Beach evolution

The shoreline is where the land meets the sea and it is continually changing. Over the long term, the water is eroding the land. Beaches represent a special case, in that they exist where sand accumulated from the same processes that strip away rocky and sedimentary material. That is, they can grow as well as erode. River deltas are another exception, in that silt that erodes up river can accrete at the river's outlet and extend ocean shorelines. Catastrophic events such as tsunamis, hurricanes and storm surges accelerate beach erosion, potentially carrying away the entire sand load. Human activities can be as catastrophic as hurricanes, albeit usually over a longer time interval.

Erosion and accretion

Extraordinary processes: tsunamis and hurricane-driven storm surges

Storm surge graphic

Tsunamis, potentially enormous waves often caused by earthquakes, have great erosional and sediment-reworking potential. They may strip beaches of sand that may have taken years to accumulate and may destroy trees and other coastal vegetation. Tsunamis are also capable of flooding hundreds of meters inland past the typical high-water level and fast-moving water, associated with the inundating tsunami, can crush homes and other coastal structures.

A storm surge is an onshore gush of water associated with a low pressure weather system—storms. Storm surges can cause beach accretion and erosion.[1] Historically notable storm surges occurred during the North Sea Flood of 1953, Hurricane Katrina, and the 1970 Bhola cyclone.

Gradual processes

The gradual evolution of beaches often comes from the interaction of longshore drift, a wave-driven process by which sediments move along a beach shore, and other sources of erosion or accretion, such as nearby rivers.

Deltas

Deltas are nourished by alluvial systems and accumulate sand and silt, growing where the sediment flux from land is large enough to avoid complete removal by coastal currents, tides, or waves.

Most modern deltas formed during the last five thousand years, after the present sea-level high stand was attained. However, not all sediment remains permanently in place: in the short term (decades to centuries), exceptional river floods, storms or other energetic events may remove significant portions of delta sediment or change its lobe distribution and, on longer geological time scales, sea-level fluctuations lead to destruction of deltaic features.

Historical accretion of European beaches

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Main stages of Holocene evolution of the Rhone delta

In the Mediterranean sea, deltas have been continuously growing for the last several thousand years. Six to seven thousand years ago, the sea level stabilized, and continuous river systems, ephemeral torrents, and other factors began this steady accretion. Since intense human use of coastal areas is a relatively recent phenomenon (except in the Nile delta), beach contours were primarily shaped by natural forces until the last centuries.

In Barcelona, for example, the accretion of the coast was a natural process until the late Middle Ages, when harbor-building increased the rate of accretion.

The port of Ephesus, one of the great cities of the Ionian Greeks in Asia Minor, was filled with sediment due to accretion from a nearby river; it is now 5 kilometers (3.1 mi) from the sea. Likewise, Ostia, the once-important port near ancient Rome, is now several kilometers inland, the coastline having moved slowly seaward.

Bruges became a port during the early Middle Ages and was accessible by sea until around 1050. At that time, however, the natural link between Bruges and the sea silted up. In 1134, a storm flood opened a deep channel, the Zwin, linking the city to the sea until the fifteenth century via a canal from the Zwin to Bruges. Bruges had to use a number of outports, such as Damme and Sluis, for this purpose. In 1907, a new seaport was inaugurated in Zeebrugge.

Modern beach recession

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Eroding beach in Portugal.

At the present time important segments of low coasts are in recession, losing sand and reducing beach dimensions. This loss can occur very rapidly. There are various reasons for beach recession, some more natural than others (degree of anthropization). Examples of this are occurring at Sète, in California, in Poland, in Aveiro (Portugal), and in the Netherlands and elsewhere along the North Sea. In Europe, coastal erosion is widespread (at least 70%) and distributed very irregularly.

France

Atlantic coast

Capbreton Blockhauss vus du Sud
Old German-built WWII bunkers at Capbreton, south-west of France

Some of the coastal defence bunkers of the Atlantic Wall, built by the German soldiers during the Second World War at the top of the dunes are now underwater 2/3 of the times. It shows 200 meters of recession of the beach in 65 years.

Sète

The coast recession near Sète is related with coastal drift sand supply interruption due to growth of the Rhone delta, which (like most deltas) is becoming independent of the rest of the coast. The present lido shoreline is 210 meters away from the Roman lido.

