COASTAL EROSION

'Coastal erosion' see also (beach evolution) is the wearing away of land or the removal of beach or dune sediments by wave action, tidal currents, wave currents, or drainage. Waves, generated by storms or fast moving moter craft, cause coastal erosion, which may take the form of long-term losses of sediment and rocks, or merely in the temporary redistribution of coastal sediments; erosion in one location may result in accretion nearby. The study of erosion and sediment redistribution is called 'coastal morphodynamics'.
On rocky coasts, coastal erosion results in dramatic rock formations in areas where the coastline contains rock layers or fracture zones with different resistances to erosion. The softer areas become eroded much faster than the harder ones, which can result in typical landforms such as tunnels, bridges, columns, and pillars.

Contents

Effect on human establishments

Wave action

Factors affecting the erosion rate

First order (most important)

Second order

Third order

See also

External links

Effect on human establishments

On sedimentary coasts, coastal erosion typically poses more of a danger to human settlements than it does to nature itself. Dunwich, the capital of the English medieval wool trade, disappeared over the space 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 that was washed away overnight, an event possibly exacerbated by 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 erode. Damage in Pacifica is shown at right. Devil's Slide, Santa Barbara and Malibu are regularly affected.
The Holderness coastline on the east coast of England, just north of the Humber Estuary, is the fastest eroding coastline in Europe due to its soft clay cliffs and powerful waves. Groynes and other artificial measure to keep it under control has only sped up the process further down the coast, because longshore drift starves the beaches of sand, leaving them more exposed.

Wave action

The ability of waves to cause erosion of the cliff face depends on number of factors, which include:

★ The hardness or ‘erodibility’ of the rocks exposed at the base of the cliff

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★ The key factors in determining erodibility include the rock strength along with 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

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★ Debris removal from the foreshore is dependent on the power of the waves crossing the beach, and this energy must reach a critical level or material will not be removed from the debris lobe. On many cliffs these debris lobes can be very persistent and may take many years before they are completely removed.

★ The presence or absence of a beach at the base of the cliff

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★ Beaches help dissipate wave energy on the foreshore and can provide a measure of protection to the cliff from marine erosion.

★ The stability of the foreshore, or its resistance to lowering

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★ Lowering of the beach or shore platform through wave action is a key factor controlling the rate of cliff recession. If the beach is not lowered the foreshore should widen and become more effective at dissipating the wave energy, so that fewer and less powerful waves reach the cliff.

★ The adjacent bathymetry

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★ The nearshore bathymetry controls the wave energy arriving at the coast, and can have an important influence on the rate of cliff erosion.

★ The supply of beach material in the coastal cell from updrift

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★ The provision of material eroded updrift coming onto the foreshore beneath the cliff will help ensure a stable beach, thus providing a measure of protection.

Factors affecting the erosion rate

First order (most important)

★ Geological structure and lithology: hardness, height, fractures/faults

★ Wave climate: prevailing wave direction

★ Sub-aerial climate: weathering (frost, etc.), stress relief swelling/shrinkage

★ Water-level change: groundwater fluctuations, tidal range

★ Geomorphology

Second order

★ Weathering and transport slope processes

★ Slope hydrology

★ Vegetation

★ Cliff foot erosion

★ Cliff foot sediment accumulation

★ Resistance of cliff foot sediment to attrition and transport

Third order

★ Coastal land use

★ Resource extraction

★ Coastal management

See also

★ Coastal and oceanic landforms

★ Natural arch

★ Blowhole

★ Bioerosion

★ Modern recession of beaches

★ Coastal defense

★ Beach nourishment

★ Streisand effect#Etymology

★ Submersion

External links

★ Coastal Erosion Information from the Coastal Ocean Institute, Woods Hole Oceanographic Institution

★ Wave Erosion

★ Examine an example of wave erosion

★ Erosion & Flooding in the Parish of Easington

★ Some interesting teaching resources

★ Examples of coastal landforms
Images:

★ Work to reduce coastal erosion at Lyme Regis in Dorset 2006

★ Images of Coastal features