Waves, Currents, and Coastlines

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Waves, Currents, and Coastlines

• Chapter 10

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Morris Island Lighthouse, SC
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Coastlines

• Active vs. passive margins
• Population concentration
• Seven of 20 largest US cities on or near
  coastline
• 53 US population lives in coastal counties

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Deep-water wave form (water depth gt 0.5L)
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Water particle motion
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Factors controlling waves

• Wind speed
• Duration
• Fetch

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Plunging breakers
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Spilling breakers
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Coastal erosion along beach at Santa Barbara, CA
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Longshore drift and transport
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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 typelow
coastlines most affected
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Shifting barrier island
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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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• Groins built perpendicular to shoreline
• Problem is the area down drift from groin is not
  fully replenished
• Fix by beach nourishment

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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, FL24 million cubic yards over 10
years

• Before beach nourishment

• After beach nourishment

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Cape Hatteras lighthouse

• Built 500 m from water

• Later moved 850 m inland