Let’s Study Coastlines!
Wave - a moving, periodic undulation of a medium (air, water, rock, etc.)
-   Crest     Trough      Wave Height    Wavelength  
 
 
 
 

Wave interaction with shorelines -- Waves slow down as the water shallows
 
 
 
 

Breaking Waves (Breakers) - a wave tripping over its own two feet.  Front end slows down and....
 
 
 

Wave Refraction - bending of the path of a wave.
(one part of wave is slower than the rest of it)

 - Waves curve in toward the beach.
 
 
 
 

Longshore Drift - current and sediment transported along a shoreline due to waves approaching the beach at an angle.
 

Deposition along the Shoreline:
- Beaches - loose, unconsolidated sediment concentrated at the shoreline

- Deltas - sediments dumped at a river mouth (like the Mississippi River)

- Barrier Islands - long, low islands parallel to the shoreline (most of them have nice Beaches)
 
- Estuaries - bays (shoreline indentations) with brackish water (some riverine input)
 
- Spits - beach extending out across a bay by the action of longshore drift.  Ex. Cape Cod, Mass.  See examples in the book.
 

Depositional vs. Erosional Coastlines: Some beaches are eroding, some are growing....
 

  • local supply of sediment = _________________ Coast.

    •  
  • rapid subsidence = ___________________ Coast.

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  • rising global sea level = ____________________ Coasts in many areas.

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  • northern coastlines rebounding from melting glaciers = _________________ Coasts.

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    Erosion of the Shoreline:
    - Rates of Erosion: cm/yr to 10's of meters/yr
    - Hurricanes: winds >75 mph.  Big storms cause most of the coastal erosion, not the everyday waves and currents.
    - Storm Surge: a rise of local sea level caused by strong onshore winds and lowered barometric pressure.  May be 2-5 meters of sea level rise associated with hurricanes.
     

    Case Study: Ocean City, Maryland 

     Longshore drift sediment: 150,000 m3/year
     
     
     
     
     
     
     

    1933 Hurricane broke through Fenwick, Assateague Island, just south of Ocean City.

    1935: Jetties constructed to keep the inlet open, halting longshore drift to the south.
    1962: Winter storm: Storm surge (2m) plus waves = $7.5mm damages
    1996:  Development moving northward into less protected areas.  Dunes removed.  Rapid erosion.
    1935-1996: Assateague Island retreating (eroding) at 11m/year.