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Coastal erosion is the loss or displacement of land, or the long-term removal of
sediment Sediment is a naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of wind, water, or ice or by the force of gravity acting on the particles. For example, sa ...
and rocks along the coastline due to the action of waves, currents,
tide Tides are the rise and fall of sea levels caused by the combined effects of the gravitational forces exerted by the Moon (and to a much lesser extent, the Sun) and are also caused by the Earth and Moon orbiting one another. Tide tables can ...
s, wind-driven water, waterborne ice, or other impacts of storms. The landward retreat of the shoreline can be measured and described over a temporal scale of tides, seasons, and other short-term cyclic processes. Coastal erosion may be caused by hydraulic action, abrasion, impact and
corrosion Corrosion is a natural process that converts a refined metal into a more chemically stable oxide. It is the gradual deterioration of materials (usually a metal) by chemical or electrochemical reaction with their environment. Corrosion engi ...
by wind and water, and other forces, natural or unnatural. 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,
bridge A bridge is a structure built to span a physical obstacle (such as a body of water, valley, road, or rail) without blocking the way underneath. It is constructed for the purpose of providing passage over the obstacle, which is usually somethi ...
s, 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. Also erosion commonly happens in areas where there are strong winds, loose
sand Sand is a granular material composed of finely divided mineral particles. Sand has various compositions but is defined by its grain size. Sand grains are smaller than gravel and coarser than silt. Sand can also refer to a soil texture, textur ...
, 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 erosion is grinding and wearing away of rock surfaces through the mechanical action of other rock or sand particles. According to the IPCC,
sea level rise Globally, sea levels are rising due to human-caused climate change. Between 1901 and 2018, the globally averaged sea level rose by , or 1–2 mm per year on average.IPCC, 2019Summary for Policymakers InIPCC Special Report on the Ocean and Cry ...
caused by
climate change In common usage, climate change describes global warming—the ongoing increase in global average temperature—and its effects on Earth's climate system. Climate change in a broader sense also includes previous long-term changes to ...
will increase coastal erosion worldwide, significantly changing the coasts and low-lying coastal areas.


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 A cave or cavern is a natural void in the ground, specifically a space large enough for a human to enter. Caves often form by the weathering of rock and often extend deep underground. The word ''cave'' can refer to smaller openings such as sea ...
. 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 Scree is a collection of broken rock fragments at the base of a cliff or other steep rocky mass that has accumulated through periodic rockfall. Landforms associated with these materials are often called talus deposits. Talus deposits typically ha ...
) 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 Corrasion is a geomorphological term for the process of mechanical erosion of the earth's surface caused when materials are transported across it by running water, waves, glaciers, wind or gravitational movement downslope. An example is the wear ...
(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.


Abrasion

Abrasion, also known as
corrasion Corrasion is a geomorphological term for the process of mechanical erosion of the earth's surface caused when materials are transported across it by running water, waves, glaciers, wind or gravitational movement downslope. An example is the wear ...
, 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 Corrosion is a natural process that converts a refined metal into a more chemically stable oxide. It is the gradual deterioration of materials (usually a metal) by chemical or electrochemical reaction with their environment. Corrosion engi ...
or solution/chemical weathering occurs when the sea's pH (anything below pH 7.0) corrodes rocks on a cliff face.
Limestone Limestone ( calcium carbonate ) is a type of carbonate sedimentary rock which is the main source of the material lime. It is composed mostly of the minerals calcite and aragonite, which are different crystal forms of . Limestone forms wh ...
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

