Impact of Sea Level Changes on Barrier Islands
We’re all
going to die!
The Myth of Sea Level Rise and Global
Warming
“Even if the polar ice caps melted, there would be no rise in ocean
levels... After all, if you have a glass of water with ice cubes in it, as
the ice melts, it simply turns to liquid and the water level in the glass
remains the same."
The Reality of Sea Level Rise and Global
Warming
Excellent theory...... The only problem is Antarctica is a
CONTINENT with large quantities of ice on top of it.
When the ice melts, new water will enter the ocean.
The History of Sea Level Rise
• Throughout history, sea level is constantly
rising and falling because of the glacial and
interglacial periods
• Currently we are in a state of sea level rise
History cont’d...
• Major changes in Quaternary period
• In the past 20,000 the sea level has oscillated 130m
• Since human occupation of coasts, sea level has
risen less than 3 m
Recently
• Recently on the coasts we are seeing a general
rise in sea level of 3-4mm/yr
• Mississippi delta region is seeing a 9mm/yr
rise resulting in 40 acres land lost/month
Sea level is never a constant over space and time
Variations in sea level may be local or regional:
1) Atmospheric pressure and winds
2) Freshwater discharge from rivers
3) Ocean Currents
4) Geophysical conditions
The Pacific Ocean is approximately 1 meter higher than the
Atlantic Ocean
Sea level rise is also never consistent
and not accurate because it is
measured by tide gage data. This
date is not evenly distributed, it is
measured near population centers
where the data is skewed
Causes for Sea Level Rise
• Tectonic Activity
• Subsidence
• Isostacy
• Eustatic
Plate Tectonics
• Upheaval and subsidence of plates
• May be local or regional and may be sudden or gradual
• Volcanic eruptions and faulting
Subsidence
Withdraw of fluids from pore space
in the sediment which therefore
causes it to collapse
Subsidence
• Local rise in sea level based of fluid removal and compaction
• Construction of oil wells and drainage of aquifers
• Construction of high rises and discharge of sediment loads in
the Mississippi Valley Delta (ie. New Orleans)
• 6-7 mm of the 9-10mm/yr rise in Mississippi delta is dues to
subsidence
Isostacy
Equilibrium condition of the
earth’s crust due to balancing
In other words...
• Looking at the earth’s surface and the forces on it
• Some forces want to push up (elevate the
lithosphere) while some want to push down (depress
the lithosphere)
Isostacy
• Volume of water remains the same, land
rises or falls because of weight of ice sheet
• Glacial compaction and rebound Weight of glaciers on plates depress the
the lithosphere 100’s m forming a
peripheral bulge
Isostacy cont’d
• Subsequent melting of glaciers cause the land to
rebound
• Causes bulge to move back to original shape
1)
3)
2)
4)
Eustatic
Global change in sea level based on
changes of the volume/density of water.
The relative position of land does not
change
Eustatic cont’d
• Related to the climate and the shape changes in
the holding capacity of the oceans basins
1) Melting of polar ice caps
2) Thermal expansion of the oceans
(biggest factor)
With an average water column of
3000 m and a basin that stays the
same, the sea level could rise by 60
cm for every degree of warming
What causes thermal expansion?
• Global warming which is caused by the
introduction of CO2 into the atmosphere
• Estimates indicate an increase in greenhouse
gases, temperature and sea level rise. Predict
a temperature rise of 1.5C to 4.5C for CO2
alone and as much as 3-9C for all gases.
Why do we care?
•Shoreline Retreat
•Flooding
•Saltwater Intrusion
Shoreline Retreat
For every unit of sea level rise, the high water mark
increases by 1000x that distance
80% of the population of the United States lives within
100 miles of the coast
The Bruun Rule. Beaches follow a characteristic profile shape based on the wave climate
and the types of sediments. When sea level rises, the initial effect is inundation; but
eventually enough material will be deposited offshore to re-establish the profile at the
higher elevation. Thus, the shore retreat will be based on the slope of the entire beach
profile, which is usually flatter than the slope just above the shore.
Flooding
1) Because of the effects of sea level rise, a one meter rise in
sea level will allow 15-year storm to flood areas that would
only previously be flooded by a 100-year storm
2) Beach erosion would leave coastal infrastruction more
vulnerable to storm waves
3) Coastal drainage would be reduced, increasing the
impacts of coastal rainstorms
4) Finally, a rise in sea level would raise water tables
Saltwater Intrusion
1) Increased sea level would allow further penetration of
saltwater up rivers, bays, estuaries and aquifers
2) This would harm plants and animals not adapted to salt
or brackish waters
3) Contamination of aquifers would threaten human uses of
potable waters
Possible Impacts of Sea Level Rise for the
Atlantic Coast
Responses to Sea Level Rise
1) Protection by hard structures and coastal
armoring
2) Strategic Retreat
3) Beach Renourishment
4) Elevating Roads and Structures
Bulkheads and Levees
Expensive process that can cost between $130-$500 per linear
foot
Wave action into bulkhead projects energy downward,
actually increasing erosion seaward of the bulkhead
Bulkhead and other hard structures are illegal in some states
Sea Bright, New Jersey
Strategic Retreat
Relocation of property away from eroding beach
Paul Foster’s house on Figure 8 island, approximately $25,000
to relocate a house.
Price may seem high, but it protects investments of millions of
dollars
Not all houses can be moved
Amount of relocation space is finite, erosion may still destroy
the house
Beach Renourishment
Relocation and addition of beach quality sand from source
destination to eroding beach
Beach renourishment projects have the potential to be very
costly (~$3-$4 a cubic yard)
Beach renourishment is not permanent and will require
additional renourishment within a couple of years.
Before
After
Elevation of Roads and Houses
Extremely expensive alternative that will not stop the rise of
sea level.
Was used in Galveston, TX at the turn of the century, as a
response to hurricane flood damage.
Estimated Cost of Coastal Protection in the
United States
270-475 billion dollars
Remember......
We’re all
going to die!
http://www.epa.gov/globalwarming/publications/impacts/sealevel/barrier_islands.html
http://www.erols.com/jtitus/Holding/NRJ.html
http://www.nap.edu/books/0309037816/html/40.html
http://www.greenpeace.org/~climate/arctic99//reports/seachange.html
http://www.uncwil.edu/people/hosier/CMGMT/SeaLevel.htm
http://www.edf.org/programs/GRAP/hotny/
Rising Seas, Coastal Erosion, and the Takings Clause: How to Save Wetlands and Beaches Without Hurting Property Owners
– Maryland Law Review, Volume 57, 1279-1399 (1998).
The Risk of Sea Level Rise: A Delphic Monte Carlo Analysis in which Twenty Researchers Specify Subjective Probability Distributions for Model
Coefficients within their Respective Areas of Expertise
– Climatic Change, 33: 151-212 (1996).
The Probability of Sea Level Rise
– U.S. Environmental Protection Agency, #EPA 230-R-95-008 (1995).