Coastal erosion

There are two common definitions of coastal erosion. It is often defined as the loss or displacement of land along the coastline due to the action of waves, currents, tides, wind-driven water, waterborne ice, or other impacts of storms.[1][2] In this case, landward retreat of the shoreline, measured to a given spatial datum, is described over a temporal scale of tides, seasons, and other short-term cyclic processes.[3] Alternatively, it is defined as the process of long-term removal of sediment and rocks at the coastline, leading again to loss of land and retreat of the coastline landward.[4] Coastal erosion may be caused by hydraulic action, abrasion, impact and corrosion by wind and water, and other forces, natural or unnatural.[3]

On non-rocky coasts, coastal erosion results in rock formations in areas where the coastline contains rock layers or fracture zones with varying resistance to erosion. Softer areas become eroded much faster than harder ones, which typically result in landforms such as tunnels, bridges, columns, and pillars. Over time the coast generally evens out. The softer areas fill up with sediment eroded from hard areas, and rock formations are eroded away.[5] Also abrasion commonly happens in areas where there are strong winds, loose sand, and soft rocks. The blowing of millions of sharp sand grains creates a sandblasting effect. This effect helps to erode, smooth and polish rocks. The definition of abrasion is grinding and wearing away of rock surfaces through the mechanical action of other rock or sand particles.

Coastal Erosion Hunstanton Cliffs
Heavy marine erosion: cliff fall at Hunstanton in the east of England
Valiyathura. jpg
Sea erosion at Valiyathura
大连国家地质公园11-蟹将出洞-海蚀崖
Tunnel-like structures formed by erosion in Jinshitan Coastal National Geopark, Dalian, Liaoning Province, China

Examples

SIRT railwalking jeh
Small-scale erosion destroys abandoned railroad tracks

A place where erosion of a cliffed coast has occurred is at Wamberal in the Central Coast region of New South Wales where houses built on top of the cliffs began to collapse into the sea. This is due to waves causing erosion of the primarily sedimentary material on which the buildings foundations sit.[6]

Dunwich, the capital of the English medieval wool trade, disappeared over the period of a few centuries due to redistribution of sediment by waves. Human interference can also increase coastal erosion: Hallsands in Devon, England, was a coastal village washed away over the course of a year, 1917, directly due to earlier dredging of shingle in the bay in front of it.

The California coast, which has soft cliffs of sedimentary rock and is heavily populated, regularly has incidents of housing damage as cliffs erodes.[7] Devil's Slide, Santa Barbara, the coast just north of Ensenada, and Malibu are regularly affected.

The Holderness coastline on the east coast of England, just north of the Humber Estuary, is one of the fastest eroding coastlines in Europe due to its soft clay cliffs and powerful waves. Groynes and other artificial measures to keep it under control has only accelerated the process further down the coast, because longshore drift starves the beaches of sand, leaving them more exposed. The White Cliffs of Dover have also been affected.

Malta - Kalkara - Fort Ricasoli (MSTHC) 02 ies
Fort Ricasoli in Kalkara, Malta already showing signs of damage where the land is being eroded

Fort Ricasoli, a historic 17th century fortress in Malta is being threatened by coastal erosion, as it was built on a fault in the headland which is prone to erosion. A small part of one of the bastion walls has already collapsed since the land under it has eroded, and there are cracks in other walls as well.

In El Campello, Spain, the erosion and failure of a Roman farm fish excavated on rock during the first century B.C. was exacerbated by the construction of a close sport harbour[8].

Coastal processes

Hydraulic action

Hydraulic Action occurs when waves striking a cliff face compress air in cracks on the cliff face. This exerts pressure on the surrounding rock, and can progressively splinter and remove pieces. Over time, the cracks can grow, sometimes forming a cave. The splinters fall to the sea bed where they are subjected to further wave action.

Attrition

Attrition occurs when waves cause loose pieces of rock debris (scree) to collide with each other, grinding and chipping each other, progressively becoming smaller, smoother and rounder. Scree also collides with the base of the cliff face, chipping small pieces of rock from the cliff or have a corrasion (abrasion) effect, similar to sandpapering.