The ability of waves to cause
erosion Erosion is the action of surface processes (such as water flow or wind) that removes soil, rock, or dissolved material from one location on the Earth's crust, and then transports it to another location where it is deposited. Erosion is di ...
of the cliff face depends on many factors. The
hardness In materials science, hardness (antonym: softness) is a measure of the resistance to localized plastic deformation induced by either mechanical indentation or abrasion (mechanical), abrasion. In general, different materials differ in their hardn ...
(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 Silt is granular material of a size between sand and clay and composed mostly of broken grains of quartz. Silt may occur as a soil (often mixed with sand or clay) or as sediment mixed in suspension with water. Silt usually has a floury feel wh ...
and fine
sand Sand is a granular material composed of finely divided mineral particles. Sand has various compositions but is defined by its grain size. Sand grains are smaller than gravel and coarser than silt. Sand can also refer to a soil texture, textur ...
. The rate at which cliff fall debris is removed from the foreshore depends on the power of the waves crossing the
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, etc., or biological sources, such as mollusc shell ...
. 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 Bathymetry (; ) is the study of underwater depth of seabed, ocean floors (''seabed topography''), lake floors, or river floors. In other words, bathymetry is the underwater equivalent to hypsometry or topography. The first recorded evidence of w ...
, 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. 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. File:Erodedcliffpacifica.jpg, Pacifica, California coast after major storms in 1997 (resulting from the strongest El Niño on record) destroyed the houses shown above. File:BeachErosionCabrillo.jpg, Beach erosion at Cabrillo National Monument, California. File:BeachErosionTP.jpg, Large-scale coastal erosion at Torrey Pines State Reserve, California. File:Coastal-erosion-inland.jpg, Coastal erosion at Torrey Pines State Reserve, California, resulted in the necessary relocation of a scenic overlook. File:Daniabeach-coastal erosion 10-04-2017.jpg, Coastal erosion during a king tide, Dania Beach, Florida File:Cromer Coastal Erosion.jpg, Erosion of cliffs on the Norfolk coast.


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 Activities


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

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. 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. 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. As we learn more about hard erosion controls it can be said for certain that these structural solutions cause more problems than they solve. They interfere with the natural water currents and prevent sand from shifting along coasts, along with the high costs to install and maintain them, their tendency to cause erosion in adjacent beaches and dunes, and the unintended diversion of stormwater and into other properties. Natural forms of hard-erosion control include planting or maintaining native vegetation, such as
mangrove A mangrove is a shrub or tree that grows in coastal saline or brackish water. The term is also used for tropical coastal vegetation consisting of such species. Mangroves are taxonomically diverse, as a result of convergent evolution in several ...
forests and
coral Corals are marine invertebrates within the class Anthozoa of the phylum Cnidaria. They typically form compact colonies of many identical individual polyps. Coral species include the important reef builders that inhabit tropical oceans and secre ...
reefs.


Soft-erosion controls

Soft erosion strategies refer to temporary options of slowing the effects of erosion. These options, including Sandbag and
beach nourishment Beach nourishment (also referred to as beach renourishment, beach replenishment, or sand replenishment) describes a process by which sediment, usually sand, lost through longshore drift or erosion is replaced from other sources. A wider beach ...
, are not intended to be long-term solutions or permanent solutions. 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. 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. 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. Dynamic revetment, which uses loose cobble to mimic the function of a natural storm beach, may be a soft-erosion control alternative in high energy environments such as open coastlines. Over the years beach nourishment has become a very controversial shore protection measure: It has the potential to negatively impact several of the natural resources. Some large issues with these beach nourishment projects are that they must follow a wide range of complex laws and regulations, as well as the high expenses it takes to complete these projects. Just because sand is added to a beach doesn't mean it will stay there. Some communities will bring in large volumes of sand repeatedly only for it to be washed away with the next big storm. Despite these factors, beach nourishment is still used often in many communities. Lately, the U.S. Army Corps of Engineers emphasized the need to consider a whole new range of solutions to coastal erosion, not just structural solutions. Solutions that have potential include native vegetation, wetland protection and restoration, and relocation or removal of structures and debris.


Living Shorelines

The solutions to coastal erosion that include vegetation are called "living shorelines". Living shorelines use plants and other natural elements. Living shorelines are found to be more resilient against storms, improve water quality, increase biodiversity, and provide fishery habitats. Marshes and oyster reefs are examples of vegetation that can be used for living shorelines; they act as natural barriers to waves. Fifteen feet of marsh can absorb fifty percent of the energy of incoming waves.


Relocation

Relocation of infrastructure any housing farther away from the coast is also an option. The natural processes of both absolute and relative
sea level rise Globally, sea levels are rising due to human-caused climate change. Between 1901 and 2018, the globally averaged sea level rose by , or 1–2 mm per year on average.IPCC, 2019Summary for Policymakers InIPCC Special Report on the Ocean and Cry ...
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. A coproduction approach combined with managed retreat has been proposed as a solution that keeps in mind environmental justice. Typically, there has been low public support for "retreating." However, if a community does decide to relocate their buildings along the coast it is common that they will then turn the land into public open space or transfer it into land trusts in order to protect it. These relocation practices are very cost-efficient, can buffer storm surges, safeguard coastal homes and businesses, lower carbon and other pollutants, create nursery habitats for important fish species, restore open space and wildlife, and bring back the culture of these coastal communities.


