THE EDITOR, Sir:
WE READ the letter by Messrs. Smith and Warner concerning the protection of the Palisadoes road with great interest, and agree that the kind of solution that they propose is the most appropriate one at this time. Regeneration of the dunes on the ocean side of the road will give a measure of protection, and will provide that "emergency savings account".
However, we see that work is ongoing to offer protection to the road by placing a boulder rampart along the line of a prominent beachrock layer on the seaward side of the road. This layer is one of a series of layers of beach sand and cobbles that have been cemented by natural processes over the years, to form a hardened set of surfaces in the beach region. These layers themselves offer a natural back-up protection, inhibiting the effects of erosion from storm waves.
UNNECESSARY AND DANGEROUS
The placement of boulders along this natural rampart would seem to be both unnecessary and, perhaps, even dangerous. Abnormally intense storms are able to move boulders of this size many metres. Unless very securely anchored, these boulders would be converted into missiles, able to block the roadway much more effectively than windblown sand if a storm similar to, or more intense than Hurricane Ivan should pass close to the shore.
In a well-written report on the effects of the 1980 Hurricane Allen on the north coast of Jamaica, Conliffe Wilmot-Simpson, then of the Government's Mines & Geology Division, drew attention to the displacement of large boulders by the storm at Trident Villas, Port Antonio, and Galina Point. We have re-examined the boulder group at Galina, St. Mary Parish, and can confirm the evidence from eyewitnesses that some were moved more than 30 metres during the storm. One of us (D-A R) has also re-examined a boulder field in Grand Cayman that tells a similar story. Some of the boulders moved at Galina in 1980 are considerably larger than any of the boulders recently put in place for protection along the Palisadoes.
STORMS
We would also like to point out that, although it is more exposed than other parts of the Palisadoes to the fury of tropical storms and hurricanes, this narrow, eastern part has been in existence for a long time, probably extending into thousands of years. Along with the stretch of coastline fronting the airport, it is probably the most stable part of the whole Palisadoes system. The sand and cobbles there are cemented into beachrock, providing a natural, solid foundation for the road.
Future storms may block the road and damage its surface, but it is most unlikely that a storm would be able to cut deep channels through the Palisadoes, even at its narrowest point. We do not know the details of the breaches that were made in this section resulting from the hurricane of 1722, but it is our guess that they were eroded as relatively shallow paths across the spit. Test drilling on the sites of those breaches might give a more definitive answer.
One cannot compare the erosion problems of the Palisadoes spit with, say, the problems experienced along the east coast of North America, where massive, storm-induced breaches are frequently made in the soft, unconsolidated sand of the barrier islands. Up north there is no beach rock. In tropical areas beach rock is quite a common feature, and wherever it is present, it appears to add structural strength to the beach system as a whole.
We are, etc.,
EDWARD ROBINSON,
Director
DEBORAH-ANN ROWE,
Research Associate
SHAKIRA KHAN,
Research Associate
The Marine Geology Unit
Department of Geography & Geology
University of the West Indies, Mona
Email:
mgu@uwimona.com.
