Lagoon

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Balos coastal lagoon of northwestern Crete. The shallow lagoon is separated from the Mediterranean sea by narrow shoals connecting to a small, rocky mountain. BalosLagoonCreta.jpg
Balos coastal lagoon of northwestern Crete. The shallow lagoon is separated from the Mediterranean sea by narrow shoals connecting to a small, rocky mountain.
Garabogaz-Gol lagoon in Turkmenistan Kara-Bogaz Gol from space, September 1995.jpg
Garabogaz-Göl lagoon in Turkmenistan
Venice Lagoon Venice Lagoon December 9 2001.jpg
Venice Lagoon

A lagoon is a shallow body of water separated from a larger body of water by barrier islands or reefs. Lagoons are commonly divided into coastal lagoons and atoll lagoons. They have also been identified as occurring on mixed-sand and gravel coastlines. There is an overlap between bodies of water classified as coastal lagoons and bodies of water classified as estuaries. Lagoons are common coastal features around many parts of the world.

Barrier island A 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. 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.

Reef A bar of rock, sand, coral or similar material, lying beneath the surface of water

A reef is a bar of rock, sand, coral or similar material, lying beneath the surface of water. Many reefs result from natural, abiotic processes—deposition of sand, wave erosion planing down rock outcrops, etc.—but the best known reefs are the coral reefs of tropical waters developed through biotic processes dominated by corals and coralline algae.

Atoll Ring-shaped coral reef, generally formed over a subsiding oceanic volcano, with a central lagoon and perhaps islands around the rim

An atoll, sometimes called a coral atoll, is a ring-shaped coral reef including a coral rim that encircles a lagoon partially or completely. There may be coral islands or cays on the rim. The coral of the atoll often sits atop the rim of an extinct seamount or volcano which has eroded or subsided partially beneath the water. The lagoon forms over the volcanic crater or caldera while the higher rim remains above water or at shallow depths that permit the coral to grow and form the reefs. For the atoll to persist, continued erosion or subsidence must be at a rate slow enough to permit reef growth upward and outward to replace the lost height.

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Definition

Lagoon vs. estuary

Lagoons are shallow, often elongated bodies of water separated from a larger body of water by a shallow or exposed shoal, coral reef, or similar feature. Some authorities include fresh water bodies in the definition of "lagoon", while others explicitly restrict "lagoon" to bodies of water with some degree of salinity. The distinction between "lagoon" and "estuary" also varies between authorities. Richard A. Davis Jr. restricts "lagoon" to bodies of water with little or no fresh water inflow, and little or no tidal flow, and calls any bay that receives a regular flow of fresh water an "estuary". Davis does state that the terms "lagoon" and "estuary" are "often loosely applied, even in scientific literature." [1] Timothy M. Kusky characterizes lagoons as normally being elongated parallel to the coast, while estuaries are usually drowned river valleys, elongated perpendicular to the coast. [1] [2] [3] [4] [5]

Shoal A natural landform that rises from the bed of a body of water to near the surface and is covered by unconsolidated material

In oceanography, geomorphology, and earth sciences, a shoal is a natural submerged ridge, bank, or bar that consists of, or is covered by, sand or other unconsolidated material, and rises from the bed of a body of water to near the surface. Often it refers to those submerged ridges, banks, or bars that rise near enough to the surface of a body of water as to constitute a danger to navigation. Shoals are also known as sandbanks, sandbars, or gravelbars. Two or more shoals that are either separated by shared troughs or interconnected by past or present sedimentary and hydrographic processes are referred to as a shoal complex.

Fresh water Naturally occurring water with low amounts of dissolved salts

Fresh water is any naturally occurring water except seawater and brackish water. Fresh water includes water in ice sheets, ice caps, glaciers, icebergs, bogs, ponds, lakes, rivers, streams, and even underground water called groundwater. Fresh water is generally characterized by having low concentrations of dissolved salts and other total dissolved solids. Though the term specifically excludes seawater and brackish water, it does include mineral-rich waters such as chalybeate springs.

Salinity The proportion of salt dissolved in a body of water

Salinity is the saltiness or amount of salt dissolved in a body of water, called saline water. This is usually measured in . Salinity is an important factor in determining many aspects of the chemistry of natural waters and of biological processes within it, and is a thermodynamic state variable that, along with temperature and pressure, governs physical characteristics like the density and heat capacity of the water.

