In 2020, Transpower screened its network of 170 substations across the country to identify any that were at risk of flooding for any reason, including sea-level change and the increasing frequency of extreme weather events related to climate change.
We found 12 that could be vulnerable to a range of flood scenarios and that are particularly critical for network resilience. These were then evaluated through desktop studies to better understand the risks.
A vulnerability does not mean a substation will suffer acute damage in a flood, or that power supply will be interrupted should a flood occur. The impacts of different flood levels at each site are unique to the design and construction used at that site and the relative height of equipment. Considerations include the heights of key equipment such as sensitive control equipment in control rooms.
We had plans in place to begin detailed investigations at the 12 sites, beginning in July 2023. As a result of Cyclone Gabrielle, we 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.
We had also developed a funding proposal to address the two to three highest priority sites beginning in July 2025. This is included in our investment plans for 2025-2030 due to be submitted to the Commerce Commission for approval later this year but we are looking at how we can bring that work forward.
Types of flooding mitigations we typically consider for substations include:
- full relocation of a site (which is often cost prohibitive)
- increasing the height of critical equipment
- improving drainage and water flows around a site.
Lower cost interventions are generally effective at increasing the resilience from a lower level of resilience from a one-in-100-year flood event towards a 1:250 level. However, they are often insufficient to realise a resilience level equivalent to our new build standard of 1:450 years.
Cyclone Gabrielle and last month’s flooding in Auckland highlight just how critical this work is, and also demonstrate the scale of the challenge to improve resilience in our network.
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.
The following substations were identified as vulnerable to extreme flooding and critical for local network resilience:
- Albany, Auckland
- Edgecumbe, Bay of Plenty
- Redclyffe, Napier
- Whakatu, Hastings
- Whirinaki, Hastings
- Southbrook, near Rangiora
- Bromley, Christchurch
- Temuka, north of Timaru
- Studholme, north of Oamaru
- Frankton, near Queenstown airport
- South Dunedin
- Gore, Southland
We have advised councils and our connected electricity lines company partners at these substation sites about the flooding risks and will continue to engage with them on this and other resilience matters.
Proposed Resilience Programme
As a monopoly, Transpower is regulated by the Commerce Commission. Every five years we submit a proposed five-year workplan to the Commission, which consults on and determines our spending allowance, our quality targets, and earnings. We are currently midway through our third regulatory control period (RCP3) which covers 2020-2025. We are working on the proposal for our “RCP4” period for 2025-2030.
As noted above, in our RCP4 Proposal Consultation, we proposed expenditure specifically for increasing the resilience of the grid ($109.6 million). As indicated, we are reconsidering whether that needs to be expanded. We will use the information from our detailed investigations into the 12 substation sites to help right-size the proposed programme.
Following our final submission at the end of 2023, the Commerce Commission will review our proposal and consult on it in 2024, before providing its final decision toward the end of 2024. We would encourage you to submit to that consultation.
For further information about our asset management approach we point you to our RCP4 Proposal Consultation (resilience comes up in Part 4), our Asset Management Plan 2022, and our Asset Health and Network Risk Roadmap and its Nov 2022 update.