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Waves, Beaches and Coastal Erosion

Waves, Beaches and Coastal Erosion. 1. Tidal forces associated with Moon. Tidal forces associated with Sun and Moon. High tide stays aligned with moon but Earth rotates, yielding 2 high and 2 low tides each day. Tidal forces associated with Sun and Moon.

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Waves, Beaches and Coastal Erosion

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  1. Waves, Beaches and Coastal Erosion

  2. 1 Tidal forces associated with Moon

  3. Tidal forces associated with Sun and Moon High tide stays aligned with moon but Earth rotates, yielding 2 high and 2 low tides each day.

  4. Tidal forces associated with Sun and Moon Neap tides: Sun and Moon tides are out of phase Spring tides: Two tides are in phase-- High tide will be higher than usual Tides are cyclical floods

  5. Tidal Ranges Are Highly Variable: Bay of Fundy--17 m!

  6. Tidal Ranges influenced by local conditions and bathymetry Bays tend to focus the water and create larger ranges Organisms are stratified based on tidal zone

  7. Mean sea level is the average height of the sea… Relative to what? When? High or low tide? Measured with tide gauges 2) Sea Level: What and When?

  8. Sea Level: Changes through time

  9. Eustatic Sea Level Changes “Eustatic” refers to changes related to amount of water in the oceans

  10. 3) Tidal Flats: exposed mud at low tide

  11. 4) Waves and Sediment Transport

  12. Wave Velocity-Deep Water

  13. Wave Energy Doubling wave height quadruples energy: Ew = 0.125rgH2L where: Ew = energy of wave r = water density (g/cm3; close to 1) g = acceleration of gravity (9.8 m/sec2) H = wave height (m) L = wavelength (m)

  14. Passive continental margin Submarine canyons Deep-sea fan Coastal plain Abyssal plain Continental shelf Continental slope Continental crust Oceanic crust Mantle Continental rise

  15. 5) Waves approaching the shore at an angle cause a longshore current. Path of sand particles Rip current Path of water particles Longshore current Longshore drift results from movement of sand particles by swash and backwash.

  16. The beach is a “river of sand” Sand will move in this direction

  17. 6)Headlands receive strong wave energy-leads toerosion

  18. 7) Rip Currents

  19. 7) Rip Currents

  20. 8) Sand Supply/Loss

  21. 8) Sand Supply/Loss

  22. Offshore sand bars migrate to beach during summer Winter storms remove beach sand to deeper water Hurricanes result in summer beach sand loss 8) Sand Supply/Loss

  23. 8) Sand Supply/Loss

  24. Engineered Beach Protection Structures

  25. 9) Erosion of Gently Sloping Coasts and Barrier Islands

  26. Beach migrated 400 m in 60 years

  27. Barrier Islands are Geologically Temporary

  28. Chandeleur Islands Before (above) and after (below) Hurricane Katrina

  29. Headlands erode from wave action Creates caves, arches, sea stacks 10) Sea Cliff Erosion

  30. Sea Cave

  31. Arches

  32. Sea Stacks

  33. Sea Stacks

  34. Sea Stacks

  35. Sea Cliff Erosion

  36. Coastal Erosion

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