Coastal Change & Conflict

Erosion
1. Hydraulic action
  1. Waves hit the rocks, forcing pockets of air into cracks. The trapped air is released quickly, which breaks up the rock.
2. Abrasion
  1. Waves pick up stones and hurl them against the cliff face,wearing it away.
3. Attrition
  1. Pebbles become rounder and smaller as the waves force them to smash into each other.
Coastal landforms
1. Cave
  1. Formed when waves erode a weakness in the rock
2. Arch
  1. Formed when two caves erode from both side of a headland and meet in the middle
3. Stack
  1. Formed when the top of an arch collapses
4. Stump
  1. Formed after a stack has been eroded by the wind and/or water
5. Wave-cut platforms
  1. Waves undercut the cliff face to form a wave-cut notch
    1. This leaves an overhanging cliff face
      1. The overhanging rock collapses, and the cliff retreats. This leaves a wave-cut platform
Waves
1. Swash
  1. Moves up the beach, depositing sand and gravel
2. Backwash
  1. Moves back down the beach, carrying sand and gravel away
3. Constructive wave
  1. The swash is stronger than the backwash, so material is deposited on the beach
4. Destructive wave
  1. The backwash is stinger than the swash, so material is taken away from the beach.
5. Deposition (Longshore drift)
  1. Waves approach the coast at an angle
    1. Swash carries material up the beach
      1. Backwash carries material back down the beach at 90º
        This causes sand and gravel to move along the beach in a zigzag motion.
        Sand is lighter than gravel, so moves further up
  2. Sand spits
    1. If there is a break in the coastline, such as an estuary, longshore drift will still continue beyond it. The sand builds up to form a sand spit.
      1. The sheltered water behind the spit becomes a salt marsh.
      2. The end of the spit becomes curved, when it meets with strong winds and waves.
      3. If a sand spit joins up with the coastline on the other side, it forms a bar.
Geology of coastlines
1. Hard rock coasts
  1. Granite, limestone, chalk
  2. Resistant to erosion
  3. High, steep, rugged, bare cliff face
  4. Some rocks and boulders at the foot of the cliff
  5. Features such as caves, arches and stacks
2. Soft rock coasts
  1. Clay
  2. May be high, but not very rugged or steep
  3. Piles of mud and clay collect at the bottom
  4. Very few hard rocks
3. Lulworth Cove
  1. Waves cut through a weakness in the resistant limestone, forming the entrance to the cove.
    1. Waves erode the soft clay behind.
4. Concordant coasts
  1. Bands of hard/soft rock run parallel to the coastline
5. Discordant coasts
  1. Bands of hard/soft ruck run perpendicular to the coastline
Factors effecting coastal erosion
1. Rock type
2. Number of faults in the cliff
3. Fetch
  1. The length of water over which the wind has blown
4. Cliff exposure
5. Storms
6. Sea defences
Coastal management
1. Hard engineering
  1. Sea wall
    1. Protects cliffs and buildings
    2. Expensive
  2. Groynes
    1. Prevents longshore drift
    2. Exposes other areas of coast
  3. Rip rap
    1. Rocks absorb wave energy
    2. Expensive
  4. Off-shore reef
    1. Waves lose power after breaking on reef
    2. Expensive and interferes with fishing
2. Soft engineering (Holistic management)
  1. Beach replenishment
    1. Reduces wave energy and maintains tourism
    2. Expensive
  2. Managed retreat
    1. Businesses and people avoid the effects of erosion
    2. Expensive
  3. Cliff regrading
    1. Foot of cliff is not protected
    2. Less steep: reduces slippage
Case study: Coastal retreat
1. The Holderness coastline
  1. 60km long
  2. Low, easily eroded cliffs (boulder clay/glacial till)
  3. Retreating 2m per year
  4. Management
    1. Scarborough - soft engineering
      1. Beach replenishment, £100/m
    2. Mappleton
      1. Groynes and rip-rap, £2 million
2. Recurved sea wall, Robin Hood's Bay
  1. 500 feet long and 40 feet high
  2. Built in 1975 for £578,000

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	Criado por J_McNally mais de 9 anos atrás