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A tale of two lighthouses.

America stands at a great crossroads with regard to shoreline policy. Many buildings on the East Coast beachfront are threatened by the Atlantic Ocean, or soon will be if current erosion rates continue. How we, as a society, should respond in the face of this impending doom is a matter of great controversy. The story of two lighthouses, Cape Hatteras Lighthouse in North Carolina and Morris Island Lighthouse in South Carolina, illustrates some of the complexities involved.

At 63 meters high, Cape Hatteras Lighthouse is the tallest brick lighthouse in the US, and one of the most famous. The present Cape Hatteras Lighthouse replaced a shorter, dimmer, light built in 1803. Since 1870 it has warned mariners of the treacherous waters of Diamond Shoals that have earned North Carolina's Outer Banks the nickname "Graveyard of the Atlantic." Readily accessible by car, Cape Hatteras Lighthouse is today one of the East Coast's major tourist attractions. Morris Island Lighthouse, also known as Charleston Lighthouse, was first lit in 1876 and is about 50 meters high. Perhaps because Morris Island has always been inaccessible by car, it never became the tourist attraction that Cape Hatteras Lighthouse did, but it is a well-known local landmark for the important port city of Charleston. The present Morris Island Light replaced a pre-Revolutionary War light that was destroyed during the Civil War (by some accounts during the battle for Garrison Wagner that was made famous in the movie Glory).

How are the Cape Hatteras and Morris Island lights linked with respect to coastal policy? Cape Hatteras Lighthouse is in imminent danger of being destroyed by storm waves. It was originally built some 500 meters from the shore, but erosion has moved the shoreline to within 20 meters of the light. Morris Island Light has also been the victim of a rapidly retreating shoreline. To find it today, don't look on land or even near the shore, because it's in the water, some 500 meters offshore!

The Controversy

Controversy over whether or not to try to save Cape Hatteras Light, and if so, how, has raged since the 1930s. The arguments have strengthened since 1980, and are centered around whether to:

* armor the shoreline in an attempt to protect the lighthouse in place,

* relocate the lighthouse landward,

* replenish the beach, or

* do nothing, and let the lighthouse collapse when its time comes.

All sides have been steadfast, with impassioned arguments touting their different viewpoints. Many times it seemed likely the approaching shoreline would destroy Cape Hatteras Lighthouse before a decision could be reached about saving it! High erosion rates, high wave energy, and the lighthouse's vulnerability to hurricanes and other winter storms (such as nor'easters) meant time was of the essence.

In the 1930s shoreline migration brought the sea to within 30 meters of Cape Hatteras Lighthouse, and in 1936 the light was abandoned. By 1950 the shoreline had stabilized naturally. At this point, ownership was transferred from the US Coast Guard to the National Park Service, and Cape Hatteras Lighthouse was reactivated. In the 1960s and 1970s three groins were built, subsequently destroyed by a storm, and rebuilt. Nylon sandbags were emplaced in front of the lighthouse, and three other unsuccessful beach replenishment projects were also undertaken.

In 1980, a March storm washed away the remaining ruins of the original lighthouse and threatened the present Cape Hatteras Lighthouse. Quick thinking by the resourceful Park Service saved the light: They tore up the parking lot and placed the rubble in front of the light to protect it from the storm. In 1981, the National Park Service asked the US Army Corps of Engineers for their evaluation. In 1985, the National Park Service decided that protecting the lighthouse in place with a massive seawall was the best way to save it. Under pressure from local opponents of shoreline armoring, however, they decided to reconsider the options, and in 1987 they asked the National Research Council for help. A Research Council committee concluded that relocation was the best option. As of this writing, the National Park Service is pursuing relocation of the lighthouse.

Morris Island Lighthouse was never surrounded by such controversy. The light has been along the beach or offshore since the late 1930s, so perhaps no one thought of it in terms of needing to be "saved." When Morris Island Light survived a direct hit from Hurricane Hugo in 1989, it was reported that Cape Hatteras Light could also survive a major storm in place, and therefore relocation was not required to save it. In addition, many reckoned that relocating such structures did not necessarily set a good precedent for coastal zone management philosophy.

Comparing these two lighthouses and saying that what is good for the goose is good for the gander is an oversimplification of the problem. Cape Hatteras Lighthouse and Morris Island Lighthouse differ in several ways and need to be considered separately.

The Coastal Physical Setting--More than Meets the Eye

Cape Hatteras Lighthouse is in a more dangerous physical location than Morris Island Lighthouse. Cape Hatteras juts out into the Atlantic, and somehow seems to attract winter storms and hurricanes, while Morris Island is somewhat sheltered by sand shoals. The continental shelf is narrow off Cape Hatteras and wide off Charleston, which has a profound effect on overall wave energy, tidal range, and the maximum potential storm surge. Mean wave heights are relatively high off Cape Hatteras, and low off Charleston, yet the tidal range distribution (the mean water height, between successive high and low tides) is exactly the opposite. The bottom line is that there is greater potential for wave damage at Cape Hatteras Lighthouse than at Morris Island Lighthouse, but the potential maximum storm surges at Morris Island are higher than at Cape Hatteras.