California beaches

California's beaches and other shoreline features change according to the availability of beach sand, the wave and current energy impinging on the coast, and other physical processes that affect the movement of sand. A constant supply of sand is necessary for beaches to form and be maintained along this shoreline. Many human activities, including dam construction and river channelization, have reduced the supply of sand that reaches the ocean. This, in turn, has prevented beaches from being replenished and has thus created greater vulnerability for shorelines that have always been subject to varying levels of erosion. There are few practical solutions to improving sand supply from inland sources, so management of shoreline erosion will likely continue to focus at the land/sea interface along the California coastline.

Construction of breakwaters, jetties, or groyne fields to protect harbor entrances, maintain beaches, or protect coastal structures have both helped and harmed the movement of sand along the shoreline. Protective armoring formations trap sand and allow beaches to expand up-coast from the device, but can interrupt the flow of sand to beaches located down-coast.

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Southern California beach 10/97 (before winter storms boosted by El Niño)
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Same location 4/98 (after winter storms boosted by El Niño)

Poland

During the last glaciation, the Baltic Polish area was covered in ice and associated morainal sediments. Deglaciation left a substantial amount of unconsolidated sediment. Currently, these unconsolidated sediments are strongly eroded and reworked by the sea.

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Aveiro

The North Portuguese coast and its beaches were fed by large Iberian rivers. The massive building of dams in the Douro River basin has cut the sediment supply to the Aveiro coast, resulting in its recession. Hard protective works have been done all along.

Dourodammed
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The Netherlands

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Holland coast

The Dutch coast consists of sandy, multi-barred beaches and can be characterised as a wave-dominated coast. Approximately 290 km of the coast consists of dunes and 60 km is protected by structures such as dikes and dams. With the melting of the ice at the end of the last ice age the coastline shifted eastward until about 5000 years ago the present position of the Dutch coastline was reached.

As the sea level rise stagnated, the sand supply decreased and the formation of the beach ridges stopped, after which when the sea broke through the lines of dunes during storms, men started to defend the land by building primitive dikes and walls. The dunes, together with the beach and the shoreline, offer a natural, sandy defence to the sea. About 30% of the Netherlands lies below sea level.

Holland recession
Holland coast recession

Over the last 30 years, approximately 1 million m³ sand per year has been lost from the Dutch coast to deep water. In most northern coastal sections, erosion occurs in deep water and also in the nearshore zone. In most southern sections, sedimentation occurs in the nearshore zone and erosion in deep water.

Structural erosion is due to sea level rise relative to the land and, in some spots, it is caused by harbour dams. The Dutch coast looked at as a single unit shows erosive behaviour. Approximately 12 million m³ of sand is transferred annually from the North Sea to the Wadden Sea as a result of relative rising sea level and coastal erosion.

Relative sea level changes

Several geological events and the climate can change (progressively or suddenly) the relative height of the Earth's surface to the sea-level. These events or processes continuously change coastlines.

Volcanism and earthquakes

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Old sea level mark before these tremors.
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New quay at the Bay of Pozzuoli

Volcanic activity can create new islands. The 800 meters (2,600 ft) in diameter Surtsey Island, Iceland, for example, was created between November 1963 and June 1967. The island has since partially eroded, but it is expected to last another 100 years.

Some earthquakes can create sudden variations of relative ground level and change the coastline dramatically. Structurally controlled coasts include the San Andreas fault zone in California and the seismic Mediterranean belt (from Gibraltar to Greece).

The Bay of Pozzuoli, in Pozzuoli, Italy experienced hundreds of tremors between August 1982 and December 1984. The tremors, which reached a peak on October 4, 1983, damaged 8,000 buildings in the city center and raised the sea bottom by almost 2 meters (6.6 ft). This rendered the Bay of Pozzuoli too shallow for large craft and required the reconstruction of the harbour with new quays. The photo at the upper right shows the harbor before the uplift while the one on the bottom right shows the new quay.

Gradual processes: subsidence and uplift

Subsidence is the motion of the Earth's surface downward relative to the sea level due to internal geodynamic causes. The opposite of subsidence is uplift, which increases elevation.

