Coastal Erosion and Deposition

Constructive and destructive waves.

They have a low frequency and a weak backwash.

They are high and deep, have a high frequency and they have a strong backwash and a weak swash.

Headlands and bays, Cliffs and wave-cut platforms, Stacks and stumps, and Shoreline platforms

Spits, beaches, offshore bars and tombolos, cuspate forelands, salt marshes, estuarine mudflats, and sand dunes.

Solution, saltation, suspension, and traction.

The gradual breakdown of rocks, in situ, at or close to the ground surface.

Mechanical, chemical, and biological.

This is the movement of materials downslope, because of gravity, at a range of speeds. Water acts as the common lubricant involved in mass movement.

Types of mass movement are soil creep, solifluction, earth and mudflows, rock falls, rock / debris slides, and slumps.

Waves are produced by friction between the wind and water, resulting in an energy transfer from the wind to the sea. Ripples are created; these ripples will become waves if the wind is sustained.

Waves move up and down – there is no horizontal movement. It is only when the water enters shallower areas that the water itself moves forward.

wave crest

The wave height.

As a result of the coastal feature, the depth of water around a coast varies. As the wave approaches a coast, its progress is modified due to friction from the seabed, halting the motion of waves. In addition, as waves approach a coast, they are refracted so that their energy is concentrated around headlands but reduced around bays.

Constructive and destructive waves.

They are also called spilling or surging waves. They are gentle, flat waves with a strong swash and a weak backwash; as a result, constructive waves build beaches. As the wave breaks, it carries material up the beach in its swash. Beach material is deposited as a bridge of sediment (berm) at the top of the beach. The relatively gentle profile of the beach with a steep ridge at the top of the beach means that the backwash soaks into the sand or slowly drains away. When the following wave breaks, its swash will deposit more material without it being 'captured' by the backwash of the preceding wave.

These waves are also known as plunging waves. Not surprisingly, destructive waves destroy beaches. As the wave approaches the coast, it gains height and drops onto a steep beach. As a result, it does not travel far up it. The swash of a destructive wave is much weaker than its backwash. This means that these waves transport beach material back into the sea, lowering the height of a beach. The more the waves crash onto the beach, the more sediment is washed out to sea. Because the waves are so frequent, the backwash has less time to soak into the sand. During a storm, the most common waves are destructive.

Hydraulic action, attrition, abrasion, and corrosion.

This is where waves approach the cliff; air may become trapped and compressed in joints and cracks along a cliff face. Then when the wave retreats, the compressed air expands again. This continual process can weaken the joints and cracks in the cliff, causing pieces of rock to break off.

Bits of rock and sand that the waves have picked up are thrown against the cliff face. The sediment acts as a tool on the cliff, chiselling away at the surface and gradually wearing it down by removing small particles.

When a wave breaks upon the shore, rocks and pebbles that are being carried collide with each other breaking them and eventually making them smaller and smoother. The net result is that the sediment gets smaller and smaller over time.

Corrosion is also known as solution. It is where salts and acids within the seawater will gradually dissolve some types of rock found along the coast. This process happens over thousands of years.

Because it is economically beneficial, for example, through tourism, as people love to visit the coast, through trade as deltas and estuaries make ideal ports, and as a result of agriculture, they have fertile soil.

The height of land above sea level, the degree of erosion and subsidence, deforestation and vegetation removal and storm surges.

 The mega-deltas of Asia.

Through the drainage of saturated sediment/soil for agriculture, e.g. Fens of East Anglia. The weight of coastal towns and cities and built environment can also compress sediment, leading to subsidence, e.g. Venice. And through land reclaimed from the sea, the Netherlands.

Vegetation intercepts the rainfall, slowing down its movement by removing it. As a result, infiltration and interception are reduced and surface run-off increases. The vegetation also stabilises existing sediment and traps new sediment, raising the height of the land above sea level. In addition, it absorbs wave energy, reducing wave impact and erosion, and reduces the distance waves travel onshore before the energy is exhausted.

They are a short term change in sea level caused by intense low-level pressure systems from depressions (a low-pressure weather system) and tropical cyclones (hurricanes, typhoons).

They can be exacerbated through land subsidence, the removal of natural vegetation, and global warming.

Storm Xaver, December 2013.

As a direct result of the storm, there will be some deaths and injuries to people through drowning or collapsing buildings. Infrastructure such as roads, railways, ports, and airports will be flooded or destroyed. There will be damaged water pipes, electricity transmission lines and sewage systems; as a result, there is likely to be no power or water. Homes will be destroyed, homes on marginally low lying land (slums and shantytowns) will be more vulnerable. Businesses (factories) causing an interruption of raw material delivery and agricultural land contaminated - crop harvest lost.

Most of the area is low lying; storm surges often meet the outgoing river discharges from the rivers resulting in the river and coastal flooding; most of the coastline is made up of unconsolidated sediment from the deltas, which is easily eroded. Intense rainfall is associated with cyclones and the shallow and conical shape of the Bay near Bangladesh.

Land that was forested initially has now been cleared and used for growing rice, and 4000km of barriers has been built along the coast. This prevented the natural deposition of sediment used to maintain the island's height. Also, the mangrove forests have been removed, they stabilize the coastline against erosion, collect nutrient-rich sediment, protect extreme weather events such as tsunamis, and absorb and disperse tidal surges.

2014.

Sea levels will rise by between 28 - 98cm by 2100, with the most likely rise being 55cm by 2100. And that the world's significant deltas risk of coastal flooding was likely to increase by 50 per cent.

There is no solution, but there are two possible approaches for dealing with the risk associated with adaptation and mitigation.

A change in the local coastline of land height relative to the sea level.

1. Land in the north and west, which was covered by ice sheets during the last ice age, is still rising due to the recent isostatic recovery. 
2. Land in the south and east (not covered by the ice sheet)is sinking. As a result, rivers pour water and sediment into the Thames estuary. The weight of this caused the crust to drop there and relative sea levels to rise. Resulting in an increased flooding risk due to isostatic change and rising sea levels caused by global warming.

Global changes to sea levels.

A coastline that is sinking relative to the sea level of the time.

Examples of these can be found along the south coast of England and the east coast of America.

A Rias.