Tidal range

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.[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, 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)[2].


The typical tidal range in the open ocean is about 0.6 metres (2 feet). Closer to the coast, this range is much greater. Coastal tidal ranges vary globally and can differ anywhere from near zero to over 16 metres.[3] 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] 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.[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.

M2 tidal constituent
The M2 tidal constituent, the amplitude indicated by color. The white lines are cotidal lines spaced at phase intervals of 30° (a bit over 1 hr).[6] The amphidromic points are the dark blue areas where the lines come together.


The tidal range has been classified[7] as:

  • Micro-tidal, when the tidal range is lower than 2 metres.
  • Meso-tidal, when the tidal range is between 2 metres and 4 metres.
  • Macro-tidal, when the tidal range is higher than 4 metres.


  1. ^ Hydrographic and Oceanographic Agencies
  2. ^ NOAA. "Tidal Datums". Retrieved 26 Mar 2019.
  3. ^ a b c NOAA. "FAQ2 Where are the highest tides?". Retrieved 27 Jan 2011.
  4. ^ NOAA. "It appears that the range of the tides gets larger the further the location from the equator. What causes this??". Retrieved 27 Jan 2011.
  5. ^ NOAA. "The highest tide in the world is in Canada". Retrieved 23 January 2014.
  6. ^ 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
  7. ^ 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.
Advocate Harbour

Advocate Harbour (2011 pop.: 826) is a Canadian rural community located in Cumberland County, Nova Scotia

The community is situated on Route 209 and has a small well-protected fishing harbour opening on the Bay of Fundy; the harbour dries at low tide.The community's economy is tied to the seasonal industries of fishing and tourism. The scenic Cape d'Or Lighthouse and Cape Chignecto Provincial Park attract tourists and hikers. Due to the extreme tidal range in this area it is also a well-known sea kayaking destination. The coastal erosion creates sea stacks, caves and arches, and a long rocky beach with large amounts of driftwood is popular with beachcombers. The community is featured on the Fundy Shore Ecotour.

Low-lying parts of the community are protected by a seawall which was damaged by a storm in 2008. Some residents are prepared for 72 hours of isolation in the event of a storm that breaches the seawall, with supplies of food and bottled water.

As of 2012, the seawall has been repaired and reinforced by construction crews. The reinforcements of the seawall are several piles of very large boulders within tidal range, and the seawall itself is reinforced with medium-sized boulders of the same nature.

Amphidromic point

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 (the peak-to-peak amplitude, or height difference between high tide and low tide) for that harmonic constituent increases with distance from this point.The term amphidromic point derives from the Greek words amphi (around) and dromos (running), referring to the rotary tides running around them.

Amphidromic points occur because the Coriolis effect and interference within oceanic basins, seas and bays creates a wave pattern — called an amphidromic system — which rotates around the amphidromic point. At the amphidromic points of the dominant tidal constituent, there is almost no vertical movement from tidal action. There can be tidal currents since the water levels on either side of the amphidromic point are not the same. A separate amphidromic system is created by each periodic tidal component.In most locations the "principal lunar semi-diurnal", known as M2, is the largest tidal constituent, with an amplitude of roughly half of the full tidal range. Having cotidal points means they reach high tide at the same time and low tide at the same time. In the accompanying figure, the low tide lags or leads by 1 hr 2 min from its neighboring lines. Where the lines meet are amphidromes, and the tide rotates around them; for example, along the Chilean coast, and from southern Mexico to Peru, the tide propagates southward, while from Baja California to Alaska the tide propagates northward.

Barrier island

Barrier islands are coastal landforms and a type of dune system that are exceptionally flat or lumpy areas of sand that form by wave and tidal action parallel to the mainland coast. They usually occur in chains, consisting of anything from a few islands to more than a dozen. They are subject to change during storms and other action, but absorb energy and protect the coastlines and create areas of protected waters where wetlands may flourish. A barrier chain may extend uninterrupted for over a hundred kilometers, excepting the tidal inlets that separate the islands, the longest and widest being Padre Island of Texas. The length and width of barriers and overall morphology of barrier coasts are related to parameters including tidal range, wave energy, sediment supply, sea-level trends, and basement controls. The amount of vegetation on the barrier has a large impact on the height and evolution of the island.Chains of barrier islands can be found along approximately 13-15% of the world's coastlines. They display different settings, suggesting that they can form and be maintained in a variety of environmental settings. Numerous theories have been given to explain their formation.

