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General sketch-map of a tidal plain, showing the typical tripartition in supratidal, intertidal and subtidal zones. The most apparent character of the area is the development of tidal channels, affecting mainly the intertidal zone. In this case, the tidal flat is protected seaward by a beach barrier, but in many cases (low-energy waves and longshore currents) the tidal flats may directly pass into a shallow marine environment. Tidal flat general sketch.png
General sketch-map of a tidal plain, showing the typical tripartition in supratidal, intertidal and subtidal zones. The most apparent character of the area is the development of tidal channels, affecting mainly the intertidal zone. In this case, the tidal flat is protected seaward by a beach barrier, but in many cases (low-energy waves and longshore currents) the tidal flats may directly pass into a shallow marine environment.

Mudflats or mud flats, also known as tidal flats, are coastal wetlands that form in intertidal areas where sediments have been deposited by tides or rivers. A global analysis published in 2019 suggested that tidal flat ecosystems are as extensive globally as mangroves, covering at least 127,921 km2 (49,391 sq mi) of the Earth's surface. [1] They are found in sheltered areas such as bays, bayous, lagoons, and estuaries; they are also seen in freshwater lakes and salty lakes (or inland seas) alike, wherein many rivers and creeks end. [2] Mudflats may be viewed geologically as exposed layers of bay mud, resulting from deposition of estuarine silts, clays and aquatic animal detritus. Most of the sediment within a mudflat is within the intertidal zone, and thus the flat is submerged and exposed approximately twice daily.


A recent global remote sensing analysis estimated that approximately 50% of the global extent of tidal flats occurs within eight countries (Indonesia, China, Australia, United States, Canada, India, Brazil, and Myanmar) and that 44% of the world's tidal flats occur within Asia (56,051 km2 or 21,641 sq mi). [1]

In the past tidal flats were considered unhealthy, economically unimportant areas and were often dredged and developed into agricultural land. [3] Several especially shallow mudflat areas, such as the Wadden Sea, are now popular among those practising the sport of mudflat hiking.

On the Baltic Sea coast of Germany in places, mudflats are exposed not by tidal action, but by wind-action driving water away from the shallows into the sea. This kind of wind-affected mudflat is called Windwatt in German.


Mudflats near Oban on Stewart Island, New Zealand Stewart Island Oban Mudflats.jpg
Mudflats near Oban on Stewart Island, New Zealand

Tidal flats, along with intertidal salt marshes and mangrove forests, are important ecosystems. [4] They usually support a large population of wildlife, and are a key habitat that allows tens of millions of migratory shorebirds to migrate from breeding sites in the northern hemisphere to non-breeding areas in the southern hemisphere. They are often of vital importance to migratory birds, as well as certain species of crabs, [5] mollusks and fish. [6] In the United Kingdom mudflats have been classified as a Biodiversity Action Plan priority habitat.

The maintenance of mudflats is important in preventing coastal erosion. However, mudflats worldwide are under threat from predicted sea level rises, land claims for development, dredging due to shipping purposes, and chemical pollution. [1] In some parts of the world, such as East and South-East Asia, mudflats have been reclaimed for aquaculture, agriculture, and industrial development. For example, around the Yellow Sea region of East Asia, more than 65% of mudflats present in the early 1950s had been destroyed by the late 2000s. [7] [8] It is estimated that up to 16% of the world tidal flats have disappeared since the mid-1980s. [1]

Mudflat sediment deposits are focused into the intertidal zone which is composed of a barren zone and marshes. Within these areas are various ratios of sand and mud that make up the sedimentary layers. [9] The associated growth of coastal sediment deposits can be attributed to rates of subsidence along with rates of deposition (example: silt transported via river) and changes in sea level. [9]

Barren zones extend from the lowest portion of the intertidal zone to the marsh areas. Beginning in close proximity to the tidal bars, sand dominated layers are prominent and become increasingly muddy throughout the tidal channels. Common bedding types include laminated sand, ripple bedding, and bay mud. Bioturbation also has a strong presence in barren zones.

