Storm surge’s wall of water

Some called it a wall of water, others compared it to a tsunami.

However you describe it, the storm surge that flooded Firth of Thames locales last Friday was among the worst on record for the area.

The sea level at the peak of the storm was near that of the Hauraki Plains floods of 1938, according to Waikato Regional Council data. This time, homes, farms and roads around the coast were soaked and battered, prompting a Civil Defence response which involved the NZ Defence Force and the Red Cross.

‘‘We are still assessing . . . but, as a guide, this is one of the biggest events that have occurred in the Firth of Thames in recorded history,’’ Waikato Regional Council’s Rick Liefting said.

An offshore tide gauge in Tararu recorded a 2.8m water level, the regional hazards team leader said, though waves would have exceeded that.

The biggest ‘‘storm tide event’’ on the Firth of Thames was in 1938, he said, when much of the Hauraki Plains was submerged and the water level was estimated at 3m.

Stopbanks on the plains stopped them going under this time, Liefting said, but mid-storm, the water was nearing the top of those built by the Piako River.

Three key factors combined to beef up the storm, he said: low atmospheric pressure, winds, and a king tide.

‘‘It occurred smack bang on the highest tide of the year.’’

The only thing missing to create a perfect storm was heavy rain.

’Three potential whammies’

‘‘We were hit with three potential whammies all at one time,’’ Hauraki District Civil Defence Controller Steve Fabish told viewers in a live-streamed update on Wednesday.

‘‘So [the water level] was at least 0.4m higher than that ’95 flood that most of us can certainly remember.’’

The storm started in the moisture-filled subtropics, where a strong low pressure system developed, Niwa meteorologist Ben Noll said.

That essentially charged up as it travelled over the warmer-thanusual Tasman Sea – ‘‘ boon in terms of strengthening’’.

In the mix were the highest tides of 2018 and northerly winds which blew right down the firth and pushed water on to the coast.

‘‘They all sort of worked together to generate what was a pretty impactful situation.’’

Up the Thames Coast

The Thames Coast has been hit before and will be again, Thames Coromandel District Mayor Sandra Goudie said – though this is the worst she’s seen.

The NZ Transport Agency had been going hard and fast to repair the battered Thames Coast Road and keep it open to at least one lane.

People affected by the floods were barely over the clean-up, she said, but in future they would have to think about whether they wanted to lift up their homes or cut their losses.

The climate change question

The after-effects of the storm have prompted plenty of comments about climate change.

It affects all weather that we experience, Niwa’s principal scientist for climate Dr Brett Mullan said.

‘‘The difficult thing is to say this is the climate change part of that storm surge compared to what you might have got anyway.’’

Continued sea level rises could heighten the base that storm surges start from, increasing the effect, he said.