When used within the context of a distinctive portion of coral reef ecosystems, the term "lagoon" is synonymous with the term "back reef" or "backreef", which is more commonly used by coral reef scientists to refer to the same area. [6] Coastal lagoons are classified as inland bodies of water. [7] [8]

Names

Many lagoons do not include "lagoon" in their common names. Albemarle and Pamlico sounds in North Carolina, [9] Great South Bay between Long Island and the barrier beaches of Fire Island in New York, [10] Isle of Wight Bay, which separates Ocean City, Maryland from the rest of Worcester County, Maryland, [11] Banana River in Florida, [12] Lake Illawarra in New South Wales, [13] Montrose Basin in Scotland, [14] and Broad Water in Wales have all been classified as lagoons, despite their names. In England, The Fleet at Chesil Beach has also been described as a lagoon.

Albemarle Sound An estuary on the coast of North Carolina, United States

Albemarle Sound is a large estuary on the coast of North Carolina in the United States located at the confluence of a group of rivers, including the Chowan and Roanoke. It is separated from the Atlantic Ocean by the Currituck Banks, a barrier peninsula upon which the town of Kitty Hawk is located, at the eastern edge of the sound, and part of the greater Outer Banks region. Roanoke Island is situated at the southeastern corner of the sound, where it connects to Pamlico Sound. Much of the water in the Albemarle Sound is brackish or fresh, as opposed to the saltwater of the ocean, as a result of river water pouring into the sound.

Pamlico Sound The largest lagoon along the North American East Coast

Pamlico Sound in North Carolina in the US is the largest lagoon along the North American East Coast, extending 80 mi (130 km) long and 15 to 20 miles wide. It is part of a large, interconnected network of lagoon estuaries that includes Albemarle Sound, Currituck Sound, Croatan Sound, Pamlico Sound, Bogue Sound, Core Sound, and Roanoke Sound. Together, these sounds, known as the Albemarle-Pamlico sound system, comprise the second largest estuary in the United States, covering over 3,000 sq. mi. of open water.(Chesapeake Bay is the largest.) The Pamlico Sound is separated from the Atlantic Ocean by the Outer Banks, a row of low, sandy barrier islands that include Cape Hatteras National Seashore, Cape Lookout National Seashore, and Pea Island National Wildlife Refuge. The Albemarle-Pamlico Sound is one of nineteen great waters recognized by the America's Great Waters Coalition.

North Carolina U.S. state in the United States

North Carolina is a state located in the southeastern region of the United States. North Carolina is the 28th largest and 9th-most populous of the 50 United States. North Carolina is bordered by Virginia to the north, the Atlantic Ocean to the east, Georgia and South Carolina to the south, and Tennessee to the west. Raleigh is the state's capital and Charlotte is its largest city. The Charlotte metropolitan area, with an estimated population of 2,569,213 in 2018, is the most populous metropolitan area in North Carolina, the 23rd-most populous in the United States, and the largest banking center in the nation after New York City. North Carolina's second largest metropolitan area is the Raleigh metropolitan area, with an estimated population of 1,337,331 in 2018, and is home to the largest research park in the United States, Research Triangle Park, in Chapel Hill, Durham, and Raleigh.

Latin American laguna

In Latin America, the term laguna in Spanish, which lagoon translates to, may be used for a small fresh water lake in a similar way a creek is considered a small river. However, sometimes it is popularly used to describe a full-sized lake, such as Laguna Catemaco in Mexico, which is actually the third largest lake by area in the country. The brackish water lagoon may be thus explicitly identified as a "coastal lagoon" (laguna costera). In Portuguese the same usage is found: lagoa may be a body of shallow sea water, or a small freshwater lake not linked to the sea.

Lake A body of relatively still water, in a basin surrounded by land

A lake is an area filled with water, localized in a basin, surrounded by land, apart from any river or other outlet that serves to feed or drain the lake. Lakes lie on land and are not part of the ocean, and therefore are distinct from lagoons, and are also larger and deeper than ponds, though there are no official or scientific definitions. Lakes can be contrasted with rivers or streams, which are usually flowing. Most lakes are fed and drained by rivers and streams.

Stream A body of surface water flowing down a channel

A stream is a body of water with surface water flowing within the bed and banks of a channel. The stream encompasses surface and groundwater fluxes that respond to geological, geomorphological, hydrological and biotic controls.

