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76-526: In past centuries the barrier protecting the lagoon was sometimes breached by the Baltic Sea during storm surges that flooded across the island of Usedom, when the narrowest part of the land bridge between Zempin and Koserow at Rieckgraben (near Lüttenort ) was flooded. This land bridge between the Achterwasser and the Baltic Sea is only 300 metres wide. The Achterwasser is not very deep, and

152-487: A Category 4 hurricane that struck Galveston, Texas , drove a devastating surge ashore; between 6,000 and 12,000 people died, making it the deadliest natural disaster ever to strike the United States. The highest storm tide noted in historical accounts was produced by the 1899 Cyclone Mahina , estimated at almost 44 feet (13.41 m) at Bathurst Bay , Australia , but research published in 2000 concluded that

228-573: A harsh environment for organisms. Sediment often settles in intertidal mudflats which are extremely difficult to colonize. No points of attachment exist for algae , so vegetation based habitat is not established. Sediment can also clog feeding and respiratory structures of species, and special adaptations exist within mudflat species to cope with this problem. Lastly, dissolved oxygen variation can cause problems for life forms. Nutrient-rich sediment from human-made sources can promote primary production life cycles, perhaps leading to eventual decay removing

304-529: A map of MOMs or Maximum of Maximums. For hurricane evacuation studies, a family of storms with representative tracks for the region, and varying intensity, eye diameter, and speed are modeled to produce worst-case water heights for any tropical cyclone occurrence. The results of these studies are typically generated from several thousand SLOSH runs. These studies have been completed by the United States Army Corps of Engineers , under contract to

380-529: A number of coastal water bodies such as coastal lagoons and brackish seas. A more comprehensive definition of an estuary is "a semi-enclosed body of water connected to the sea as far as the tidal limit or the salt intrusion limit and receiving freshwater runoff; however the freshwater inflow may not be perennial, the connection to the sea may be closed for part of the year and tidal influence may be negligible". This broad definition also includes fjords , lagoons , river mouths , and tidal creeks . An estuary

456-439: A number of days as water was continually built-up inside the estuary from the onshore winds and freshwater rains flowing into the bay. In many locations, water levels were shy of records by only 0.1 feet (3 cm). Surge can be measured directly at coastal tidal stations as the difference between the forecast tide and the observed rise of water. Another method of measuring surge is by the deployment of pressure transducers along

532-453: A phenomenon referred to as wind setup , which is the tendency for water levels to increase at the downwind shore and to decrease at the upwind shore. Intuitively, this is caused by the storm blowing the water toward one side of the basin in the direction of its winds. Strong surface winds cause surface currents at a 45° angle to the wind direction, by an effect known as the Ekman spiral . Because

608-478: A station provides a translation from the geodetic vertical datum to mean sea level (MSL) at that location, then subtracting the tidal prediction yields a surge height above the normal water height. The U.S. National Hurricane Center forecasts storm surge using the SLOSH model, which is an abbreviation for Sea, Lake and Overland Surges from Hurricanes. The model is accurate to within 20 percent. SLOSH inputs include

684-511: A storm surge. This was the case on the western Florida coast in 2017, just before Hurricane Irma made landfall, uncovering land usually underwater. This phenomenon is known as a reverse storm surge , or a negative storm surge . The deadliest storm surge on record was the 1970 Bhola cyclone , which killed up to 500,000 people in the area of the Bay of Bengal . The low-lying coast of the Bay of Bengal

760-418: A storm's wind-powered currents. Powerful wind whips up large, strong waves in the direction of its movement. Although these surface waves are responsible for very little water transport in open water, they may be responsible for significant transport near the shore. When waves are breaking on a line more or less parallel to the beach, they carry considerable water shoreward. As they break, the water moving toward

836-408: A type of ecosystem in some estuaries that have been negatively impacted by eutrophication. Cordgrass vegetation dominates the salt marsh landscape. Excess nutrients allow the plants to grow at greater rates in above ground biomass, however less energy is allocated to the roots since nutrients is abundant. This leads to a lower biomass in the vegetation below ground which destabilizes the banks of

