Coastal Change & Conflict

Coastal Change & Conflict

1. Erosion

   • Hydraulic action
     • Waves hit the rocks, forcing pockets of air into cracks. The trapped air is released quickly, which breaks up the rock.
   • Abrasion
     • Waves pick up stones and hurl them against the cliff face,wearing it away.
   • Attrition
     • Pebbles become rounder and smaller as the waves force them to smash into each other.

2. Coastal landforms

   • Cave
     • Formed when waves erode a weakness in the rock
   • Arch
     • Formed when two caves erode from both side of a headland and meet in the middle
   • Stack
     • Formed when the top of an arch collapses
   • Stump
     • Formed after a stack has been eroded by the wind and/or water
   • Wave-cut platforms
     • Waves undercut the cliff face to form a wave-cut notch
       • This leaves an overhanging cliff face
         • The overhanging rock collapses, and the cliff retreats. This leaves a wave-cut platform

3. Waves

   • Swash
     • Moves up the beach, depositing sand and gravel
   • Backwash
     • Moves back down the beach, carrying sand and gravel away
   • Constructive wave
     • The swash is stronger than the backwash, so material is deposited on the beach
   • Destructive wave
     • The backwash is stinger than the swash, so material is taken away from the beach.
   • Deposition (Longshore drift)
     • Waves approach the coast at an angle
       • Swash carries material up the beach
         • 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
     • Sand spits
       • 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.
         • The sheltered water behind the spit becomes a salt marsh.
         • The end of the spit becomes curved, when it meets with strong winds and waves.
         • If a sand spit joins up with the coastline on the other side, it forms a bar.

4. Geology of coastlines

   • Hard rock coasts
     • Granite, limestone, chalk
     • Resistant to erosion
     • High, steep, rugged, bare cliff face
     • Some rocks and boulders at the foot of the cliff
     • Features such as caves, arches and stacks
   • Soft rock coasts
     • Clay
     • May be high, but not very rugged or steep
     • Piles of mud and clay collect at the bottom
     • Very few hard rocks
   • Lulworth Cove
     • Waves cut through a weakness in the resistant limestone, forming the entrance to the cove.
       • Waves erode the soft clay behind.
   • Concordant coasts
     • Bands of hard/soft rock run parallel to the coastline
   • Discordant coasts
     • Bands of hard/soft ruck run perpendicular to the coastline

5. Factors effecting coastal erosion

   • Rock type
   • Number of faults in the cliff
   • Fetch
     • The length of water over which the wind has blown
   • Cliff exposure
   • Storms
   • Sea defences

6. Coastal management

   • Hard engineering
     • Sea wall
       • Protects cliffs and buildings
       • Expensive
     • Groynes
       • Prevents longshore drift
       • Exposes other areas of coast
     • Rip rap
       • Rocks absorb wave energy
       • Expensive
     • Off-shore reef
       • Waves lose power after breaking on reef
       • Expensive and interferes with fishing
   • Soft engineering (Holistic management)
     • Beach replenishment
       • Reduces wave energy and maintains tourism
       • Expensive
     • Managed retreat
       • Businesses and people avoid the effects of erosion
       • Expensive
     • Cliff regrading
       • Foot of cliff is not protected
       • Less steep: reduces slippage

7. Case study: Coastal retreat

   • The Holderness coastline
     • 60km long
     • Low, easily eroded cliffs (boulder clay/glacial till)
     • Retreating 2m per year
     • Management
       • Scarborough - soft engineering
         • Beach replenishment, £100/m
       • Mappleton
         • Groynes and rip-rap, £2 million
   • Recurved sea wall, Robin Hood's Bay
     • 500 feet long and 40 feet high
     • Built in 1975 for £578,000