12.2 Types of Coasts
Chapter 12 Coasts, Beaches, and Estuaries
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Primary coasts
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Effect of ice ages
Effect of sediment carried by rivers
Effect of wind
Effect of volcanic activity
Effect of tectonic activity
Secondary coasts
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Erosion due to wave activity
Barrier islands
Coral atolls and reef coasts
Mangrove swamps and salt marshes
Time scales, natural forces (waves, tides, winds, storms, sediment
supply etc.), anthropogenic forces (nourishment, armoring,
dredging etc.)
Fig. 12.4
Barrier Island
•Barrier chains are aligned parallel
to the coast
•Most have formed in a regime of
slow eustatic sea-level rise
•They are separated from the
mainland by shallow lagoons,
marshes, and/or tidal flats
•Tidal inlets separate individual
barriers along a chain
•They are composed mainly of sand
•They formed during periods of
sand abundance
NOTES
NY: Glacial Deposit, reworked by wave activity
Coastlines are influenced by hydrodynamic forces
(waves, tides (currents), rivers, changing sea levels)
Longshore Transport of Sand
Barrier and Spit Formation
Beach Dynamics:
Summer: gentler waves move sand shoreward
Winter: large storm waves remove sand to offshore bars
•Coastline changes can be
gradual.
•Barrier island rollover at
Assateague Island
Coastline changes will be enhanced as sea level rise accelerates
New York City Panel on Climate Change, 2009
1 Based on 16 GCMs (7 GCMs for sea level rise) and 3 emissions scenarios. Baseline is 1971-2000 for temperature and precipitation and 2000-2004 for sea level rise.
Data from National Weather Service (NWS) and National Oceanic and Atmospheric Administration (NOAA). STET and sea level data is from the Battery at the
southern tip of Manhattan (the only location in NYC for which comprehensive historic sea level rise data are available).
2 Central range = middle 67% of values from model-based probabilities; temperatures ranges are rounded to the nearest half-degree, precipitation to the nearest 5%, and
sea level rise to the nearest inch.
3 The model-based sea level rise projections may represent the range of possible outcomes less completely than the temperature and precipitation projections. See page
18 for more information.
4 “Rapid ice-melt scenario” is based on acceleration of recent rates of ice melt in the Greenland and West Antarctic Ice sheets and paleoclimate studies.
Influence of Storms
Influence of Sea Level Rise
Barrier Island Breaching
Inundation
9 ft
Shinnecock Inlet, 1938
15 ft
Coastlines are influenced by vegetation
•Coastal wetlands occupy 27
million acres.
•Four times more productive
than the most productive
farmland.
•80 percent of commercial fish
are dependent on food chains
which can be traced back to
these coastal environments
Coastal Wetland: vegetated intertidal environment
Global Distribution of Coastal Wetlands
Mangroves can not survive in freezing temperatures
Coral Reefs
Estuaries: where the ocean meets fresh water
Types:
Drowned River Mouths
Fjords
Bar-Built
Tectonic
oEstuary characteristics are influenced by water
density and flow
oEstuaries support complex marine communities
Shoreline Erosion: Methods for maintaining coastline stability
•Hard solutions: groins, seawalls
•Soft solutions: nourishment, geotubes
Anthropogenic Influence
Tidal Inlet Formation
Barrier Island Breaching
Pikes Inlet, 1992