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912-563: A well-mixed water column and the disappearance of the vertical salinity gradient . The freshwater-seawater boundary is eliminated due to the intense turbulent mixing and eddy effects . The lower reaches of Delaware Bay and the Raritan River in New Jersey are examples of vertically homogeneous estuaries. Inverse estuaries occur in dry climates where evaporation greatly exceeds the inflow of freshwater. A salinity maximum zone

988-436: A wholly marine embayment to any of the other estuary types. The most important variable characteristics of estuary water are the concentration of dissolved oxygen, salinity and sediment load. There is extreme spatial variability in salinity, with a range of near-zero at the tidal limit of tributary rivers to 3.4% at the estuary mouth. At any one point, the salinity will vary considerably over time and seasons, making it

1064-414: A wide effect on the surrounding water bodies.  In turn, this can decrease fishing industry sales in one area and across the country. Production in 2016 from recreational and commercial fishing contributes billions of dollars to the United States' gross domestic product (GDP). A decrease in production within this industry can affect any of the 1.7 million people the fishing industry employs yearly across

1140-455: Is a dynamic ecosystem having a connection to the open sea through which the sea water enters with the rhythm of the tides . The effects of tides on estuaries can show nonlinear effects on the movement of water which can have important impacts on the ecosystem and waterflow. The seawater entering the estuary is diluted by the fresh water flowing from rivers and streams. The pattern of dilution varies between different estuaries and depends on

1216-541: 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

1292-402: Is a popular surfing and sailing area. The beach sand on the Achterwasser on the peninsula of Gnitz is not as fine-grained as that on the Baltic Sea beach of Usedom. The bottom of the Achterwasser is very stony. On some maps from medieval and early modern times, the lagoon is named as "Lassansches Water" or as plural "Lassansche Waters“. The description is related to the town of Lassan , which as

1368-430: Is another important element in storm surge extent. Areas, where the land lies less than a few meters above sea level, are at particular risk from storm surge inundation. The size of the storm also affects the surge height; this is due to the storm's area not being proportional to its perimeter. If a storm doubles in diameter, its perimeter also doubles, but its area quadruples. As there is proportionally less perimeter for

1444-416: Is defined as the rise of water beyond what would be expected by the normal movement caused by tides, storm surge is measured using tidal predictions, with the assumption that the tide prediction is well-known and only slowly varying in the region subject to the surge. Since tides are a localized phenomenon, storm surge can only be measured in relationship to a nearby tidal station. Tidal benchmark information at

1520-513: Is derived from the Latin word aestuarium meaning tidal inlet of the sea, which in itself is derived from the term aestus , meaning tide. There have been many definitions proposed to describe an estuary. The most widely accepted definition is: "a semi-enclosed coastal body of water, which has a free connection with the open sea, and within which seawater is measurably diluted with freshwater derived from land drainage". However, this definition excludes

1596-411: Is formed, and both riverine and oceanic water flow close to the surface towards this zone. This water is pushed downward and spreads along the bottom in both the seaward and landward direction. Examples of an inverse estuary are Spencer Gulf , South Australia, Saloum River and Casamance River , Senegal. Estuary type varies dramatically depending on freshwater input, and is capable of changing from

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1672-566: Is less restricted, and there is a slow but steady exchange of water between the estuary and the ocean. Fjord-type estuaries can be found along the coasts of Alaska , the Puget Sound region of western Washington state , British Columbia , eastern Canada, Greenland , Iceland , New Zealand, and Norway. These estuaries are formed by subsidence or land cut off from the ocean by land movement associated with faulting , volcanoes , and landslides . Inundation from eustatic sea-level rise during

1748-421: Is measured as the rise in water level above the normal tidal level, and does not include waves. The main meteorological factor contributing to a storm surge is high-speed wind pushing water towards the coast over a long fetch . Other factors affecting storm surge severity include the shallowness and orientation of the water body in the storm path, the timing of tides , and the atmospheric pressure drop due to

1824-684: Is particularly high, there are specific storm surge warnings. These have been implemented, for instance, in the Netherlands , Spain , the United States, and the United Kingdom . Similarly educating coastal communities and developing local evacuation plans can reduce the relative impact on people. A prophylactic method introduced after the North Sea flood of 1953 is the construction of dams and storm-surge barriers ( flood barriers ). They are open and allow free passage, but close when