Laguna Catemaco lake in Mexico

Laguna Catemaco is a freshwater lake located at the center of the Sierra de Los Tuxtlas in south central Veracruz, in east central Mexico.

Etymology

Lagoon is derived from the Italian laguna, which refers to the waters around Venice, the Lagoon of Venice. Laguna is attested in English by at least 1612, and had been Anglicized to "lagune" by 1673. In 1697 William Dampier referred to a "Lagune or Lake of Salt water" on the coast of Mexico. Captain James Cook described an island "of Oval form with a Lagoon in the middle" in 1769. [15]

Italian language Romance language

Italian is a Romance language of the Indo-European language family. Italian descended from the Vulgar Latin of the Roman Empire and, together with Sardinian, is by most measures the closest language to it of the Romance languages. Italian is an official language in Italy, Switzerland, San Marino and Vatican City. It has an official minority status in western Istria. It formerly had official status in Albania, Malta, Monaco, Montenegro (Kotor) and Greece, and is generally understood in Corsica and Savoie. It also used to be an official language in the former Italian East Africa and Italian North Africa, where it still plays a significant role in various sectors. Italian is also spoken by large expatriate communities in the Americas and Australia. Italian is included under the languages covered by the European Charter for Regional or Minority languages in Bosnia and Herzegovina and in Romania, although Italian is neither a co-official nor a protected language in these countries. Many speakers of Italian are native bilinguals of both Italian and other regional languages.

Venice Comune in Veneto, Italy

Venice is a city in northeastern Italy and the capital of the Veneto region. It is situated on a group of 118 small islands that are separated by canals and linked by over 400 bridges. The islands are located in the shallow Venetian Lagoon, an enclosed bay that lies between the mouths of the Po and the Piave rivers. In 2018, 260,897 people resided in the Comune di Venezia, of whom around 55,000 live in the historical city of Venice. Together with Padua and Treviso, the city is included in the Padua-Treviso-Venice Metropolitan Area (PATREVE), which is considered a statistical metropolitan area, with a total population of 2.6 million.

Linguistic anglicisation is the practice of modifying foreign words, names, and phrases in order to make them easier to spell, pronounce, or understand in English. The term commonly refers to the respelling of foreign words, often to a more drastic degree than that implied in, for example, romanisation. One instance is the word "dandelion", modified from the French dent-de-lion. The term can also refer to phonological adaptation without spelling change: spaghetti, for example, is accepted in English with Italian spelling, but anglicised phonetically.

Atoll lagoons

Satellite picture of the Atafu atoll in Tokelau in the Pacific Ocean Atafutrim.jpg
Satellite picture of the Atafu atoll in Tokelau in the Pacific Ocean

Atoll lagoons form as coral reefs grow upwards while the islands that the reefs surround subside, until eventually only the reefs remain above sea level. Unlike the lagoons that form shoreward of fringing reefs, atoll lagoons often contain some deep (>20m) portions.

Coastal lagoons

Anzali Lagoon in southwestern Caspian Sea coast, Iran Anzali lagoon Barry Kent.jpg
Anzali Lagoon in southwestern Caspian Sea coast, Iran
Coastal lagoon landscapes around the island of Hiddensee near Stralsund, Germany. Many similar coastal lagoons can be found around the Western Pomerania Lagoon Area National Park. Hiddensee (2011-05-21).JPG
Coastal lagoon landscapes around the island of Hiddensee near Stralsund, Germany. Many similar coastal lagoons can be found around the Western Pomerania Lagoon Area National Park.

Coastal lagoons form along gently sloping coasts where barrier islands or reefs can develop off-shore, and the sea-level is rising relative to the land along the shore (either because of an intrinsic rise in sea-level, or subsidence of the land along the coast). Coastal lagoons do not form along steep or rocky coasts, or if the range of tides is more than 4 metres (13 ft). Due to the gentle slope of the coast, coastal lagoons are shallow. A relative drop in sea level may leave a lagoon largely dry, while a rise in sea level may let the sea breach or destroy barrier islands, and leave reefs too deep under water to protect the lagoon. Coastal lagoons are young and dynamic, and may be short-lived in geological terms. Coastal lagoons are common, occurring along nearly 15 percent of the world's shorelines. In the United States, lagoons are found along more than 75 percent of the Eastern and Gulf coasts. [3] [4]

