Tidal range

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Tidal Range.jpg

Tidal range is the difference in height 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 depends on time and location.


Larger tidal range occur during spring tides (spring range), when the gravitational forces of both the Moon and Sun are aligned (at syzygy), reinforcing each other in the same direction (new moon) or in opposite directions (full moon). The largest annual tidal range can be expected around the time of the equinox if it coincides with a spring tide. Spring tides occur at the second and fourth (last) quarters of the lunar phases.

By contrast, 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 (neap range) is smallest. Neap tides occur at the first and third quarters of the lunar phases.

Tidal data for coastal areas is published by national hydrographic offices. [1] 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 can cause ranges in excess of predicted values and can cause localized flooding. These weather-related effects 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). [2]


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. [ citation needed ] Coastal tidal ranges vary globally and can differ anywhere from near zero to over 16 m (52 ft). [3] [ failed verification ] 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. [4] The world's largest tidal range of 16.3 metres (53.5 feet) occurs in Bay of Fundy, Canada, [3] [5] [ failed verification ] a similar range is experienced at Ungava Bay also in Canada [6] and the United Kingdom regularly experiences tidal ranges up to 15 metres (49 feet) between England and Wales in the Bristol Channel. [7]

The fifty coastal locations with the largest tidal ranges worldwide are listed by the National Oceanic and Atmospheric Administration of the United States. [3]

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.

The M2 tidal constituent, peak amplitude indicated by color. White lines are cotidal lines spaced at phase intervals of 30deg (a bit over 1 hr). Amphidromic points are the dark blue areas where the lines come together. M2 tidal constituent.jpg
The M2 tidal constituent, peak amplitude indicated by color. White lines are cotidal lines spaced at phase intervals of 30° (a bit over 1 hr). Amphidromic points are the dark blue areas where the lines come together.


The tidal range has been classified [9] as:

Related Research Articles

Tide Rise and fall of the sea level under astronomical gravitational influences

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.

Bay of Fundy Bay on the east coast of North America

The Bay of Fundy is a bay between the Canadian provinces of New Brunswick and Nova Scotia, with a small portion touching the U.S. state of Maine. Its extremely high tidal range is the highest in the world. The name is likely a corruption of the French word fendu, meaning 'split'.

Lunar node Where the orbit of the Moon intersects the Earths ecliptic

A lunar node is either of the two orbital nodes of the Moon, that is, the two points at which the orbit of the Moon intersects the ecliptic. The ascending node is where the Moon moves into the northern ecliptic hemisphere, while the descending node is where the Moon enters the southern ecliptic hemisphere.

Amphidromic point Point of zero amplitude of one harmonic constituent of the tide

Tides play a key role in the dynamics of coastal regions and estuaries. Tide induced currents and changes in water level cause morphological changes in coastal areas. Moreover, tides play an important role in coastal management. 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. As such, amphidromic points are crucial in understanding the tidal behaviour.

The lunitidal interval measures the time lag from lunar culmination to the next high tide at a given location. It is also called the high water interval (HWI). Sometimes a term is not used for the time lag, but instead the terms age or establishment of the tide are used for the entry that is in tide tables.

Pelorus Sound Body of water

Pelorus Sound / Te Hoiere is the largest of the sounds which make up the Marlborough Sounds at the north of the South Island, New Zealand. The Marlborough Sounds is a system of drowned river valleys, which were formed after the last ice age around 10,000 years ago. Pelorus Sound has a main channel which winds south from Cook Strait for about 55 kilometres (34 mi), between steeply sloped wooded hills, until it reached its head close to Havelock town. Pelorus has several major arms, notably Tennyson Inlet, Tawhitinui Reach, Kenepuru Sound and the Crail/Clova/Beatrix Bay complex. Its shoreline runs for 380 kilometres (240 mi).

Tidal marsh Marsh subject to tidal change in water

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.

