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Overview

P. Overview. Coastal region constantly changes Primarily due to waves Erosion Deposition Many people live in coastal regions 80% of people in U.S. live within easy access of coast. P. Coastal Processes. Wave Refraction and the Longshore Current Convergence and Divergence of Wave Energy

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Overview

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  1. P Overview • Coastal region constantly changes • Primarily due to waves • Erosion • Deposition • Many people live in coastal regions • 80% of people in U.S. live within easy access of coast

  2. P Coastal Processes • Wave Refraction and the Longshore Current • Convergence and Divergence of Wave Energy • Sediment Cells • Sediment Budget • Grain Size and Beach Slope

  3. S Fig. 10-1

  4. P Fig. 10.3b

  5. P Composition of beaches • Locally available material • May be coarse or fine • Boulders from local cliffs • Sand from rivers • Mud from rivers • Significant biologic material at tropical beaches • Example, Coral reef material

  6. Longshore current P • Wave refraction causes water and sand to move parallel to shore • Zigzag motion in surf zone • Longshore current • Longshore transport

  7. S Longshore transport • Millions of tons of sediment moved yearly • Direction of transport changes due to wave approach • In general, sediment transported southward along Atlantic and Pacific coasts of U.S.

  8. S Wave Refraction

  9. S

  10. P

  11. S Convergence Divergence

  12. S Lower energy, sand settles out

  13. Beach compartments P • Rivers supply sediment • Beach • Offshore submarine canyons “drain” sediments from beach

  14. P

  15. P Fig. 10.12

  16. S

  17. P

  18. S

  19. S Winter Summer

  20. 10_02a S Summer

  21. 10_02b S Winter

  22. 10_Ar S

  23. 10_26Al P

  24. Changing sea level P • Local tectonic processes • Example, Pacific Coast of U.S. and active plate margin • Isostatic adjustments • Ice-loading • Global (eustatic) changes in sea level • Changes in sea floor spreading rates • Lake buildup or destruction • Ice volume changes

  25. P Eustatic changes in sea level • Ice build up (glaciation) • Ice melting (deglaciation) • Thermal contraction and expansion of • seawater • About 120 m (400 ft) change in sea level

  26. P Fig. 10.15

  27. P Global warming and changing sea level • About 0.6oC (1.1oF) warmer over last 130 years • Sea level rose 10-15 cm (4-10 in) over past 100 years • If global warming continues, higher sea level Fig. 10.15

  28. P .37 cm/yr or 7.5” in 50 years .25 cm/yr or 5” in 50 years

  29. S Alternatives to hard stabilization • Construction restrictions • Limit building near shorelines • National Flood Insurance Program encouraged construction • Beach replenishment • Sand added to beach/longshore current

  30. Alternatives to hard stabilization S • Relocation • Move structures rather than protect them in areas of erosion Fig. 10B

  31. Portrait of a Coast Video • Repeated coastal damage • Once every 4 years on average • Seawall rebuilt once every 2 years on average • Rising sea level (1 foot/ 100 years) • Seasonal changes in beaches • Buildings and other man-made structures restrict beach mobility

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