Solution

Solution is the process in which acids contained in sea water will dissolve some types of rock such as chalk or limestone.[9]

Abrasion

abrasion, also known as Corrasion, occurs when waves break on cliff faces and slowly erode it. As the sea pounds cliff faces it also uses the scree from other wave actions to batter and break off pieces of rock from higher up the cliff face which can be used for this same wave action and attrition.

Corrosion

Corrosion or solution/chemical weathering occurs when the sea's pH (anything below pH 7.0) corrodes rocks on a cliff face. Limestone cliff faces, which have a moderately high pH, are particularly affected in this way. Wave action also increases the rate of reaction by removing the reacted material.

Factors that influence erosion rates

Primary factors

Sea-dune Erosion at Talace beach, Wales

The ability of waves to cause erosion of the cliff face depends on many factors.

The hardness (or inversely, the erodibility) of sea-facing rocks is controlled by the rock strength and the presence of fissures, fractures, and beds of non-cohesive materials such as silt and fine sand.

The rate at which cliff fall debris is removed from the foreshore depends on the power of the waves crossing the beach. This energy must reach a critical level to remove material from the debris lobe. Debris lobes can be very persistent and can take many years to completely disappear.

Beaches dissipate wave energy on the foreshore and provide a measure of protection to the adjoining land.

The stability of the foreshore, or its resistance to lowering. Once stable, the foreshore should widen and become more effective at dissipating the wave energy, so that fewer and less powerful waves reach beyond it. The provision of updrift material coming onto the foreshore beneath the cliff helps to ensure a stable beach.

The adjacent bathymetry, or configuration of the seafloor, controls the wave energy arriving at the coast, and can have an important influence on the rate of cliff erosion. Shoals and bars offer protection from wave erosion by causing storm waves to break and dissipate their energy before reaching the shore. Given the dynamic nature of the seafloor, changes in the location of shoals and bars may cause the locus of beach or cliff erosion to change position along the shore.[10]

Coastal erosion has been greatly affected by the rising sea levels globally. There has been great measures of increased coastal erosion on the Eastern seaboard of the United States. Locations such as Florida have noticed increased coastal erosion. In reaction to these increases Florida and its individual counties have increased budgets to replenish the eroded sands that attract visitors to Florida and help support its multibillion-dollar tourism industries.

Erodedcliffpacifica

Pacifica, California coast after major storms in 1997 (resulting from the strongest El Niño on record) destroyed the houses shown above.

BeachErosionCabrillo

Beach erosion at Cabrillo National Monument, California.

BeachErosionTP

Large-scale coastal erosion at Torrey Pines State Reserve, California.

Coastal-erosion-inland

Coastal erosion at Torrey Pines State Reserve, California, resulted in the necessary relocation of a scenic overlook.

Daniabeach-coastal erosion 10-04-2017

Coastal erosion during a king tide, Dania Beach, Florida

Secondary factors

  • Weathering and transport slope processes
  • Slope hydrology
  • Vegetation
  • Cliff foot erosion
  • Cliff foot sediment accumulation
  • Resistance of cliff foot sediment to attrition and transport
  • Human Activity

Tertiary factors

  • Resource extraction
  • Coastal management

Control methods

There are three common forms of coastal erosion control methods. These three include: soft-erosion controls, hard-erosion controls, and relocation.

Hard-erosion controls

Seawall (Phetchaburi Province)
This image represents a typical seawall that is used for preventing and controlling coastal erosion.

Hard-erosion control methods provide a more permanent solution than soft-erosion control methods. Seawalls and groynes serve as semi-permanent infrastructure. These structures are not immune from normal wear-and-tear and will have to be refurbished or rebuilt. It is estimated the average life span of a seawall is 50–100 years and the average for a groyne is 30–40 years.[11] Because of their relative permanence, it is assumed that these structures can be a final solution to erosion. Seawalls can also deprive public access to the beach and drastically alter the natural state of the beach. Groynes also drastically alter the natural state of the beach. Some claim that groynes could reduce the interval between beach nourishment projects though they are not seen as a solution to beach nourishment.[12] Other criticisms of seawalls are that they can be expensive, difficult to maintain, and can sometimes cause further damage to the beach if built improperly.[13]

Natural forms of hard-erosion control include planting or maintaining native vegetation, such as mangrove forests and coral reefs.