Chart datum Level of water from which depths displayed on a nautical chart are measured

A chart datum is the water level surface serving as origin of depths displayed on a nautical chart. A chart datum is generally derived from some tidal phase, in which case it is also known as a tidal datum. Common chart datums are lowest astronomical tide (LAT) and mean lower low water (MLLW). In non-tidal areas, e.g. the Baltic Sea, mean sea level (MSL) is used. A chart datum is a type of vertical datum and must not be confused with the horizontal datum for the chart.

Tide table Tabulated data used for tidal prediction

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.

Tide clock Specially designed clock that keeps track of the Moons apparent motion around the Earth

A tide clock is a specially designed clock that keeps track of the Moon's apparent motion around the Earth. Along many coastlines, the Moon contributes the major part (67%) of the combined lunar and solar tides. The exact interval between tides is influenced by the position of the Moon and Sun relative to the Earth, as well as the specific location on Earth where the tide is being measured. Due to the Moon's orbital prograde motion, it takes a particular point on the Earth 24 hours and 50.5 minutes to rotate under the Moon, so the time between high lunar tides fluctuates between 12 and 13 hours. A tide clock is divided into two roughly 6 hour tidal periods that shows the average length of time between high and low tides in a semi-diurnal tide region, such as most areas of the Atlantic Ocean.

Botn is an inland fjord in the Rissa area of the municipality of Indre Fosen in Trøndelag county, Norway. It flows through a short, small river into the Sundsbukta, a small bay off the Trondheimsfjorden. The village of Årnset lies on the north shore of Botn.

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.

Theory of tides Scientific interpretation of tidal forces

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, Nova Scotia Human settlement in Nova Scotia, Canada

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.

King tide Colloquial term for an especially high spring tide, such as a perigean spring tide.

A king tide is an especially high spring tide, especially the perigean spring tides which occur three or four times a year. King tide is not a scientific term, nor is it used in a scientific context.

Vertical datum Reference surface for vertical positions

In geodesy, surveying, hydrography and navigation, vertical datum or altimetric datum, is a reference coordinate surface used for vertical positions, such as the elevations of Earth-bound features and altitudes of satellite orbits and in aviation. In planetary science, vertical datums are also known as zero-elevation surface or zero-level reference.

Ocean power in New Zealand

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.

Supermoon Full or new moon which appears larger due to coinciding with perigee

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 fullMoon around perigee. Because the term supermoon is astrological in origin, it has no precise astronomical definition.

Syzygy (astronomy) Configuration of celestial bodies

In astronomy, a syzygy is a roughly straight-line configuration of three or more celestial bodies in a gravitational system.

Tidal flooding Temporary inundation of low-lying areas during exceptionally high tide events

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 be a high risk to property or human safety, but further stress coastal infrastructure in low lying areas.


  1. Hydrographic and Oceanographic Agencies
  2. NOAA. "Tidal Datums" . Retrieved 26 Mar 2019.
  3. 1 2 3 NOAA. "FAQ Where are the highest tides?" . Retrieved 20 Aug 2021.
  4. NOAA. "It appears that the range of the tides gets larger the further the location from the equator. What causes this??" . Retrieved 23 Oct 2020.
  5. NOAA. "The highest tide in the world is in Canada" . Retrieved 23 Oct 2020.
  6. Charles T. O'Reilly, Ron Solvason, and Christian Solomon. "Resolving the World's largest tides", in J.A Percy, A.J. Evans, P.G. Wells, and S.J. Rolston (Editors) 2005: The Changing Bay of Fundy-Beyond 400 years, Proceedings of the 6th Bay of Fundy Workshop, Cornwallis, Nova ScotiSackville, NB.
  7. "Tidal range".
  8. Picture credit: R. Ray, TOPEX/Poseidon: Revealing Hidden Tidal Energy GSFC, NASA. Redistribute with credit to R. Ray, as well as NASA-GSFC, NASA-JPL, Scientific Visualization Studio, and Television Production NASA-TV/GSFC
  9. Masselink, G.; Short, A. D. (1993). "The effect of tidal range on beach morphodynamics and morphology: a conceptual beach model". Journal of Coastal Research. 9 (3): 785–800. ISSN   0749-0208.