Half-empty dams await thorough soak
Hopes that heavy weekend rainfall could go long way towards alleviating Auckland’s water woes
A heavy soaking forecast this weekend is hoped to help relieve Auckland’s dams — half empty after another dry summer.
As at yesterday, capacity across Watercare’s 10 dams stood at 51.1 per cent — compared with a historic average of 77.3 per cent, and dismally close to where it was last year, after the region’s worst drought in 25 years.
Watercare’s head of servicing and consents, Mark Bourne, said the region hadn’t received the near-normal rainfall initially predicted for the summer, when a now-fading La Nina climate system played out dramatically differently to its traditional patterns.
“In reality, the rainfall we recorded in our catchment areas, where the water is caught and stored, was only 26 per cent of normal in December.”
Totals stayed on the low side of normal over January (69 per cent), February (67 per cent) and March (77 per cent).
But Bourne said storage capacity had still hovered around where Watercare forecast it to be.
That was partly down to water restrictions put in place — which hadn’t been nearly as stringent as in the past — along with Aucklanders changing their behaviour to keep consumption rates within targets.
“That’s been things like people taking shorter showers, or popping the plug in the sink when doing the dishes,” he said.
“Individually, they’re all small measures, but when you’ve got 1.7 million people doing it, it makes a huge difference.”
Watercare’s aggressive leak reduction efforts had prevented the loss of millions of litres of water — while bringing new sources online had bumped up storage.
That included increasing takes from the Waikato River, reinstating an underground aquifer in Pukekohe and upgrading the Onehunga Water Treatment Plant.
When it goes live this winter, the new Waikato Water Treatment Plant, brought forward amid the drought, will deliver up to 50 million litres a day.
With the addition of further plant upgrades at Papakura and Waita¯kere, by the end of the year, Watercare will have ramped up supply by more than 100 million litres a day — enough to serve all of Palmerston North, Tauranga and Hamilton.
They’re all small measures, but when you’ve got 1.7 million people doing it, it makes a huge difference. Mark Bourne, Watercare
Looking ahead, Bourne expected lake level totals to “bottom out” over May, but then start to fill again.
“The amount they’ll fill will be dependent upon rainfall, but under current forecasts, we can expect similar levels to last year.”
Niwa’s latest seasonal outlook predicted that rainfall levels would be either near or above normal in the north and west of the North Island during the next three months.
As for next summer, Bourne didn’t expect Aucklanders would be hit with tougher restrictions.
The three potential scenarios — that restrictions be removed, retained, or tightened — depended on what capacity looked like at the end of the year.
“Based on the forecast today, and if we receive continued levels of savings that we’ve got at the moment, we’re certainly not anticipating a need for more severe restrictions at this point in time.”
Meanwhile, Niwa forecaster Ben Noll said much of the Auckland region still remained dry, more than a month after summer.
Soil moisture levels were running at a deficit of between 90mm and 110mm across Auckland — and elsewhere, pockets of severe dryness could be found in places such as southern Hawke’s Bay, Canterbury and central Otago.
“In Auckland, we’re probably a good two or three soakings away from getting the groundwater recharged,” Noll said.
“Then we can expect more water going into waterways — and then into the dams.”