Coastal Depositional Landforms

Beaches Waves which slow down, lose their energy and can no longer transport beach material. This happens most commonly when waves flow into a bay. They stretch out and lose their energy, at the same time that friction with the sea bed is slowing them down. As a result, they deposit their material, which builds up as a beach.

Beach

Spits A spit is a finger of beach material, stretching along the coast after the original coastline has changed direction. They are caused by longshore drift, which continues to transport material along the shoreline in the direction of the prevailing winds.

The development of Spit 1.Longshore drift moves material along the coastline. 2.A spit forms when the material is deposited. 3.Over time, the spit grows and develops a hook if wind direction changes further out. 4.Waves cannot get past a spit, which creates a sheltered area where silt is deposited and mud flats or salt marshes form.

Bars or Barrier Islands A ridge of sand and shingle which has joined two headlands, cutting off a bay. A spit grows the whole way across a bay. Behind the bar a lagoon is created, where water has been trapped and the lagoon may gradually be in filled as a salt marsh.

Bars/ Barrier Islands

Bars and Barrier Islands Bar: A spit that connects two headlands or runs across the face of a small cove (bay). Barrier islands are not static structures. They are extremely dynamic systems that are constantly changing and moving. Wave, wind and tidal energies are the primary factors that shape and regulate the barrier island ecosystem. For barrier islands to form you need a large sand supply to build the island with moderate wave energy to shape the island. Barrier islands form in three ways: spits, from drowned dune ridges or from sand bars.

Tombolos A ridge of sand and shingle joining the mainland to an island. They are created through the process of longshore drift. A tombolo is formed when the spit continues to grow until it reaches an island.

The long shore drift transports materials along the coast The long shore drift transports materials along the coast. If there is a sudden change in the direction of the coast, the longshore drift continues to transport the materials in the original direction to the deep sea. When the spit is connected the island to the mainland to form a feature is called the Tombolos. As the longshore drift enters the deep water, the materials are deposited. Over time, these materials accumulate above the water to form a spit. The spit continues to grow with the continuous deposition of materials. The spit join a nearby island to the mainland to form a tombolo.

Coastal Management

Why protect? Coasts account for 15% of the earth’s land surface Coasts accommodate more than 50% of the world’s population it is estimated that 3.1 billion people live within 2000 kilometers from the sea It contains rich resources to produce goods and services Fishing, shipping and tourism industry Sea level is rising and the strenght of waves are increasing due to global warming

Types of Coastal Management Hard engineering - this involves building structures to protect the coast. Soft engineering - this involves working with nature by using natural materials or allowing nature to take back areas.

Challenges Accelerated increase on sea level High Costs of seawalls and breakwaters Change in the coastal systems: sediment displacement

HARD ENGINEERING Advantages Disadvantages Protects the area behind the wall Helps prevent flooding Sea wall Very expensive Waves bounce off the wall and scour the beach, removing material Can look ugly Helps to stop longshore drift moving material along the coast Traps sediment and builds up beaches Groynes May create problems elsewhere because they starve other beaches of sediment Large boulders absorb wave energy and reduce the power of the waves Rip rap or rock armour Strong waves can move or undermine the boulders

SOFT ENGINEERING Advantages Disadvantages Adding more sand or shingle widens the beach and waves lose power travelling across it Looks natural Beach nourishment Doesn’t last very long Land becomes marsh, slowing waves and reducing erosion Creates new habitats Managed retreat Land is lost                                      

What can we do?

Construction techniques Hard Contruction techniques: Groynes, sea walls, revetments, rock armour, gabions, offshore breakwater, cliff stabilisation, entrance training walls, floodgates Soft construction techniques: beach drainage, sand dune stabilization, beach nourishment

Can be expensive to obtain and transport the boulders. Hard engineering solutions Disadvantages Can be expensive to obtain and transport the boulders. Allows the build up of a beach. Absorb the energy of waves. Advantages                                                                       Allows the bulid up of a beach (a natural defence against erosion and a an attraction for tourists). Can be costly to build and maintain. Can be seen as unatractive. Prevents the movement of beach material along the coast throught the process of longshore drift. Protects the base of cliffs against erosion. Can prevent coastal flooding in some areas. Land and buildings are protected from erosion. A sea wall is expensive to build. Curved sea waves reflect the energy of the waves back to the sea.This means that the waves remain powerful. Over time the wall may begin to erode. The cost of maintenance is high. Pros and cons Type of defence Disadvantages Can be expensive to obtain and transport the boulders. Allows the build up of a beach. Absorb the energy of waves. Advantages                                                                       Allows the bulid up of a beach (a natural defence against erosion and a an attraction for tourists). Can be costly to build and maintain. Can be seen as unatractive. Prevents the movement of beach material along the coast throught the process of longshore drift. Protects the base of cliffs against erosion. Can prevent coastal flooding in some areas. Land and buildings are protected from erosion. A sea wall is expensive to build. Curved sea waves reflect the energy of the waves back to the sea.This means that the waves remain powerful. Over time the wall may begin to erode. The cost of maintenance is high. Pros and cons Type of defence Hard engineering solutions Disadvantages Can be expensive to obtain and transport the boulders. Allows the build up of a beach. Absorb the energy of waves. Advantages                                                                       Allows the bulid up of a beach (a natural defence against erosion and a an attraction for tourists). Can be costly to build and maintain. Can be seen as unatractive. Prevents the movement of beach material along the coast throught the process of longshore drift. Protects the base of cliffs against erosion. Can prevent coastal flooding in some areas. Land and buildings are protected from erosion. A sea wall is expensive to build. Curved sea waves reflect the energy of the waves back to the sea.This means that the waves remain powerful. Over time the wall may begin to erode. The cost of maintenance is high. Pros and cons Type of defence Hard engineering solutions Advantages Protects the base of cliffs against erosion. Can prevent coastal flooding in some areas. Land and buildings are protected from erosion. Disadvantages A sea wall is expensive to build. Curved sea waves reflect the energy of the waves back to the sea. This means that the waves remain powerful. Over time the wall may begin to erode. The cost of maintenance is high. Advantages Prevents the movement of beach material along the coast through the process of longshore drift. Allows the build up of a beach (a natural defense against erosion and a an attraction for tourists). Disadvantages Can be seen as unattractive. Can be costly to build and maintain. Advantages Absorb the energy of waves. Allows the build up of a beach. Disadvantages Can be expensive to obtain and transport the boulders.

This replaces beach or cliff material that has been removed by erosion or longshore drift. The main advantage is that beaches are a natural defense against erosion and coastal flooding. Beaches also attract tourists. While it can be a relatively inexpensive option it requires constant maintenance to keep replacing the beach material as it is washed away. Managed Retreat This is where areas of the coast are allowed to erode and flood naturally. Usually this will be areas considered to be low value. The advantages are that it encourages the development of beaches (a natural defence) and salt marshes (important for the environment) and cost is low. While this is a cheap option, it will not be free as people will need to be compensated for loss of buildings and farmland.

Chesil Beach