1900-572: Is particularly vulnerable to surges caused by tropical cyclones. The deadliest storm surge in the twenty-first century was caused by Cyclone Nargis , which killed more than 138,000 people in Myanmar in May 2008. The next deadliest in this century was caused by Typhoon Haiyan (Yolanda), which killed more than 6,000 people in the central Philippines in 2013. and resulted in economic losses estimated at $ 14 billion (USD). The 1900 Galveston hurricane ,

1976-699: Is relatively steep and deep; storm surge is not as great but the waves are larger compared to the west coast of Florida. Conversely, on the Gulf side of Florida, the edge of the Floridian Plateau can lie more than 160 kilometres (99 mi) offshore. Florida Bay , lying between the Florida Keys and the mainland, is very shallow with depths between 0.3 m (0.98 ft) and 2 m (6.6 ft). These shallow areas are subject to higher storm surges with smaller waves. Other shallow areas include much of

2052-646: Is the whitefish species from the European Alps . Eutrophication reduced the oxygen levels in their habitats so greatly that whitefish eggs could not survive, causing local extinctions. However, some animals, such as carnivorous fish, tend to do well in nutrient-enriched environments and can benefit from eutrophication. This can be seen in populations of bass or pikes. Eutrophication can affect many marine habitats which can lead to economic consequences. The commercial fishing industry relies upon estuaries for approximately 68 percent of their catch by value because of

2128-602: The Coriolis effect , which bends currents to the right in the Northern Hemisphere and to the left in the Southern Hemisphere. When this bend brings the currents into more perpendicular contact with the shore, it can amplify the surge, and when it bends the current away from the shore it has the effect of lessening the surge. The effect of waves, while directly powered by the wind, is distinct from

2204-733: The Federal Emergency Management Agency (FEMA) , for several states and are available on their Hurricane Evacuation Studies (HES) website. They include coastal county maps, shaded to identify the minimum category of hurricane that will result in flooding, in each area of the county. Storm surge is responsible for significant property damage and loss of life as part of cyclones. Storm surge both destroys built infrastructure, like roads and undermines foundations and building structures. Unexpected flooding in estuaries and coastal areas can catch populations unprepared, causing loss of life. The deadliest storm surge on record

2280-449: The Gulf of Mexico coast, and the Bay of Bengal . The difference is due to how much flow area the storm surge can dissipate to. In deeper water, there is more area and a surge can be dispersed down and away from the hurricane. On a shallow, gently sloping shelf, the surge has less room to disperse and is driven ashore by the wind forces of the hurricane. The topography of the land surface

2356-748: The Holocene Epoch has also contributed to the formation of these estuaries. There are only a small number of tectonically produced estuaries; one example is the San Francisco Bay , which was formed by the crustal movements of the San Andreas Fault system causing the inundation of the lower reaches of the Sacramento and San Joaquin rivers . In this type of estuary, river output greatly exceeds marine input and tidal effects have minor importance. Freshwater floats on top of

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2432-610: The Mandovi estuary in Goa during the monsoon period. As tidal forcing increases, river output becomes less than the marine input. Here, current induced turbulence causes mixing of the whole water column such that salinity varies more longitudinally rather than vertically, leading to a moderately stratified condition. Examples include the Chesapeake Bay and Narragansett Bay . Tidal mixing forces exceed river output, resulting in

2508-640: The Mid-Atlantic coast, and Galveston Bay and Tampa Bay along the Gulf Coast . Bar-built estuaries are found in a place where the deposition of sediment has kept pace with rising sea levels so that the estuaries are shallow and separated from the sea by sand spits or barrier islands. They are relatively common in tropical and subtropical locations. These estuaries are semi-isolated from ocean waters by barrier beaches ( barrier islands and barrier spits ). Formation of barrier beaches partially encloses

2584-671: The Severn Estuary in the United Kingdom and the Ems Dollard along the Dutch-German border. The width-to-depth ratio of these estuaries is typically large, appearing wedge-shaped (in cross-section) in the inner part and broadening and deepening seaward. Water depths rarely exceed 30 m (100 ft). Examples of this type of estuary in the U.S. are the Hudson River , Chesapeake Bay , and Delaware Bay along

