Storage pond gets consent

UPGRADE: A new intake for the Waimakariri Irrigation scheme at Brown’s Rockjust downstream from the Waimakariri Gorgente should improve the scheme’s efficiency.
UPGRADE: A new intake for the Waimakariri Irrigation scheme at Brown’s Rockjust downstream from the Waimakariri Gorgente should improve the scheme’s efficiency.

The planned 8.2 million cubic metre storage pond for the Waimakariri irrigation scheme has received a building consent from Environment Canterbury and construction could start as early as November this year.

Waimakariri farmers will welcome the news after losing an estimated $30 million of production last summer because of interruptions to irrigation water supply but opponents are likely to carry on fighting the plan.

The ECan consent is for a high potential impact category (PIC) pond, an upgrade on the medium PIC pond originally proposed, to future proof it as population in the area close to the Wrights Rd site near Burnt Hill grows.

Waimakariri Irrigation Ltd (WIL) general manager Brent Walton believes the redesign means that even if a Greendale Fault-sized seismic event occurred beneath it, the pond would not fail.

"The embankments are a bit flatter so instead of being 1:2 gradient it's 1:2.5 and there has been a lot more in-depth study into seismic stuff and more investigation into localised ground conditions," he said.

"In a medium PIC you might need an engineer visiting the site once or twice a week during construction whereas now there has to be an independent engineer on site the whole time. The walls are probably built the same but a lot more consideration is given to why and how they're built.

"In some instances we've used double liner so if we got a Greendale in there, you've got that elasticity effect going on that would contain the water. It's acceptable to have damage in the banks but it's designed to contain the water. All of the concrete structures have been beefed up to deal with significant earthquakes."

While the building consent is a "significant milestone", the storage pond has yet to gain resource consent and an application for that will be lodged soon. But Walton believes all engineering issues relating to the pond have now been addressed.

"You can't build this to emotion, you've got to build it to a set of codes that actually exist. Resource consent is about whether it's appropriate use of that land to have that structure in there in much the same way as is it appropriate to have a prison or a pig farm."

The facility will include two ponds on a 120-hectare site with a combined footprint of 1 square kilometre. They will hold enough water for nine days of full irrigation flow to 18,000ha of farmland.

Under the proposal, no more water than already consented will be drawn from the Waimakariri River but water will now be able to be stored when river flows are high and irrigation demand is low. WIL already has consent to take 10.5 cumecs, Ngai Tahu has 4 cumecs and 2.1 cumecs is allowed for stock water.

"It's not a new scheme and every step is about improving the efficiency of delivery and maximising the efficient use of that available water. It ticks all the environmental boxes, we're not nicking anyone's recreational activity on the river and we're not damming the river," Walton said.

The plan includes several small power stations on the irrigation canals, to be built and operated by Mainpower. The intake at Brown's Rock, downstream of Waimakariri Gorge, is being upgraded to improve the scheme's efficiency.

The Press was unable to contact the principal objectors to the storage ponds, the Eyre Community Environmental Safety Society, which will have its annual meeting on Sunday.

The Press