The Science of Beach Erosion

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
Its 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

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Average annual Sand and Gravel Flux (m3/year)
Willis and Griggs, 2003
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Intentional human changes

• Seawalls and breakwaters
• Jetties/groins
• Beach nourishment

www.coastalchange.ucsd.edu
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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/allenbeachnourishment200
5.html
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Beach Nourishment

• Makes beaches wider
• Not a natural state, not necessarily sustainable,
  but good for tourism

Flick, 1993
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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
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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/allenbeachnourish
  ment2005.html
• http//www.mgs.md.gov/coastal/osr/ocsand2.html