Bay of Fundy

The Bay of Fundy (French: Baie de 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".

Burnham-on-Sea Round Tower

The Round Tower was a lighthouse in Burnham-on-Sea, Somerset, England. It is now a private dwelling.

Burnham-on-Sea is notable for its beach and mudflats, which are characteristic of Bridgwater Bay and the rest of the Bristol Channel where the tide can recede for over 1.5 miles (2.4 km). Burnham is close to the estuary of the River Parrett where it flows into the Bristol Channel, which has the second highest tidal range in the world of 15 metres (49 ft), second only to Bay of Fundy in Eastern Canada.

The constantly shifting sands have always been a significant risk to shipping in the area.

Cobequid Bay

Cobequid Bay is an inlet of the Bay of Fundy and the easternmost part of the Minas Basin, located in the Canadian province of Nova Scotia. The bay was carved by rivers flowing into the eastern end of the Bay of Fundy.The eastern end of the bay hosts the estuary of the Salmon River, whereas the west end of the bay is less well-defined, typically delineated by Burntcoat Head on the southern shore and Five Islands or Economy Mountain on the northern shore.

The highest tidal range in the world was measured at Burntcoat Head where average tidal ranges measure a 12.4 m (41 ft) vertical difference in water level between low tide and high tide.

The bay's name is derived from the Acadian spelling of We'kopekwitk, the Mi'kmaq name for the area. Acadian settlers came to this area in the early 1700s.

Fundy Shore Ecotour

The Fundy Shore Ecotour is a scenic drive in the Canadian province of Nova Scotia and encircles several sub-basins of the Bay of Fundy, which contains the highest tidal range on the planet.

The Fundy Shore Ecotour runs from Brooklyn, Hants County in the south, to Amherst, Cumberland County near the inter-provincial boundary with New Brunswick in the north.

The route follows the shores of Chignecto Bay, Minas Basin, and Cobequid Bay and overlaps with and extends the Glooscap Trail in many places.

Gat (landform)

A gat (German: Seegatt, Seegat or diminutive Gatje) is a strait that is constantly eroded by currents flowing back and forth, such as tidal currents. It is usually a relatively narrow but deep, up to 30 m (100 ft) passage between land masses (such as an island and a peninsula) or shallow bars in an area of mudflats. A gat is sometimes a shallower passage on lagoon coasts, including those without any tidal range.

According to Whittow a gat is either an inshore channel or strait dividing offshore islands from the mainland e.g. the Frisian Islands, or it is an opening in a line of sea cliffs allowing access to the coast from inland. It is similar, but not identical, to a gut, which is a narrow river channel or strait prior to joining an open ocean or estuary. Leser restricts its use to deep, but relatively narrow inlets in the Wadden Sea that are scoured out by currents, giving the example of the gap between the Frisian islands of Juist and Nordeney.

Gulf of Martaban

The Gulf of Martaban (Burmese: မုတ္တမပင်လယ်ကွေ့) or the Gulf of Mottama is an arm of the Andaman Sea in the southern part of Burma. The gulf is named after the port city of Mottama (formerly known as Martaban). The Sittaung, Salween and Yangon rivers empty into it.

A characteristic feature of the Gulf of Martaban is that it has a tide-dominated coastline. Tides ranges between 4–7 m with the highest tidal range at the Elephant Point in the western Gulf of Martaban.

During spring tide, when the tidal range is around 6.6 m, the turbid zone covers an area of more than 45,000 km2 making it one of the largest perennially turbid zones of the world's oceans. During neap tide, with tidal range of 2.98 m, the highly turbid zone coverage drops to 15,000 km2. The edge of the highly turbid zone migrates back-and-forth in-sync with every tidal cycle by nearly 150 km.The gulf is home to varieties of species and the Eden's whale was scientifically recognized in the water.In 2008, the region was found to be rich with oil deposits. It has been a site of oil exploration since 2014 under the "Zawtika development project", an international consortium of American, British, French, Chinese, Thai, Indonesian (PT Gunanusa) and Indian oil and construction companies exploring oil in M7, M9 and M11 blocks.

Half tide dock

A half tide dock is a partially tidal dock. Typically the dock is entered at high tide. As the tide ebbs a sill or weir prevents the level dropping below a certain point, meaning that the ships in the dock remain afloat, although they still rise and fall with the tides above this. Half tide docks are particularly useful in areas with a large tidal range.