Coastal lagoons are usually connected to the open ocean by inlets between barrier islands. The number and size of the inlets, precipitation, evaporation, and inflow of fresh water all affect the nature of the lagoon. Lagoons with little or no interchange with the open ocean, little or no inflow of fresh water, and high evaporation rates, such as Lake St. Lucia, in South Africa, may become highly saline. Lagoons with no connection to the open ocean and significant inflow of fresh water, such as the Lake Worth Lagoon in Florida in the middle of the 19th century, may be entirely fresh. On the other hand, lagoons with many wide inlets, such as the Wadden Sea, have strong tidal currents and mixing. Coastal lagoons tend to accumulate sediments from inflowing rivers, from runoff from the shores of the lagoon, and from sediment carried into the lagoon through inlets by the tide. Large quantities of sediment may be occasionally be deposited in a lagoon when storm waves overwash barrier islands. Mangroves and marsh plants can facilitate the accumulation of sediment in a lagoon. Benthic organisms may stabilize or destabilize sediments. [3] [4]

River-mouth lagoons on mixed sand and gravel beaches

Two similar freshwater lagoons close to the Salar de Atacama. The eyes of Atacama.jpg
Two similar freshwater lagoons close to the Salar de Atacama.

River-mouth lagoons on mixed sand and gravel (MSG) beaches form at the river-coast interface where a typically braided, although sometimes meandering, river interacts with a coastal environment that is significantly affected by longshore drift. [17] The lagoons which form on the MSG coastlines are common on the east coast of the South Island of New Zealand and have long been referred to as hapua by the Māori. This classification differentiates hapua from similar lagoons located on the New Zealand coast termed waituna. Hapua are often located on paraglacial coastal areas [18] where there is a low level of coastal development and minimal population density. Hapua form as the river carves out an elongated coast-parallel area, blocked from the sea by a MSG barrier which constantly alters its shape and volume due to longshore drift. [17] [19] Longshore drift continually extends the barrier behind which the hapua forms by transporting sediment along the coast. Hapua are defined as a narrow shore-parallel extensions of the coastal riverbed. [19] They discharge the majority of stored water to the ocean via an ephemeral and highly mobile drainage channel or outlet. [20] The remainder percolates through the MSG barrier due to its high levels of permeability. Hapua systems are driven by a wide range of dynamic processes that are generally classified as fluvial or marine; changes in the balance between these processes as well as the antecedent barrier conditions can cause shifts in the morphology of the hapua, in particular the barrier. New Zealand examples include the Rakaia, Ashburton and Hurunui river-mouths.

Hapua environment

Hapua have been identified as establishing in the Canterbury Bight coastal region on the east coast of the South Island. They are often found in areas of coarse-grained sediment where contributing rivers have moderately steep bed gradients. [17] MSG beaches in the Canterbury Bight region contain a wide range of sediment sizes from sand to boulders [21] and are exposed to the high energy waves that make up an east coast swell environment. [22] MSG beaches are reflective rather than dissipative energy zones due to their morphological characteristics. They have a steep foreshore which is known as the ‘engine room’ of the beach profile. In this zone, swash and backwash are dominating processes alongside longshore transport. [23] MSG beaches do not have a surf zone; instead a single line of breakers is visible in all sea conditions. [17] Hapua are associated with MSG beaches as the variation in sediment size allows for the barrier to be permeable.

The east coast of the South Island has been identified as being in a period of chronic erosion of approximately 0.5 metres per year. [24] This erosion trend is a result of a number of factors. According to the classification scheme of Zenkovich, [18] the rivers on the east coast can be described as ‘small’; this classification is not related to their flow rate but to the insufficient amount of sediment that they transport to the coast to nourish it. The sediment provided is not adequate to nourish the coast against its typical high energy waves and strong longshore drift. These two processes constantly remove sediment depositing it either offshore or further up drift. [25] As the coastline becomes eroded the hapua have been 'rolling back' by eroding the backshore to move landwards. [19]

Hapua or river-mouth lagoons form in micro-tidal environments. A micro-tidal environment is where the tidal range (distance between low tide and high tide) is less than two metres. [17] Tidal currents in a micro-tidal zone are less than those found on meso-tidal (two – four metres) and macro-tidal (greater than four metres) coastlines. [26] Hapua form in this type of tidal environment as the tidal currents are unable to compete with the powerful freshwater flows of the rivers therefore there is no negligible tidal penetration to the lagoon. [17] A fourth element of the environment in which hapua form is the strong longshore drift component. [17] Longshore or littoral drift is the transportation of sediments along the coast at an angle to the shoreline. In the Canterbury Bight coastal area; the dominant swell direction is northwards from the Southern Ocean. [17] Therefore, the principal movement of sediment via longshore drift is north towards Banks Peninsula. Hapua are located in areas dominated by longshore drift; because it aids the formation of the barrier behind which the hapua is sited.