2660-478: The black-tailed godwit , rely on estuaries. Two of the main challenges of estuarine life are the variability in salinity and sedimentation . Many species of fish and invertebrates have various methods to control or conform to the shifts in salt concentrations and are termed osmoconformers and osmoregulators . Many animals also burrow to avoid predation and to live in a more stable sedimental environment. However, large numbers of bacteria are found within

2736-538: The Atlantic Coast. Coasts with sea ice may experience an "ice tsunami" causing significant damage inland. Extratropical storm surges may be possible further south for the Gulf coast mostly during the wintertime, when extratropical cyclones affect the coast, such as in the 1993 Storm of the Century . November 9–13, 2009, marked a significant extratropical storm surge event on the United States east coast when

2812-456: The Ekman spiral effects spread vertically through the water, the effect is proportional to depth. The surge will be driven into bays in the same way as the astronomical tide. The pressure effects of a tropical cyclone will cause the water level in the open ocean to rise in regions of low atmospheric pressure and fall in regions of high atmospheric pressure. The rising water level will counteract

2888-400: The United States. Estuaries are incredibly dynamic systems, where temperature, salinity, turbidity, depth and flow all change daily in response to the tides. This dynamism makes estuaries highly productive habitats, but also make it difficult for many species to survive year-round. As a result, estuaries large and small experience strong seasonal variation in their fish communities. In winter,

2964-513: The above definition of an estuary and could be fully saline. Many estuaries suffer degeneration from a variety of factors including soil erosion , deforestation , overgrazing , overfishing and the filling of wetlands. Eutrophication may lead to excessive nutrients from sewage and animal wastes; pollutants including heavy metals , polychlorinated biphenyls , radionuclides and hydrocarbons from sewage inputs; and diking or damming for flood control or water diversion. The word "estuary"

3040-452: The bottom where they are harmless. Historically the oysters filtered the estuary's entire water volume of excess nutrients every three or four days. Today that process takes almost a year, and sediment, nutrients, and algae can cause problems in local waters. Some major rivers that run through deserts historically had vast, expansive estuaries that have been reduced to a fraction of their former size, because of dams and diversions. One example

3116-404: The central pressure of a tropical cyclone, storm size, the cyclone's forward motion, its track, and maximum sustained winds. Local topography, bay and river orientation, depth of the sea bottom, astronomical tides, as well as other physical features, are taken into account in a predefined grid referred to as a SLOSH basin. Overlapping SLOSH basins are defined for the southern and eastern coastline of

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3192-434: The coastline just ahead of an approaching tropical cyclone. This was first tested for Hurricane Rita in 2005. These types of sensors can be placed in locations that will be submerged and can accurately measure the height of water above them. After surge from a cyclone has receded, teams of surveyors map high-water marks (HWM) on land, in a rigorous and detailed process that includes photographs and written descriptions of

3268-644: The continental U.S. Some storm simulations use more than one SLOSH basin; for instance, Hurricane Katrina SLOSH model runs used both the Lake Pontchartrain / New Orleans basin, and the Mississippi Sound basin, for the northern Gulf of Mexico landfall. The final output from the model run will display the maximum envelope of water, or MEOW, that occurred at each location. To allow for track or forecast uncertainties, usually several model runs with varying input parameters are generated to create

3344-409: The dissolved oxygen from the water; thus hypoxic or anoxic zones can develop. Nitrogen is often the lead cause of eutrophication in estuaries in temperate zones. During a eutrophication event, biogeochemical feedback decreases the amount of available silica . These feedbacks also increase the supply of nitrogen and phosphorus, creating conditions where harmful algal blooms can persist. Given

3420-401: The effects of modifying the estuarine circulation. Fjord -type estuaries are formed in deeply eroded valleys formed by glaciers . These U-shaped estuaries typically have steep sides, rock bottoms, and underwater sills contoured by glacial movement. The estuary is shallowest at its mouth, where terminal glacial moraines or rock bars form sills that restrict water flow. In the upper reaches of