Marshes contain an abundance of herbaceous plants while the sediment layers consist of thin sand and mud layers. Mudcracks are a common as well as wavy bedding planes. [9] Marshes are also the origins of coal/peat layers because of the abundant decaying plant life. [9]

Salt pans can be distinguished in that they contain thinly laminated layers of clayey silt. The main source of the silt comes from rivers. Dried up mud along with wind erosion forms silt dunes. When flooding, rain or tides come in, the dried sediment is then re-distributed. [9]

Mudflats in Brewster, Massachusetts, United States, extending hundreds of yards offshore at the low tide. The line of wrack and seashells in the foreground indicates the high-water mark. Brewster mudflat.jpg
Mudflats in Brewster, Massachusetts, United States, extending hundreds of yards offshore at the low tide. The line of wrack and seashells in the foreground indicates the high-water mark.
Gulls feeding on mudflats in Skagit Bay, Washington. Skagit Bay 6308.JPG
Gulls feeding on mudflats in Skagit Bay, Washington.

Selected example areas

See also

Related Research Articles

Estuary Partially enclosed coastal body of brackish water

An estuary is a partially enclosed coastal body of brackish water with one or more rivers or streams flowing into it, and with a free connection to the open sea. Estuaries form a transition zone between river environments and maritime environments and are an example of an ecotone. Estuaries are subject both to marine influences such as tides, waves, and the influx of saline water and to fluvial influences such as flows of freshwater and sediment. The mixing of seawater and freshwater provides high levels of nutrients both in the water column and in sediment, making estuaries among the most productive natural habitats in the world.

Salt marsh Coastal ecosystem between land and open saltwater that is regularly flooded

A salt marsh or saltmarsh, also known as a coastal salt marsh or a tidal marsh, is a coastal ecosystem in the upper coastal intertidal zone between land and open saltwater or brackish water that is regularly flooded by the tides. It is dominated by dense stands of salt-tolerant plants such as herbs, grasses, or low shrubs. These plants are terrestrial in origin and are essential to the stability of the salt marsh in trapping and binding sediments. Salt marshes play a large role in the aquatic food web and the delivery of nutrients to coastal waters. They also support terrestrial animals and provide coastal protection.

Barrier island Coastal dune landform that forms by wave and tidal action parallel to the mainland coast

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. Sometimes an important inlet may close permanently, transforming an island into a peninsula, thus creating a barrier peninsula. 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.

Deposition (geology) Geological process in which sediments, soil and rocks are added to a landform or landmass

Deposition is the geological process in which sediments, soil and rocks are added to a landform or landmass. Wind, ice, water, and gravity transport previously weathered surface material, which, at the loss of enough kinetic energy in the fluid, is deposited, building up layers of sediment.

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.

Yaquina Bay

Yaquina Bay is a coastal estuarine community found in Newport, Oregon, United States. Yaquina Bay is a semi-enclosed body of water, approximately 8 km² (3.2 mi²) in area, with free connection to the Pacific Ocean, but also diluted with freshwater from the Yaquina River land drainage. The Bay is traversed by the Yaquina Bay Bridge. There are three small communities that border the Yaquina River and Bay; Newport, Toledo and Elk City. The Yaquina Bay in Newport is a popular tourist destination along the Pacific Coast Highway. It is also an important estuary for the ecology and economy of the area.


In ecology, a halosere is a succession in a saline environment. An example of a halosere is a salt marsh.

Bay mud Type of soil formed by sedimentation in estuaries

Bay mud consists of thick deposits of soft, unconsolidated silty clay, which is saturated with water; these soil layers are situated at the bottom of certain estuaries, which are normally in temperate regions that have experienced cyclical glacial cycles. Example locations are Cape Cod Bay, Chongming Dongtan Reserve in Shanghai, China, Banc d'Arguinpreserve in Mauritania, The Bristol Channel in the United Kingdom, Mandø Island in the Wadden Sea in Denmark, Florida Bay, San Francisco Bay, Bay of Fundy, Casco Bay, Penobscot Bay, and Morro Bay. Bay mud manifests low shear strength, high compressibility and low permeability, making it hazardous to build upon in seismically active regions like the San Francisco Bay Area.

