Stuff - Irrigators group revives reservoir scheme as alternative to Waimea dam

Written by Cherie Sivignon

A group of Waimea irrigators has revived its proposal for riverside reservoirs as an alternative water storage scheme to the troubled Waimea dam project.

Waimea Irrigators and Waters Users Society consultant Brian Halstead said the group's updated proposal for three lined storage ponds might get Tasman District Council "out of a hole".

The relaunch of the reservoir scheme comes after a blowout in the expected build price of the controversial Waimea dam, earmarked for the Lee Valley, near Nelson.

Updated costs have added an estimated $26 million to $75.9m in expected capital costs remaining for the dam project in which the council is a proposed partner.

First unveiled in August 2016, the society's reservoir scheme incorporates a trio of storage ponds 7m to 8m deep – one each side of the Wairoa River just below the Waimea East Irrigation Scheme intake off Clover Road East and the third along the Waimea River at Challies Island.

Filled during the winter months, the reservoirs would store an estimated 5 million to 6 million cubic metres of water, which could be released into the river to augment its flow, if needed, in the dry summer months.

Water in the third pond at Challies Island would be released into the Waimea River to stop any salt intrusion, protecting the well fields near the coast.

Halstead estimated the proposed council-owned scheme would cost about "$40m all up" including land purchases. He suggested the funding could include $25m from the council, a $10m interest-free loan from Crown Irrigation Investments Ltd, $7m from the Government's Freshwater Improvement Fund and $5m from Nelson City Council – all of which was already earmarked for the dam project.

"There's no subsidy from the general ratepayer nor any capital required from the irrigators," Halstead said.

Repayment would be on a user-pays basis over 20 years involving a $200 to $250-per-hectare annual flat fee for irrigators along with a volumetric charge of about 15c to 20c per cubic metre.

The bona fide reviews of irrigators' water use, completed in 2017, would be left on the shelf with all Waimea water consents issued at 300 cubic metres per hectare a week "to accommodate the flat charge".

"This will allow any crop to be grown without restriction," Halstead said.

Urban dwellers in the Richmond, Hope, Mapua, Brightwater and Redwood Valley areas would also be charged but for the water they used only.

"They wouldn't subsidise the irrigators," Halstead said. "It's user pays."

Operational costs would be minimal for the scheme, which would cover about 75ha over the three blocks of land.

"It's simple, everything's there," Halstead said. "It ticks all the boxes as far as I can see."

The proposed scheme would kick in during dry times to maintain the flow of the Waimea River at 1100 litres a second at the Appleby Bridge.

"Generally, we have enough water in the run up to Christmas time," Halstead said. "It's usually February and half of March that is a problem, about six weeks."

Fish traps would be incorporated and protective measures put in place around the ponds to prevent "blow outs" from catastrophic flooding.

Material removed to create the ponds could be used to construct a stopbank to help protect Brightwater from flooding, strengthen the Waimea River banks or be sold.

"The proposal is about water conservation and does not envisage waste," Halstead said. "User pays will effectively put a brake on excessive water usage."