The sill of a half tide dock must be set sufficiently far below the daily high tide mark to allow ships to pass over it. Obviously this was easier to achieve with small ships of shallow draught, or in areas with a large tidal range. Inside the dock, the depth of water beneath the sill's level depends only on the depth to which the dock was excavated, although this obviously increases construction costs.

The importance of the sill, and the tide's height above it, is reflected by these dock sills becoming an important local datum level and for tide tables being calculated for heights above it (i.e. clear draught in and out of the dock). This importance has often continued for many years after the original sill had been replaced, as at Sharpness on the Severn Estuary, or where the dock had disappeared entirely, such as Old Dock Sill in Liverpool.

Intertidal zone

The intertidal zone, also known as the foreshore or seashore, is the area that is above water level at low tide and underwater at high tide (in other words, the area within the tidal range). This area can include several types of habitats with various species of life, such as starfish, sea urchins, and many species of coral. Sometimes it is referred to as the littoral zone, although that can be defined as a wider region.

The well-known area also includes steep rocky cliffs, sandy beaches, or wetlands (e.g., vast mudflats). The area can be a narrow strip, as in Pacific islands that have only a narrow tidal range, or can include many meters of shoreline where shallow beach slopes interact with high tidal excursion. The peritidal zone is similar but somewhat wider, extending from above the highest tide level to below the lowest.

Organisms in the intertidal zone are adapted to an environment of harsh extremes. The intertidal zone is also home to several species from different phyla (Porifera, Annelida, Coelenterata, Mollusca, Arthropoda, etc.). Water is available regularly with the tides, but varies from fresh with rain to highly saline and dry salt, with drying between tidal inundations. Wave splash can dislodge residents from the littoral zone. With the intertidal zone's high exposure to sunlight, the temperature can range from very hot with full sunshine to near freezing in colder climates. Some microclimates in the littoral zone are moderated by local features and larger plants such as mangroves. Adaptation in the littoral zone allows the use of nutrients supplied in high volume on a regular basis from the sea, which is actively moved to the zone by tides. Edges of habitats, in this case land and sea, are themselves often significant ecologies, and the littoral zone is a prime example.

A typical rocky shore can be divided into a spray zone or splash zone (also known as the supratidal zone), which is above the spring high-tide line and is covered by water only during storms, and an intertidal zone, which lies between the high and low tidal extremes. Along most shores, the intertidal zone can be clearly separated into the following subzones: high tide zone, middle tide zone, and low tide zone. The intertidal zone is one of a number of marine biomes or habitats, including estuary, neritic, surface, and deep zones.

King Sound

King Sound is a large gulf in northern Western Australia. It expands from the mouth of the Fitzroy River, one of Australia's largest watercourses, and opens to the Indian Ocean. It is about 120 km long, and averages about 50 km in width. The port town of Derby lies near the mouth of the Fitzroy River on the eastern shore of King Sound. King Sound has the highest tides in Australia, and amongst the highest in the world, reaching a maximum tidal range of 11.8 metres at Derby. The tidal range and water dynamic were researched in 1997–1998.Other rivers that discharge into the sound include the Lennard River, Meda River, Robinson River and May River.

King Sound is bordered by the island clusters of the Buccaneer Archipelago to the East and Cape Leveque to the West.The traditional owners and original inhabitants of the area are the Indigenous Australians the Nimanburu, Njulnjul, Warwa peoples.The first European to explore the Sound was William Dampier who visited the region aboard Cygnet in 1688.

Philip Parker King surveyed the coastline in 1821 and named the area Cygnet Bay.The area was later visited by John Stokes and John Wickham aboard HMS Beagle in 1838. The Sound is named after the noted surveyor, Philip Parker King.In the 1880s it was one the sites in the Kimberleys of a short-lived gold rush.

Liman (landform)

Liman is defined in Bulgarian, Ukrainian, Russian (лиман) and Romanian (liman) as an enlarged estuary formed as a lagoon at the widening mouth of one or several rivers, where flow is blocked by a bar of sediments, as in the Dniester Liman or the Razelm liman. A liman can be maritime (the bar being created by the current of a sea) or fluvial (the bar being created by the flow of a bigger river at the confluence). The term is usually used in place of the more universal delta, with its implication of landform, to describe wet estuaries in the Black Sea and the Sea of Azov; a synonymous term guba (губа) is used in Russian sources for estuaries of the Russian shores in the north.Water in a liman is brackish with a variable salinity: during periods of low fresh-water intake, it may become significantly more saline as a result of evaporation and inflow of sea water.

