Tidal range is the height difference between high tide and low tide. Tides are the rise and fall of sea levels caused by gravitational forces exerted by the Moon and Sun and the rotation of Earth. Tidal range is not constant but changes depending on the locations of the Moon and Sun.
The most extreme tidal range occurs during spring tides, when the gravitational forces of both the Moon and Sun are aligned (syzygy), reinforcing each other in the same direction (new moon) or in opposite directions (full moon). During neap tides, when the Moon and Sun's gravitational force vectors act in quadrature (making a right angle to the Earth's orbit), the difference between high and low tides is smaller. Neap tides occur during the first and last quarters of the Moon's phases. The largest annual tidal range can be expected around the time of the equinox if it coincides with a spring tide.
Tidal data for coastal areas is published by national hydrographic services.The data is based on astronomical phenomena and is predictable. Sustained storm-force winds blowing from one direction combined with low barometric pressure can increase the tidal range, particularly in narrow bays. Such weather-related effects on the tide, which can cause ranges in excess of predicted values and can cause localized flooding, are not calculable in advance.
Mean tidal range is calculated as the difference between Mean High Water (i.e., the average high tide level) and Mean Low Water (the average low tide level).
The typical tidal range in the open ocean is about 0.6 metres (2 feet) (blue and green on the map on the right). Closer to the coast, this range is much greater. Coastal tidal ranges vary globally and can differ anywhere from near zero to over 16 m (52 ft). The exact range depends on the volume of water adjacent to the coast, and the geography of the basin the water sits in. Larger bodies of water have higher ranges, and the geography can act as a funnel amplifying or dispersing the tide. The world's largest tidal range of 16.3 metres (53.5 feet) occurs in Bay of Fundy, Canada, a similar range is experienced at Ungava Bay also in Canada and the United Kingdom regularly experiences tidal ranges up to 15 metres (49 feet) between England and Wales in the Severn Estuary.
The fifty coastal locations with the largest tidal ranges worldwide are listed by the National Oceanic and Atmospheric Administration of the United States.
Some of the smallest tidal ranges occur in the Mediterranean, Baltic, and Caribbean Seas. A point within a tidal system where the tidal range is almost zero is called an amphidromic point.
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The tidal range has been classifiedas:
Tides are the rise and fall of sea levels caused by the combined effects of the gravitational forces exerted by the Moon and the Sun, and the rotation of the Earth.
A tsunami is a series of waves in a water body caused by the displacement of a large volume of water, generally in an ocean or a large lake. Earthquakes, volcanic eruptions and other underwater explosions above or below water all have the potential to generate a tsunami. Unlike normal ocean waves, which are generated by wind, or tides, which are generated by the gravitational pull of the Moon and the Sun, a tsunami is generated by the displacement of water.
The Bay of Fundy is a bay between the Canadian provinces of New Brunswick and Nova Scotia, with a small portion touching the US state of Maine. It has an extremely high tidal range. The name is likely a corruption of the French word Fendu, meaning "split".
Tidal power or tidal energy is harnessed by converting energy from tides into useful forms of power, mainly electricity using various methods.
An amphidromic point, also called a tidal node, is a geographical location which has zero tidal amplitude for one harmonic constituent of the tide. The tidal range for that harmonic constituent increases with distance from this point.
Physical oceanography is the study of physical conditions and physical processes within the ocean, especially the motions and physical properties of ocean waters.
A tidal marsh is a marsh found along rivers, coasts and estuaries which floods and drains by the tidal movement of the adjacent estuary, sea or ocean. Tidal marshes experience many overlapping persistent cycles, including diurnal and semi-diurnal tides, day-night temperature fluctuations, spring-neap tides, seasonal vegetation growth and decay, upland runoff, decadal climate variations, and centennial to millennial trends in sea level and climate. Tidal marshes are formed in areas that are sheltered from waves, in upper slops of intertidal, and where water is fresh or saline. They are also impacted by transient disturbances such as hurricanes, floods, storms, and upland fires.
A chart datum is the water level that depths displayed on a nautical chart are measured from. A chart datum is generally derived from some phase of the tide. Common chart datums are lowest astronomical tide and mean lower low water. In non-tidal areas, e.g. the Baltic Sea, mean sea level (MSL) is used.
Tide tables, sometimes called tide charts, are used for tidal prediction and show the daily times and levels of high and low tides, usually for a particular location. Tide heights at intermediate times can be approximated by using the rule of twelfths or more accurately calculated by using a published tidal curve for the location. Tide levels are typically given relative to a low-water vertical datum, e.g. the mean lower low water (MLLW) datum in the US.
The Saxby Gale was a tropical cyclone which struck eastern Canada's Bay of Fundy region on the night of October 4–5, 1869. The storm was named for Lieutenant Stephen Martin Saxby, a naval instructor who, based on his astronomical studies, had predicted extremely high tides in the North Atlantic Ocean on October 1, 1869, which would produce storm surges in the event of a storm.
The Hopewell Rocks, also called the Flowerpots Rocks or simply The Rocks, are rock formations caused by tidal erosion in The Hopewell Rocks Ocean Tidal Exploration Site in New Brunswick. They stand 40–70 feet tall.
Earth tide is the displacement of the solid earth's surface caused by the gravity of the Moon and Sun. Its main component has meter-level amplitude at periods of about 12 hours and longer. The largest body tide constituents are semi-diurnal, but there are also significant diurnal, semi-annual, and fortnightly contributions. Though the gravitational force causing earth tides and ocean tides is the same, the responses are quite different.
The theory of tides is the application of continuum mechanics to interpret and predict the tidal deformations of planetary and satellite bodies and their atmospheres and oceans under the gravitational loading of another astronomical body or bodies.
Burntcoat Head is an unincorporated rural Canadian community in Hants County, Nova Scotia and is known internationally as the site where it was officially recorded that the Bay of Fundy, and specifically Burntcoat, has the highest tides in the world.
A king tide is an especially high spring tide, especially the perigean spring tides which occur three or four times a year.
A vertical datum, altimetric datum, or height datum is a reference surface for vertical positions, such as the elevations of Earth features including terrain, bathymetry, water level, and man-made structures. Commonly adopted criteria for a vertical datum include the following approaches:
New Zealand has large ocean energy resources but does not yet generate any power from them. TVNZ reported in 2007 that over 20 wave and tidal power projects are currently under development. However, not a lot of public information is available about these projects. The Aotearoa Wave and Tidal Energy Association was established in 2006 to "promote the uptake of marine energy in New Zealand". According to their 10 February 2008 newsletter, they have 59 members. However, the association doesn't list its members.
A supermoon is a full moon or a new moon that nearly coincides with perigee—the closest that the Moon comes to the Earth in its elliptic orbit—resulting in a slightly larger-than-usual apparent size of the lunar disk as viewed from Earth. The technical name is a perigee syzygy or a full Moon around perigee. The term supermoon is astrological in origin and has no precise astronomical definition.
In astronomy, a syzygy is a roughly straight-line configuration of three or more celestial bodies in a gravitational system.
Tidal flooding, also known as sunny day flooding or nuisance flooding, is the temporary inundation of low-lying areas, especially streets, during exceptionally high tide events, such as at full and new moons. The highest tides of the year may be known as the king tide, with the month varying by location. These kinds of floods tend not to a high risk to property or human safety, but further stress coastal infrastructure in low lying areas.