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.
Remote sensing Remote sensing is the acquisition of information about an object or phenomenon without making physical contact with the object, in contrast to in situ or on-site observation. The term is applied especially to acquiring information about Ear ...
data such as Landsat scenes can be used for large scale and multi year assessments of coastal erosion.


Examples

A place where erosion of a cliffed coast has occurred is at
Wamberal Wamberal () is a coastal suburb of the Central Coast region of New South Wales, Australia, just north of Terrigal. It is part of the local government area and is located adjacent to the Wamberal Lagoon. Wamberal is an Aboriginal word meaning ' ...
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. Dunwich, the capital of the English medieval
wool Wool is the textile fibre obtained from sheep and other mammals, especially goats, rabbits, and camelids. The term may also refer to inorganic materials, such as mineral wool and glass wool, that have properties similar to animal 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 Hallsands is a village and beach in south Devon, England, in a precarious position between cliffs and the sea, between Beesands to the north and Start Point to the south. History The early history of Hallsands is unknown, but a chapel has exi ...
in
Devon Devon ( , historically known as Devonshire , ) is a ceremonial and non-metropolitan county in South West England. The most populous settlement in Devon is the city of Plymouth, followed by Devon's county town, the city of Exeter. Devon is ...
, England, was a coastal village washed away over the course of a year, 1917, directly due to earlier
dredging Dredging is the excavation of material from a water environment. Possible reasons for dredging include improving existing water features; reshaping land and water features to alter drainage, navigability, and commercial use; constructing d ...
of
shingle Shingle may refer to: Construction *Roof shingles or wall shingles, including: **Wood shingle ***Shake (shingle), a wooden shingle that is split from a bolt, with a more rustic appearance than a sawed shingle ***Quercus imbricaria, or shingle oak ...
in the
bay A bay is a recessed, coastal body of water that directly connects to a larger main body of water, such as an ocean, a lake, or another bay. A large bay is usually called a Gulf (geography), gulf, sea, sound (geography), sound, or bight (geogra ...
in front of it. The California coast, which has soft cliffs of sedimentary rock and is heavily populated, regularly has incidents of house damage as cliffs erodes. Devil's Slide, Santa Barbara, the coast just north of Ensenada, and Malibu are regularly affected. The
Holderness Holderness is an area of the East Riding of Yorkshire, on the north-east coast of England. An area of rich agricultural land, Holderness was marshland until it was drained in the Middle Ages. Topographically, Holderness has more in common wi ...
coastline on the east coast of England, just north of the
Humber Estuary The Humber is a large tidal estuary on the east coast of Northern England. It is formed at Trent Falls, Faxfleet, by the confluence of the tidal rivers Ouse and Trent. From there to the North Sea, it forms part of the boundary between ...
, 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 Longshore drift from longshore current is a geological process that consists of the transportation of sediments (clay, silt, pebbles, sand, shingle) along a coast parallel to the shoreline, which is dependent on the angle incoming wave direction ...
starves the beaches of sand, leaving them more exposed. The white cliffs of Dover have also been affected. The coastline of
North Cove, Washington North Cove is an unincorporated community in Pacific County, Washington. North Cove is mostly residential, with some vacation rentals and a general store being the only commercial properties. The community suffers from the extreme coastal erosi ...
has been eroding at a rate of over 100 feet per year, earning the area the nickname "Washaway Beach." Much of the original town has collapsed into the ocean. The area is said to be the fastest-eroding shore of the United States' West Coast. Measures were finally taken to slow the erosion, with substantial slowing of the process noted in 2018. Fort Ricasoli, a historic 17th century fortress in
Malta Malta ( , , ), officially the Republic of Malta ( mt, Repubblika ta' Malta ), is an island country in the Mediterranean Sea. It consists of an archipelago, between Italy and Libya, and is often considered a part of Southern Europe. It lies ...
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 fish farm excavated from rock during the first century B.C. was exacerbated by the construction of a close sport harbour. Hampton-On-Sea is suffering from this problem as well. Hampton-On-Sea is located in Kent, England. It was at one time very popular for its oyster fishing and was very reliant on the sea. Hampton-On-Sea has undergone the effects of coastal erosion since before the 1800s. Hampton-On-Sea's coastal erosion worsened with the increase in global warming and climate change. Global warming is causing a rise in sea level, more intense and frequent storms, and an increase in ocean temperature and precipitation levels. Another reason Hampton-On-Sea had such a horrific case of coastal erosion is due to an increase in the frequency and the intensity of storms it experienced. These natural events had destroyed the Hampton Pier, Hernecliffe Gardens, a set of villas, several roads, and many other structures that once lay on Hampton-On-Sea. After this destruction, in 1899 they started building a sea wall to protect the rest of the remaining land and buildings. However, the sea wall did not offer much help: buildings continued to be affected by the erosion. Then a storm came and broke the sea wall, it then flooded the land behind it. These events cause many land investors to back out. Eventually, Hampton-On-Sea had to be abandoned because the erosion overtook so much of the land. By 1916 Hampton-On-Sea had been completely abandoned. By the 1920s only a couple of structures still stood. It was at that point that
Hampton-On-Sea Hampton-on-Sea is a drowned and abandoned village in what is now the Hampton area of Herne Bay, Kent. It grew from a tiny fishing hamlet in 1864 at the hands of an oyster fishery company, was developed from 1879 by land agents, abandoned in 19 ...
was said to have been finally drowned. Today only three landmarks have survived the tragedy that Hampton-On-Sea had faced. These landmarks include The Hampton Inn, The Hampton Pier, and a few roads. Although The Hampton Pier is not the same size as the original it is still working as a great place for people to fish. Today The Hampton inn is now a popular little pub known for its delicious food and its beautiful sunset view. To this day they are sharing the history of Hampton-On-Sea with others.