Much is made in news reports about the dangerous combination of a hurricane making landfall at high tide. That is precisely what occurred during Hurricane Hugo when a 4-plus-meter storm surge was added to a 1.5-meter astronomical high tide. In low tidal-range settings, such as Cape Hatteras, low water levels are not significantly different from high water levels. No matter what point during the tidal cycle a hurricane hits, it will always be near mean water level. On the other hand, in high tidal-range settings, such as Morris Island, there is a significant quantitative difference between high and low water levels. If a storm happens to hit during maximum low water, the storm's impact will actually be lessened.

The erosion histories of the two locations also differ. Morris Island's shoreline has essentially been moving straight back. Cape Hatteras, however, has been fluctuating back and forth, although over the long term, the shoreline has moved back as well. This difference may be attributed to the differences between a cape and a barrier island.

The Shoreline Engineering Setting is Vitally Important

Cape Hatteras is not a highly engineered shoreline. An artificial dune was built along a large portion of the Outer Banks shoreline in the 1930s. Other than the beach replenishment projects and groins mentioned, the shore is unstabilized. Morris Island, however, sits in the sand-transport "shadow" of the Charleston Harbor jetties, and is greatly affected by shoreline engineering. The jetties interrupt the predominantly southward transport of sand along the shore, resulting in severe erosion south of the jetties.

The Cape Hatteras shoreline is being held in place by the groins that have also likely protected Cape Hatteras Lighthouse so far. Meanwhile, Morris Island is being destroyed by the jetties.

Lighthouse Design Differences

The foundation of Cape Hatteras Lighthouse is only about 2 meters thick, consisting of granite rubble and masonry laid on top of two courses of yellow pine. The foundation's base is about .3 meters above sea level, and the lighthouse extends about 63.4 meters from there. Except for a wall of large nylon sandbags partially encircling the base, the lighthouse foundation is not armored, leaving it vulnerable to storm-wave scouring and destruction via undermining and toppling.

The base of the foundation of Morris Island Lighthouse is below sea level, and is far more substantial than that of Cape Hatteras Lighthouse. Morris Island Lighthouse's 2.5-meter-thick concrete foundation sits atop piles driven up to 15 meters deep and overlain by two courses of timber encased in concrete. Beyond this, the lighthouse extends 50 meters. To protect against damage from the extreme erosion rates common to this region, the base of the lighthouse was strengthened in 1938 with a sheet pile cylindrical wall with a concrete cap. Morris Island Lighthouse's base is obviously much better protected from wave scour than is Cape Hatteras Lighthouse's, and is therefore much more likely to withstand the fury of storm waves.

Forging Shoreline Policies is Complicated

The Cape Hatteras and Morris Island lighthouses differ in several important ways. Cape Hatteras has higher wave energies, erosion that is often unpredictable in the short term yet severe in the long term, and lower tidal range, meaning maximum storm surges will always occur. It is protected by relatively modest shoreline engineering, and has a shallow, unprotected foundation. Morris Island has a relatively low wave climate, a high erosion rate, and a high tidal range, which can increase or decrease a storm's impact depending on when the storm hits. It is severely affected by erosion caused by the Charleston Harbor jetties, and has a deep, highly engineered foundation that is armored against wave scour.

Coastal-zone managers must take into account all the differences: physical, geomorphic, engineering, and political, when devising shoreline policy. The future is bright for these kinds of considerations, mostly because the past is so dark. Small steps are being made in the right direction. Several states are banning seawalls, and South Carolina has begun a 40-plus year process of removing seawalls from its beaches. On a national level, the US Congress is considering including erosion rates and erosion zones as part of the National Flood Insurance Program (NFIP), restricting building in high-erosion-rate zones. Revision of relocation provisions in the Upton-Jones Amendment to NFIP to pay for relocation of large structures such as condominiums and hotels is being considered.

David Bush was deeply involved with the Cape Hatteras Lighthouse controversy as a member of the "Move the Lighthouse Committee," so is biased toward relocation as a viable coastal management alternative. He finds it hard to leave Duke University where he received his Ph.D. in geology, and continues there as a Research Associate in the Program for the Study of Developed Shorelines.

After 15 years of researching deep-ocean sedimentation, Orrin Pilkey realized that at cocktail parties people would listen more attentively when he talked about coastal erosion, hurricanes, and shoreline processes than about turbidity currents and abyssal plains. He subsequently stopped going on deep-sea research cruises and started going to the beach. For over 25 years he has plied his trade on the faculty of Duke University where he is James B. Duke Professor of Geology and Director of the Program for the Study of Developed Shorelines.
COPYRIGHT 1993 Woods Hole Oceanographic Institution
No portion of this article can be reproduced without the express written permission from the copyright holder.
Copyright 1993 Gale, Cengage Learning. All rights reserved.

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Author:Bush, David M.; Pilkey, Orrin H.
Publication:Oceanus
Date:Mar 22, 1993
Words:1833
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