coastal environments

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  • Coasts
    • Waves
      • Constructive waves- longer wavelengths, lower wave height and frequency, awash stronger.
        • Destructive waves- shorter wavelength, higher wave height and frequency, stronger backwash
      • Created by wind blowing over the surface of the sea. Friction causes a circular motion.
      • wave height affected by- wind speed, fetch.
    • Tides
      • Rising and falling movements of the surface of the sea caused by the gravitational pull of the moon.
      • Spring tide- when the moon, sun and earth align the gravitational pull creates a high, high tide and a low, low tide.
      • Neap tide- when the moon sun and earth are at a right angle, the gravitational pull creates a low, high tide and a high low tide.
    • Sub-aerial weathering
      • Freeze- Thaw- water repeatedly freezing and melting In cracks, pressure is exerted and rocks are broken off.
      • Salt crystallization- evaporation of water from rock surfaces leads to crystallization of dissolved salts that exert pressure.
      • chemical weathering- decomposition of rock caused by chemical change
      • Corrosion - minerals in rocks that are soluble are removed and dissolve in water.
      • Biological weathering- organic acids and plant and animal activity.
    • Mass movements
      • The movement of soil, sand, weathered material and rock downslope due to gravity.
        • Slides, slumps, rockfalls, earth/mud flow, soil creep and runoff.
    • Erosion
      • Corrosion - waves smash and grind. Over rock surfaces.
      • Hydraulic action- air in cracks is compressed when waves crash in, when pressure is released bits of rock break off.
      • Rock quarrying- wave energy pulls away loses rock
      • Solution- soluble rocks are dissolved by sea water.
      • wave pounding- a breaking wave exerts a shock wave weakening rock.
      • Attrition- rocks in the water smash against each other and break into smaller bits.
      • Factors affecting erosion
        • Beach width- wide/flat beaches slow down erosion
        • Breaking point of waves- a wave breaking directly at the foot of a cliff transfers the most energy.
        • Wave energy- more energy= more erosion
        • Wave refraction - increased erosion on headlands decreased in bays
        • Geology- more resistant rocks erode slower
        • Human activity- sea walls slow the rate of erosion.
    • Transportation of sediemnt
      • Longshore drift- when breaking waves create a movement of water parallel to the coast.
      • Beach drift- waves approach at an oblique angle, swash moves material up beach, backwash pulls it down at right angles, creating a zigzag movement.
    • Landforms- erosion
      • wave cut notches- waves break against cliff causing undercutting
      • wave cut platform- the undercut section of the cliff collapses resulting in the cliff retreating landward.
      • Bays and headlands- alternating bands of more and less resistant rock tune perpendicular to coast at discordant coastlines.
      • coves- small circular inlet of water in. Concordat coastlines, parallel to shore
      • Caves- erosion excavated material from a joint of weakness forming an underground chamber.
      • Arches- a cave extends further in to the cliff and cuts through.
      • Stacks- Sub-aerial weathering causes the arch to collapse leaving a steep, vertical column
      • Stumps- small rock island after further erosion and weathering.
    • Landforms- deposition
      • Beaches- constructive waves deposit sediment.
      • berrms- ridges of sand/pebbles formed by deposition of coarse material at the limit of awash.
      • runnels- grooves of sand running parallel to the shore by backwash
      • Beach cusps- crescent shaped indentations that form on mixed sand/shingle beaches, where waves break parallel to the beach..
      • Spits- formed where the coast suddenly changes direction, longshore drift deposits material, leaving a bank of sand sticking out, changes to wind and waves leaves a curved end.
      • Barrier beaches- long, narrow ridge of sand/shingle lies parallel to the coastline, separated by a lagoon.
      • Sand dunes- accumulations of sand grains by the wind.sand trapped by debris is colonised by plants, vegetation stabilises the sand and encourages more sand to accumulate.
      • salt marshes- silt and mud are deposited by the tide in sheltered water, mudflats develop that are colonised by vegetation, plants trap more silt and mud.
    • Sea level change
      • Eustatic change- sea levels fall when the earths climate cools (glacial), more water is stored on land - ice sheets/ glaciers. Sea levels rise when the earths climate warms(interglacial)
      • isostatic change- a rise in the land. isostatic depression, earths crust sinks into asthenosphere by a heavy weight on earths surface.
      • Impacts- more frequent and severe flooding.
      • Impacts- cliffs more susceptible to erosion- cliff and coastal retreat accelerated, valleys will be drowned.
      • Impacts; ecosystems- wetlands, saltmarshes ad sand dunes threatened. Coastal squeeze resulting in offshore migration.
      • Impacts- Coastal management- defences need to be larger and more expensive, increased pressure on manmade defences.
    • Managing issues
      • cost-benefit analysis- scheme cost needs to be less than benefits.
      • Technical feasibility- design must be tested
      • Environmental sustainability- sea defences may affect rate of erosion elsewhere.
      • hard of soft engineering- hard= expensive, highest protection level soft= less likely to affect other areas.
      • Consulting shareholders- different people have different opinions.
      • Social justice- for people who are unable to sell their hoes due to blight.
      • Blight- house prices drop ,investor confident plummets
    • Hard engineering
      • Sea wall- concrete wall structure to reflect wave energy.
      • revetments- wooden/ concrete structure to reflect wave energy.
      • Rock armour- large boulders in front of a cliff to reflect and absorb wave energy.
      • gabions- smaller rocks in a steel cage to reflect and absorb wave energy.
      • Cliff drainage- buried pipes to collect and remove water.
      • Offshore breakwater- bags made from rocks to make waves break before they reach the shore.
      • groyne- wooden/ rock breakwater at right angles traps sediment moved by longhorn drift.
    • Soft engineering
      • Beach nourishment- the addition of material to make a beach higher/ deeper.
      • dune regeneration- planting Mariam grass to stabilise dunes, forestation, areas fenced off, preventing people trampling vegetation.
      • Public awareness- alerting people of the risk of erosion.
      • Land use management- the local authority restricting activity in vulnerable areas.
      • Maintaining coastal communities- government policy used to help ensure areas affected remain attractive for people to live/visit.
      • Managed realignment-breaching existing sea walls or shopping maintenance of beaches to let sea water deposit sediment to create salt marshes.
    • Managing human activity
      • recreational use- walkers trample vegetation exposing soil to erosion- footpaths are located away from edge of cliff. Sand dunes stabilised by panting Mariam grass.
      • sediment mining- sand and gravel extracted is used for infrastructure, this can impact the wider sediment cell.
      • Commercial development - areas have been removed to make way for development providing a buffer against erosion and a nursery for fish, also trapping sediment.
      • Coral reef damage- coral reefs absorb wave energy, they are continually being damaged reducing this protection. Marine Protected Areas promote responsible fishing and habitat management only 27% of coral reefs are MPA's.

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