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The Science of Beach Erosion

The Science of Beach Erosion. Lauren Elmegreen ES P Seminar December 1, 2006. Outline. What is natural? Sand Budgets Normal changes How have humans intervened? Changing sources and sinks of sand Case studies Southern California Beaches Ocean City, MD. Sand Budgets.

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The Science of Beach Erosion

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  1. The Science of Beach Erosion Lauren Elmegreen ESP Seminar December 1, 2006

  2. Outline • What is natural? • Sand Budgets • Normal changes • How have humans intervened? • Changing sources and sinks of sand • Case studies • Southern California Beaches • Ocean City, MD

  3. Sand Budgets • Sources: runoff, cliff erosion, onshore transport, longshore transport • Sinks: offshore transport, longshore transport Qc Qoff Qon + Qc + Qon - Qoff Willis and Griggs, 2003

  4. It’s normal for beaches to change! • Sand dissipates the energy from waves • Seasonal changes • Beaches move landward as sea level rises www.coastalchange.ucsd.edu

  5. Unintentional human changes: dams • Dams in California greatly reduce the amount of sand that reaches the beaches from runoff

  6. Average annual Sand and Gravel Flux (m3/year) Willis and Griggs, 2003

  7. Intentional human changes • Seawalls and breakwaters • Jetties/groins • Beach nourishment www.coastalchange.ucsd.edu

  8. Sea Walls • Reduce the amount of wave energy that reaches cliffs/dunes • Can cause more beach loss • Can cause more cliff destruction www.soest.hawaii.edu/SEAGRANT/CEaBLiH.html

  9. Jetties/Groins • Designed to prevent sand loss from longshore currents • Result: accumulation of sand on one side, erosion on the other www.vsv.cape.com/~harharb/allenbeachnourishment2005.html

  10. Beach Nourishment • Makes beaches wider • Not a natural state, not necessarily sustainable, but good for tourism Flick, 1993

  11. Case Study: Ocean City, MD • Jetties were built to protect the inlet • The Northern part of Fenwick island is moving landward, leaving Ocean City behind • Assateague Island is rapidly moving landward- reduced sand supply http://www.mgs.md.gov/coastal/osr/ocsand2.html

  12. Conclusions • Beaches erode through weather processes, sea level rise, and human actions • Erosion is bad for tourism and buildings near the shore, so actions are taken to prevent erosion • Some of these actions can cause even more erosion in the long run

  13. References • Flick, RE (1993) The Myth and Reality of Southern California Beaches. Shore and Beach: 61 (3), 3-13. • Pinet, PR (2003) Invitation to Oceanography, 3rd ed., Sudbury, MA: Jones and Bartlett. • Willis, CM and GB Griggs (2003) Reductions in Fluvial Sediment Discharge by Coastal Dams in California and Implications for Beach Sustainability: 111, 167-182. • http://www.soest.hawaii.edu/SEAGRANT/CEaBLiH.html • http://coastalchange.ucsd.edu/index.html • http://www.vsv.cape.com/~harharb/allenbeachnourishment2005.html • http://www.mgs.md.gov/coastal/osr/ocsand2.html

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