Coastal Geomorphology

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Coastal geomophology

coast are not perminant in the landscape they can quickly change due to erosion. the location of the coast is dependant on the tectonic activity in the area and the tides and water level. the shape of the coast is also changed over time and is influenced by many processess such as the geology of the coast and the temperature of the area that they are found in.

the coastal zone boundaries where established by Masselink and Hughes in 2003.

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coastal importance

the coast is important for a varity of factors as it is arguuable the most used of all the habitats. 40% of the global population live within 100km of the coast. a CCSR report predicted that between 1995 and 2025 there will be an increase of 35% in the amount of people living within 60 miles of the sea, further more 75% of the global population will live in coastal locations.

the predicted change in teh demographic is important as it allows the goverenment to plan for the increased use of water, energy and waste production  in coastal areas. however sea level rise makes this hard to do as we don't know the extent that it will effect us.

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waves

waves are created by the transfer of energy from wind blowing over the sea. the exeption to this is tsunamis that are casued by tectonic events that happen under water or landslides into the sea. the size of waves is affected by the strength of the wind that caused them - the stronger the wave the bigger the wave. 

waves created by local wind are known as sea waves, where as waves created by distant storms are swell waves.

there are lots of terminology related to waves such as:

  • Wavelength, trough, crest, still water mark
  • velocity C - movement of crest given time, height H - crest to trough generally 6m max., period T - tiem between two waves, length L - distance between sucseive crests
  • energy E - mean 11 tonnes/m2, and steepness H/L - cannot exceed 1.7-0.14
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waves continued

there are  different types of wave:

  • spilling (constructive)
  • surging (constructive)
  • plunging (destructive)

deep water waves have a different shape to shallow water waves:

  • deep water waves are orbital/sinusoidal symmetrical hence a smooth repetitive oscillation
  • shallow water waves are elliptical, asymmetrical

shallow processes of waves:

  • breaking
  • plunge line (depth and height approx. equal)
  • swash
  • backwash
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currents near the shore

these current cause large scale movement of sediments. there are different types of currents

  • longshore - wind direction, wave angle, refractions, coastal orientation = longshore transportation
  • cross shore - up and down beach are very important in beach erosion
  • undertow - average flow near the bed offshore
  • rip tides - strong narrow currents that flow seawards stronger at low tides
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tides

tides are the product of the gravitational forces of the sun and moon. spring tides are the biggest tides and neep tides are the smallest.

tidal ranges are spilt into 3 different catergies:

  • micro - >2m
  • mesa - 2-4m
  • macro - <4m

amphidromes:

  • tidal systems due to topography
  • tides rise around them
  • tidal currents - ebb and flood vary in strength and duration
  • tides rise from the amphidrome waves
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tsunami

tsunamis are waves caused by a big displacement of water in the ocean. there are 2 causes:

  • submarine earthquake - 2004 Sumatra, 100000 dead, habitat destruction
  • landslide into ocean - 1883 Krakatoa, 36000 dead, habitats changed

in the open ocean they have a long wave length that typically spreads at 700km/hour at depths of 5km. when they reach the coastal shelf they shoal and reduce wavelength, but increase height. finally when they reach the shore they grow to tens of metres high, devastation in a short period of time.

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beach type

·         Described between wide and flat to narrow and steep

·         Waves dominated or tide dominated beaches

·         Wet sand reduces percolation:

  • Therefore, limited energy loss (most of the energy returns in backwash)
  • Creates a longshore bar at low tide (hence waves break further from the shore – energy dissipation)
  • If sand dries in prevailing winds sand dunes form beyond the backshore

·         Dynamic between waves, sediment, and beach profile. Generally:

  • Destructive waves move material seawards
  • Constructive waves move material landwards
  • Shingle beach move material landwards
  • Sand move material seawards
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sediment size

the sediments on a beach are sorted by size by the sea. this is due to the fact that the larger sediments cannot be carried as far down the beach so they are depositied first. this results in sorted material at the beach with the larger sediments at the back and the smaller sediments at the front.

  •  beach gradient is normally relative to sediment size (large=steep, small=shallow)
  • rate of percolation reduces backwash = steepness
  • forms a berm at spring HT standline
  • storm beach at the back of large material
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erosion

the loss of land through erosion at the coast is because of the wave action and slope process (coastal cliffs). the different types of ersoion are:

  • hydralic action - when waves hit the cliff the force air in cracks to compress putting more pressure on the cracks causing them to break
  • abrasion - sediments and small rocks in the water hit against the cliff breaking it down
  • attrition - sediments hitting each other and slowly getting smaller
  • corrosion - chemical reactions on rocks usually happens on linestone
  • wave pounding - waves hitting the cliff
  • sub aerial - from above the water e.g. freeze thaw
  • athropogenic - human factor affecting coasts

erosional landfroms

  • headlands and bays
  • wave-cut notch and wave-cut platforms
  • caves, geos, arches, stacks and sumps
  • blowholes
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