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Coastal Regions and Land Loss. Chapter 10. Morris Island Lighthouse, SC. Coastlines. Active vs. passive margins Population concentration Seven of 20 largest US cities on or near coastline 53% US population lives in coastal counties. Deep-water wave form (water depth > 0.5L).

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Active vs. passive margins

Population concentration

  • Seven of 20 largest US cities on or near coastline
  • 53% US population lives in coastal counties
factors controlling waves

Factors controlling waves

Wind speed



sea level changes
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
shoreline conditions
Shoreline conditions


  • Earthquakes and uplift/downdrop
  • Glacial rebound
  • Area: New England


  • Higher sea level
  • Irregular shorelines common
  • Area: Mid-Atlantic area – Chesapeake Bay (VA)
very short term changes
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)
minimizing coastal hazards
Minimizing coastal hazards

Hard stabilization

Seawalls: concrete, large blocks

Cause more problems than they solve; they enhance beach erosion

Groins: built perpendicular to shoreline

Problem is the area down drift from groin is not fully replenished

Fix by beach nourishment


Built to protect shoreline by intercepting waves


Usually pairs of protrusions

Note beach modifications

soft beach stabilization
Soft (beach) Stabilization

Moving sand around, usually from offshore

Temporary solution due to dynamics

Must be repeated

managed retreat solution
Managed “retreat” solution

Prevent building

Relocate threatened buildings

miami beach fl 24 million cubic yards over 10 years
Miami Beach, FL24 million cubic yards over 10 years

Before beach nourishment

After beach nourishment

cape hatteras lighthouse
Cape Hatteras lighthouse

Built 500 m from water

Later moved 850 m inland