CPW scales back irrigation project

The Central Plains Water (CPW) irrigation project is no longer a "giant dairy scheme", with proposed dairy conversion scaled back to 3000 hectares.

Backers of the $135 million project are trying to convince independent commissioners of the revamped scheme's benefits at a resumed hearing in Christchurch this week.

In April, commissioners signalled they would probably reject plans for a 55-metre-high dam in the Waianiwaniwa Valley, about 60 kilometres west of Christchurch – necessitating a CPW rethink.

Commissioner Bob Nixon asked yesterday whether less-reliable water supply meant the project was no longer a "giant dairy scheme".

Farm consultant Andrew Macfarlane, for CPW, agreed the project had "absolutely moved away from that now".

As the scheme would rely more on run-of-river water backed up by groundwater, Macfarlane said there would be fewer dairy conversions and process crops.

A proposed 24,500ha increase in dairy land had been scaled back to about 3000ha.

Macfarlane said there would probably be an increase in mixed cropping and carrying stock over winter to get better prices.

Irrigation expert Cliff Tipler said the scheme would rely on water from the Rakaia River, meaning much less water was needed from the Waimakariri River.

About 760,000 kilograms of nitrates – 30 per cent more than the existing "mass" – would be leached.

However, he said this would cause little change to the groundwater's nitrate concentrations.

Freshwater scientist Dr Greg Burrell said increased intensive farming on the central plains could cause extra nitrates to enter lowland streams.

However, he said because of existing high levels a catchment-wide approach would be necessary to tackle the issue.

More nutrients could cause a small increase in algae.

CPW lawyer Matthew Casey, QC, said there were positives in the reduced scheme, including some groundwater recharge and improved lowland stream flows.

"The economic benefits which, while not as stellar as under the original scheme, are still significant and should weigh heavily in your decision," he said.

"Concerns about nitrates are acknowledged but can be accommodated."

CPW economic expert Philip Donnelly said the revamped scheme would still generate significant exports.

However, he said his estimates did not include the "true magnitude" of the scheme having less reliable water.

Commission chairman Philip Milne said a proposed change to the Waimakariri River regional plan, advertised by Environment Canterbury in August, would be given "very little weight" in their deliberations.

The proposed plan change allows for a "gap" of 30 cubic metres a second (cumecs) between the priority A block water allocations and the lower-priority B block.

At the time, green groups hailed the move as providing "important breathing space" for Waimakariri River species.

The hearing continues today.

- © Fairfax NZ News