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PowerPoint Presentation Coastal Processes

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PowerPoint Presentation Coastal Processes Powered By Docstoc
					          This Week & Next
• Today
  – Coastal Processes, problems, solutions
  – 7 pm Review Session ES100
• Friday:
  – Midterm #2
              Today‟s Plan
•   Deltas
•   Sea level changes
•   Tides
•   Coastal Features
•   Coastal Problems
•   Coastal Solutions
                 Deltas
• Deltas are a delicate balance of
  aggrading (up) and subsiding (down)
  processes
  – Up: deposition of sediment, accumulation
    of organic material
  – Down: compaction of seds, tectonic
    subsidence (wt of seds), erosion
     Deltas
• Why is there no
  Columbia River
  Delta?
      Why no C.R. Delta?
1. because it is a smaller river than
   the Mississippi thus it does not
   generate the amount of sediment
   that would be needed.
      Why no C.R. Delta?
1. because of the many dams that have
   been built which control the
   sediment flow along with the river,
   so no large amounts of sediments
   are being deposited where the river
   enters the ocean.
     Why no C.R. Delta?
1. ...in the case of the Columbia
   river, the ocean waves and
   powerful currents quickly
   redistribute the material that
   is being deposited so it
   allows for no sediment to
   build up and form a delta
   rather it redistributes it.
                   Deltas
• Deltas are a delicate balance of
  aggrading (up) and subsiding (down)
  processes
  – Up: deposition of sediment, accumulation
    of organic material
  – Down: compaction of seds, tectonic
    subsidence (wt of seds), erosion
    • Effective ‘down’: sea level rise
Which way is
the longshore
  current?
                  Tides
• The Moon‟s gravitational pull causes the
  tides

 (but NOT „tidal‟ waves)

• Note that tides ≠ waves
  – waves are caused by wind
   Coastal Features - erosion
• Sea stacks, arches
  – Linked to wave refraction & headland
    erosion
   Coastal Features - erosion
• Sea stacks, arches
  – Linked to wave refraction
• Wave-cut cliffs, platforms
    Coastal Features - deposition
•   Tombolo
•   Baymouth bar
•   Spits
•   Barrier islands

• Mostly linked to longshore drift
    Coastal Problems - Beach
             erosion
• Depends on many factors. Mainly:
  – How much sand moving down coast?
• [Show aerial photo website]
• 25% of homes within 500 feet of US
  shorelines will be victims of coastal
  erosion in next 60 yrs (FEMA)
    Beach Erosion - solutions
• Shelter the sand from waves
  – Breakwaters
  – Seawalls
• Hold the sand in place
  – Jetties, Groins
  – Plant the dunes
   Beach Erosion - solutions
• Shelter the sand from waves
• Hold the sand in place
• Replenish the sand (“nourishment”)
  – dumping (from elsewhere)
  – pumping (from offshore)
      Beach Erosion - solutions
•   Shelter the sand from waves
•   Hold the sand in place
•   Replenish the sand (“nourishment”)
•   Best: Remove development
    – Your tax & insurance dollars subsidize
      stupid development

				
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