Opuha shutdown reinforces need for more storage

February 25, 2015

The Opuha dam has provided water for irrigation, recreational users and wildlife since 1998.

But irrigation has to stop today:

. . .The Opuha Dam serves 250 farmer-shareholders, who have 16,000ha under irrigation.

“We have reached the bottom of the bucket,” Opuha Water chief executive Tony McCormick said in circular to members. By Wednesday the lake will be at 371m with a little under 1.5 per cent storage remaining, he said.

As part of an agreement to reduce the minimum Opihi river flows in early February, Opuha Water will cease irrigation and the last remaining storage will be used to try to keep the river flowing for the next 10 to 12 days, he said.

The lake level is falling at just over half a per cent a day, he said.

“There have been several small rain events in the area over the last fortnight but they have had very little effect on inflows to the dam and in the catchment generally,” McCormick said. . .

The lack of water will have environmental, economic and social implications and reinforces the need fro more water storage, a need that will be partially met by a new storage lake:

A man-made lake that could hold enough water to fill 12,000 Olympic-sized swimming pools is planned to supply more reliable irrigation in Canterbury.

The lake would likely hold 30 million cubic metres of water with storage options ranging from 5m/cum to 100m/cum and was expected by managers of the Rangitata Diversion Race (RDR) to go to the resource consent stage by the end of the year.

A 30m/cum development would cost $120 million and depended on irrigator and bank backing and the support of the community and nearby neighbours.

RDR managers said initial support was from farming, hydro, environmental, Maori and government groups. They have been told to “hurry up” and get on with the project as drought hits farmland around Lake Opuha in South Canterbury.

A large lake would open up the possibility of supplying water to South Canterbury farmers as well as the four irrigation schemes and hydro-generation the RDR has serviced over the past 70 years in Mid Canterbury.

The lake would be developed on Ruapuna farming land next to the Rangitata River, about 10 kilometres  downstream of the RDR canal intake, most of which was already owned by the company.

RDR management chief executive Ben Curry said the business case for building a large water storage pond had become more compelling because of drought on Canterbury’s east coast.

He said RDR managers had been working on the project for four years, buying the farm in 2009, and believed the time was right to move forward.

“We only have to look at what is happening with the Opuha to see the need for water storage and we are looking at creating something which could have a regional context to it. We could build a relatively modest storage pond of 10m/cum which would serve it’s purpose and we could get a digger in and get the job done, but … there is opportunity because of the locality we have chosen on the boundary between South and Mid Canterbury that could serve the region.”

Curry said the pond could relieve some of the pressure from rivers off Lake Opuha and help recharge lowland streams and aquifer water.

The project would likely be funded mostly by debt, he said. . .

Irrigation New Zealand is supportive:

Tomorrow’s early cessation of irrigation from Lake Opuha reinforces the need for further storage infrastructure like the Klondyke Storage Pond proposal being launched today by the Rangitata Diversion Race Management Ltd (RDRML), says IrrigationNZ Chairwoman Nicky Hyslop.

“It’s devastating for South Canterbury that Lake Opuha can no longer support irrigation for the remainder of the season. The Opuha Water Team has done everything they can to eke out supply, but without rain they have no further options and any remaining water will need to be diverted to maintain the health of the river,” says Mrs Hyslop.

“Opuha’s early shut-down reinforces again how water-short South Canterbury is and illustrates the need for a wider network of water storage infrastructure across the region to enable reliable water supply during dry periods,” she says.

“IrrigationNZ applauds today’s announcement by the RDRML of its intentions to build a storage pond at Klondyke in the Mid Canterbury foothills. As well as improving security of supply for Mid Canterbury irrigators, this project has the potential to deliver water south which would be of huge benefit to South Canterbury farmers,” says Mrs Hyslop.

“IrrigationNZ supports further investigation of this proposal as New Zealand needs to be thinking laterally about how we redistribute water resources in the most effective manner. The RDRML Klondyke Storage Pond project is a fantastic first step in this direction,” says Mrs Hyslop.

I ran into a friend with a business in Oamaru yesterday. She said they had been expecting a slow-down and it had come as a result of the lower dairy pay out and the drought.

Most North Otago irrigation schemes are fed from the Waitaki River which gives 99% reliability but some people rely on other schemes which have imposed restrictions and not everyone in the district has irrigation.

In South Canterbury, the impact of the drought has been more severe because of wider irrigation restrictions.

Droughts are an ongoing concern for farmers on much of the South Island’s east coast and increase water storage is the answer to that problem.


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