Cover Story
A Perfect Horror
Heta had all 5 factors needed to inflict maximum damage
Heta, a category five hurricane (the worst), was a horror, but was it a perfect horror?
The hurricane watch centre at Nadi Airport, Fiji, initially described it as being the most powerful hurricane ever recorded in the South Pacific. Later, after detailed analysis, it backed away from that verdict but said that Heta's passage past Niue had all five factors needed to inflict maximum damage.
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Russell Howorth, acting director of the South Pacific Applied Geoscience Commission (SOPAC), part of whose business is to draw lessons from horrors like Heta, says, "Certain aspects of Heta makes its impact unusual if not a rare event."
A category five hurricane is not normal nor were the characteristics and route through the region it took causing severe damage in five countries, he says. Alofi town, rather than all Niue, suffered most because of its location on the island's west coast in a niche with a shore fringed by a shallow submerged coral shelf.
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This became a ramp on which waves built up to heights great enough to crash over Niue's 40-metre high cliffs and devastate the town.
The Heta experience emphasises the danger of storm or sea-surge and associated coastal flooding, Howorth says. "Awareness and preparedness for wind and rain damage of cyclones is well established, but not so for storm surges.
It is worrying that natural coastal protection like mangroves are being removed," he says. "Storm surges can cause severe damage hundreds of kilometres away from the main weather system. Such was the case with Heta and its impact on the west coast of Alofi."
Heta's storm surge hit Samoa, American Samoa, Tonga and the Cook Islands, besides Niue.
Niue's storm surge experience is an example of what contributes to form a surge and the potential ferocity of the impact, Howorth says. If a cyclone passes at high tide, as Heta did, particularly at high spring tide, the sea-level will be at its normal highest tide position. As a cyclone approaches a coast, its intensity pushes the sea-level above normal.
The lower the cyclone's atmospheric pressure, the more sea-level rises. If winds are onshore, they drive waters ashore. If the coast is parallel to incoming waves, then the surge impact worsens. If the coastline shallows offshore, waves are ramped up as they travel ashore.
"Sadly for Niue, all these were satisfied in the Alofi south village area and close to the main government centre," Howorth says. Heta passed just a few tens of kilometres to the west of Niue, close to high tide and close to a full moon (spring) tide."
Passing west of Niue, it smashed Alofi with onshore northerly winds. Wind speed increased because Heta was moving in a southerly direction. Alofi south is quite a small section of the west coast and actually faces northeast. It was thus badly exposed to Heta's full blast.
The offshore submerged flat terrace, about 15 metres deep and about 50 metres wide, was a perfect wave ramper, Howorth says.
He says the lessons from Heta and from cyclone and storm damage in 1990, 1960 and 1959, show that buildings should be set further back from the cliff edge at Alofi. A coastal hazard zone should be identified and subjected to development restrictions.
Hotels and restaurants built in the hazard zone, and also houses, because of the view from it should be designed and built to be able to withstand such calamities. Howorth says Heta's assault on Niue came in a year in which the United Nations is to review a plan for small islands countries agreed to at Barbados 10 years ago.
This lays emphasis on the difficulty islands have in coping with their economic, social and environmental vulnerabilities compared with other parts of the world. "For the Pacific, and regrettably Niue in particular, Heta most emphatically restates the case that the vulnerability of our islands is not reducing."
Howorth says the review to be concluded at Mauritius in August must arrive at ways of establishing comprehensive hazard assessment and risk management practices so that vulnerable countries can build lasting resilience to support sustainable development.