Soft-erosion controls

Hurricane Sandy - sandbagged beach, Cape Hatteras
Sandbagged beach at the site of Hurricane Sandy.

Soft erosion strategies refer to temporary options of slowing the effects of erosion. These options, including Sandbag and beach nourishment, are not intended to be long term solutions or permanent solutions.[11] Another method, beach scraping or beach bulldozing allows for the creation of an artificial dune in front of a building or as means of preserving a building foundation. However, there is a U.S. federal moratorium on beach bulldozing during turtle nesting season, 1 May – 15 November.[14] One of the most common methods of soft erosion control is beach nourishment projects. These projects involve dredging sand and moving it to the beaches as a means of reestablishing the sand lost due to erosion.[11] In some situations, beach nourishment is not a suitable measure to take for erosion control, such as in areas with sand sinks or frequent and large storms.[13]

Relocation

Relocation of infrastructure any housing farther away from the coast is also called managed retreat. The natural processes of both absolute and relative sea level rise and erosion are considered in rebuilding. Depending on factors such as the severity of the erosion, as well as the natural landscape of the property, relocation could simply mean moving inland by a short distance or relocation can be to completely remove improvements from an area.[13] Typically, there has been low public support for “retreating.”[15]

Tracking

Storms can cause erosion hundreds of times faster than normal weather. Before-and-after comparisons can be made using data gathered by manual surveying, laser altimeter, or a GPS unit mounted on an ATV.[16] Remote sensing data such as Landsat scenes can be used for large scale and multi year assessments of coastal erosion.[17]

See also

References

  1. ^ Ueberman, A.S. and O'Neill Jr, C.R., 1988. Vegetation use in coastal ecosystems. Cornell Cooperative Extension Information Bulletin 198, Cornell University, Ithica, New York. 32 pp.
  2. ^ New York Coastal Erosion Hazard Areas Act of 1981.
  3. ^ a b Stephenson, W., 2013, Coastal Erosion. in Bobrowsky, P.T., ed., pp. 94-96. Encyclopedia of Natural Hazards, Springer Dordrecht, New York, New York. 1135 pp. ISBN 978-9048186990
  4. ^ Gibb, J. G., 1978. Rates of coastal erosion and accretion in New Zealand. New Zealand Journal of Marine and Freshwater Research, 12(4): 429–456.
  5. ^ Valvo, Lisa M.; Murray, A. Brad; Ashton, Andrew (1 June 2006). "How does underlying geology affect coastline change? An initial modeling investigation". Journal of Geophysical Research: Earth Surface. 111 (F2): F02025. doi:10.1029/2005JF000340.
  6. ^ "The Impact of Coastal Erosion in Australia". Archived from the original on 15 March 2016. Retrieved 15 March 2016.
  7. ^ Xia, Rosanna (13 March 2019). "Destruction from sea level rise in California could exceed worst wildfires and earthquakes, new research shows". Los Angeles Times. Retrieved 15 March 2019.
  8. ^ Luís Aragonés, Roberto Tomás, Miguel Cano, Emilio Rosillo, and Isabel López (2017). "Influence of Maritime Construction within Protected Archaeological Sites along Coastal Areas: Los Baños De La Reina (Alicante), Spain". Journal of Coastal Research. 33 (3): 642–652. doi:10.2112/JCOASTRES-D-16-00016.1.CS1 maint: Multiple names: authors list (link)
  9. ^ Cambers, Gary; Sibley, Steve (10 September 2015). Cambridge IGCSE® Geography Coursebook with CD-ROM. Cambridge University Press. ISBN 9781107458949.
  10. ^ Oldale, Robert N. "Coastal Erosion on Cape Cod: Some Questions and Answers". U.S. Geological Survey. Archived from the original on 6 May 2009. Retrieved 11 September 2009.
  11. ^ a b c Dean, J. "Oceanfront Sandbag Use in North Carolina: Management Review and Suggestions for Improvement" (PDF). Nicholas School of the Environment of Duke University. Archived (PDF) from the original on 4 March 2016. Retrieved 11 October 2013.
  12. ^ Knapp, Whitney. "Impacts of Terminal Groins on North Carolina's Coast" (PDF). Nicholas School of the Environment of Duke University. Archived (PDF) from the original on 12 March 2014. Retrieved 15 October 2013.
  13. ^ a b c Managing Coastal Erosion. National Academies Press. 1989. ISBN 9780309041430.
  14. ^ "Coastal Hazards & Storm Information: Protecting Oceanfront Property from Erosion". North Carolina Division of Coastal Management. Retrieved 17 September 2013.
  15. ^ McPherson, M. "Adaptation to Sea-Level Rise in North Carolina" (PDF). Nicholas School of the Environment of Duke University. Archived (PDF) from the original on 4 March 2016. Retrieved 25 October 2013.
  16. ^ "Tracking Coastal Erosion From Storms". npr.org. Archived from the original on 4 March 2016. Retrieved 3 May 2018.
  17. ^ KUENZER, C., OTTINGER, M., LIU, G., SUN, B., DECH, S., 2014: Earth Observation-based Coastal Zone Monitoring of the Yellow River Delta: Dynamics in China’s Second Largest Oil Producing Region over four Decades. Applied Geography, 55, 72-107

