coasts

• Waves are caused by the wind dragging on the surface of the water.
• Fetch: the length of water the wind blows over.
• The stronger the wind is, and the longer it blows for, and the longer the fetch, means the larger the waves and the more energy they'll have.
• • When they reach the coast, the waves break. The water that rushes up the sand is called the swash. The water that rolls back into the sea is called the backwash.
  • The backwash is always at a right angle to the beach.
• Constructive waves

  • They build the beach.
  • Low, flat and have low energy.
  • Constructive waves a have a strong swash and weak backwash. This means material is carried on to the shore and left there.
• Destructive waves

  • They erode the beach.
  • High, steep and have high energy.
  • Destructive waves have a weak swash and strong backwash. This means that material is dragged out from the beach and out to sea.
• Ways a coast erodes

  • Abrasion/corrasion: Stones scrape into the cliffs and erode them away.
  • Hydraulic action: The force of the water gets into small cracks and compresses the air, wears away the cliff and erodes loose material.
  • Solution/corrosion: Acids in the water slowly dissolve the cliff.
  • Attrition: Rocks being carried by the sea, smash together and break into smaller pieces.
• Longshore drift

  • LSD occurs when prevailing wind blows at an angle to the coastline.
  • When this happens the waves come in at an angle.
  • Swash will move the sediment up the beach at a 45 degree angle, backwash will move it back into the sea at a 90 degree angle.
• Bay: An indented area normally found between two headlands. They are usually more sheltered so there is less erosive power, meaning you often find beaches in bays.
• Headland: A piece if land that sticks out into the sea. Waves refract around headlands so they experience a lot of erosion. Piece of land between two bays.
• Formation of bays/headlands

  • There are bands of hard and soft rocks.
  • Differential erosion occurs.
  • Soft/weak rocks worn rapidly by HA and abrasion.
  • Bays formed in soft rocks.
  • Headlands form from hard rocks.
• Formation of beaches:

  • By constructive waves.
  • Swash moves material up the beach.
  • Backwash does not have energy to remove it.
  • Longshore drift occurs.
  • Zig zag movement of materials.
  • Deposition in sheltered bays.
• Wave cut notch and wave cut platforms:

  • Erosion of cliffs by hydraulic action/corrasion.
  • Wave cut notch formed in the land.
  • Undercutting makes it erode further back.
  • The top of the cliff collapses as it cannot hold weight anymore.
  • The cliff retreats.
  • Leaves a wave cut platform, a bare area of land.
  • Smoothed by waves over time.
• Caves, arches, stacks & stumps

  • The waves attack the cracks in the headland.
  • Hydraulic action will be the main type of erosion.
  • Over time the crack may turn into a cave.
  • Slowly the cave will get bigger and cut the way through the headland, making an arch.
  • As the arch gets bigger the weight of the arch roof gets too great and it collapses, leaving a stack.
  • The stack is then eroded by the sea leaving a stump.
• Coastal sand dunes: Ridges of sand formed at the back of beaches. e.g. Ainsdale Dunes, near Southport.
• Formation of coastal sand dunes

  • Wind blows on shore picking up dry sand from beach.
  • Obstacles cause wind to slow and deposit sand.
  • This increases the size of obstacles so deposition continues an dune grows.
  • Sand dune builds up over time, an embryo dune becomes an established dune.
  • Over time, the sand dune is colonised by maram grass.
• Spits: Long narrow ridges of shingle and sand extending out into the sea or across a river.
• Formation of spits

  • LSD transports material across the coastline.
  • Formed in areas of relatively low water.
  • Deposition occurs resulting in build-up of sand and shingle.
  • Large material deposited due to reduction in wave energy. Finer material deposited helping to build the rest of the spit.
  • Curving at the end due to change in wind direction. Marsh could be found behind spit.
• Coral reef

  • Animals that join to live as a colony (polyps).
  • Develop in warm, shallow seas.
  • Marine/ocean ecosystem.
  • Found in a narrow belt between the tropic of cancer and tropic of capricorn.
  • Usually near the equator where the water is 20 to 25 degrees.
• Case study - Seychelles

  • Warm water - Indian Ocean between 20 to 25 degrees is best.
  • Vallon Bay - Clear, shallow water, no deeper than 60m to allow sunlight to penetrate.
  • Plenty of sunlight to aid photosynthesis of algae.
  • Water free from sediment and clear so sun can shine through.
  • Vallon Bay is not polluted as it's not industrialized, plenty of oxygen for photosynthesis.
  • Plenty supply of plankton.
  • calm seas/lack of destructive waves.
• Lagoon: A stretch of salt water separated from the sea by a low sandback or coral reef.
• Types of coral reefs

