The Coastal Zone

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  • Created by: GBushell
  • Created on: 08-04-14 11:23
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  • The Coastal Zone
    • Waves
      • waves are formed when the wind blows over the sea
      • water rushes up the beach - SWASH
        • then it drains back down the beach - BACKWASH
      • the size and strength of the aves depends on:
        • wind strength
        • how long the wind blows for
        • how far it travels
          • the distance the wind blows is called the FETCH
      • there are 2 types of waves:
        • DESTRUCTIVE / plunging waves: a weak swash, strong backwash which pulls the sand + pebbles back down the beach when the water retreats
        • CONSTRUCTIVE / spilling waves: strong swash, weak backwash = drags sand + pebbles up onto the beach
    • Coastal Erosion
      • EROSION is the process of wearing away and breaking down rocks
      • waves hit the bottom of the cliff, eroding a WAVE-CUT NOTCH
      • as the cliff erodes, it leaves behind flat rocks and rock pools - WAVE-CUT PLATFORM
      • Processes of erosion
        • HYRDRAULIC ACTION - water is forced into cracks in the rock = air inside compressed and blasts out when water retreats = rock falls apart
        • ABRASION - sediment is thrown against the cliff by the water = chips off bits of rock
        • ATTRITION - sediment is knocked off cliff and swirled around by the waves collides with other bits of sediment = get worn away into smaller bits of sediment
        • SOLUTION - seawater dissolves material from the rock, e.g. limestone, chalk
      • Caves, Arches and Stacks
        • 1. a joint or fault resistant to rock
        • 2. abrasion + hydraulic action widen the joint to form a cave
        • 3. waves make the cave larger until it cuts through the headland to make an arch
        • 4. the arch is eroded and the roof becomes too heavy and collapses
        • 5. this leaves a tall stack
        • 6. the stack is eroded and collapses leaving a stump
    • Coastal Transport
      • SUSPENSION - fine sediment is carried as a suspension in the water, making it look muddy or murky
      • SOLUTION - dissolved material is carried along in solution.
      • TRACTION - larger pebbles and cobbles are rolled along the sea bed
      • SALTATION - small pebbles are moved when 1 pebble hits another, causing it to bounce = chain reaction
      • LONGSHORE DRIFT
        • 1. waves approach the beach at a slight ngle
        • 2. as th waves beak, the swash carries material up the beach at the same angle as the wave approched it
        • 3. as the swash dies away, the backwash and any material carried by it falls straight back down the beach under the influence of gravity
        • 4. this means material is moved along the beach zig-zag route
    • Coastal Deposition
      • Beaches
        • sandy beaches tend to be flat, wind can blow sand inland to form sand dunes which are held in place by marram grass
        • beaches can also be made up of pebbles or shingle.
      • Spits
        • long narrow ridges of sand and shingle stretching out from the coast
        • many spits develop a hooked or recurved end
        • behind a spit, a sheltered area of saltwater marshes and mudflats form which is covered by the sea at high tide
      • Bars
        • narrow ridges of sand and shingle that grow accross a bay
        • they can trap shallow lakes (lagoons)
          • narrow ridges of sand and shingle that grow accross a bay
        • the lagoon may eventually fill up with sediment
          • they can trap shallow lakes (lagoons)
          • storm waves sometimes crash over the top / break through the bar
      • Managing the Coast
        • Hard-engineering
          • SEA WALL - concrete structures that absorb the energy from the waves
          • GROYNES - long wooden fences/piles of rocks built out into the sea to prevent long-shore drift.
          • ROCK ARMOUR - large boulders piled at the foot of cliffs to absorb the energy from the waves
          • GABIONS - rocks / boulders held in wire mesh cages used to protect vulnerable areas by filling up with sediment
        • Soft-engineering
          • BEACH NOURISHMENT - building up beaches by adding more sand in front of cliffs
          • SAND DUNE REGENERATION - allowing sand dunes to build up around wooden structures
          • SALT MARSH CREATION - allowing the sea to flood and spread over a large area, creating salt mashes
          • MANAGED RETREAT - abandoning the existing sea defences and building new ones further inland a salt marsh
      • Case Studies
        • Maldives
        • East Head
        • Christchurch Bay
        • Essex Marshes

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