The Coastal Zone
- 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)
- they can trap shallow lakes (lagoons)
- storm waves sometimes crash over the top / break through the bar
- Beaches
- 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
- Hard-engineering
- Case Studies
- Maldives
- East Head
- Christchurch Bay
- Essex Marshes
- Waves
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