Nationwide electricity grid operator Transpower is working “at pace” to determine the future of its Redclyffe substation, which was submerged and put out of action when the Tūtaekurī River’s banks were breached near Taradale during Cyclone Gabrielle.
A spokesperson said its field teams are working hard to restore Redclyffe and the Hawke’s Bay network to a “normal configuration and level of security and resilience” as a short-term step and priority.
While it was just four days before some of the supply was restored in Napier, it’s been progressive work for both Transpower and network local network supplier Unison - some people are still being supplied power via a generator, but most areas now have supply restored, almost six weeks after floodwaters raged through the substation’s control room at ceiling-height during the storm.
On Friday, Unison reported they had switched Glengarry from generation to network supply, and that good progress was also being made restoring the network north of Napier at Whirinaki, which Unison aims to “re-liven” this week.
Unison had to deal with numerous local supply issues such as fallen lines and poles in addition to the Redclyffe failure, and Unison incident controller and general manager of commercial, Jason Larkin, said that switching the areas back to network supply removed the need to bring in diesel to keep the generator running.
“Glengarry recorded the highest rainfall in the region during the cyclone, and the damage to our network in the area was considerable,” she said.
“This has been a massive job for our crews over recent weeks, as they have worked extremely hard to restore the new poles and lines after parts of the network were destroyed by the cyclone and flooding.”
Prior to the catastrophe, Transpower plans were emerging to enhance the site’s resilience, with work possibly to have started later this year, but Transpower says even then, it would not have been a guarantee of resilience against the cyclone that plunged all of Napier and thousands of other power users into darkness.
Transpower is looking at options to both improve medium-term flooding resilience and find the best long-term solution for a substation built almost a century ago.
“This includes options like a new site, or rebuilding back better at Redclyffe with equipment installed above possible flood levels,” the spokesperson said.
In mid-February, Transpower chief executive Alison Andrew said that in 2020, as part of a growing awareness of the need to manage increasing climate risk and natural hazards, Transpower undertook a desktop exercise to understand flood risks on the assets, under both current and climate change scenarios.
The Redclyffe substation was one of 12 substations identified as being critical for improving resilience to a one-in-250-year flood, and more detailed studies are scheduled for later this year, she said.
With expenditure regulated by the Commerce Commission, Transpower is consulting on a proposal for its spending plans from 2025 to 2030.
“Our base funding includes incremental improvements in resilience as part of ongoing maintenance,” Andrews said. “In addition to that, we have taken action and proposed a resilience programme as part of our next regulatory funding period. We have requested approval to spend an extra $109 million on resilience work.”
“As part of this plan, planning for any additional resilience measures for Redclyffe would have commenced later this year in anticipation of the funding being approved,” she said, but added: “Cyclone Gabrielle was a catastrophic event. Even if we had completed resilience work at Redclyffe prior to the cyclone, there are no guarantees that it would have been sufficient to withstand the effects of the cyclone.”
Redclyffe was initially constructed in 1927 and then upgraded in the 1970s, when engineers assessed the stopbanks as being sufficient to prevent flooding at the substation.
“While it was constructed to high resilience standards at the time (standards fit for a one-in-100-year flood), our understanding of risk continues to evolve and we now build substations to [a standard fit for a] one-in-450-year flood,” she said.
“As an example, our Wairau Road substation in Auckland was built in 2013 to a one-in-450-year standard,” she said. “During the Auckland floods in late January, this substation had 1.5 metres of water through it but remained fully operational, and power continued to flow to 500,000 people as a result.”
She said all infrastructure providers strive to achieve the right balance of affordability, sustainability and reliability from their assets, but it is not possible for any infrastructure company to build its network to the extent that outages never occur.
But, she said, Cyclone Gabrielle will prompt infrastructure providers, including Transpower, to reconsider investment approaches to resilience and whether it is sufficient for the future.