Sabkha Salt lake above the tide line, where evaporite deposits accumulate

A term typically used by Earth scientists, a sabkha is a coastal, supratidal mudflat or sandflat in which evaporite-saline minerals accumulate as the result of semiarid to arid climate. Sabkhas are gradational between land and intertidal zone within restricted coastal plains just above normal high-tide level. Within a sabkha, evaporite-saline minerals sediments typically accumulate below the surface of mudflats or sandflats. Evaporite-saline minerals, tidal-flood, and aeolian deposits characterize many sabkhas found along modern coastlines. The accepted type locality for a sabkha is at the southern coast of the Persian Gulf, in the United Arab Emirates. Sabkha is a phonetic transliteration of the Arabic word used to describe any form of salt flat. A sabkha is also known as a sabkhah,sebkha, or coastal sabkha.

Seal Beach National Wildlife Refuge

The Seal Beach National Wildlife Refuge is a wildlife refuge encompassing 965 acres (3.91 km2) located in the California coastal community of Seal Beach. Although it is located in Orange County it is included as part of the San Diego National Wildlife Refuge Complex. It was established in 1972.

An intertidal wetland is an area along a shoreline that is exposed to air at low tide and submerged at high tide. This type of wetland is defined by an intertidal zone and includes its own intertidal ecosystems.

Brackish marsh Marsh with brackish level of salinity

Brackish marshes develop from salt marshes where a significant freshwater influx dilutes the seawater to brackish levels of salinity. This commonly happens upstream from salt marshes by estuaries of coastal rivers or near the mouths of coastal rivers with heavy freshwater discharges in the conditions of low tidal ranges.

Classification of wetlands has been a problematical task, with the commonly accepted definition of what constitutes a wetland being among the major difficulties. A number of national wetland classifications exist. In the 1970s, the Ramsar Convention on Wetlands of International Importance introduced a first attempt to establish an internationally acceptable wetland classification scheme.

Lenticular bedding Sedimentary bedding pattern displaying alternating layers of mud and sand

Lenticular bedding is a sedimentary bedding pattern displaying alternating layers of mud and sand. Formed during periods of slack water, mud suspended in the water is deposited on top of small formations of sand once the water's velocity has reached zero. Lenticular bedding is classified by its large quantities of mud relative to sand, whereas a flaser bed consists mostly of sand. The sand formations within the bedding display a 'lens-like' shape, giving the pattern its respected name. They are commonly found in high-energy environments such as the intertidal and supratidal zones. Geologists use lenticular bedding to show evidence of tidal rhythm, tidal currents and tidal slack, in a particular environment.

Lower Saxon Wadden Sea National Park

The Lower Saxon Wadden Sea National Park was established in 1986 and embraces the East Frisian Islands, mudflats and salt marshes between the Bay of Dollart on the border with the Netherlands in the west and Cuxhaven as far as the Outer Elbe shipping channel in the east. The national park has an area of about 345,800 hectares (1,335 sq mi). The National Park organisation is located in Wilhelmshaven. In June 2009, the National Park become a UNESCO World Heritage Site along with the Schleswig-Holstein Wadden Sea and the Dutch Wadden Sea, highlighting its unique intertidal ecosystem and high biodiversity.

Marine habitats Habitat that supports marine life

Marine habitats are habitats that support marine life. Marine life depends in some way on the saltwater that is in the sea. A habitat is an ecological or environmental area inhabited by one or more living species. The marine environment supports many kinds of these habitats. Marine habitats can be divided into coastal and open ocean habitats. Coastal habitats are found in the area that extends from as far as the tide comes in on the shoreline out to the edge of the continental shelf. Most marine life is found in coastal habitats, even though the shelf area occupies only seven percent of the total ocean area. Open ocean habitats are found in the deep ocean beyond the edge of the continental shelf.