External links

Images:

Ballycotton

Ballycotton (Irish: Baile Choitín) is a coastal village in County Cork, Ireland, situated about 25 miles (40 km) east of Cork city. It is a fishing village that sits on a rocky ledge overlooking Ballycotton Bay and has a sandy beach that stretches for about 25 kilometres (16 mi) east to Knockadoon Head. The current village is actually a re-settlement of an older village which is now entirely underwater. Ballycotton experiences severe coastal erosion with metres of land crumbling into the sea every few years. It is a site of international research interest on coastal erosion.

Cliff stabilization

Cliff stabilization is a coastal management erosion control technique. This is most suitable for softer or less stable cliffs. Generally speaking, the cliffs are stabilised through dewatering (drainage of excess rainwater to reduce water-logging) or anchoring (the use of terracing, planting, wiring or concrete supports to hold cliffs in place).

Covehithe

Covehithe is a hamlet and civil parish in the East Suffolk district of the English county of Suffolk. It lies on the North Sea coast around 4 miles (6.4 km) north of Southwold and 7 miles (11 km) south of Lowestoft. Neighbouring settlements include Benacre, South Cove and Frostenden.

The coastline in the Covehithe area suffers from the highest rate of erosion in the UK, and the settlement has suffered significant loss of land and buildings in the past. It is located within the Suffolk Coast & Heaths AONB.

Dunwich

Dunwich is a village and civil parish in Suffolk, England. It is in the Suffolk Coast and Heaths AONB around 92 miles (148 km) north-east of London, 9 miles (14 km) south of Southwold and 7 miles (11 km) north of Leiston, on the North Sea coast.

In the Anglo-Saxon period, Dunwich was the capital of the Kingdom of the East Angles, but the harbour and most of the town have since disappeared due to coastal erosion. At its height it was an international port similar in size to 14th century London. Its decline began in 1286 when a storm surge hit the East Anglian coast followed by a great storm in 1287 and another great storm also in 1287, and it was eventually shrank to the village it is today. Dunwich is possibly connected with the lost Anglo-Saxon placename Dommoc.

The population of the civil parish at the 2001 census was 84, which increased to 183 according to the 2011 Census, though the area used by the Office of National Statistics for 2011 also includes part of the civil parish of Westleton. There is no parish council; instead there is a parish meeting.

Fetch (geography)

The fetch, also called the fetch length, is the length of water over which a given wind has blown. Fetch is used in geography and meteorology and its effects are usually associated with sea state and when it reaches shore it is the main factor that creates storm surge which leads to coastal erosion and flooding. It also plays a large part in longshore drift as well.

