Why did this storm cause so much electricity havoc?

Tuesday, 17 April 2018

People living in areas with lots of trees might need to consider their contingency plans, Vector said.

Nine hundred Auckland households are still without power, almost a week after a storm ripped through the city.

Gale-force winds and heavy downpours downed hundreds of trees across the city last Tuesday. Some of those trees snapped power lines, causing widespread damage to the city's electricity network. About 180,000 properties were affected.

Lines company Vector described it as the worst network damage in a decade.

Who's affected?

The houses still without power now are predominantly in the more rural areas of northwest Auckland. For some, their water is also affected because their tank systems require electricity to function.

Vector group chief executive Simon Mackenzie said the network had suffered an unprecedented amount of damage due to trees being uprooted and taking out power lines, or branches falling off.

'All over large parts of Auckland there are over 1000 trees down over the network.'

He said 2500km of lines had been damaged.

Recovery efforts had moved into trickier areas and half the houses without power needed their service lines, on their private property, fixed.

Economist Gareth Kiernan said the economic impact on the city was likely to be minimal because few businesses were affected.

If the central city had lost power for this sort of period, it could have had a material impact on GDP, he said.

Customers will not qualify for the 'Vector Promise' of $50 if power is not restored in 2.5 hours, because the company does not apply the pledge to events outside its control, such as storms.

Why this storm?

You might think that in a city such as Auckland, storms are a frequent occurrence. So why did this one cause so much damage?

Mackenzie said tree damage could be expected when winds were faster than 70 km/h. This time, gusts hit 200 km/h.

Forecaster Philip Duncan, of WeatherWatch, agreed the storm was unusual. 'It was different to most other wind events because only a narrow part of the country was hit by winds and they were particularly fierce, with speed that trees can't stand up to, in Auckland anyway.'

Auckland trees grow quickly because of the warm climate and as a result are larger than some of a similar age in other parts of the country and more likely to break in a storm such as this one.

Would underground lines be better?

Underground power lines would not have been damaged by falling trees but they can have their own problems, including interference from tree roots.

Vector said its teams were discovering more damage than predicted.

If there is an earthquake or other natural disaster affecting the ground, it can be hard to pinpoint where the damage is.

What can be done to stop this happening again?

At the moment, trees around low-voltage lines, such as on side streets, have to be trimmed half a metre away from power lines.

In high-voltage areas, it's 1.5m. Mackenzie said more trimming would not have helped in most cases. Some of the trees were uprooted and fell across from the other side of the road. There were hundreds of thousands of trees across the network, he said.

The Electricity Network Association said it was difficult to get risky trees removed. Chief executive Graeme Peters told media high-risk trees should be considered on a case-by-case basis, not with such a prescriptive approach.

Mackenzie said Vector would not want to see people planting trees under powerlines or close to them. Climate change modeling would help to understand what was happening with the weather, he said.

Vector was talking to Auckland Council about tree management policies.

Wind speeds were too much for trees and power lines.

The council's head of operational management and maintenance Agnes McCormack said it was done according to routine schedules, inspections by council arborists and after requests from the public.

'We will be working with our contractors to consider lessons learned in relation to tree maintenance and power line clearance in our review of the response to last week's storm.'

Mackenzie was aware Vector could improve its communication with customers. Its outage app had not performed as it should, he said.

He said people living in areas with a lot of trees might need to consider having small stand-by power generators to run their water pumps during an outage.

When there were new residential developments where their infrastructure relied on electricity, communities would need to consider their contingency plans.

'The challenge is, how does a country that has a love of trees and a fast-growing tree environment also provide electrical supply through these events? What can be done to make sure customers get an understanding of the trade-offs?'