Muthupet Lagoon thiruvarur

Muthupet Lagoon is located at the southern end of the Cauvery river delta on the Bay of Bengal, covering an area of approximately 6,803.01 ha of which only 4% is occupied by well-grown mangroves. The rivers Paminiyar, Koraiyar, Kilaithankiyar, Marakkakoraiyar and other tributaries of the river Cauvery flow through Muthupet and adjacent villages. At the tail end, they form a lagoon before meeting the sea. The northern and western borders of the lagoon are occupied by muddy silt ground which is devoid of mangroves. The mangroves beyond Muthupet lagoon are discontinuously found along the shore and extended up to Point Calimere. Muthupet mangrove forest was under the control of Chatram Department from 1853 to 1912. The Government of the Presidency of Madras Gazette (1937) shows, from 1923 to 1936, half of the revenue obtained from selling mangrove products was paid to the revenue department and the remaining half was spent to maintain the "Chatrams". The Government declared the Muthupet mangrove forest as revenue forest in February 1937 and accordingly the mangrove forest was handed over to the forest department of the Madras Presidency.

Blue carbon Carbon captured by the worlds marine ecosystems

Blue carbon is carbon sequestration by the world's oceanic and coastal ecosystems, mostly by algae, seagrasses, macroalgae, mangroves, salt marshes and other plants in coastal wetlands. This occurs through plant growth and the accumulation and burial of organic matter in the soil. Because oceans cover 70% of the planet, ocean ecosystem restoration has the greatest blue carbon development potential. Research is ongoing, but in some cases it has been found that these types of ecosystems remove far more carbon than terrestrial forests, and store it for millennia.

Kendall-Frost Mission Bay Marsh Reserve

The Kendall-Frost Mission Bay Marsh Reserve is a 20-acre University of California Natural Reserve System reserve on the northern shore of Mission Bay in San Diego County, California. Administered by UC San Diego, the site is owned by the University of California and managed for teaching and research.

Sedimentation enhancing strategy

Sedimentation enhancing strategies are environmental management projects aiming to restore and facilitate land-building processes in deltas. Sediment availability and deposition are important because deltas naturally subside and therefore need sediment accumulation to maintain their elevation, particularly considering increasing rates of sea-level rise. Sedimentation enhancing strategies aim to increase sedimentation on the delta plain primarily by restoring the exchange of water and sediments between rivers and low-lying delta plains. Sedimentation enhancing strategies can be applied to encourage land elevation gain to offset sea-level rise. Interest in sedimentation enhancing strategies has recently increased due to their ability to raise land elevation, which is important for the long-term sustainability of deltas.


  1. 1 2 3 4 Murray, N.J.; Phinn, S.R.; DeWitt, M.; Ferrari, R.; Johnston, R.; Lyons, M.B.; Clinton, N.; Thau, D.; Fuller, R.A. (2019), "The global distribution and trajectory of tidal flats", Nature, 565 (7738): 222–225, Bibcode:2019Natur.565..222M, doi:10.1038/s41586-018-0805-8, PMID   30568300 /
  2. Swamps and marshes (with thick and deep mud beneath surfaces in hot season) are either freshwater, salty, or brackish.
  3. Dredging Indian River Lagoon Wetlands 1920 - 1950s
  4. Tidal flat habitats
  5. Triño, A. T., & Rodriguez, E. M. (2000). Mud crab (Scylla serrata) culture in tidal flats with existing mangroves. In J. H. Primavera, M. T. Castaños, & M. B. Surtida (Eds.), Mangrove-Friendly Aquaculture: Proceedings of the Workshop on Mangrove-Friendly Aquaculture organized by the SEAFDEC Aquaculture Department, January 11–15, 1999, Iloilo City, Philippines (pp. 171–176). Aquaculture Department, Southeast Asian Fisheries Development Center.
  6. Manko - Tidal Flat, Mangrove Forest
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