Wave Dominated Coasts

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Wave Dominated Coasts
Objective to examine some of the processes and
characteristics active on a wave-dominated coast
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Weathering Erosion
What is? Weathering Breakdown of rock (Geology)
to form sediment in situ Weathering is a set of
physical, chemical and biological processes that
alter the physical and chemical state of rocks
and soil at or near the earth's surface. Rock and
soil is altered physically by disintegrating and
chemically by decomposing. Nearly all weathering
involves water, mostly directly frost
shattering, wetting and drying, salt weathering,
and all chemical weathering is in solution. That
is, weathering is climatically driven and thus
the term weathering. Because weather and climate
occur at the earth's surface, the intensity of
weathering decreases with depth and most of it
occur within less than a metre of the surface of
soil and rock. ErosionTransport of weathered
material from one location to another...The
wearing away of land or the removal of beach
and/or dune sediments by wave action, tidal
currents, wave currents, drainage, or wind.
Erosion includes, but is not limited to,
horizontal recession and scour and can be induced
or aggravated by human activities.
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Wave Dominated Coasts

• Coasts are exposed to the elements
• Open to the sea
• Little shelter from waves
• Waves erode the coastline
• Waves move rocks/sediment
• Wave energy

Erosion Sediment Transport
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Wave Energy

• Wave Energy is typically HIGH
• Cliff erosion, formation, maintenance,
  remobilisation of sediments
• Fine sediments generally absent
• Depositional areas include sands, shingles -
  beach forms
• Longshore currents (action of waves) leads to
  movement of sediment

Q. What happens when wave energy is low?
A. Refashion beach profile
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Waves

• Constructive or Destructive
• Accretion versus Removal
• Seasonal
• Waves are generated by wind, gravity (tides) and?
• Waves classified into capillary waves, gravity
  waves (wind), infra-gravity waves (interaction),
  long-period waves (tidal)
• Wave form moves not the water
• Depth of water shallows closer to the coast,
  causing waves to break at the surf line -
  frictional drag causing top of wave to break over
  bottom
• Point at which wave touches bottom leads to
  sediment pick up and transfer
• Calm versus storm conditions

Seismic activity
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Waves

• Angle of wave approach to coast leads to
  refraction
• Bays and Headlands - hard versus soft rock -
  differential erosion
• More erosive power on headlands than bays or
  embayments
• Spatial wave gradients due to differential wave
  activity lead to development of longshore
  currents and sediment movement
• Development of edge waves (secondary waves) can
  amplify the impact of waves at the coast rather
  than usual dissipation of energy

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Wave Refraction
refracted wave fronts
reduced wave energy in embayment
concentrated wave energy on headland
concentrated wave energy on headland
parallel wave fronts
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Beaches

• Beaches often refashioned rather than removed on
  high energy coast
• Beaches tend to dissipate energy - natural
  coastal defence
• Depends on materials making up the beach
• Water running up a beach will return by
  throughflow or surface flow (dependent on
  materials) determining sediment removal/transport
• Beaches and dunes are sediment stores
• Wave approach angle Swash and Backwash
• Sediment moved up, down and along the shore
• Shore parallel, nomal and rip currents
• Circulation cells formed leading to cusps

BEACH
BACKWASH
SWASH
Longshore Drift
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Cliff Erosion
Cliff Face

• Geology
• Type
• Strength
• Hardness
• Structure
• Strata (dip, permeability)

SedimentMovement
Cliff Profile
Wave
Cutback
Sediment Accumulation/Loss
Shore Platform
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Remote Sensing, Monitoring, Mapping and Coastal
Erosion
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Task Worksheet No. 2
Visualisation

• http//www.coastal.udel.edu/faculty/rad/linearplot
  .html

Input Wave Data, Examine the Output and Tabulate
to see if you can find out what this model does
and any relationships/patterns that exist