3496-601: The estuary impacted by human activities, and over time may shift the basic composition of the ecosystem, and the reversible or irreversible changes in the abiotic and biotic parts of the systems from the bottom up. For example, Chinese and Russian industrial pollution, such as phenols and heavy metals, has devastated fish stocks in the Amur River and damaged its estuary soil. Estuaries tend to be naturally eutrophic because land runoff discharges nutrients into estuaries. With human activities, land run-off also now includes

3572-424: The estuary, the depth can exceed 300 m (1,000 ft). The width-to-depth ratio is generally small. In estuaries with very shallow sills, tidal oscillations only affect the water down to the depth of the sill, and the waters deeper than that may remain stagnant for a very long time, so there is only an occasional exchange of the deep water of the estuary with the ocean. If the sill depth is deep, water circulation

3648-776: The estuary, with only narrow inlets allowing contact with the ocean waters. Bar-built estuaries typically develop on gently sloping plains located along tectonically stable edges of continents and marginal sea coasts. They are extensive along the Atlantic and Gulf coasts of the U.S. in areas with active coastal deposition of sediments and where tidal ranges are less than 4 m (13 ft). The barrier beaches that enclose bar-built estuaries have been developed in several ways: Fjords were formed where Pleistocene glaciers deepened and widened existing river valleys so that they become U-shaped in cross-sections. At their mouths there are typically rocks, bars or sills of glacial deposits , which have

3724-482: The evaluation, HWMs are divided into four categories based on the confidence in the mark; in the U.S., only HWMs evaluated as "excellent" are used by the National Hurricane Center in the post-storm analysis of the surge. Two different measures are used for storm tide and storm surge measurements. Storm tide is measured using a geodetic vertical datum ( NGVD 29 or NAVD 88 ). Since storm surge

3800-609: The fish community is dominated by hardy marine residents, and in summer a variety of marine and anadromous fishes move into and out of estuaries, capitalizing on their high productivity. Estuaries provide a critical habitat to a variety of species that rely on estuaries for life-cycle completion. Pacific Herring ( Clupea pallasii ) are known to lay their eggs in estuaries and bays, surfperch give birth in estuaries, juvenile flatfish and rockfish migrate to estuaries to rear, and anadromous salmonids and lampreys use estuaries as migration corridors. Also, migratory bird populations, such as

3876-400: The great biodiversity of this ecosystem. During an algal bloom , fishermen have noticed a significant increase in the quantity of fish. A sudden increase in primary productivity causes spikes in fish populations which leads to more oxygen being utilized. It is the continued deoxygenation of the water that then causes a decline in fish populations. These effects can begin in estuaries and have

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3952-420: The impacts do not end there. Plant death alters the entire food web structure which can result in the death of animals within the afflicted biome . Estuaries are hotspots for biodiversity , containing a majority of commercial fish catch, making the impacts of eutrophication that much greater within estuaries. Some specific estuarine animals feel the effects of eutrophication more strongly than others. One example

4028-987: The land is under threat of a storm surge. Major storm surge barriers are the Oosterscheldekering and Maeslantkering in the Netherlands, which are part of the Delta Works project; the Thames Barrier protecting London ; and the Saint Petersburg Dam in Russia . Another modern development (in use in the Netherlands) is the creation of housing communities at the edges of wetlands with floating structures, restrained in position by vertical pylons. Such wetlands can then be used to accommodate runoff and surges without causing damage to

4104-438: The low atmospheric pressure such that the total pressure at some plane beneath the water surface remains constant. This effect is estimated at a 10 mm (0.39 in) increase in sea level for every millibar (hPa) drop in atmospheric pressure. For example, a major storm with a 100 millibar pressure drop would be expected to have a 1.0 m (3.3 ft) water level rise from the pressure effect. The Earth's rotation causes

4180-410: The majority of this likely was wave run-up because of the steep coastal topography. However, much of this storm surge was likely due to Mahina's extreme intensity, as computer modeling required an intensity of 880 millibars (26 inHg) (the same intensity as the lowest recorded pressure from the storm) to produce the recorded storm surge. In the United States, one of the greatest recorded storm surges

