notes - united states coasts & stabilization
TRANSCRIPT
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United States CoastsAtlantic coastPacific coastGulf coast
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1. Atlantic CoastMost coasts open to storm wave attackBarrier islands common from Massachusetts
southBedrock
Florida bedrock is resistant limestone.Northward through New Jersey is comprised of
easily erodable recent deposits.New York through Maine has glacier-affected
rocks.
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Atlantic CoastStrong storms called nor’easters can damage
the coast north of Cape Hatteras, NC.Nor’easters can generate storm waves
up to 6 meters (20 feet).
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Atlantic Coast
Barrier islandsDrowned river
valleys
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2. Gulf CoastLow tidal rangeGenerally low wave energyTectonically subsidingMississippi delta dominates
Locally sea level rises due to compaction of delta sediments
Average rate of erosion is 1.8 meters (6 feet) per year
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3. Pacific CoastTectonically risingExperiencing less erosion than Atlantic
or Gulf coastsOpen exposure to high energy wavesAverage rate of erosion 0.005 meter
(0.016 feet) per year
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StabilizationStructures built to decrease coastal erosion
and interfere with sand movementAlso called armoring of the shoreOften results in unwanted outcomes
Some structures may increase wave erosion
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StabilizationFour major types of stabilization structures:
1. Groins and groin fields2. Jetties3. Breakwaters4. Seawalls
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1. Groins and Groin FieldsBuilt perpendicular to
the beachOften made of rip rap,
or large blocky materialTraps sand upcoast,
which can cause erosion downstream of the longshore current
May necessitate a groin field, or a series of groins built along a beach
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2. JettiesBuilt perpendicular to shoreBuilt in pairsBuilt to protect harbor entrances
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3. BreakwatersBuilt parallel to a shorelineDesigned to protect harbors from wavesCan cause excessive erosion, requiring
dredging to keep area stable
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SeawallsDestructive to
environmentDesigned to armor
coastline and protect human developments
One large storm can remove beach
Wave activity eventually undermines seawall structure; need continual repair or will collapse
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Alternatives to Hard StabilizationThree major alternatives
1. Construction restrictions2. Beach replenishment3. Relocation
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Alternatives to Hard Stabilization1. Construction restrictions
Simplest alternativeLimit building near shorelines
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Alternatives to Hard Stabilization2. Beach replenishment
Sand added to beach/longshore current
Expensive; costs between $5 and $10 per cubic yard
Sand must be dredged from elsewhere.
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Alternatives to hard stabilization
RelocationMove structures rather than protect them in
areas of erosion