A hapua also requires sediment to form the lagoon barrier. Sediment which nourishes the east coast of New Zealand can be sourced from three different areas. Material from the highly erodible Southern Alps is removed via weathering; then carried across the Canterbury Plains by various braided rivers to the east coast beaches. [19] [25] The second source of sediment is the high cliffs which are located in the hinterland of lagoons. [25] These can be eroded during the occurrence of high river flow or sea storm events. Beaches further south provide nourishment to the northern coast via longshore transport.

Hapua characteristics

Hapua have a number of characteristics which includes shifts between a variety of morphodynamic states due to changes in the balance between marine and fluvial processes as well as the antecedent barrier conditions. [19] The MSG barrier constantly changes size and shape as a result of the longshore drift. Water stored in the hapua drains to the coast predominately though an outlet; although it can also seep through the barrier depending on the permeability of the material. [19] [27]

Changes in the level of the lagoon water do not occur as a result of saltwater or tidal intrusion. Water in a hapua is predominately freshwater originating from the associated river. Hapua are non-estuarine, there is no tidal inflow however the tide does have an effect on the level of water in the lagoon. As the tide reaches its peak, the lagoon water has a much smaller amount of barrier to permeate through so the lagoon level rises. [28] This is related to a physics theory known as hydraulic head. The lagoon level has a similar sinusoidal wave shape as the tide but reaches its peak slightly later. [27] In general, any saltwater intrusion into the hapua will only occur during a storm via wave overtopping or sea spray. [19] [25]

Hapua can act as both a source and sink of sediment. [24] [25] The majority of sediment in the hapua is fluvial sourced. [17] During medium to low river flows, coarser sediment generally collects in the hapua; while some of the finer sediment can be transported through the outlet to the coast. [25] During flood events the hapua is 'flushed out' with larger amounts of sediment transferred through the outlet. This sediment can be deposited offshore or downdrift of the hapua replenishing the undernourished beach. [25] If a large amount of material is released to the coast at one time it can be identified as a 'slug'. These can often be visible from aerial photographs.

Antecedent barrier conditions combined with changes in the balance between marine and fluvial processes results in shifts between a variety of morphological states in a hapua or river-mouth lagoon on a MSG beach. Marine processes includes the direction of wave approach, wave height and the coincidence of storm waves with high tides. [29] Marine processes tend to dominate the majority of morphodynamic conditions until there is a large enough flood event in the associated river to breach the barrier. [17] The level and frequency of base or flood flows are attributed to fluvial processes. Antecedent barrier conditions are the permeability, volume and height of the barrier as well as the width and presence of previous outlet channels. [29] During low to medium river flows, the outlet from the lagoon to the sea becomes offset in the direction of longshore drift. [25] Outlet efficiency tends to decrease the further away from the main river-mouth the outlet is. [19] A decrease in efficiency can cause the outlet to become choked with sediment and the hapua to close temporarily. The potential for closure varies between different hapua depending on whether marine or fluvial processes are the bigger driver in the event. A high flow event; such as a fresh or flood can breach the barrier directly opposite the main river channel. [19] [25] This causes an immediate decrease in the water level of the hapua; as well as transporting previously deposited sediments into the ocean. Flood events are important for eroding lagoon back shores; this is a behaviour which allows hapua to retreat landward and thus remain coastal landforms even with coastal transgression and sea level rise. [19] During high flow events there is also the possibility for secondary breaches of the barrier or lagoon truncation to occur.

