Deluge misses southern hydro lakes

There was flooding in nearby Oamaru, but the southern hydro lakes missed out on the rain. Photo / Supplied

Last weekend may have been Oamaru's wettest since daily rainfall records began in 1950, but the deluge that hit eastern coastal parts of the South Island over the weekend all but missed the southern hydro lakes, which remain at critically low levels for the time of year.

The managers of the southern catchments, Meridian Energy, Contact Energy and Genesis Energy, all reported either little or no additional rainfall, although national grid operator Transpower said lake levels now sit at 62 per cent of the national average level for this time of year, compared with 58 per cent before the weekend.

A Meridian Energy spokeswoman said the weekend weather "did not bring inflows to our catchments" above the Waitaki River hydro system and in Lake Manapouri in Fiordland, although a small amount of rain had fallen today in Lakes Te Anau and Manapouri.
Genesis Energy said its southern lake storage was at 51 per cent of average levels for this time of year and less than a third full.

Further south, the catchment fed by Lakes Wakatipu, Hawea, Roxburgh and the storage Lake Dunstan, Contact Energy reported "a short increase of additional water flowing into one of tributary rivers of Lake Roxburgh, where the Roxburgh Dam generates electricity, but did not result in any significant or prolonged increase in the Clutha River as a whole.
"As at today, storage levels in Lake Hawea are at 11 per cent of mean, or 7 per cent of full", and just above minimum operating levels.

Wholesale electricity price still spiked to nearly $250 per Gigawatt hour at the South and North Island reference nodes of Benmore and Haywards respectively for the breakfast demand surge this morning. Customers of power companies such as Flick Electric, which charge for power according to movements in wholesale spot prices, have been experiencing far higher and more volatile power bills in recent weeks as dry conditions in the hydro catchment areas have combined with heavy winter electricity demand to push prices up.

Customers on fixed-price tariffs charged by the majority of electricity retailers are unaffected, although the power companies are watching closely to see whether a general upward trend in prices forecast for next winter and 2019 could justify increased energy charges in the medium term, with Contact Energy having already moved earlier this winter in many areas after a long period of stability in the energy component of their power tariffs.

A Meridian spokeswoman said also that there was a below average annual winter build-up of snow in the Southern Alps this year, although with some weeks of winter still to go, that could change.

The so-called 'snow-pack' in the mountains is the source of an annual spring melt that tends to refill the hydro lakes ahead of the following winter.

The National Institute for Water and Atmospheric Research, NIWA, said Oamaru's 161.2 milllimetres of rain last Friday was the most ever recorded in 24 hours in 67 years of record-keeping, while at Winchmore, South Canterbury, between 9am on Friday and 9am on Saturday, 150.7mm of rain was recorded - more than the twice the normal total for the whole of July.