Vegetation that lines firms couldn't trim was the biggest cause of cyclone power cuts

Wednesday, 11 October 2023

A review of the damage caused to electricity networks by Cyclone Gabrielle suggests that lines companies may need more rights to trim trees to avoid future storms causing a similar level of damage.

It also suggests that the standards to which power networks are built may need to be toughened up to take account of a growing risk of strong winds caused by climate change.

About 240,000 homes, or 11% of households, lost power during the peak of Cyclone Gabrielle on February 14, according to the review completed by the Electricity Networks Aotearoa (ENA).

Richard Krogh, managing director of consulting firm Energia, who led the review, said the biggest single cause of power outages was damage from vegetation that had not grown close enough to power lines for trimming to be mandatory, but which nevertheless fell on lines during the storm.

That caused power outages for 67,000 homes.

Two other causes of damage, wind damage to the network and flooding, including the flooding of some substations in Hawke’s Bay, individually resulted in slightly fewer outages, although in most cases the problems they did cause were longer lasting.

Krogh said the resilience of electricity networks would be improved if lines companies were allowed to ensure vegetation was kept further away from power lines.

They currently have an obligation to perform the first cut or trim of encroaching vegetation, after which responsibility passes to the landowner.

But the ENA suggested in a submission to the Government in May that lines companies might be willing to take on more responsibility for ensuring trees in people’s gardens were trimmed back from power lines.

That would be in return for foresters and commercial land-owners taking full responsibility for vegetation on their own land, including for any “first cuts”.

Since lines companies can factor allowable expenditure into their charges through a process regulated by the Commerce Commission, taking on more of the cost and responsibility for tree-trimming on residential land would not necessarily leave them worse off financially.

Relatively little damage was caused during Cyclone Gabrielle by trees that lines companies could have required to be trimmed but which weren’t, Krogh said.

“We can be pretty comfortable that electricity distribution businesses were doing a good job at managing vegetation within the constraints that they have.”

Krogh said the review indicated lines companies were well-prepared to deal with the storm damage.

“We did look at the weather warnings that were issued by MetService and I think it would only be with hindsight that you could suggest that they were indicating the level of severity that actually occurred.”