Storm events also have the ability to close hapua outlets as waves overtop the barrier depositing sediment and choking the scoured channel. [24] The resultant swift increase in lagoon water level causes a new outlet to be breached rapidly due to the large hydraulic head that forms between the lagoon and sea water levels. Storm breaching is believed to be an important but unpredictable control on the duration of closures at low to moderate river flow levels in smaller hapua. [24]

Hapua are extremely important for a number of reasons. They provide a link between the river and sea for migrating fish as well as a corridor for migratory birds. [17] [30] To lose this link via closure of the hapua outlet could result in losing entire generations of specific species as they may need to migrate to the ocean or the river as a vital part of their lifecycle. River-mouth lagoons such as hapua were also used a source for mahinga kai (food gathering) by the Māori people. [17] [30] However, this is no longer the case due to catchment degradation which has resulted in lagoon deterioration. River-mouth lagoons on MSG beaches are not well explained in international literature.

Hapua case study

Aerial photograph of the Rakaia river-mouth and associated hapua Rakaia River Mouth.jpg
Aerial photograph of the Rakaia river-mouth and associated hapua

The hapua located at the mouth of the Rakaia River stretches approximately three kilometres north from where the river-mouth reaches the coast. The average width of the hapua between 1952 and 2004 was approximately 50 metres; whilst the surface area has stabilised at approximately 600,000 square metres since 1966. [31] The coastal hinterland is composed of erodible cliffs and a low-lying area commonly known as the Rakaia Huts. This area has changed notably since European Settlement; with the drainage of ecologically significant wetlands and development of the small bach community.

The Rakaia River begins in the Southern Alps, providing approximately 4.2 Mt per year of sediment to the east coast. It is a braided river with a catchment area of 3105 kilometres squared and a mean flow of 221 cubic metres per second. [32] The mouth of the Rakaia River reaches the coast south of Banks Peninsula. As the river reaches the coast it diverges into two channels; with the main channel flowing to the south of the island. [24] As the hapua is located in the Canterbury Bight it is in a state of constant morphological change due to the prevailing southerly sea swells and resultant northwards longshore drift.

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Related Research Articles

Beach Area of loose particles at the edge of the sea or other body of water

A beach is a landform alongside a body of water which consists of loose particles. The particles composing a beach are typically made from rock, such as sand, gravel, shingle, pebbles. The particles can also be biological in origin, such as mollusc shells or coralline algae.

Estuary 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

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.

Salt marsh A coastal ecosystem in the upper coastal intertidal zone between land and open saltwater or brackish water that is regularly flooded by the tides

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.

Spit (landform) A coastal bar or beach landform deposited by longshore drift

A spit or sandspit is a deposition bar or beach landform off coasts or lake shores. It develops in places where re-entrance occurs, such as at a cove's headlands, by the process of longshore drift by longshore currents. The drift occurs due to waves meeting the beach at an oblique angle, moving sediment down the beach in a zigzag pattern. This is complemented by longshore currents, which further transport sediment through the water alongside the beach. These currents are caused by the same waves that cause the drift.

Longshore drift Sediment moved by the longshore current

Longshore drift from longshore current is a geological process that consists of the transportation of sediments along a coast parallel to the shoreline, which is dependent on oblique incoming wind direction. Oblique incoming wind squeezes water along the coast, and so generates a water current which moves parallel to the coast. Longshore drift is simply the sediment moved by the longshore current. This current and sediment movement occur within the surf zone.

Groyne rigid hydraulic structure

A groyne is a rigid hydraulic structure built from an ocean shore or from a bank that interrupts water flow and limits the movement of sediment. It is usually made out of wood, concrete or stone. In the ocean, groynes create beaches or prevent them being washed away by longshore drift. In a river, groynes slow down the process of erosion and prevent ice-jamming, which in turn aids navigation. Ocean groynes run generally perpendicular to the shore, extending from the upper foreshore or beach into the water. All of a groyne may be under water, in which case it is a submerged groyne. The areas between groups of groynes are groyne fields. Groynes are generally placed in groups. They are often used in tandem with seawalls. Groynes, however, may cause a shoreline to be perceived as unnatural.

Coastal morphodynamics refers to the study of the interaction and adjustment of the seafloor topography and fluid hydrodynamic processes, seafloor morphologies and sequences of change dynamics involving the motion of sediment. Hydrodynamic processes include those of waves, tides and wind-induced currents.