Such features are found in places with low tidal range, for example along the western and northern coast of the Black Sea, in the Baltic Sea (Vistula Lagoon, the Curonian Lagoon), as well as along the lowest part of the Danube. Examples of limans include Lake Varna in Bulgaria, Lake Razelm in Romania, the Dniester Liman in Ukraine and the Anadyrskiy Liman and Amur Liman in Siberia.


Lézardrieux (Breton: Lezardrev) is a commune in the Côtes-d'Armor department of Brittany in northwestern France.

The village is situated near the mouth of the estuary of the Trieux river - the suspension bridge (Pont de Lézardrieux) across the river at this point is a French national monument. There is a marina with moorings for several hundred pleasure boats and the tidal range experienced is remarkable.

There are a variety of shops and other commercial enterprises - including two bakeries, a butcher and several restaurants and bars.

Moolack Beach

Moolack Beach (also Moolack Shores) is an undeveloped sandy beach on the Oregon Coast about 4 miles (6 km) north of Newport in Lincoln County, United States. It is almost 8 km (5 mi) in length with the south end at Yaquina Head and the north end at Otter Rock, the site of Devils Punch Bowl State Natural Area. The northern beach is the site of Beverly Beach State Park and the community of Beverly Beach. The beach has no obvious break delineating what would seem to be Beverly Beach, though Wade Creek is a likely candidate. The nearly ten foot (3 m) tidal range and seasonally-varying slope of the beach can cause the sandy beach to completely disappear at times; at other times it can be hundreds of feet wide. The beach is bounded by U.S. Route 101.

The name is from a Chinook Jargon word for "elk". The area is rich with geologic history.

Severn Estuary

The Severn Estuary (Welsh: Môr Hafren) is the estuary of the River Severn, the longest river in Great Britain. It is the confluence of four major rivers, being the Severn, Wye, Usk and Avon, and other smaller rivers. Its high tidal range, approximately 50 feet (15 m), means that it has been at the centre of discussions in the UK regarding renewable energy.

Shannon Estuary

The Shannon Estuary (Irish: Inbhear na Sionainne) is a large estuary where the River Shannon flows into the Atlantic Ocean. The estuary has Limerick City at its head and its seaward limits are marked by Loop Head to the north and Kerry Head to the south. The estuary defines the main boundary between County Kerry/County Limerick to the south and County Clare to the north.

The length of the Shannon Estuary is 97 km (60 mi). The Shannon has a high tidal range, up to around 5.44 m (17.8 ft) at Limerick docks, such that the estuary has been considered for tidal power schemes, despite occasionally experiencing a tidal bore.In the second half of the 19th century about 65 km² of the estuary's lowlands have been embanked and reclaimed, largely for agricultural purposes.

Swansea Bay

Swansea Bay (Welsh: Bae Abertawe) is a bay on the southern coast of Wales. The River Neath, River Tawe, River Afan, River Kenfig and Clyne River flow into the bay. Swansea Bay and the upper reaches of the Bristol Channel experience a large tidal range. The shipping ports in Swansea Bay are Swansea Docks, Port Talbot Docks and Briton Ferry wharfs.

Each stretch of beach within the bay has its own individual name:

Aberavon Beach

Baglan Bay

Jersey Marine Beach

Swansea Beach

Mumbles Beach

Tidal resonance

In oceanography, a tidal resonance occurs when the tide excites one of the resonant modes of the ocean.

The effect is most striking when a continental shelf is about a quarter wavelength wide. Then an incident tidal wave can be reinforced by reflections between the coast and the shelf edge, the result producing a much higher tidal range at the coast.

Famous examples of this effect are found in the Bay of Fundy, where the world's highest tides are reportedly found, and in the Bristol Channel. Less well known is Leaf Bay, part of Ungava Bay near the entrance of Hudson Strait (Canada), which has tides similar to those of the Bay of Fundy. Other resonant regions with large tides include the Patagonian Shelf and on the continental shelf of northwest Australia.Most of the resonant regions are also responsible for large fractions of the total amount of tidal energy dissipated in the oceans. Satellite altimeter data shows that the M2 tide dissipates approximately 2.5 TW, of which 261 GW is lost in the Hudson Bay complex, 208 GW on the European Shelves (including the Bristol Channel), 158 GW on the North-west Australian Shelf, 149 GW in the Yellow Sea and 112 GW on the Patagonian Shelf.

Ocean zones
Sea level


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