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‘Dodged a bullet’: NSW coast battered by one-in-40-year waves

The NSW coast faces several more days of hazardous surf after a powerful low-pressure system churned up huge waves and a storm surge seen only once every couple of decades.

A buoy in Botany Bay registered significant wave heights reaching 8.44 metres, an event that would typically be seen about once in 40 years, said Mitchell Harley, a senior lecturer in the University of NSW’s Water Research Laboratory.

Children hold the fence chains at North Narrabeen rockpool as huge waves hammer the Sydney coast and other parts of NSW.

Children hold the fence chains at North Narrabeen rockpool as huge waves hammer the Sydney coast and other parts of NSW.Credit:Nick Moir

The storm surge was about 47 centimetres, or about a one-in-20-year event, Dr Harley said, adding “we kind of dodged a bullet”.

Beach erosion could have been much worse had Tuesday night’s big storm coincided with king tides, or if the angle of the waves had been about 30 degrees further to the east. Instead, the waves were mostly from the south, hitting parts of the coastline that tend to get hammered more regularly, he said.

Ed Couriel, director of Manly Hydraulics Laboratory, said the waves were not quite as big as had been forecast, which might have put them close to the heights of a big storm in 1974 that caused a lot of damage to beaches.

Dr Couriel said the government’s offshore wave and ocean water levels network operated by the Manly Lab for the Department of Planning confirm the recorded wave heights were not major nor extreme for a coastal storm.

However, “the ocean water level anomalies along the NSW coast (attributable to non-astronomical factors comprising mainly barometric uplift and likely some wind setup) were higher than during typical coastal storms, and close to the maximum recorded anomaly that occurred during the 1974 storms of about 0.5 metres above astronomical tide levels”, he said.

The storm system also formed close to the coast and moved away quickly. With a longer range for the waves to develop given the strong winds, the impacts would have been more dramatic, he said.

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