4256-525: The many chemicals used as fertilizers in agriculture as well as waste from livestock and humans. Excess oxygen-depleting chemicals in the water can lead to hypoxia and the creation of dead zones . This can result in reductions in water quality, fish, and other animal populations. Overfishing also occurs. Chesapeake Bay once had a flourishing oyster population that has been almost wiped out by overfishing. Oysters filter these pollutants, and either eat them or shape them into small packets that are deposited on

4332-422: The marine environment, such as plastics , pesticides , furans , dioxins , phenols and heavy metals . Such toxins can accumulate in the tissues of many species of aquatic life in a process called bioaccumulation . They also accumulate in benthic environments, such as estuaries and bay muds : a geological record of human activities of the last century. The elemental composition of biofilm reflect areas of

4408-415: The marks. HWMs denote the location and elevation of floodwaters from a storm event. When HWMs are analyzed, if the various components of the water height can be broken out so that the portion attributable to surge can be identified, then that mark can be classified as storm surge. Otherwise, it is classified as storm tide. HWMs on land are referenced to a vertical datum (a reference coordinate system). During

4484-575: The marsh causing increased rates of erosion . A similar phenomenon occurs in mangrove swamps , which are another potential ecosystem in estuaries. An increase in nitrogen causes an increase in shoot growth and a decrease in root growth. Weaker root systems cause a mangrove tree to be less resilient in seasons of drought, which can lead to the death of the mangrove. This shift in above ground and below ground biomass caused by eutrophication could hindered plant success in these ecosystems. Across all biomes, eutrophication often results in plant death but

4560-440: The now off-balance nitrogen cycle , estuaries can be driven to phosphorus limitation instead of nitrogen limitation. Estuaries can be severely impacted by an unbalanced phosphorus cycle, as phosphorus interacts with nitrogen and silica availability. With an abundance of nutrients in the ecosystem, plants and algae overgrow and eventually decompose, which produce a significant amount of carbon dioxide. While releasing CO 2 into

4636-422: The only town on the Achterwasser possessed the fishing rights for the waters. 54°0′3″N 13°58′17″E  /  54.00083°N 13.97139°E  / 54.00083; 13.97139 Storm surge A storm surge , storm flood , tidal surge , or storm tide is a coastal flood or tsunami -like phenomenon of rising water commonly associated with low-pressure weather systems, such as cyclones . It

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4712-475: The remnants of Hurricane Ida developed into a nor'easter off the southeast U.S. coast. During the event, winds from the east were present along the northern periphery of the low-pressure center for a number of days, forcing water into locations such as Chesapeake Bay . Water levels rose significantly and remained as high as 8 feet (2.4 m) above normal in numerous locations throughout the Chesapeake for

4788-427: The seawater in a layer that gradually thins as it moves seaward. The denser seawater moves landward along the bottom of the estuary, forming a wedge-shaped layer that is thinner as it approaches land. As a velocity difference develops between the two layers, shear forces generate internal waves at the interface, mixing the seawater upward with the freshwater. An examples of a salt wedge estuary is Mississippi River and

4864-411: The sediment which has a very high oxygen demand. This reduces the levels of oxygen within the sediment often resulting in partially anoxic conditions, which can be further exacerbated by limited water flow. Phytoplankton are key primary producers in estuaries. They move with the water bodies and can be flushed in and out with the tides . Their productivity is largely dependent upon the turbidity of

4940-471: The shore has considerable momentum and may run up a sloping beach to an elevation above the mean water line, which may exceed twice the wave height before breaking. The rainfall effect is experienced predominantly in estuaries . Hurricanes may dump as much as 12 in (300 mm) of rainfall in 24 hours over large areas and higher rainfall densities in localized areas. As a result, surface runoff can quickly flood streams and rivers. This can increase

5016-458: The shoreline, tends to produce a lower surge but higher and more powerful waves. A wide shelf, with shallower water, tends to produce a higher storm surge with relatively smaller waves. For example, in Palm Beach on the southeast coast of Florida , the water depth reaches 91 metres (299 ft) 3 km (1.9 mi) offshore, and 180 m (590 ft) 7 km (4.3 mi) out. This

