COASTS

COASTS

1. Erosion

   • Weathering
     • Freeze thaw - water gets in cracks and freezes, expanding the crack
     • The breaking down of man made things by weather
   • Mass Movement
     • The downhill movement of material under the influence of gravity
     • Impacting factors:
       • Undercutting the cliff
       • Building on the cliff top increases the weight
       • Rain saturates the rock which increases the weight
       • Weaker rocks (eg. clay) are more likely to collapse than srong rocks (eg. granite)
   • Coastal erosion
     • Hydraulic action - waves trap air in rock forcing it apart
     • Abrasion - rocks thrown at cliff face by waves scraping it away
     • Attrition - rocks bump into each other and get smaller
     • Solution - sea water dissolves the rocks
   • Erosional landforms
     • Headlands and bays
       • Soft rock (eg. clay) erodes quickly to make bays
         • Swanage bay - Dorset
       • Hard rocks (eg. limestone) erodes slowly to make headlands
         • The Foreland - Dorset
     • Caves, arches, stacks and stumps
       • 1. A crack in the headland is expanded by hydraulic action
       • 2. The crack becomes a cave
       • 3. The cave is opened up to form an arch
         • Durdle door - Dorset
       • 4. The top of the arch collapses to form a stack
         • Old Harry -Dorset
       • 5. The stack is eroded to form a stump
         • Old Harry's wife - Dorset
     • Wave cut notches and platforms
       • Waves undercut a cliff to leave an overhanging platform above a wave cut notch.
         • The platform eventually collapses and the process happens again

2. Transportation

   • Transportation of different rocks
     • Traction - big rocks roll along the sea bed
     • Saltation - pebbles bounce along the sea bed
     • Suspension - sediment is small enough to be carried along by the water
     • Solution - tiny particles dissolve in the water and move with it
   • Longshore drift
     • Direction depends on the prevailing wind
     • Constructive waves have a strong swash
     • Destructive waves have a strong backwash
     • Sediment is moved along the shore by a diagonal swash and a straight backwash
     • Swash - a wave moving inland
     • Backwash - a wave moving back towards the sea

3. Beaches

   • Sand beaches
     • Formed by constructive waves
     • Can have sand dunes
     • Shallow gradient, almost flat
   • Pebble beaches
     • Formed by destructive waves
     • Steep gradient, often has berms
     • Large pebbles at the back of the beach
   • Depositional landforms
     • Spit
       • A finger of sand formed by longshore drift
       • Hook
         • A spit with a marsh behind it curves due to the low energy of the marsh to create a hook
       • Bar
         • A spit grows between headlands to create a bar
   • Sand dunes
     • 1. Embryo dune
       • Small dune closest to the water
       • Plant found: Couch grass
     • 2. Fore dune/yellow dune
       • Plant found: Marram grass
     • 3. Grey dune
       • Plant found: Willow
     • 4. Dune slack
       • A big dip between high dunes where water can get trapped
       • Plant found: Common sallow
     • 5. Mature dune
       • Big dune furthest from the water
       • Plant found: Pine

4. Coastal management

   • Hard engineering - building defenses
     • Sea wall
       • Absorbs energy from waves and can redirect them (if curved at the top)
       • Advantage: Strong and effective
       • Disadvantage: Expensive - £6000 per meter
     • Rip rap
       • Absorbs energy from waves
       • Advantage: Simple to maintain
       • Disadvantage: Expensive - £1000 per meter, can look messy, can be dangerous
     • Groynes
       • Traps sediment from longshore drift and absorbs energy from waves
       • Advantage: Helps to build up a natural defence
       • Disadvantage: Expensive - £10000
   • Soft engineering - in line with the natural environment
     • Cliff regrading
       • Makes a cliff less steep
       • Advantage: Cheap
       • Disadvantage: Loss of some cliff
     • Dune stabalisation
       • Planting marram grass to hold dunes together
       • Advantage: Cheap, sustainable, looks natural
       • Disadvantage: Doesn't always work
   • Managed retreat
     • Allowing an area to become flooded by removing costal protection
     • Aims
       • Improve costal stability
       • Protect areas further inland
       • Rely on natural defences
       • Creates saltmarsh - a low energy environment
     • Northen Island, Essex - River Blackwater flooded in 1991, 8000sq metres, nature reserve
     • Advantages
       • Earth banks develop
       • Maintinence costs are low
       • Saltmarsh and vegitation provide protection from storms
       • Beaches can naturally replenish
     • Disadvantages
       • Land will be lost
       • Settlements will be destroyed
       • Not socially acceptable and compensasion will be needed for land owners
       • Schemes are unpredictable
   • Case study
     • Minehead
       • A coastal town on the Bristol channel and the north-west coast of Somerset
       • Coastal management strategies used
         • A 0.6m high seawall with a curve to deflect waves
           • Expensive but the walkway build beside it is popular with tourists
         • Rock armour
           • Expensive but low maintenance and asthentically pleasing
           • Wildlife can benefit by creating new habitats in it
         • More sand put on the beach (beach nourishment)
           • Forces waves to break further out to sea
           • Attracts tourists
         • Four rock groynes
           • Helps to stop sand movement from longshore drift
           • Provides wind shelter for tourists
           • Can increas erosion further down the coast