With a new minimum flow regime in effect, Waitaki irrigators and Meridian Energy signed an agreement last week to manage water levels in the lower Waitaki River.
Both sides say the agreement will protect the long-term future of the river, which, with an average flow at Kurow of 359cumecs, is the fourth-largest in the country.

At the Waitaki Irrigators Collective (WIC) office in Thames St, Oamaru, a memorandum of understanding was signed on Thursday agreeing to: joint support of the outcomes from Plan Change 3 of Environment Canterbury's Waitaki Catchment Water Allocation Regional Plan; sharing information; and determining the lower Waitaki River flow requirements to support irrigation.

Under Plan Change 3, from September 8, Meridian's resource consent changed, increasing how much water the hydro company was required to put through the dams, and irrigators' takes were changed to reflect the new "flow regime", Meridian environmental strategy manager Jeff Page said. On September 8, the plan's requirements of a minimum flow of 172cumecs at Kurow came into effect.

"That's making it real out there for the river," Mr Page said. "And this basically is then just cementing us continuing to work together going forward."

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At the height of the river's use, from October to March, the minimum flow would be 190cumecs.

While the previous low-flow rules allowed Meridian to lower flows to 120cumecs, the energy company itself used 150cumecs as the low bar, he said.

"This is kind of the sharp end of Plan Change 3," Mr Page said on Thursday.

"We all want a healthy river, that's the bottom line, but we also want a river that is healthy and is managed in a way that we all agree it should be managed.

"We are all signing up to 'now this is how the river should look going into the future' and it's - for us - it's having that, if you like, stable peg to work from, it gives you confidence to do other things. But while you're still not quite sure how that regime should look, you're always going to be a little bit more cautious, and then you end up doing things that you might regret later."

WIC director of strategy and policy Elizabeth Soal said the irrigators' collective, which consists of six schemes plus a group of independent irrigators, represented about 600 farmers who irrigated a combined 85,000ha - and those farmers needed irrigation to continue "with certainty into the future", which Plan Change 3 allowed.

The Waitaki River has generated electricity since the 1930s, WIC's website says. A series of hydro-electric dams, with Lakes Benmore, Aviemore and Waitaki, generate around 20% to 25% of New Zealand's electricity.

Meridian general manager of markets and production Guy Waipara, of Wellington, said both hydro-electricity and agriculture were important industries for the area's future, as was the river.

"That's how you get over short-term self-interest; if you look longer term, you can always find lots of common ground, even if at face value you look to be competing."

In July last year, the Otago Daily Times reported ECan commissioner Prof Peter Skelton said the economic benefits of Plan Change 3 - providing for "high reliability of supply" - would be between $2.8 million a year and $6.9 million a year, but Lower Waitaki River Management Society chairman Ian McIlraith said the ECan decision, which lowered the minimum flow at the Waitaki River mouth below levels set in 2006, tipped the balance between business interests and the health of the river in favour of industry.