Coastal geography The study of the region between the ocean and the land

Coastal geography is the study of the constantly changing region between the ocean and the land, incorporating both the physical geography and the human geography of the coast. It includes understanding coastal weathering processes, particularly wave action, sediment movement and weather, and the ways in which humans interact with the coast

Swash A turbulent layer of water that washes up on the beach after an incoming wave has broken

Swash, or forewash in geography, is a turbulent layer of water that washes up on the beach after an incoming wave has broken. The swash action can move beach materials up and down the beach, which results in the cross-shore sediment exchange. The time-scale of swash motion varies from seconds to minutes depending on the type of beach. Greater swash generally occurs on flatter beaches. The swash motion plays the primary role in the formation of morphological features and their changes in the swash zone. The swash action also plays an important role as one of the instantaneous processes in wider coastal morphodynamics.

Cuspate foreland Geographical features found on coastlines and lakeshores that are created primarily by longshore drift

Cuspate forelands, also known as cuspate barriers or nesses in Britain, are geographical features found on coastlines and lakeshores that are created primarily by longshore drift. Formed by accretion and progradation of sand and shingle, they extend outwards from the shoreline in a triangular shape. Some cuspate forelands may be stabilised by vegetation, while others may migrate down the shoreline. Because some cuspate forelands provide an important habitat for many flora and fauna, effective management is required to reduce the impacts from both human activities and physical factors such as climate change and sea level rise.

Depositional environment The combination of physical, chemical and biological processes associated with the deposition of a particular type of sediment

In geology, depositional environment or sedimentary environment describes the combination of physical, chemical and biological processes associated with the deposition of a particular type of sediment and, therefore, the rock types that will be formed after lithification, if the sediment is preserved in the rock record. In most cases the environments associated with particular rock types or associations of rock types can be matched to existing analogues. However, the further back in geological time sediments were deposited, the more likely that direct modern analogues are not available.

Sedimentary budget

Sedimentary budgets are a coastal management tool used to analyze and describe the different sediment inputs (sources) and outputs (sinks) on the coasts, which is used to predict morphological change in any particular coastline over time. Within a coastal environment the rate of change of sediment is dependent on the amount of sediment brought into the system versus the amount of sediment that leaves the system. These inputs and outputs of sediment then equate to the total balance of the system and more than often reflect the amounts of erosion or accretion affecting the morphology of the coast.

Washdyke Lagoon is a brackish shallow coastal lagoon approximately 1 kilometre north of Timaru, South Canterbury, New Zealand. The lagoon has drastically reduced in size since 1881 when it was approximately 253 hectares, now it is less than 48 hectares in area. It is enclosed by a barrier beach that is 3 kilometres long and 3 metres above high tide at its largest point. The reduced lagoon size is due to the construction of the Timaru Port breakwater which is preventing coarse sediments from reaching and replenishing Washdyke Barrier. This is important as the lagoon and the surrounding 250 hectares are classified as a wildlife refuge and it demonstrates the role human structures have on coastline evolution.

Canterbury Bight is a 135 kilometres (84 mi) stretch of coastline between Dashing Rocks and the southern side of Banks Peninsula on the eastern side of the South Island, New Zealand. The bight faces southeast, which exposes it to high-energy storm waves originating in the Pacific Ocean. The most frequent wave approach direction for the Canterbury Bight is from the southeast and the most dominant the south with wave heights of over 2m common. The bight is a large, gently curving bend of shoreline of primarily mixed sand and gravel (MSG) beaches. The MSG beaches are steep, highly reflective and composed of alluvial gravel deposits. The alluvial gravels are the outwash products of multiple glaciations that occurred in the Southern Alps during the Pleistocene. Large braided rivers transported this material to the edge of the current continental shelf, which, due to sea level rise is 50 km seaward of the coasts current position. The MSG beaches of the Canterbury Bight therefore occur where the alluvial fans of the Canterbury Plains rivers are exposed to high-energy ocean swells. The dominant rock ‘greywacke’ in the Southern Alps is consequently the primary constituent of the MSG beaches, which is partially indurated sandstone of the Torlesse Supergroup. River-mouth lagoons are a relatively common occurrence on the MSG beaches of the Canterbury Bight.

Marine habitats A 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.

Coastal sediment supply is the transport of sediment to the beach environment by both fluvial and aeolian transport. While aeolian transport plays a role in the overall sedimentary budget for the coastal environment, it is paled in comparison to the fluvial supply which makes up 95% of sediment entering the ocean. When sediment reaches the coast it is then entrained by longshore drift and littoral cells until it is accreted upon the beach or dunes.

Estuaries of Australia are features of the Australian coastline. They are linked to tides, river mouths and coastal features and conditions. In many cases the features of estuaries are also named inlets.

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