Transpower identifies 12 substations for additional resilience work

Transpower has released a list of 12 substations it has assessed as vulnerable to extreme flooding and that are also critical for the continued operation of local power networks.

The substations were identified in a 2020 desktop review of the risk of flooding at Transpower’s 170 substations across the country.

Transpower General Manager Grid Development John Clarke said Transpower performed the desktop study to identify flooding threats to its critical infrastructure given the evolving understanding of risk from sea-level change and the increasing frequency of extreme weather events related to climate change.

“Our substations were assessed for their vulnerability against a range of potential flood events, as well as the likely impact on local electricity supply if they were to be extensively flooded,” he said. “A vulnerability does not mean a substation would suffer serious damage in a flood or that power supply would be interrupted.

“Redclyffe substation in Hawke’s Bay, which was flooded as a result of Cyclone Gabrielle, was identified as one of these 12 at-risk substations and we were due to start a more detailed assessment of risk and start planning additional resilience measures later this year.”

Redclyffe substation was initially constructed in 1927 and then upgraded in the 1970s. Engineers at the time assessed the stopbanks as being sufficient to prevent flooding at the substation in a major event.

“Our desktop assessment identified Redclyffe as being at risk of around 20cm of flooding during a one-in-100-year event, 50cm during a one-in-200-year event, and significant inundation in a one-in-500-year event where the Tūtaekurī River stopbanks were overrun,” Mr Clarke said.

“Cyclone Gabrielle was a catastrophic event and the impact at Redclyffe exceeded what had been modelled in even the one-in-500-year event scenario. This means that had we implemented any planned resilience work, it would not have been sufficient to withstand the extent of the flooding experienced as a result of Cyclone Gabrielle.”

Whirinaki and Whakatu substations in the Hawke’s Bay are also on the list. Whirinaki was flooded but sustained less damage than Redclyffe. It supplies power solely to Pan Pac Forest Products Limited and is also the grid entry point for generation from Contact Energy. Whakatu was not affected other than having its supply from Redclyffe cut.

Mr Clarke said that understanding of risk continues to evolve and Transpower now builds substations to withstand a 1-in-450-year flood.

“As an example, our Wairau Road substation in Auckland was built in 2013 to the new 1-in-450-year standard,” he 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.”

Transpower recently added a $8m switch room at Redclyffe that was built to the new standards and that withstood the impact of the flooding in the Hawke’s Bay. The resilience of the switch room has allowed it to be used to temporarily connect to a 33kV line that Unison Networks is using to restore supply to additional parts of Napier.

“Because we built the switch room to our current resilience standards, it did not suffer serious damage, unlike other parts of the substation, which assisted us in restoring some power more quickly than we otherwise would have been able to,” Mr Clarke said.
 

Resilience work planned
Transpower had plans in place to begin detailed investigations at the 12 sites, beginning in July 2023. As a result of Cyclone Gabrielle, Mr Clarke said it will accelerate that work.

“The investigations will help us more deeply understand  the risks, options for mitigations, costs of mitigations, which sites and mitigations should be prioritised, and whether our current programme needs to be expanded,” he said.

Transpower had also developed a funding proposal to address the two to three highest priority sites beginning in July 2025. This was included in its investment plans for 2025-2030 due to be submitted to the Commerce Commission for approval later this year, but Mr Clarke said that Transpower will also be looking at how it can bring that work forward.

He added that as a state-owned  infrastructure company, it is important that Transpower balances reliability, affordability and sustainability for the benefit of New Zealanders as it maintains and upgrades its network.

“We announced last year that we were planning to ask for around $109 million funding for additional resilience work for the 2025-2030 period,” he said. “This resilience work is over and above incremental improvements in resilience built into our regular network strengthening and maintenance work.

“Cyclone Gabrielle and January’s flooding in Auckland highlight just how critical this work is, but they also demonstrate the scale of the challenge facing us all.

“We’ll be taking a good look at these risk assessments and talking with our regulator the Commerce Commission, the Government, our partners in the power industry, councils and the wider community about what more needs to be done.”

Transpower has advised councils and its electricity lines company partners about the flooding risks at the 12 sites and will continue to engage with them on this and other resilience matters.
 

Note on Transpower regulation
While Transpower is state-owned,  as a natural monopoly, its expenditure is regulated by the Commerce Commission in five-year periods.  Transpower’s spending is recovered from consumers in the form of transmission charges to lines companies. These make up 8-10% of the average consumer’s total electricity bill.

12 substations and risk assessment

For more information, contact Principal Advisor Corporate Communications Nathan Green, 027 387 5256.