Beach recovery may take several months, says IMA

Unlike a tsunami, which reaches down to the sea floor, the large waves which ravaged local beaches were the result of a wind wave, generated on the ocean surface by the powerful forces of a storm.

According to officials of the Institute of Marine Affairs (IMA), the swells were possibly generated as a result of storm activity and low-pressure systems within the Atlantic and Caribbean Seas. At the time, Hurricane Wilma, which eventually developed into a powerful Category Five hurricane, was gathering strength several hundred miles north of this country in the vicinity of the Cayman Islands.

The IMA reported, "These large swells began pounding the beaches of the north coast from as early as 11 am on Sunday October 16, causing severe damage to beaches, fishing boats and coastal infrastructure. Three days after the event, large waves continued to pound the beaches."

Research shows that giant waves are not uncommon during hurricanes. According to a study by the Naval Research Laboratory (NRL) at Stennis Space Center, Mississippi, in the United States, such waves come out of nowhere, across the ocean waters, and pose a real danger for even large ships and oil rigs.

Because shipping avoids hurricanes, many large waves are unseen by humans, let alone measured.

Known as rogue, or freak waves, they seem to spring up from the ocean floor and are usually so large that they can overwhelm and sink even the sturdiest ships. Researchers have started using satellites to try to identify and track these unruly waves. The results have been surprising. While rogue waves were once thought to be the stuff of sailing legend, satellite photos found ten huge waves welling up over a three-week period.

Giant waves sometimes appear in areas of extended storms or converging weather fronts. Waves coming in from different systems could build up into big waves.

To track rogue waves, researchers looked at data from archives of images shot from the satellites. The satellites’ radar makes images of six-by-three-mile patches of the sea surface every 120 miles. With the consecutive images, scientists get a bird’s-eye view of the ocean’s dynamics.

Researchers have broken down these images into elements of wave energy and wave direction, called ocean-wave spectra, which can be used by weather stations for forecasting. In the process, they spotted more than ten rogue waves during a three-week period. Each wave swelled to 82 feet or more.

Waves are normally caused by high winds whipping over the sea surface. However, giant waves, which cannot be predicted by standard meteorology, continue to baffle scientists. Even in the worst of storms, waves should not reach more than 40 feet. However, in recent times walls of water more than twice that height have been observed.

One theory is that waves and winds heading straight into powerful ocean currents could be triggering the monster waves. It has also been suggested that under certain conditions, waves can become unstable and start to suck in energy from neighbouring waves and so grow rapidly and massively.

This is of major concern globally but particularly to small island states like Trinidad and Tobago and the other islands of the Caribbean which are already being affected by rising sea levels as a result of global warming.

Rising seas are accelerating coastal erosion and experts are warning that some islands of the Caribbean stand to lose 300-370 metres of prime coastline by 2020, accompanied by extensive damage to seaports and major coastal infrastructure.

When the waves first started hitting the long stretch of coastline in north Trinidad, panicked sea bathers, fishermen and onlookers thought a tsunami had hit the country but according to data from the Seismic Research Unit at St Augustine, there was no evidence of earthquakes occurring anywhere in the region to generate such waves.

"Scientists have concluded that these waves were not related to any hydro-geologic phenomena and they therefore cannot be classified as tsunamis," the agency said.

Sea bathers and others said the waves took them by surprise. However, the Trinidad and Tobago Meteorological Service had issued a rough seas advisory at 6 am on Sunday, several hours before the first giant waves struck, advising the public to exercise caution in approaching coastal areas throughout the country.

Eyewitnesses at Maracas Bay, one of the hardest hit areas, reported that the huge waves seemed to appear out of nowhere on seas that had been very calm. They said the waves rapidly gained speed as they rushed toward the shore, giving seabathers very little time to get out of the way.

Affected areas included Maracas Bay, Las Cuevas, Blanchisseuse, Matelot, San Fernando, Fullerton, Icacos and Los Gallos in Trinidad, as well as Castara, Black Rock and Plymouth in Tobago.

There was one fatality in Castara, Tobago, where a man who was fishing on a rock was swept out to sea.

In other areas, while there were no casualties, there was significant damage to fishing boats, severe erosion of beach fronts, flooding and damage to coastal roads and other infrastructure.

Last Tuesday, two days after the waves started affecting TT, officials of the IMA carried out beach profiles and site assessments at Maracas, Las Cuevas and Blanchisseuse. The beach profile is a cross-section of a beach which extends from the edge of the vegetation line or cliff to the sea or surf zone.

At Las Cuevas, the IMA assessment revealed that the waves had removed "significant quantities of sediment from the beach", causing it to become steep in its upper part and causing a significant drop in its elevation.

The hardest hit area of Maracas Bay was the central section where there was the greatest loss of sediment.

A significant drop in the elevation of the beach was also noted. According to the IMA this "could prove to be very significant in the alteration of the northern coastal area of Trinidad."

The IMA added, "There may also be permanent damage to some sections of the coastline, especially in cliffed areas where natural recovery is not possible.

"The beaches on Trinidad’s north coast can be classified as high wave energy environments. Most of these beaches can also be characterised as dynamic.

"Beaches which are dynamic undergo erosion during the period from November to April when large waves occur. Waves move sediment from the beach into deeper waters.

Between May and October when there is a decrease in wave energy, except during periods of storm and hurricanes, much of that sediment may again be returned to the beaches." According to the IMA, the affected beaches should recover within a few months.

However, if there is no significant recovery "within 12 months of an extreme event", it may be necessary to take remedial action in the form of soft engineering (beach nourishment) or hard engineering (construction of sea walls).

Meanwhile, clean up crews have been at work in the hardest hit areas for several days. Personnel and heavy equipment from the Siparia Regional Corporation have been dispatched to Icacos and Cedros to clear sediment from roadways and blocked water channels.

At Maracas and other areas along the north coast, the San Juan/Laventille Regional Corpo-ration embarked on clean-up operations immediately after the water subsided and rough seas advisories were discontinued. Also involved on coastal clean-ups were crews from the Sangre Grande Regional Corporation and the San Fernando City Corporation.