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Fighting
the Tide:
Cape Hatteras Lighthouse Retreats from Rising
Sea
Andrew Shepard, Associate
Director, National Undersea Research Center
at UNCW
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| What is 200 feet high
and travels 100 feet per day? If you live on the Outer Banks
of North Carolina, you probably know the answer. Cape Hatteras
lighthouse has been a beacon for seamen for 130 years from its
perch on the north end of Hatteras Island. Sea level rise and
erosion have forced the lighthouse off its roost and it is being
moved a half mile inland (see details at the National
Park Service Web site).
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| Hatteras Island is a
barrier island. Barrier islands are massive dunes with bases
below the tideline and peaks ten feet above low tide. As sea
level rises and falls over time, the islands migrate both along
and perpendicular to the beach. Now, they are migrating inland
as sea level rises. According to a National Research Council
study on the lighthouse’s predicament (Lighthouse
Report on National Park Service Web site), if present trends
continue, sea-level will rise up to 0.5 feet and the shoreline
in front of the lighthouse will retreat 400 feet by the year
2018. By the year 2088, the retreat may reach over a half a
mile inland.
Evidence of past barrier islands can be found hundred of
miles inland and well offshore of the Carolinas. Before human’s
developed the coast, it was like a tree falling in the woods--
nature did its thing and no one noticed the quiet movement
of the beaches. Things are different now. By 2018, well over
half the nation’s population will live within five miles of
a beach. Houses and hotels now extend from end to end on most
of North Carolina’s barrier islands.
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In order to protect billions of
dollars of property and lives, few options remain for keeping
a beach in place. First is "hardening" using seawalls, groins
and a variety of man-made structures in front of the weak points.
Unfortunately, these devices tend to transfer the vulnerable
points to either side, creating a problem for someone else.
The lighthouse has lots of rip-rap and debris around it from
past hardening attempts. The resulting trash does not make for
a very desirable beach front. Finally, the sea will not be stopped
this way for long. This option is outlawed in North Carolina,
unless special variance is granted. |
| The preferred option to fight erosion
is replenishment; placing new sand on the beach from another
location. The sand may come from offshore or behind the barrier
island. Projects usually involve hundreds of thousands of cubic
yards of sand, at a cost of one to two dollars per yard. Carolina’s
beaches are among the most replenished in the world. |
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At six o’clock in the morning, vessels
start to stir from Wanchese, NC. Most are hardy fishermen heading
out to hunt for tuna and other species that populate the Gulf
Stream edges and eddies. Captain Dan pilots the University of
North Carolina at Wilmington’s R/V Cape Fear alongside them,
to a spot just a few hundred yards off Hatteras Island. |
| Dr, Stan Riggs, recently retired
professor from East Carolina University, sips coffee and looks
at underwater maps. "The barrier islands are in real trouble"
notes Dr. Riggs. "Dare County is going to have to spend sixty
million dollars to replenish its beaches, plus ten million every
two years to protect the urbanized sections of its islands.
The next category three hurricane [sustained winds of greater
than 110 mph] will likely break through one of the islands."
Dr. Riggs, like many other scientists, knows that well-planned
replenishment projects can save dollars and lives. Dr. Riggs
and Dr. Bill Cleary, University of North Carolina at Wilmington
are being supported by the NOAA's
Undersea Research Program's (NURP) Center at UNCW to provide
data for this purpose. As Associate Director of the funding
agency, I am there for the day to follow progress on the project
and get an update from Dr. Riggs on the problems we all face
on the coast. |
| Our objective this day,
and in the weeks to come, is to describe the deep end of the
barrier island that lies below water and try to answer several
questions. What lies underneath the sand offshore? What kind
of sand is there and where did come from? Do outcrops poke through
the sand and affect how sand moves? Are there good sources of
sand that could be pumped up on the beach? |
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On previous trips,
acoustic samplers were used to do fast surveys
of a broad area, but these samplers cannot
provide enough detail to answer our questions.
Divers equipped with cameras and cores will
do the work, diving on targets picked out
from the acoustic maps. Although our day was
cut short by weather and high seas after a
few dives, the line of samples off the north
end of Hatteras Island revealed no exposed
reefs where the acoustic record suggested
possible outcrops. There is no better way
to know what is down there than by going there.
Dr. Cleary and Dr. Riggs, and several
colleagues, have been instrumental in helping
the US Army Corps of Engineers plan their
replenishment efforts—they often turn to
the scientists for advice on potential sand
sources and where erosion is likely to be
worse. Our goal is not to abandon the beaches
we all love, but to protect them as best
we can. The lighthouse is not the last sizeable
object that will likely be moving in the
coming decades.
For further information
contact: Dr. William Cleary, Center for Marine
Science Research, University of North Carolina
at Wilmington, 7205 Wrightsville Ave., Wilmington,
NC 28409, tel: 910-256-5133, Inet: clearyw@uncwil.edu.
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