Cyclone Gabrielle was one of the most calamitous weather events in New Zealand’s recent history.
While New Plymouth experienced power cuts, big swells and high winds, we were spared the tragic outcome experienced in other parts of New Zealand.
If the cyclone’s trajectory had deviated only slightly, it could have been a very different story.
In late November 2020, Taranaki was lashed by rain. Parts of New Plymouth were under water, slips closed state highways, the Mangaotuku Stream burst its banks and Huatoki Stream covered the steps in the downtown plaza. A culvert took out a chunk of Waitotara Valley Road. A small number of homes and garages were soaked, and intersections became ponds.
In one 18 hour period, the 90mm that fell at New Plymouth Airport was more than it had in the whole of November the year prior. At its heaviest, 80mm fell in central New Plymouth in five hours. The rainfall was significantly higher further inland, with the North Egmont Visitor Centre getting 195.5mm over two days.
It was a fair-sized storm, and just one of a number of recent examples that have impacted Taranaki. But the rainfall numbers pale in comparison to the devastation we’ve seen around other parts of New Zealand in January and February.
Cyclone Gabrielle dumped nearly 550mm of rain at one weather station in the ranges above Hawke’s Bay. In Tairawhiti, a number of stations recorded more than 400mm. The ensuing flooding, loss of lives and livelihoods and damage are on a scale that’s difficult to comprehend, let alone articulate.
So if New Plymouth has areas of flooding with much less, what would happen if we did get hit by that much rain? How prepared are we for more regular, severe storms brought about by climate change? And what should we be doing to prepare for the inevitability that something like Cyclone Gabrielle will hit us at some point?
Likely impact
Plainly, any predictions about what could have happened with a more direct hit from Cyclone Gabrielle are hypothetical. However, organisations such as Taranaki Regional Council, New Plymouth District Council and Taranaki Civil Defence do have a good understanding of where the region is vulnerable and how it tends to be affected by high rainfall.
TRC Director of Operations Daniel Harrison says there are two types of flooding; river-related flooding like what happened in parts of Hawke’s Bay and elsewhere in Cyclone Gabrielle, and localised flooding that occurred in New Plymouth in November 2020.
“Localised ponding occurs with intense rainfall in a very short period of time, and literally the stormwater system can’t cope. People’s lawns fill up with water, garages might get flooded – it’s unsettling and a hassle, but it’s usually not dangerous, certainly not like we saw in Esk Valley, for example.
“That river flooding is something different, where you have rain falling over a wider area within the catchment of a river, causing the river to come up rapidly, burst the banks and spread through the flood plain. That’s very dangerous, and we’ve sadly seen many stories from Cyclone Gabrielle that illustrate that.”
Harrison says most of New Plymouth is in a part of Taranaki known as the “ring plain”, which is the country that runs from the city down to Hāwera and everything west of it out to the sea. He says the typography of the area means it doesn’t get the type of river flooding seen in the wake of Cyclone Gabrielle.
“Those ring plain rivers are relatively steep and incised, and they’re used to that heavy rainfall; it’s how the landscape was formed. They carry the water down the mountain and out to sea, usually with relatively little damage or flooding occurring.”
To demonstrate, he refers to intense rain that fell around Taranaki at Waitangi weekend last year. Harrison says around 450mm of rain fell at a weather station at North Egmont over two days, and a similar amount fell at Cape Egmont – comparable rainfall to what Cyclone Gabrielle brought.
“We had some bank erosion and culverts washed out, but nothing like the kind of devastation they’ve had on the east coast.”
In saying that, there’s no such thing as zero risk when it comes to weather events. Central city streams such as the Huatoki and Te Henui can flood, and while they’re well equipped to handle it and don’t have many nearby homes, it would be going too far to say it could never happen.
Risk areas
So with Cyclone Gabrielle levels of rainfall, it seems extremely unlikely that New Plymouth would have experienced similar flooding to the east coast.
While that’s encouraging, Harrison says it’s a slightly different picture for the rest of Taranaki. He refers to it as the eastern hill country, running from Urenui and Uruti, across to Whangamōmona and down through Toko to Waitotara.
“That area will behave quite differently,” he says. “We’ve had a number of events in recent years where we’ve seen quite a lot of flooding, landslides, sediment, forestry slash, culverts washed out and fences washed away. It behaves similarly to the Gisborne district.