5092-561: The storm. As extreme weather becomes more intense and the sea level rises due to climate change , storm surges are expected to cause more risk to coastal populations. Communities and governments can adapt by building hard infrastructure, like surge barriers , soft infrastructure, like coastal dunes or mangroves , improving coastal construction practices and building social strategies such as early warning, education and evacuation plans. At least five processes can be involved in altering tide levels during storms. Wind stresses cause

5168-523: The structures while also protecting conventional structures at somewhat higher low-lying elevations, provided that dikes prevent major surge intrusion. Other soft adaptation methods can include changing structures so that they are elevated to avoid flooding directly, or increasing natural protections like mangroves or dunes . For mainland areas, storm surge is more of a threat when the storm strikes land from seaward, rather than approaching from landward. Water can also be sucked away from shore prior to

5244-500: The surge to dissipate to, the surge height ends up being higher. Similar to tropical cyclones, extratropical cyclones cause an offshore rise of water. However, unlike most tropical cyclone storm surges, extratropical cyclones can cause higher water levels across a large area for longer periods of time, depending on the system. In North America, extratropical storm surges may occur on the Pacific and Alaska coasts, and north of 31°N on

5320-456: The volume of freshwater, the tidal range, and the extent of evaporation of the water in the estuary. Drowned river valleys are also known as coastal plain estuaries. In places where the sea level is rising relative to the land, sea water progressively penetrates into river valleys and the topography of the estuary remains similar to that of a river valley. This is the most common type of estuary in temperate climates. Well-studied estuaries include

5396-453: The water and atmosphere, these organisms are also intaking all or nearly all of the available oxygen creating a hypoxic environment and unbalanced oxygen cycle . The excess carbon in the form of CO 2 can lead to low pH levels and ocean acidification , which is more harmful for vulnerable coastal regions like estuaries. Eutrophication has been seen to negatively impact many plant communities in estuarine ecosystems . Salt marshes are

5472-624: The water column and in sediment , making estuaries among the most productive natural habitats in the world. Most existing estuaries formed during the Holocene epoch with the flooding of river-eroded or glacially scoured valleys when the sea level began to rise about 10,000–12,000 years ago. Estuaries are typically classified according to their geomorphological features or to water-circulation patterns. They can have many different names, such as bays , harbors , lagoons , inlets , or sounds , although some of these water bodies do not strictly meet

5548-412: The water level near the head of tidal estuaries as storm-driven waters surging in from the ocean meet rainfall flowing downstream into the estuary. In addition to the above processes, storm surge and wave heights on shore are also affected by the flow of water over the underlying topography, i.e. the shape and depth of the ocean floor and coastal area. A narrow shelf , with deep water relatively close to

5624-835: The water. The main phytoplankton present are diatoms and dinoflagellates which are abundant in the sediment. A primary source of food for many organisms on estuaries, including bacteria , is detritus from the settlement of the sedimentation. Of the thirty-two largest cities in the world in the early 1990s, twenty-two were located on estuaries. As ecosystems, estuaries are under threat from human activities such as pollution and overfishing . They are also threatened by sewage, coastal settlement, land clearance and much more. Estuaries are affected by events far upstream, and concentrate materials such as pollutants and sediments. Land run-off and industrial, agricultural, and domestic waste enter rivers and are discharged into estuaries. Contaminants can be introduced which do not disintegrate rapidly in

5700-712: Was generated by Hurricane Katrina on August 29, 2005, which produced a maximum storm surge of more than 28 feet (8.53 m) in southern Mississippi , with a storm surge height of 27.8 feet (8.47 m) in Pass Christian . Another record storm surge occurred in this same area from Hurricane Camille in 1969, with a storm tide of 24.6 feet (7.50 m), also at Pass Christian. A storm surge of 14 feet (4.27 m) occurred in New York City during Hurricane Sandy in October 2012. Estuary An estuary

5776-401: Was the 1970 Bhola cyclone . Additionally, storm surge can cause or transform human-utilized land through other processes, hurting soil fertility , increasing saltwater intrusion , hurting wildlife habitat, and spreading chemical or other contaminants from human storage. Although meteorological surveys alert about hurricanes or severe storms, in the areas where the risk of coastal flooding

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