Venezia acqua alta notte 2005 modificata
St. Mark's Square, Venice, during flooding

Venice is probably the best-known example of a subsiding location. It experiences periodic flooding when extreme high tides or surges arrive. This phenomenon is caused by the compaction of young sediments in the Po River delta area, magnified by subsurface water and gas exploitation. Man-made works to solve this progressive sinking have been unsuccessful.

Mälaren, the third-largest lake in Sweden, is an example of deglacial uplift. It was once a bay on which seagoing vessels were once able to sail far into the country's interior, but it ultimately became a lake. Its uplift was caused by deglaciation: the removal of the weight of ice-age glaciers caused rapid uplift of the depressed land. For 2,000 years as the ice was unloaded, uplift proceeded at about 7.5 centimeters (3.0 in)/year. Once deglaciation was complete, uplift slowed to about 2.5 centimeters (0.98 in) annually, and it decreased exponentially after that. Today, annual uplift rates are 1 centimeter (0.39 in) or less, and studies suggest that rebound will continue for about another 10,000 years. The total uplift from the end of deglaciation may be up to 400 meters (1,300 ft).

See also

Notes

  1. ^ [1]

External links

Accretion (coastal management)

Accretion is the process of coastal sediment returning to the visible portion of a beach or foreshore following a submersion event. A sustainable beach or foreshore often goes through a cycle of submersion during rough weather then accretion during calmer periods. If a coastline is not in a healthy sustainable state, then erosion can be more serious and accretion does not fully restore the original volume of the visible beach or foreshore leading to permanent beach loss.

Beach

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.

Some beaches have man-made infrastructure, such as lifeguard posts, changing rooms, showers, shacks and bars. They may also have hospitality venues (such as resorts, camps, hotels, and restaurants) nearby. Wild beaches, also known as undeveloped or undiscovered beaches, are not developed in this manner. Wild beaches can be appreciated for their untouched beauty and preserved nature.

Beaches typically occur in areas along the coast where wave or current action deposits and reworks sediments.

Coastal engineering

Coastal engineering is a branch of civil engineering concerned with the specific demands posed by constructing at or near the coast, as well as the development of the coast itself.

The hydrodynamic impact of especially waves, tides, storm surges and tsunamis and (often) the harsh environment of salt seawater are typical challenges for the coastal engineer – as are the morphodynamic changes of the coastal topography, caused both by the autonomous development of the system and man-made changes. The areas of interest in coastal engineering include the coasts of the oceans, seas, marginal seas, estuaries and big lakes.

Besides the design, building and maintenance of coastal structures, coastal engineers are often interdisciplinary involved in integrated coastal zone management, also because of their specific knowledge of the hydro- and morphodynamics of the coastal system. This may include providing input and technology for e.g. environmental impact assessment, port development, strategies for coastal defense, land reclamation, offshore wind farms and other energy-production facilities, etc.

Coastal geography

Coastal geography is the study of the constantly changing region between the ocean and the land, incorporating both the physical geography (i.e. coastal geomorphology, geology and oceanography) and the human geography (sociology and history) 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

Coastal management

Coastal management is defence against flooding and erosion, and techniques that stop erosion to claim lands.Coastal zones occupy less than 15% of the Earth's land area, while they host more than 45% of the world population. Nearly 1.4 billion people live within 100 km of a shoreline and 100 m of sea level, with an average density 3 times higher than the global average for population. With three-quarters of the world population expected to reside in the coastal zone by 2025, human activities originating from this small land area will impose heavy pressure on coasts. Coastal zones contain rich resources to produce goods and services and are home to most commercial and industrial activities.

Protection against rising sea levels in the 21st century is crucial, as sea level rise accelerates. Changes in sea level damage beaches and coastal systems are expected to rise at an increasing rate, causing coastal sediments to be disturbed by tidal energy.

Cuspate foreland

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.

Island

An island or isle is any piece of sub-continental land that is surrounded by water. Very small islands such as emergent land features on atolls can be called islets, skerries, cays or keys. An island in a river or a lake island may be called an eyot or ait, and a small island off the coast may be called a holm. A grouping of geographically or geologically related islands is called an archipelago, such as the Philippines.

