Download Introduction - Coastal Climate Wiki

The Coast to Come
Coastal Erosion, Storm Surges,
and Flooding
Accelerated Erosion
 As oceans rise, the pounding of waves and storm surge
will almost certainly cause barrier islands, bluffs, and
spits to erode more quickly. The result will be land loss.
 Erosion, of course, is a natural process that has been
driven by relatively slow rates of sea-level rise over the
last thousands of years.
 However, historically unprecedented future sea-level rise
will accelerate the processes of erosion.
 Higher storm surges and waves can more easily
overwash barrier islands and breach them, damaging
highways, homes, and potentially forming new inlets
across entire barriers.
Coastal Floods
 Higher sea levels also mean storm surges will more
easily reach low-lying areas.
 Scientists have already observed that low-lying regions
are flooding more often during storm surges and spring
tides as a result of 20th century sea-level rise.
 More intense rainfall from hurricanes and other storms
(which is predicted as a consequence of climate change)
could further increase the risk for coastal flooding.
 Erosion also increases the odds of flooding by removing
the protection of dunes, beaches, and wetlands, and by
moving the shoreline closer to existing properties.
Vulnerable Regions
 Though coastal erosion will increase as sea level
rises and the exact manner and rates cannot be
predicted, certain trends can.
 Scientists project that it is virtually certain that midAtlantic bluffs, headlands, spits, and barrier islands
will erode more quickly in response to future sealevel rise.
 As estuaries and lagoons deepen as sea level rises,
they may become sinks for sediment from shore,
cutting off the supply to barrier islands and
increasing the potential for erosion and shoreline
retreat.
Vulnerable Regions (cont’d)
 Wetlands are also at risk from increasing erosion.
 Those that are fed with sediment from land may be
able to withstand the erosive effects of climate
change.
 But those whose sediment source has been blocked
up or lost will suffer losses from erosion, further
increasing the danger of storm surge in these area.
 If the oceans rise between 0.7 and 2.3 ft (0.2 to 0.7
m) in the next century, it's also likely that some
barrier islands in the Atlantic region may cross an
erosive threshold where they will either move
landward, shrink, or break up suddenly.
Vulnerable Regions (cont’d)
 Barrier islands formed in response to slow sea level
rise rates.
 When an un-predetermined erosive limit is reached,
a beach, barrier island, or other feature suddenly
becomes unstable and experiences tremendous and
irreversible changes.
 Narrow, low-elevation barriers will be most at risk.
Chandeleur Islands
 The effects of accelerated sea level rise and potential
threshold crossing could be already occurring on the
Chandeleur Islands of Louisiana, where subsidence
of the Mississippi Delta from oil extraction and delta
compaction have led to unusually large sea level
rise.
 Many major storms over the last decade and little
input of island-building material from land have also
contributed to the increase.
 The Chandeleur Islands are a north-south oriented
chain of low-lying islands located approximately 100
kilometers east of the city of New Orleans,
Louisiana.
Chandeleur Islands (cont’d)
 The 45-mi (72 km) long chain of the Chandeleur
Islands suffered greatly during Hurricane Katrina in
2005, in which a storm surge 13 ft (4m) high
overtopped the islands and eroded 85% of the
islands' sand.
 The Chandeleur Islands were mapped in the late
1980s and at that time calculated to last another
250 to 300 years based on erosion rates from 1850
to present.
 Studies of the island since Hurricane Katrina seem to
indicate some sort of tipping point has been crossed
and natural processes will not be able to rebuild the
barrier.