Transpower knew Napier substation was 'critical' risk in worst case flood

Jun 27, 2023

Transpower identified its crippled Redclyffe substation in Napier two years ago as one of 12 substations around the country where improved flood protection was “critical”.

Chief executive Alison Andrew said it drew up the list in 2020 after recognising it needed to better manage the growing risks posed to the power network from climate change and natural hazards.

“In 2020 we undertook a desktop exercise to understand flood risks on our assets, under both current and climate change scenarios,” she said.

“This showed that we had a number of sites that were vulnerable to flooding under some scenarios now or in the future. 12 substations were identified as critical for improving flood resilience and more detailed studies are scheduled for later this year. Redclyffe was one of these.”

READ MORE: * Power restored to 90,000 homes, but 40,800 in Hawke's Bay still cut off * Power now restored to about 62,000 homes in Hawke's Bay and Gisborne * Gisborne and Hawke's Bay could be without power for 'weeks', Transpower warns

It is understood that it classified the risk at Redcliffe as critical based on its vulnerability to a one in 250-year flood.

The Redclyffe substation has suffered “extensive damage” after being flooded by Cyclone Gabrielle on Tuesday, leaving Transpower scrambling to put in place workarounds to provide the power needed to reconnect tens of thousands of homes and businesses in the region.

The power cuts also contributed to a collapse of communications infrastructure in Hawke’s Bay.

Transpower has been working with Napier-based lines company Unison and Gisborne-based Eastland Group to re-route power to homes and businesses around the Redclyffe substation.

It said on Thursday that it had been able to provide enough electricity to the region to restore power to about 90,000 homes.

But it said Napier lines company Unison Networks had advised there were still 40,800 homes without power in Hawke’s Bay, including 31,700 homes in Napier.

Eastland said it had 4500 customers without electricity, including more than 1600 in Wairoa, and warned them that they should be prepared to be without power for “some days”.

A consultation document Transpower published in September document showed it was not standing still in trying to address the flooding and other risks it had previously identified to its infrastructure, but is likely to raise questions over whether it has been planning to do enough, fast enough.

It shows Transpower was seeking permission to spend $109 million between 2025 and 2030 improving the resilience of its network.

Transpower’s costs ultimately flow through to electricity bills and, given its monopoly status, the state-owned enterprise needs permission from the Commerce Commission for such investments.

Its plans for 2025 to 2030 include mitigating the risk of flooding in “two to three” substations, along with a raft of other work to harden its infrastructure such as pylons and buildings against a range of natural assets, also including slips and earthquakes.

Andrew said that as part of that plan, planning for any additional resilience measures for Redclyffe would have commenced later this year if the funding was to be approved.

However, she indicated that even if the work had been done earlier, it might not have been enough to prevent a major network outage.

“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.”

Transpower said in the September document that it was designing new substations to withstand a “one in 450” flood event.

“We know the social risk appetite for resilience is changing and our assets are coming under increased pressure due to the changing climate,” it said in the document.

Andrew said the Redclyffe substation was designed in 1927 and refurbished in the 1970s and was designed to withstand a “one in 100 year” flood.

She indicated it might now consider putting in a more ambitious funding bid for approval by the Commerce Commission.

“Cyclone Gabrielle will prompt infrastructure providers, including Transpower, to reconsider our investment approach to resilience and whether it is sufficient for the future,” she said.

The state-owned enterprise said that given the damage and the time it would probably take to repair the Redclyffe substation, it was now focussing on bypassing the substation by running the high voltage 220KV power line that fed into it to a different substation in Whakatu, north-east of Hastings.

“We have been working with local lines company Unison on this bypass option and expect to be able to provide an update later today on when it will be completed,” it said in a statement on Thursday morning.

However, Transpower has been unable to confirm whether the mitigations will allow lines companies to reconnect all their customers.

Not all of the power outages are now down to the remaining issues with Transpower’s power supply, with damage to the local networks owned by Unison and Eastland now a significant factor in reconnecting additional homes.