“Fortunately, the number of people in those areas is comparatively small. The exception is Waitotara, which has flooded a few times this century alone. It’s a vulnerable community that we keep a close eye on during those events.”
Another upshot is the effect of rainfall in the catchments of the Waiwhakaiho and Waitara Rivers. The Waiwhakaiho stems from Mt Taranaki and the ring plain, while the Waitara has origins in both the ring plain and the eastern hill country.
Unlike elsewhere in New Plymouth, their urban floodplain areas could theoretically experience river flooding similar to what Hawke’s Bay has had. However, Harrison says the Taranaki Regional Council has protected these areas with comprehensive flood schemes and stopbanks.
“We also have a network of rain gauges and river level recorders which is what we use as a warning system. We’re also upgrading our warning system to take into account new technology to give us extra security and certainty around what’s happening up in the hills and in the river catchment.”
The Waiwhakaiho and Waitara stopbanks were originally constructed in the 1990s and 1960s respectively. Harrison says the stopbank at Waiwhakaiho was upgraded between 2010-2013, and Waitara had similar work done between 2015-2017. He says they’re designed for a one in 100-year flooding event that also takes climate change into consideration.
“We estimate today’s one in 100 year flood to result in 2,700 cumecs in the Waitara River, which is 2,700 cubic metres of water going under the bridge per second. The stopbanks are built to handle 3,840 cumecs of water, plus another 500mm of freeboard on top. Waitara has very good flood protection.”
For context, he says the river generally flows at around 12 cumecs, and the average largest flooding event that occurs most years is just below 1,000 cumecs.
Harrison is quick to add that having good protection doesn’t eliminate all risk. People should be aware of what the risks are where they live, and stay away from even small streams in high rainfall events, because water can rise rapidly.
In order to reduce the effect of extreme weather on new builds, New Plymouth District Council requires any new consent applications on land that’s flood or erosion-prone to take steps to mitigate the risk. It says a “handful” of resource consents have been issued on such land in the last 15 years, when strong controls have been put in place.
“We’re looking forward to central government releasing details around its Resource Management Act reform which includes climate adaptation,” says NPDC Planning Manager Juliet Johnson. “Our draft District Plan is due for final approval later this year after years of public consultation and has a strong approach to managing natural hazards and ensures that waterways and floodwater paths are identified and managed.”
Water infrastructure
With river flooding either not a major risk or well mitigated, what about the localised flooding that’s known to occur in other parts of New Plymouth?
New Plymouth District Council’s current infrastructure strategy identifies an approximate $126 million in assets that have reached the end of their operating lives and are due to be renewed. This work has been deferred in the past due to financial constraints, and much of it includes stormwater, wastewater and drinking water infrastructure.
The council has now increased its annual renewals budget from $28 million to $51 million for the next 10 years in an attempt to catch up, and a range of work has already been done to boost New Plymouth’s resilience in the last few years.
Mayor Neil Holdom rates the ability of the city’s infrastructure to handle flooding as a C. He prefaces that by saying there’s been significant investment made in recent years, particularly in vulnerable areas, and we’re much better than we were.
“In reality, I think a C is about the standard the community has been prepared to invest in until now. If we want to get to a B or an A, we probably don’t have the money to do it.
“If you look at Waitara, there are 50-80 homes that already experience surface flooding in high rainfall events. We’ve started to make investments with our stormwater infrastructure there – we’ve put $20 million in, but to get to a B standard will cost more than $100m. Is that prudent to protect that number of houses? It depends who you ask.
“These are the challenging conversations the whole country will be having over the next few years.”
Councillor Amanda Clinton-Gohdes agrees there’s a cost-prohibitive aspect at play, particularly where there’s been pressure on councils not to raise rates. She believes the ever-increasing effects of climate change, should highlight the importance of being prepared.
“For a long time experts have been predicting that the climate would change, and we’ve all been reluctant to act on that information. Now those predictions are no longer theoretical – they’re here.
“Ideally both local and central government would have responded a long time ago, but often there has been a focus on keeping costs down in the short term. Perhaps it felt too expensive to make the investments or too difficult to make hard calls. But we need to be focused on the long term – and in the long term it may be more expensive not to.”
Holdom adds that uncertainty around Labour’s Three Waters programme has spurred councils around the country to act on upgrading their water infrastructure while they still can.
