Notes - United States Coasts & Stabilization


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Notes - United States Coasts & Stabilization

  1. 1. United States Coasts Atlantic coast Pacific coast Gulf coast© 2011 Pearson Education, Inc.
  2. 2. 1. Atlantic Coast Most coasts open to storm wave attack Barrier islands common from Massachusetts south Bedrock Florida bedrock is resistant limestone. Northward through New Jersey is comprised of easilyerodable recent deposits. New York through Maine has glacier-affected rocks.© 2011 Pearson Education, Inc.
  3. 3. Atlantic Coast Strong storms called nor’easters can damage the coastnorth of Cape Hatteras, NC. Nor’easters can generate storm wavesup to 6 meters (20 feet).© 2011 Pearson Education, Inc.
  4. 4. Atlantic Coast Barrier islands Drowned rivervalleys© 2011 Pearson Education, Inc.
  5. 5. 2. Gulf Coast Low tidal range Generally low wave energy Tectonically subsiding Mississippi delta dominates Locally sea level rises due to compaction of deltasediments Average rate of erosion is 1.8 meters(6 feet) per year© 2011 Pearson Education, Inc.
  6. 6. 3. Pacific Coast Tectonically rising Experiencing less erosion than Atlantic or Gulfcoasts Open exposure to high energy waves Average rate of erosion 0.005 meter(0.016 feet) per year© 2011 Pearson Education, Inc.
  7. 7. Stabilization Structures built to decrease coastal erosion andinterfere with sand movement Also called armoring of the shore Often results in unwanted outcomes Some structures may increase wave erosion© 2011 Pearson Education, Inc.
  8. 8. Stabilization Four major types of stabilization structures:1. Groins and groin fields2. Jetties3. Breakwaters4. Seawalls© 2011 Pearson Education, Inc.
  9. 9. 1. Groins and Groin Fields Built perpendicular tothe beach Often made of rip rap, orlarge blocky material Traps sand upcoast,which can cause erosiondownstream of thelongshore current May necessitate a groinfield, or a series of groinsbuilt along a beach© 2011 Pearson Education, Inc.
  10. 10. 2. Jetties Built perpendicular to shore Built in pairs Built to protect harbor entrances© 2011 Pearson Education, Inc.
  11. 11. 3. Breakwaters Built parallel to a shoreline Designed to protect harbors from waves Can cause excessive erosion, requiring dredging tokeep area stable© 2011 Pearson Education, Inc.
  12. 12. Seawalls Destructive to environment Designed to armor coastlineand protect humandevelopments One large storm can removebeach Wave activity eventuallyundermines seawallstructure; need continualrepair or will collapse© 2011 Pearson Education, Inc.
  13. 13. Alternatives to Hard StabilizationThree major alternatives1. Construction restrictions2. Beach replenishment3. Relocation© 2011 Pearson Education, Inc.
  14. 14. Alternatives to Hard Stabilization1. Construction restrictions Simplest alternative Limit building near shorelines© 2011 Pearson Education, Inc.
  15. 15. Alternatives to Hard Stabilization2. Beach replenishment Sand added to beach/longshore current Expensive; costs between $5 and $10 percubic yard Sand must be dredged from elsewhere.© 2011 Pearson Education, Inc.
  16. 16. Alternatives to hard stabilization Relocation Move structures rather than protect them in areasof erosion© 2011 Pearson Education, Inc.