Lots of ‘nuisance’ flooding

High tides coupled with unusually high sea levels cause inundations. Photo: Hilary Hosia.
High tides coupled with unusually high sea levels cause inundations. Photo: Hilary Hosia.

Majuro and other islands in RMI have seen many “nuisance inundations” since late last year during peak high tides — and such was the case earlier this month during the full moon as drivers traveling along the airport causeway roads had to dodge rocks and debris tossed up by waves.

But these recent flooding incidents have mostly been an inconvenience, not causing damage.

The primary reason these small inundations are occurring regularly without any associated storms is that the sea level in the RMI is currently six inches higher than the long-term average.

“Astronomical spring or King tides (the highest tides of the year) are not a necessary or even sufficient condition for sea inundation in the RMI,” said the Guam-based US weather officials who monitor El Nino and related conditions in the north Pacific region. “Wind and waves (local or remotely generated) are the primary cause of damaging inundation — both on lagoon-side shores and on the seaward side,” said the latest edition of the Pacific El Nino-Southern Oscillation Applications Climate Center update.

“On February 4, there was some reported minor sea inundation at both Kwajalein and Majuro,” said the update. “At Roi Namur, nuisance flooding occurred at the time of high tide, with large waves washing rubble onto the boundary road by the seawall. At the Kwajalein Reagan Test Site, large wastes were observed, but they did not top the seawall. At Majuro, on the same day, there was some minor inundation at high tide at the bridge area and stretching farther along the coast of the Long Island area.”

These minor inundations were caused by a combination of an unusually big high tide and a large northerly swell. “Very high tides by themselves often result in nuisance inundation; damaging inundation, however, requires large waves, and may occur outside of the spring or King tide condition,” said the report. “With atolls, rising tides fill the lagoon from all directions with the only drainage, if needed, occurring over land.”

Why is the RMI’s sea level so high?

“Because of an enhanced Pacific trade win system, the sea level in the RMI is approximately six inches above the long-term average and is forecast to remain elevated to this degree for the next three months, with a possible decline in sea level thereafter as La Nina begins a slow transition to ENSO-neutral,” said the report.

Read more about this in the April 13, 2018 edition of the Marshall Islands Journal.