Roading
The widespread destruction Cyclone Gabrielle caused to the roading network across the North Island has shown how vulnerable communities can be, and how easily they can be cut off. With Taranaki having just one suitable road in from the north and out to the south, Neil Holdom says that’s what keeps him up at night.
“Particularly to the north; Mount Messenger is the big risk, but there are more than 90 other slip sites that could isolate us and take years to fix. State Highway 3 is going to take hundreds of millions of dollars to get right over the next couple of decades. There’s currently eight lots of road works between us and Te Kuiti, and lots are dedicated to slips.”
Federated Farmers Taranaki president Mark Hooper is also the organisation’s national roading spokesperson. He says damage to roads impacts farmers significantly, and can lead to serious animal welfare concerns and large implications for the local economy.
Hooper says farms on the east coast have been damaged by slips, had fences destroyed and lost water supplies, which all makes stock management extremely difficult. The only two options are to rely on donated feed or to de-stock, but if roads are damaged, neither may be possible.
“You suddenly run into an animal welfare crisis. It’s pretty stressful for farmers, and this is when mental wellbeing issues really start to kick in. If you know your animals have no water, you can’t feed them, manage them, or get them off the farm, that’s devastating. It’s the worst case scenario.”
Statistics New Zealand data shows agriculture typically makes up just under 10% of Taranaki’s annual GDP. As a sector, it’s the third-largest contributor to our regional economy, behind forestry, fishing and mining (18% of regional GDP in 2020) and manufacturing (13%). All three could be vulnerable if roads in and out of the region were damaged.
Mark Hooper says significant disruption to farming would have huge flow-on economic effects. For him, and many others, the key issue is if we’re doing enough to maintain roads to protect against damage from occurring.
“Now, nothing gets done without a traffic management plan, council work order, engineers report, multi-submission tender process, all these things. They all add cost and slow the process down, and you wonder if that’s part of the problem – our maintenance model needs addressing, because rural road quality is deteriorating and we’re losing infrastructure as a result.”
Slash
The issue of forestry slash damaging bridges and roads on the east coast has been highlighted by Cyclone Gabrielle. While slash remains a risk here, Taranaki Emergency Management Group Controller Todd Velvin says it’s less of an issue than in places like Gisborne.
“We’ve seen slash at the Waitara bridge in the past, but we don’t have it in the same intensity as on the east coast. If you get enough flooding in any river you will see debris; it doesn’t take much to wash out a riverbank with trees that can impact infrastructure along those streams and rivers.”
Locally, the risk of slash-related damage is highest on the Waiwhakaiho, Waitara and Waitotara Rivers that originate in the eastern hills where forestry blocks are more prevalent.
Things to have in an emergency survival kit (sidebar)
– Enough water for three days (nine litres per person, replaced every six months)
– Long lasting food and a can opener
– Regular medication if required
– A first aid kit
– Toilet paper and large plastic buckets for an emergency toilet
– Dust masks and work gloves
– A torch
– A transistor radio
– Spare batteries
– Spare baby supplies (if applicable)
– Pet food (if applicable)
– Cash
Being prepared
Todd Velvin believes people in Taranaki tend to be well prepared for severe weather events. He says the region gets enough bad weather that we’ve developed good resilience.
“We had several thousand properties without power through Cyclone Gabrielle, yet the community didn’t have a huge requirement for welfare support.”
He says whenever storms or bad weather damages infrastructure, it allows for fixes, upgrades and learnings that make the region better prepared for the next event.
“Cyclone Gita was another significant weather event for the region – we saw infrastructure failures in telecommunications and water, which was repaired, and highlighted resilience work that was later done in these areas. We are becoming a stronger province in response to weather events.”
Velvin says the key to being prepared is to have an up-to-date emergency grab bag, have a plan, and to make sure members of your house know what to do if an emergency happens. While there is advance warning for storms like Cyclone Gabrielle, other disasters can strike at any moment.
For example, He Mounga Puia (Transitioning Taranaki to a Volcanic Future) researchers say seismic activity in Taranaki is likely in the next 50 years, with a 50% chance of Taranaki Maunga erupting in that period.
In talking to a range of organisations with roles in protecting the community, there is a general theme that Taranaki has some natural advantages to combat the effects of bad weather. But there will always be an element of risk, and events like Cyclone Gabrielle remind us of that.