Fetch length, along with the wind speed (wind strength), determines the size (sea state) of waves produced. The wind direction is considered constant. The longer the fetch and the faster the wind speed, the more wind energy is imparted to the water surface and the larger the resulting sea state will be.

Grand-Popo

Grand-Popo is a town, arrondissement, and commune in the Mono Department of south-western Benin. The commune covers an area of 289 square kilometres and as at the 2013 Census had a population of 57,490 people.The Finno-African culture center Villa Karo has been situated in Grand-Popo since 1999.

The town grew around the slave trade, but coastal erosion has now destroyed most of the old town. The town is now a centre for voodoo and home to a Finnish-African cultural centre, Villa Karo. The town's main industry is fishing.

The town inspired the name of the French electronic music duo Grand Popo Football Club, as well as the name of the iPad application creator Grand Popo LLC.

Groyne

A groyne (in the U.S. groin) is a rigid hydraulic structure built from an ocean shore (in coastal engineering) or from a bank (in rivers) 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.

The term is derived from the Old French groign, from Late Latin grunium, "snout".

Happisburgh

Happisburgh ( (listen)) is a village and civil parish in the English county of Norfolk. The village is on the coast, to the east of a north-south road, the B1159 from Bacton on the coast to Stalham. It is a nucleated village. The nearest substantial town is North Walsham 6 miles (10 km) to the west.Happisburgh became a site of national archaeological importance in 2010 when flint tools over 800,000 years old were unearthed. This is the oldest evidence of human occupation anywhere in the UK. In May 2013, a series of early human footprints were discovered on the beach at the site, providing direct evidence of early human activity at the site.The civil parish shrank by over 0.2 km² in the 20th century by the erosion of its beaches and low cliffs. Groynes were constructed along the shore to try to stop the erosion. In the 2001 census, before the separation of Walcott parish to the north-west, the parish (which also includes the settlements of Happisburgh Common and Whimpwell Green) had a population of 1,372 in 607 households. For the purposes of local government, the parish is in the district of North Norfolk.

Hudson's equation

Hudson's equation, also known as Hudson's formula, is an equation used by coastal engineers to calculate the minimum size of riprap (rock armour blocks) required to provide satisfactory stability characteristics for rubble structures such as breakwaters under attack from storm wave conditions.

The equation was developed by the United States Army Corps of Engineers, Waterways Experiment Station (WES), following extensive investigations by Hudson (1953, 1959, 1961a, 1961b) (see Shore Protection Manual and Rock Manual referenced below).

Land loss

Land loss is the term typically used to refer to the conversion of coastal land to open water by natural processes and human activities. The term land loss includes coastal erosion. It is much broader term than coastal erosion because land loss also includes land converted to open water around the edges of estuaries and interior bays and lakes and by subsidence of coastal plain wetlands. The most important causes of land loss in coastal plains are erosion, inadequate sediment supply to beaches and wetlands, subsidence, and global sea level rise. The mixture of processes responsible for most of the land loss will vary occurring the specific part of a coastal plain being examined. The definition of and loss does not include the loss of coastal lands to agriculture, urbanization, or other development.

Longshore drift

Longshore drift from longshore current is a geological process that consists of the transportation of sediments (clay, silt, pebbles, sand and shingle) 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.

Beach sand is also moved on such oblique wind days, due to the swash and backwash of water on the beach. Breaking surf sends water up the beach (swash) at an oblique angle and gravity then drains the water straight downslope (backwash) perpendicular to the shoreline. Thus beach sand can move downbeach in a zig zag fashion many tens of meters (yards) per day. This process is called "beach drift" but some workers regard it as simply part of "longshore drift" because of the overall movement of sand parallel to the coast.

Longshore drift affects numerous sediment sizes as it works in slightly different ways depending on the sediment (e.g. the difference in long-shore drift of sediments from a sandy beach to that of sediments from a shingle beach). Sand is largely affected by the oscillatory force of breaking waves, the motion of sediment due to the impact of breaking waves and bed shear from long-shore current. Because shingle beaches are much steeper than sandy ones, plunging breakers are more likely to form, causing the majority of long shore transport to occur in the swash zone, due to a lack of an extended surf zone.

