Coastlines Active vs. passive margins Population concentration
Seven of 20 largest US cities on or near coastline 53% US
population lives in coastal counties
Sea level changes Eustatic sea level rise caused by Changes in
amount of water in oceans Short-term Changes in shapes and volumes
of oceans Very long term Related to sea floor spreading Climate is
major control Thermal expansion or contraction of water
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Shoreline conditions Emergent Earthquakes and uplift/downdrop
Glacial rebound Area: New England Submergent Higher sea level
Irregular shorelines common Area: Mid-Atlantic area Chesapeake Bay
(VA)
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Very short-term changes Storm surges Changing tides Extreme:
Bay of Fundy, eastern Canada 15 m tidal range twice daily Normal
daily changes (2 high, 2 low)
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Coastal erosion rates
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Note changes based on shoreline type low coastlines most
affected
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Minimizing coastal hazards Hard stabilization Seawalls:
concrete, large blocks Cause more problems than they solve; they
enhance beach erosion
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n n Groins : built perpendicular to shoreline n n Problem is
the area down drift from groin is not fully replenished n n Fix by
beach nourishment
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Chesil Beach on southern coast of England
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Breakwaters Built to protect shoreline by intercepting waves
Jetties Usually pairs of protrusions Note beach modifications
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Soft (beach) Stabilization Moving sand around, usually from
offshore Temporary solution due to dynamics Must be repeated
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Managed retreat solution Prevent building Relocate threatened
buildings
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Miami Beach, FL 24 million cubic yards over 10 years Before
beach nourishmentAfter beach nourishment
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Cape Hatteras lighthouse Built 500 m from waterLater moved 850
m inland