  • Fringing reef: directly attached to a coast, or borders it with an intervening shallow channel or lagoon.
  • Barrier reef: found offshore, reef separated from a mainland or island shore by a deep channel or lagoon.
  • Atoll reef: more or less circular or continuous barrier reef extends all the way around a lagoon without a central island.
• Characteristics of mangroves

  • Various types of trees up to medium height and shrubs that grow in saline coastal sediment habitats in the tropics and subtropics.
  • Near sheltered tropical coastlines - in a large area between high and low water marks.
  • Made up of evergreen mangrove trees and other plants.
  • Live in salty water.
  • Grow in areas with temps of 20 °C plus and range is no more than 5 °C.
  • Area should be calm, no strong waves or tidal currents.
  • They are found mainly between latitudes 25 ºN and 25 °S.
• Conditions of development of coastal marsh

  • Protected from high energy waves, behind a spit.
  • Shallow water.
  • Sediment accumulation.
  • Mixture of salt and fresh water.
  • Tide encourages growth of mangroves.
• Coastal hazards

  • Rapid coastal erosion.
  • Tsunami.
  • Tidal surges and coastal flooding.
  • Storm surges.
• Problems of coastal erosion

  • Farmland could be lost.
  • Houses damaged/destroyed/lost.
  • Residents may need to evacuate.
  • Roads could be damaged.
  • Making people travel along the coast take long detours inland.
  • Money can't be used for other purposes.
  • High cost of house insurance/difficulty getting insurance.
  • Happisburg - from 2004 - 2007, 20m of land lost to sea.
• CASE STUDY: tropical storm -

  Hurricane Katrina, USA - 2005:

  • Levees were breached, water pours into New Orleans.
  • Winds of 75 mph caused severe destruction.
  • Over 1500 people dead.
  • Thousands of homes destroyed.
  • 80% of New Orleans flooded up to 6 metres.
  • The hurricane caused $ 300 million worth of damage.
  • Thousands of jobs lost and millions of dollars lost in tax incomes.
• Effects of tropical storms

  • The intense winds of tropical storms can destroy whole communities, buildings and communication networks.
  • As well as their own destructive energy, the winds generate abnormally high waves and tidal surges.
  • Sometimes the most destructive elements of a storm are the subsequent high seas and flooding.
• CS: Mauritius - Benefits

  • Coast line is 322km, beautiful clear ocean with fringing coral reefs. Attractions such as Lle Aux Cerfs beach.
  • This attracts tourists who spend money. Tourism revenue $12 mil a month.
  • Local jobs created in hotels. Cooks, cleaners etc.
  • Jobs such as scuba instructors, diving etc.
  • Tourism industry has allowed the island to grow and now has industry (e.g. Plain Lauzun Industrial Zone) and ports.
  • Increases GDP of the island.
• CS: Mauritius - Problems:

  • 21 beaches have experienced coastal erosion. 22 recent flooding.
  • Erosion increased by 5x in the last decade, putting housing in River Bay area under threat.
  • 1.5m of erosion at St Geran.
  • In some areas sea walls have collapsed due to the storms and roads have eroded.
  • Risk to life and property increasing for people on coast.
  • Tropical storm, Bejisa, caused damage to the island, 166 km/h winds, roofs damaged, sea level risen by 1.8m.
• Sea walls: A wall built along the coast to prevent erosion and flooding.
• Revetments: A raised structure built along the coastline to prevent erosion and to absorb wave energy.
• Groynes: A series of wooden or concrete fences built along the coast to trap material being transported by LSD.
• Rock armour/Rip rap: Boulders or concrete blocks placed at the foot of cliffs or back of beaches to absorb wave energy.
• Gabions: rock-filled wire cages often stacked or built up as a wall to absorb wave energy.
• Beach nourishment: The process of adding sand to a beach to increase its width and length.
• Managed retreat: Move the shoreline back and allow the areas to erode away and previously protected land to flood. This means that marshes and mudflats are created - a natural defence against erosion.
• Artificial reefs: A man-made structure that is placed in the sea to provide a habitat for marine life.
• CS: Coastal Defenses - Lyme Regis:

  • Coastal defences from Cobb Gate to the harbour cost £ 17 million.

  WHAT HAS BEEN DONE?

  36,000 tonnes rock armour.

  71, 000 tonnes beach shingle - beach nourishment.

  41,000 tonnes beach sand - beach nourishment.

  Drainage materials for slope behind beach to reduce weight of cliff.

  250m new recurved sea wall.

  Stone groynes made - Stops LSD.

  Land flattened so no erosion of cliffs.