada.
The Bay of Fundy (Minas Basin) and Ungava Bay (Leaf Basin) have an unusual combination of shape and resonance (seiche), which causes the large tides.
The bays are "V" shaped. Water entering from the open ocean is funneled from the bay's wide mouth into less and less space as it moves into the head. The water is forced to pile up and form a large tide.
The water in the Bay of Fundy and Ungava Bay also has a natural rocking motion called a resonance (seiche). It takes about 13 hours for water to rock from the mouth of the bays to the head, and then back again.
The Atlantic Ocean tide rising and flooding into the bay every 12 hours and 25 minutes reinforces the rocking motion. The seiche in the bays are therefore sustained by a pulse from the ocean tides.
Other places in the world that have large tides include:
- the Port of Bristol in England (10 m)
- the Sea of Okhotsk northeast of Japan (10 m)
- Turnagain Arm in Alaska (12 m)
- the Gulf of St. Malo in France (14 m)
How we use tide data
It's important that we know tide times, heights and the extent of inflow and outflow so we can:
- provide information for underwater military engineering
- provide data useful to water sport and tourism activities, like:
- recreational boating
- work on harbour engineering projects, such as the construction of:
- navigate commercial and recreational waterways, estuaries, bays and harbours
Tide information also helps hydrography establish chart data for marking a base line or coastline. This establishes the offshore territorial limits, both on the sea surface and on the submerged lands of the Continental Shelf.