An island may be described as such, despite the presence of an artificial land bridge; examples are Singapore and its causeway, and the various Dutch delta islands, such as IJsselmonde. Some places may even retain "island" in their names for historical reasons after being connected to a larger landmass by a land bridge or landfill, such as Coney Island and Coronado Island, though these are, strictly speaking, tied islands. Conversely, when a piece of land is separated from the mainland by a man-made canal, for example the Peloponnese by the Corinth Canal or Marble Hill in northern Manhattan during the time between the building of the United States Ship Canal and the filling-in of the Harlem River which surrounded the area, it is generally not considered an island.

There are two main types of islands in the sea: continental and oceanic. There are also artificial islands.

Kennedy Space Center Launch Complex 39

Launch Complex 39 (LC-39) is a rocket launch site at the John F. Kennedy Space Center on Merritt Island in Florida, United States. The site and its collection of facilities were originally built for the Apollo program and later modified for the Space Shuttle program.

Launch Complex 39 consists of three launch sub-complexes or "pads"—39A, 39B, and 39C—a Vehicle Assembly Building (VAB), a Crawlerway used by crawler-transporters to carry Mobile Launcher Platforms between the VAB and the pads, Orbiter Processing Facility buildings, a Launch Control Center which contains the firing rooms, a news facility famous for the iconic countdown clock seen in television coverage and photos, and various logistical and operational support buildings.SpaceX leases Launch Complex 39A from NASA and has modified the pad to support Falcon 9 and Falcon Heavy launches.NASA began modifying Launch Complex 39B in 2007 to accommodate the now defunct Project Constellation, and is currently preparing it for the Space Launch System, whose first launch is scheduled for December 2019. A pad to be designated 39C, which would have been a copy of pads 39A and 39B, was originally planned for Apollo but never built. A smaller pad, 39C, was constructed from January to June 2015, to accommodate small-lift launch vehicle.NASA launches from pads 39A and 39B have been supervised from the NASA Launch Control Center (LCC), located 3 miles (4.8 km) from the launch pads. LC-39 is one of several launch sites that share the radar and tracking services of the Eastern Test Range.

Levee

A levee (), dike, dyke, embankment, floodbank or stopbank is an elongated naturally occurring ridge or artificially constructed fill or wall, which regulates water levels. It is usually earthen and often parallel to the course of a river in its floodplain or along low-lying coastlines.

List of radio stations in Florida

The following is a list of FCC-licensed radio stations in the U.S. state of Florida, which can be sorted by their call signs, frequencies, cities of license, licensees, and programming formats.

Mudflat

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 recent global analysis suggested they are as extensive globally as mangroves. They are found in sheltered areas such as bays, bayous, lagoons, and estuaries. Mudflats may be viewed geologically as exposed layers of bay mud, resulting from deposition of estuarine silts, clays and marine 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.

In the past tidal flats were considered unhealthy, economically unimportant areas and were often dredged and developed into agricultural land. 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. These wind-affected mudflats are called windwatts in German.

Natural hazard

A natural hazard is a natural phenomenon that might have a negative effect on humans or the environment. Natural hazard events can be classified into two broad categories: geophysical and biological. Geophysical hazards encompass geological and meteorological phenomena such as earthquakes, volcanic eruptions, wildfires, cyclonic storms, floods, droughts, avalanches and landslides. Biological hazards can refer to a diverse array of disease, infection, infestation and invasive species.

Many geophysical hazards are related; for example, submarine earthquakes can cause tsunamis, and hurricanes can lead to coastal flooding and erosion. Floods and wildfires can result from a combination of geological, hydrological, and climatic factors. It is possible that some natural hazards are intertemporally correlated as well. An example of the distinction between a natural hazard and a natural disaster is that the 1906 San Francisco earthquake was a disaster, whereas living on a fault line is a hazard. Some natural hazards can be provoked or affected by anthropogenic processes (e.g. land-use change, drainage and construction).

Outer Banks

The Outer Banks is a 200-mile-long (320 km) string of barrier islands and spits off the coast of North Carolina and southeastern Virginia, on the east coast of the United States. They cover most of the North Carolina coastline, separating Currituck Sound, Albemarle Sound, and Pamlico Sound from the Atlantic Ocean.

