Last year's flow Waikato River's lowest

LOW FLOW: The Waikato River
LOW FLOW: The Waikato River

Record low water levels in the Waikato River have made for a challenging year for one of the country's major power companies.

Mighty River Power's annual result this week announced that in the 2013/2014 financial year it saw the "worst hydro inflows into the Waikato River hydro catchment in the company's history".

Over the year, the electricity company generated 10 per cent less hydro power than anticipated at its eight Waikato River hydro power stations.

Waikato Regional Council has monitored the average flow at various points of the river for the past 38 years.

Council spokesperson Stephen Ward said the data indicated that the average flow at the Bridge St, Hamilton, monitoring site during 2013 was the lowest since 1976, at 191 cubic metres per second.

The highest annal average, recorded in 1996, was 343 cubic metres per second.

Ward said so far this year the average flow had been 201 cubic metres per second, but that did not take into account the remaining four months of 2014. "The averages tend to bounce about a bit and we've also had higher ones in the past decade. So it's hard to see any trend in the numbers."

Mighty River Power was able to make up for shortfalls in hydro generation using its five geothermal stations, including the new Ngatamariki station near Taupo, which became operational in September.

According to the report: "Generation volumes were 765 gigawatt-hours lower than forecast in the PFI [prospective financial information] due to the extremely low hydro inflows experienced in the Waikato catchment and reduced gas-fired generation from Southdown in line with lower utilisation of thermal plant across the industry."

Mighty River Power chair Joan Withers said the earnings guidance for financial year 2015 were in the range of $495 million to $520m, "subject to any material adverse events, significant one-off expenses or other unforeseeable circumstances including hydrological conditions".

The annual result said in providing guidance for the next financial year, the company assumed normal hydro production inflows.

Mighty River Power did not respond to questions about whether it is worried the river will continue to have low flow.

Communications manager Maria Winfield said the company will stick to its assumption of "normal hydrology" for the coming year, because "nobody can predict the weather".

Winfield said the company is flexible because it can buy power from the market and use other power sources.

"We've got a really resilient business because of that."

University of Waikato hydrologist Earl Bardsley said the river flow changes significantly in dry or wet periods.

However, he said the concern for the general public is during relatively short periods of extreme weather that can lead to power shortages and lack of feed, or at the other extreme, flooding.

Green Party candidate for Hamilton East Mark Servian said he had noticed the river had been lower in the last couple of years.

He said it was probably partly to do with dam control regulating the flow, but a lower river flow was an environmental concern.

"The lower the water is, the greater the pollution, because the amount of nutrients going in is the same or increasing."

Waikato Times