Luccombe, Isle of Wight

Luccombe is a village on the south coast of the Isle of Wight near Shanklin. There is some indication of Bronze Age settlements on the top of the nearby hill of Luccombe Down.The Luccombe area features some spectacular cliffs and scenery. It is a popular site for hang gliding and paragliding if there is an Easterly wind of around 12mph and it is low water, and on good days flights to Sandown and back can be achieved.

Luccombe forms the east end of the Ventnor Undercliff region, which extends for 12 kilometers from Blackgang to Luccombe, also encompassing the town of Ventnor and the villages of Bonchurch, St Lawrence, and Niton. There is some concern that the Ventnor Undercliff area is experiencing substantial coastal erosion.Public transport is provided by Southern Vectis bus route 3, which run between Newport, Ryde, Sandown, Shanklin and Ventnor.

Milefortlet 15

Milefortlet 15 was a Milefortlet of the Roman Cumbrian Coast defences. These milefortlets and intervening stone watchtowers extended from the western end of Hadrian's Wall, along the Cumbrian coast and were linked by a wooden palisade. They were contemporary with defensive structures on Hadrian's Wall. The site of Milefortlet 15 has been probably been destroyed by coastal erosion. A 3rd-century Roman cemetery, associated with a nearby fort at Beckfoot, was located in the area of the milefortlet.

Overstrand

Overstrand is a village (population 1,030) on the north coast of Norfolk in England, two miles east of Cromer. It was once a modest fishing station, with all or part of the fishing station being known as Beck Hythe. In the latter part of the 19th century it was catapulted into prominence, and became known as “the village of millionaires”.

Ravenspurn

Ravenspurn was a town in the East Riding of Yorkshire, England, which was lost due to coastal erosion, one of more than 30 along the Holderness Coast which have been lost to the North Sea since the 19th century. The town was located close to the end of a peninsula near Ravenser Odd, which has also been flooded. The peninsula still survives and is known as Spurn Head. The North Sea lies to the east of the peninsula, the river Humber to the west.

The nearest major city was Kingston upon Hull.

The region of coastline is known as the Holderness Coast; geologically the land is formed of glacial tills (boulder clay), which are subject to coastal erosion. Now at sea, areas around the site are being drilled for natural gas.

Ravenspurn appears in William Shakespeare's plays Richard II, Henry IV, Part 1, and Henry VI, Part 3, under the spelling "Ravenspurgh".

Two medieval English kings landed at Ravenspurn: Henry IV in 1399, on his way to dethrone Richard II, and Edward IV in 1471, on his way back from exile in the Netherlands, where he was resisted by the local lord, Sir Martin De La See.

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).

Xrobb l-Għaġin Temple

Xrobb l-Għaġin Temple (Maltese: It-Tempju ta' Xrobb l-Għaġin) is a ruined megalithic temple in Xrobb l-Għaġin, limits of Marsaxlokk, Malta. After being identified in 1913, the site was excavated between 1914 and 1915. It was believed to have been largely destroyed by coastal erosion later on in the century, but investigations carried out in 2015 revealed that the remains of the temple still survive, along with a previously unrecorded megalithic structure nearby.

Yankeetown Site

The Yankeetown Site (12W1) is a substantial archaeological site along the Ohio River in the southwestern part of the U.S. state of Indiana. Inhabited during the prehistoric Woodland period, the site has yielded important information about Woodland-era peoples in the region, but it has been damaged by substantial erosion. Despite the damage, it has been a historic site for more than thirty years.

Zmudowski State Beach

Zmudowski State Beach is located on Monterey Bay, in Moss Landing, Monterey County, northern California.It is operated by the California Department of Parks and Recreation. Coastal erosion has greatly affected Zmudowski State Beach, along with other beaches in California. It has also been impacted by an influx of marine debris, causing changes in its wildlife populations.

Landforms
Beaches
Processes
Management
Related

Languages

This page is based on a Wikipedia article written by authors (here).
Text is available under the CC BY-SA 3.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.