Tue, May 07, 2019 - Page 4 News List

Rogue wave alert mechanism urged

YILAN COUNTY TRAGEDY:The last fatal accident involving rogue waves happened on Sept. 2 last year in Nanao, when three people were killed after being swept away

By Shelley Shan  /  Staff reporter

The government should establish an alert mechanism for rogue waves because they have caused a series of deaths and injuries, a think tank of the Ministry of Transportation and Communications said in a report.

Rogue waves, also called “crazy dog waves” (瘋狗浪) by Taiwanese, usually appear between June and November each year, the Institute of Transportation said in the report.

Several factors that contribute to the occurrence of rogue waves have been identified, including the topography in certain parts of the ocean, wave-current interactions and convergence of groups of waves, the report said.

The rapid grouping and convergence of swells are also closely related to the occurrence of rogue waves, it added.

The institute said that it analyzed five fatal accidents involving rogue waves, which occurred in Pingtung County’s Mobitou Park (貓鼻頭), Keelung’s Heping Island (和平島), Bitoujiao Park (鼻頭角) along the northeast coast and Yilan County’s Nanao (南澳).

Rogue waves in all five cases occurred because of swells caused by typhoons, it said.

Among the five cases, three happened after the Central Weather Bureau had issued a typhoon alert, the institute said.

Examining the evolution of swells caused by typhoons over the years, the institute said the swells have the potential to become rogue waves when they accumulate at the Port of Suao or Port of Hualien.

Specifically, the peak period of swells in this stage abruptly jumps from less than 10 seconds to larger than 12 seconds, the institute said, adding that wave height gradually rises to exceed 1.5m.

Swells enter maturation if the peak period of the swells continues to last more than 12 seconds for about 10 hours after they pass the accumulating stage.

Wave heights can surpass 2.5m, the institute said.

Swells in the maturation stage can easily trigger the occurrence of rogue waves, which pose the most serious threat, it said.

Although the nation has yet to develop the technology to accurately forecast when and where rogue waves would happen, the government could still reduce the possibility of fatalities by formulating guidelines governing the issuance of rogue wave alerts, it said.

When a typhoon forms nearby, the public should be warned about rogue waves, the institute said, adding that the government should calculate when the swells caused by the typhoon would arrive by taking into account the typhoon’s distance from the east coast and that swells travel at an average distance of 800km a day.

The nation should issue a rogue wave alert if swells are grouping and accumulating, and lift it when the peak period drops below 10 seconds and wave height falls below 1.5m, it said.

Between the grouping and accumulating stage and maturation, the government has about 10 hours to prevent disasters from happening, it added.

The last fatal accident involving rogue waves happened on Sept. 2 last year in Nanao, when three people were killed after being swept away.

Within two hours of that accident, two other people fell into the sea because of rogue waves at Nanao Beach and Neipi Beach in Suao.

The sea had been affected by swells caused by Typhoon Jebi, which was moving toward Japan.

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