Cyclone Gabrielle: Was the catastrophe at Esk Valley avoidable?

Friday, 17 February 2023

Esk Valley resident Warwick Marshall talks about the destruction Cyclone Gabrielle caused.

Vineyard-lined Esk Valley was a prosperous Hawke’s Bay river flat, but it took just minutes for it to become a death trap in the small hours of Tuesday morning. Those who survived Cyclone Gabrielle are now asking why they weren’t evacuated from an area already known for its devastating flash floods. Kate Newton and Nadine Roberts report.

On Monday evening, as heavy rain fell, Warwick Marshall and his wife Trish went to bed. They knew Cyclone Gabrielle was on its way but were comfortable with the level of water on their Esk Valley property.

Nearer the coast, the Collins family had tucked their two preschool daughters into bed as the rain beat down.

At 8.23pm on the same evening, Hawke’s Bay Civil Defence and Emergency Management posted a reassuring message on their social media page.

“At the moment there is no reason for residents to evacuate,” the post said. Those who should move “have already been contacted”.

Just hours later, floodwaters would rip through Esk Valley and the communities downstream. The Marshalls made it to safety only with the help of their neighbours, scrambling over an archway, several roofs and using a broken gate as a makeshift ladder to get to higher ground.

Ella Collins, her husband and four-year-old daughter Imogen also escaped – but two-year-old Ivy, their “bright, shining, light”, was lost forever in the torrent.

* Toys, photos and furniture - the muddy floodwaters of Cyclone Gabrielle give up their victims

* Extraordinary images capture destruction caused by Cyclone Gabrielle in Esk Valley

* 'I can't overstate the scale of the task ahead': 4500 still out of contact after Cyclone Gabrielle

By the time Hawke’s Bay Fire and Emergency advised that evacuations were under way at 3.19am, it was too late for many in the valley.

“There was no warning, absolutely no warning,” resident Lynn Noanoa told Stuff. “There’s no blame, but it has to be addressed. Something has to be done.”

Esk Valley has a history of devastating flash floods. And as early as Saturday evening, MetService was forecasting up to 350mm of rain in the Hawke’s Bay ranges, some of which feed the Esk catchment.

Verity Johnson: “First the flooding, then the cyclone, then the ongoing post-Gabrielle devastation that just keeps punching and punching.”

But despite steadily rising river levels in the Esk Valley all day on Monday, Hawke’s Bay Regional Council confirmed it never issued a valley-wide advance evacuation notice, instead choosing to warn only those it deemed to be at specific risk.

Stuff has also confirmed that the regional council never developed specific flood hazard maps for the valley, despite a recommendation to do so following a 2018 flood.

Hawke’s Bay Regional Council interim chief executive Pieri Munro said the intensity of Cyclone Gabrielle exceeded everyone’s expectations.

“This event… exceeded all forecasts based on the data that we had at hand on the night preceding [Monday], up until 2200 hours,” he said.

“What we received was greatly in excess of that, over the conditions and over the information that we had in hand.”

Munro said that council and civil defence were also hampered after that by a lack of data, when seven of the 10 sites monitoring river flows and rainfall in the Esk Valley went offline from 1am Tuesday, after a repeater station relaying the data failed.

“So we were left rather blind just because of how quick and how focused Gabrielle was.”

An escalating situation

However, data from those stations shows the situation already escalating throughout Monday.

One of the three sites that remained online throughout the cyclone was Maunganui, a mountain station in the upper reaches of the Esk catchment.

Rainfall data from this site shows that, from early on Monday morning, rain fell steadily and heavily, building throughout the day.

By midnight, 142mm of rain had already fallen, and the intensity was still increasing.

It peaked in the small hours of Tuesday morning, when another 99mm of rain fell in a three-hour window.

The river itself rose steeply and steadily from early Monday afternoon, which is when the council says it contacted specific residents of the valley warning them to leave, including the Eskdale Holiday Park.

Hukarere Girls’ College, which has a boarding school and is located right next to the Esk, chose to evacuate its boarders on Monday night, starting around 9pm.

Pieri Munro said the alerts went to “all people in the valley we thought the forecast weather would affect, and many of them did self-evacuate”.

Those evacuation warnings were delivered via phone, email and social media, he said.

When asked if that included everyone in the valley, he said it was “those areas based on the information that we had at hand, that we thought might be affected”.

By 11pm, the river had exceeded the one-in-100-year flow rate estimated in a report from 2000. By 3:45am, when the station at Waipunga Bridge just north of Eskdale, stopped reporting data, the flow rate was nearing one-in-200-year flood levels.

When asked if evacuation warnings could have happened earlier, Munro said that staff “looked at all information we had operating at the time… Regrettably that has been proven wrong but part of that is because of the intensity of Gabrielle and the concentration of that [rainfall].”

Esk Valley’s flash-flooding history

The magnitude of damage in some areas raises the question of whether residents should return.

But long-term residents and the council knew that the valley was prone to flash-flooding.

In 1938, 300mm of rain fell in 14 hours, creating scenes eerily reminiscent of the latest events, with silt piled up outside houses to roof-height.

Rivers bursting their banks, flash floods and more intense cyclones – how climate change is making floods more extreme.

And on March 8, 2018, residents in the valley were evacuated when 270mm of rain fell in 12 hours, causing the Esk to breach its banks.

A Hawke’s Bay Regional Council report into the 2018 flood included a recommendation to “investigate the benefit and cost of setting up a text warning system for residents in the Esk Valley”.

Munro says that investigation was done, but concluded “at the time, that the system required manual entry of names and numbers, and would quickly be outdated”.

Munro said a text alert sent to residents in Taradale, another Hawke’s Bay settlement that was evacuated on Tuesday, “demonstrably failed, again because of Gabrielle’s intensity”.

The same 2019 report also recommended the council “develop updated flood hazard maps for Esk Valley”.

Esk Valley is included on the regional council’s flood risk maps but, unlike some other flood risk areas in the region, the potential flooding has not been specifically modelled.

Munro said it was decided that that work would not go ahead.

“The decision at the time was this would not be done because the one-in-100-year probability maps, we believe, could hold up.”

The 2018 was a one-in-100-year event, Munro said, “meaning it was unlikely … to reoccur for a long time”.

A one-in-100-year event is in fact a slight misnomer – climate scientists have explained to Stuff that what it actually means is that, in any given year, there is a 1% chance of the event occurring – and that number is increasing with climate change.

Julia Becker, an Associate Professor at the Joint Centre for Disaster Research at Massey University, did not want to comment on the emergency response in Hawke’s Bay while the immediate disaster was still underway.

“There was quite a bit of advance warning about the weather system itself,” she said. “But the difficulty in this situation is how do you connect what some of the weather warnings are as to what some of the impacts are going to be on the ground? You know there’s going to be a lot of rain … but exactly where it’s going to fall and in which catchments it’s going to go into and what rivers it’s going to come down and how fast all that’s going to happen is a little bit of an unknown.”

Sometimes it was possible for official agencies to get a warning or heads up out ahead of time, “and sometimes it’s just going to happen so quickly that people actually need to know what to do in that situation for themselves”.

That public education needed to happen well in advance of any disaster occurring, Becker said.

“People have to know beforehand, are they at risk? Are they in a zone that might flood? How quickly might that happen?”

On Friday, Prime Minister Chris Hipkins said he was 'not going to get into talking about things that look back over those early responses, because the people who will in due course respond to that are still involved in an emergency response'.