The Outer Banks are a major tourist destination and are known around the world for their wide expanse of open beachfront. The Cape Hatteras National Seashore has four campgrounds open to visitors. The treacherous seas off the Outer Banks and the large number of shipwrecks that have occurred there have given these seas the nickname Graveyard of the Atlantic. The Graveyard of the Atlantic Museum is located in Hatteras Village near a United States Coast Guard facility and the Hatteras ferry.

The English Roanoke Colony—where Virginia Dare was born—vanished from Roanoke Island in 1587. The Lost Colony, written and performed to commemorate the original colonists, is the second longest running outdoor drama in the United States and its theater acts as a cultural focal point for much of the Outer Banks.

The Wright brothers' first flight in a controlled, powered, heavier-than-air vehicle took place on the Outer Banks on December 17, 1903, at Kill Devil Hills near the seafront town of Kitty Hawk. The Wright Brothers National Monument commemorates the historic flights, and First Flight Airport is a small, general-aviation airfield located there.

Outer Continental Shelf

The Outer Continental Shelf (OCS) is a peculiarity of the political geography of the United States. The OCS is the part of the internationally recognized continental shelf of the United States which does not fall under the jurisdictions of the individual U.S. States.

Revetment

In stream restoration, river engineering or coastal engineering, revetments are sloping structures placed on banks or cliffs in such a way as to absorb the energy of incoming water. In military engineering they are structures, again sloped, formed to secure an area from artillery, bombing, or stored explosives. River or coastal revetments are usually built to preserve the existing uses of the shoreline and to protect the slope, as defense against erosion.

Sand dune stabilization

Sand dunes are common features of shoreline and desert environments. Dunes provide habitat for highly specialized plants and animals, including rare and endangered species. They can protect beaches from erosion and recruit sand to eroded beaches. Dunes are threatened by human activity, both intentional and unintentional. Countries such as the United States, Australia, Canada, New Zealand, the United Kingdom, and Netherlands, operate significant dune protection programs.

Stabilizing dunes involves multiple actions. Planting vegetation reduces the impact of wind and water. Wooden sand fences can help retain sand and other material needed for a healthy sand dune ecosystem. Footpaths protect dunes from damage from foot traffic.

They can also protect beaches from erosion and recruit sand to eroded beaches and to many other places too .

The location of the dune limits the types of plant that can thrive there. Beach dunes consist of the foredune, the angled side which faces the ocean, the sand plain at the top of the dune, which may or may not be present, and the backdune, the angled side that faces away from the ocean.

Strand plain

A strand plain or strandplain is a broad belt of sand along a shoreline with a surface exhibiting well-defined parallel or semi-parallel sand ridges separated by shallow swales. A strand plain differs from a barrier island in that it lacks either the lagoons or tidal marshes that separate a barrier island from the shoreline to which the strand plain is directly attached. Also, the tidal channels and inlets which cut through barrier islands are absent. Strand plains typically are created by the redistribution by waves and longshore currents of coarse sediment on either side of a river mouth. Thus, they are part of one type of wave-dominated delta.Examples of strand plains:

Western Louisiana

Eastern Texas

West coast of Namibia

South-east and south-west coasts of Australia, and in the Gulf of Carpentaria

Letea and Caraorman, Danube Delta, Romania

Submersion (coastal management)

Submersion is the sustainable cyclic portion of coastal erosion where coastal sediments move from the visible portion of a beach to the submerged nearshore region, and later return to the original visible portion of the beach. The recovery portion of the sustainable cycle of sediment behaviour is (accretion).

Surf zone

As ocean surface waves come closer to shore they break, forming the foamy, bubbly surface called surf. The region of breaking waves defines the surf zone. After breaking in the surf zone, the waves (now reduced in height) continue to move in, and they run up onto the sloping front of the beach, forming an uprush of water called swash. The water then runs back again as backswash. The nearshore zone where wave water comes onto the beach is the surf zone. The water in the surf zone, or breaker zone, is shallow, usually between 5 and 10 m (16 and 33 ft) deep; this causes the waves to be unstable.

Landforms
Beaches
Processes
Management
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