Building on Sand Seems a Pitfall
But few people are deterred by storm from building again on vulnerable barrier islands. HURRICANE HUGO: LESSONS LEARNED
ISLE OF PALMS, S.C.
THE Atlantic Ocean here looks serene and post card-scenic. Trouble is, you can now view it unobstructed through gaping holes hurricane Hugo punched in the brick walls of beachfront houses, and across now empty foundations. Once again a large storm has spotlighted a decades-old struggle: the irresistible force of wind and wave methodically shifting barrier islands like this one - and the resistance of man, determined to develop and live on such islands.
``Man wants to keep it there, and the barrier wants to move,'' says Douglas Inman, a professor at the Scripps Institution of Oceanography at the University of California, San Diego.
The tussle is unequal. Most geologists say mankind inevitably grasps the short end of the stick. They argue that development of barrier islands and many mainland coastal areas should be dramatically restricted. Two main reasons include: a changing shoreline that resists being stabilized, no matter what men do; and the continuing threat of catastrophic property damage and loss of human life under certain severe storm conditions.
Geologists say the effectiveness of legal efforts to restrict development varies from state to state. Coastal states ``are all to some extent looking at this problem, and with more or less success depending on the state,'' says Professor Inman. Nationally the situation ``is getting worse,'' he adds.
But some geologists, like Jared Lennon of the South Carolina Coastal Council, say last month's storm showed mankind how to safely develop some large, slow-moving islands like several off South Carolina's shore.
``We have known for a long time how to develop an island,'' Mr. Lennon says. ``We know what can be developed and what should not.... The storm told us [that] what we thought was in fact correct,'' that buildings can escape major damage by smaller hurricanes if built high enough and far enough from the ocean.
The storm also showed that man-made dunes can prevent island damage, Lennon says. On Litchfield Beach to the north of Isle of Palms, an 18-foot-high man-made dune withstood the tidal surge and protected the land behind it, he says. Elsewhere on the beach, unprotected land was covered with three feet of water and silt.
The bottom line is that some islands or parts of islands can be safely developed and some cannot, he says. ``The way you can tell is by monitoring the sites.''
Geologists may disagree with one another, but there is no disputing what many residents believe, even after seeing firsthand the destruction of last month's hurricane. ``This is paradise - we like it,'' says Lucy Durden, a 12-year Isle of Palms resident.
Barrier islands ``should be built on,'' says fellow-resident Bruce Conklin. ``They're beautiful islands.'' Isle of Palms moves about two feet a year, Lennon says. ``That makes it one of the most stable, developable islands anywhere.''
Hurricane or no hurricane, Isle of Palms residents are determined to remain and rebuild. ``We're not escaping'' says John Grieg, visibly startled at the thought that a mere 135 m.p.h. wind and 15-foot tidal surge would cause anyone to move.
``We feel very strongly, with all of our neighbors that have been damaged, that we want it to be just as pretty as it was before,'' says Dee Conklin. ``It's still our home.''
But nothing will make this, or almost any other island, hold completely still, geologists say. ``The coastline is one of the most dynamic environments on earth because it is the interface'' between land and water, says Rob Thieler, a research assistant in a study of developed shorelines at Duke University.
Barrier islands, like Isle of Palms, ``are receding all along the East Coast at an average of one to six feet a year and in some places much more,'' Inman says. ``Anytime there's an unusual occurrence, like a hurricane, you're going to be in serious trouble.''
Lennon's view differs slightly, but importantly. He agrees that high-velocity hurricanes, like Hugo, are more powerful than experts now know how to prepare islands to deal with: In storms of this ferocity ``all bets are off.''
But Lennon says that by building far enough from the ocean and high enough above the water level residents can gain protection against more common hurricanes of 100 m.p.h. or so.
It is the side of the island facing the sea that erodes in storms and over time, Inman says. But an island's overall size does not change much because wind and wave add sand to the mainland side of the island, he says.
Three forces combine to cause this motion: the scrubbing action of normal winds and waves against the island, powerful storms like Hugo, and the inexorable rise of the ocean level. ``Sea level has been rising for the last 18,000 years,'' Mr. Thieler says, and will continue.
Most effort to hold back the rising sea's inroads into the shore by building walls and jetties is ineffective, Inman says. Such structures may retain sand on one individual's property, but cause an equivalent amount to be scoured from nearby beaches.
When development does occur, it is important not only to build far enough from the shore, but also to build hurricane-resistant structures, experts say. Only ``houses that are well elevated'' should be constructed, Thieler says. ``Put nothing on the first floor.''
The Conklins have such a house, which they built themselves: a two-story gray house atop one-story-high hurricane-resistant concrete pillars, two blocks from the ocean. Like most other houses on this island that have no first floor, it survived the hurricane's most destructive element - the tidal surge. Most of the force of the water passed harmlessly under the building. Nearer the beach a group of homes built on one-story wooden stilts also survived without major damage.
The storm's 15-foot tidal surge packed a tremendous wallop, and most of the damage was to homes struck both by hurricane wave and wind. Waves like Hugo's struck with a force of ``over 1,200 pounds per square foot in some cases,'' Thieler says.
By contrast the pressure of a 135 mile an hour gale ``is less than 100 pounds per square foot,'' he adds. ``So it's actually fairly easy to build a house to withstand wind, but not water.''
Cinder-block homes fare the worst against tidal surges. ``They fall over very easily,'' Thieler says. A block and a half from the Conklins' home a two-story house with a cinder-block first floor illustrated his point. Hugo's tidal surge collapsed the cinder blocks in a heap. It bore the wooden second-story along as if it rode a runaway raft, ramming it into a neighbor's trees a house lot away.
Brick homes can be ``a little better'' than cinder block, Thieler says. ``It's probably a little easier to reinforce a brick structure.''
But reinforcing houses (whether of brick or wood) to withstand hurricanes is expensive - one reason that people do not build them that strongly to begin with, he says.