See also

* Beach erosion and accretion ** Beach evolution **
Beach morphodynamics Coastal morphodynamics (i.e. the dynamics of beach morphology) 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 ...
**
Beach nourishment Beach nourishment (also referred to as beach renourishment, beach replenishment, or sand replenishment) describes a process by which sediment, usually sand, lost through longshore drift or erosion is replaced from other sources. A wider beach ...
** Raised beach ** Modern recession of beaches ** Paleoshoreline *
Integrated coastal zone management Integrated coastal zone management (ICZM), integrated coastal management (ICM), or integrated coastal planning is a coastal management process for the management of the coast using an integrated approach, regarding all aspects of the coastal zo ...
** Coastal management, to prevent coastal erosion and creation of beach **
Coastal and oceanic landforms The coast, also known as the coastline or seashore, is defined as the area where land meets the ocean, or as a line that forms the boundary between the land and the coastline. The Earth has around of coastline. Coasts are important zones in n ...
** Coastal development hazards ** Coastal geography ** Coastal engineering ** Coastal and Estuarine Research Federation (CERF) *
Erosion Erosion is the action of surface processes (such as water flow or wind) that removes soil, rock, or dissolved material from one location on the Earth's crust, and then transports it to another location where it is deposited. Erosion is di ...
** Bioerosion **
Blowhole Blowhole may refer to: * Blowhole (anatomy), the hole at the top of a whale's or other cetacean's head *Blowhole (geology), a hole at the inland end of a sea cave **Kiama Blowhole in Kiama, Australia **The Blow Hole, a marine passage between Minst ...
** Natural arch ** Wave-cut platform *
Longshore drift Longshore drift from longshore current is a geological process that consists of the transportation of sediments (clay, silt, pebbles, sand, shingle) along a coast parallel to the shoreline, which is dependent on the angle incoming wave direction ...
**
Deposition (sediment) Deposition is the geological process in which sediments, soil and rocks are added to a landform or landmass. Wind, ice, water, and gravity transport previously weathered surface material, which, at the loss of enough kinetic energy in th ...
** Coastal sediment supply ** Sand dune stabilization ** Submersion


References


Works cited

*


External links


Sustainable coastal erosion management in Europe
*
Environment Agency guide to coastal erosion


*
Examine an example of wave erosion

Erosion & Flooding in the Parish of Easington

Some interesting teaching resources



US Economic Costs of Coastal Erosion & Inundation
NOAA Economics

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Images



{{authority control Coastal construction Coastal engineering Coastal geography Geomorphology