Groundwater to boost cheaper irrigation plan

A revamped Central Plains Water (CPW) irrigation scheme will cost a third of the original proposal and be boosted by groundwater.

Project manager Derek Crombie said the project's cost had fallen from $409 million to $135m because commissioners had knocked back plans for a 55-metre-high dam in the Waianiwaniwa Valley.

However, should Lake Coleridge or the Lees Valley be used for large-scale storage as identified in the recently released draft Canterbury water management strategy that would "change the game completely", he said.

"We'd be back again to the original," Crombie said.

CPW has abandoned plans to boost the region's groundwater, one of the key justifications for the controversial scheme.

Crombie argued in this paper two years ago that the scheme which plans to irrigate about 60,000 hectares using water from the Rakaia and Waimakariri rivers would restore the region's groundwater resource to its 1990 state.

Yesterday, he confirmed the scheme would have to be supplemented by groundwater from existing consents.

"The original proposal was a better one, not being dependent on groundwater at all. The commissioners decided the scheme wasn't the right one, and our hands are tied."

Environment Canterbury officers have discussed putting surface water onto the ground to recharge aquifers in winter, but nothing has been formalised.

New technical reports filed for a resumed hearing into the massive project state half of the scheme's irrigated area would now be unreliable.

A report from irrigation expert Cliff Tipler said the area of the scheme that had no access to groundwater would have reasonable reliability in spring, but poor reliability in summer and autumn.

"Consequently, there will be two very different land-management strategies for each half," it said.

CPW would take more water, proportionally, from the Rakaia River. Estimated takes from the Waimakariri would be reduced by 73 per cent, the report said.

Tipler's report shows CPW has struck a deal with the Barrhill-Chertsey irrigation scheme to use an extra seven cubic metres a second from the Rakaia River.

Less reliable water will mean less intensive farming over half the irrigated area.

Farm consultant Andrew Macfarlane said poor reliability in February and March meant land was unsuitable for dairying unless high-input supplementary feed was used.

His evidence showed a dramatically smaller area was likely to be converted to dairy farming under the new scheme.

Original figures showed the area used for dairy farming would increase from 22,000ha to 46,500ha using CPW water.

That area has been scaled back to 25,000ha.

Farm profitability would drop from $186m to about $81m, Macfarlane predicted, but the return on investment would remain about 14.8 per cent.

Freshwater scientist Greg Burrell said the revised scheme would still increase flows in lowland streams, but by a smaller amount than the original proposal.

He said increased nutrient concentrations could hurt invertebrates and fish.

Malvern Hills Protection Society spokeswoman Rosalie Snoyink was concerned there were about 60 properties still affected by notices of requirement for the headrace canal.

"People talking to us think that because the dam and reservoir has been rejected by the commissioners that the whole scheme is over," she said. "It's clear that CPW still intend to irrigate 60,000ha with run-of river water and use groundwater when the rivers are low."

The CPW hearing will resume next month.

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