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Class 30 -- The Oceans

Class 30 -- The Oceans. BEACH PROCESSES Transport of sediments along shorelines Human intervention in beach processes. Wave fronts and onshore "swash" -- oblique to beach front "Backswash" perpendicular to beach front. Net Result: Longshore transport,

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Class 30 -- The Oceans

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  1. Class 30 -- The Oceans BEACH PROCESSES Transport of sediments along shorelines Human intervention in beach processes

  2. Wave fronts and onshore "swash" -- oblique to beach front "Backswash" perpendicular to beach front

  3. Net Result: Longshore transport, • Water and sediment move parallel to the beach front

  4. Longshore transport • It’s strength depends on wave energy… • Sediment moves rapidly in areas of greater wave energy • Sediment dropped where wave energy is lesser

  5. Erosion occurs in areas of strong wave action (headlands) • Longshore transport tends to be away from headlands and toward quieter areas

  6. Both sediment and water converge in recessed areas • Sediment collects there (beaches) • Water turns back seaward • Rip currents move water offshore

  7. BEACH PROCESSES -- Natural • Beach = temporary accumulation of sediments • Seds come from rivers, headland erosion • Beach dynamics -- continuous sediment movement due to waves and longshore currents.

  8. BEACH PROCESSES -- Natural • Most beaches constantly gain and lose sediment • The budget can have a surplus or a deficit

  9. Human Impact On Beach/coastal Processes • (1) Dams on rivers • Reduce sediment input to coasts; beaches become “sediment starved” • Longshore transport continues carrying seds • Beaches are eroded

  10. Human Impact On Beach/coastal Processes • (2) "Groins" to minimize loss of beach sand • Upwind side: deposition • Downwind side: erosion; beaches starved of their sediment supply

  11. (3) Breakwaters to protect harbors • Reduce wave energy --> deposition in harbor • Need frequent dredging • Erosion of downwind beaches- sediment supply cut off

  12. Beach dynamics • 2 Common themes: • Sediment transport links all beaches, sediment sources, and sediment traps on a coastline • Intervention to address a single demand of society often leads to a chain of unforeseen consequences due to erosion or deposition.

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