Farmers supplied by the Rangitata South irrigation scheme intend to buy the scheme from the developer, says scheme chairman Ian Morten.
The scheme, which is expected to be in full operation next irrigation season, draws water from the Rangitata River in South Canterbury to fill seven huge storage ponds with a total capacity of 16.5 million cubic metres, three of which are now full or part full. Work completing the other four will resume after winter.
While initial investigation for a scheme on the south side of the Rangitata was started by a farmer group, it wasn't until earthmoving company owner Gary Rooney joined them that the scheme took off.
"We had an idea and he made it happen," Morten told a South Canterbury Federated Farmers field day. "Gary came along and said: 'I can develop it', and we signed a heads of agreement with him to build and fund it and we have the right to buy it at the cost of building."
"We joined with him and bought the land - he basically spent $20 million before we had a consent so he front-ended this to an enormous degree and if it hadn't been for his support, it would never have got off the ground."
The Waimate businessman has put at least $90m into the project which the 30 farmer shareholders have the right to buy when it's finished.
"It is feasible to buy it and we will try to buy it - there is no way we will not try and buy it, that's always been the goal," said Morten.
"We would be looking for a financial institution to assist us in paying for it and we would be looking for some equity from the farmers and I'm told that most banks will need something between 20 and 30 per cent equity."
Farmers will have to put up that equity, based on their shareholding (one share per hectare irrigated). "How they find that is their business, it could be a general security against their land because the irrigation water will increase the value of their land, it could be cash or however they want to do it."
"That will give us that equity to meet the bank's ratios and we hope to buy it that way."
The scheme overall will borrow the balance. "Over the next 15-25 years, through their water charge, they'll slowly pay the scheme off."
Water's been taken from the Rangitata River since the Great Depression for the Rangitata Diversion Race, on the north side of the river. But farmers on the south side have missed out.
In the late 1990s farmers started looking seriously at irrigation proposals but that looked to be scuppered when a conservation order was placed on the Rangitata.
"We took that to the Environment Court and we got a discussion and we got one extra off take and the ability to take high flow water," said Morten.
The scheme is now consented to take up to 20 cumecs when the river is in flood.
"We only start taking water when the river is running at 110 cumecs," said Rooney's design engineer Steve Agnew. "Once it's above 110 cumecs we can start taking water and when it gets to 130 cumecs we can start taking the full 20 cumecs."
Originally planned to irrigate 6000 ha, the scheme grew as momentum gathered. "I think we were still going through the resource consenting process as the scheme was climbing from 10,000 to 12,000 and then on up to 14,000 ha," Agnew said.
The ponds have eight metre high embankments, constructed from gravel excavated down to ground water level. The sides and a 30 metre skirt on the base are lined with a HDPE geo- membrane.
Rooneys put together it's own team to lay the Malaysian-manufactured liner which comes in eight metre wide, 140m long rolls, each weighing nearly 1.8 tonnes. The membrane will cover a total of 1 million square metres.
Rooneys Earthmoving general manager Colin Dixon said: "It's 1.5mm thick and I can assure you that when it blows about in the wind, it's quite dangerous but it's still quite susceptible to damage and that's why we're not going to allow duck shooters or boats within the ponds,"
The HDPE membrane is laid on 20 to 100mm layer of fine silt and the seams welded together. Water-borne silt from the Rangitata will settle on the unlined base of the ponds to form a seal.
"Because we're taking dirty water when the river's in flood, this will give us the sealing effects that we need for these ponds to hold water. We've been pretty happy with the results as far as the performance of the ponds go - we're getting some leakage but it's actually not too bad," said Agnew.
The ponds are filled from a ring race that runs round the outside of them to deliver water to them all at the same time, rather then being filled progressively with one pond spilling into the next as each one is full.
"This allows us to get the water into all the ponds, fill them at the same time and get the water down to the bottom end where we need it for our race and canal network.
It also allows the silt to be spread evenly in all the ponds - because otherwise most of it would settle in first pond," Agnew said.
"It's much easier handling three cumecs dropping into a pond than 20 cumecs because of velocity issues and possible damage. If you're filling one and spilling into another you've got horrendous forces on your spillways. By doing it this way, it eliminates all those forces."
With 16 scrapers, dump trucks, graders, excavators and three roller compactors working on the scheme at the peak of construction, burning 300,000 litres of fuel a month, this has been a challenging project. Some of the challenges have come from other agencies the builders have had to deal with, such as when pipes had to be laid under the main trunk rail line.
"The railways gave us a pretty small window to get through, I think it was less than 24 hours where we had to cut under the railway line," said Agnew.
"They wouldn't allow us to cut the rails, we had to work underneath them with the rails and sleepers suspended in mid air, lay the pipes, backfill around the pipes, replace the ballast and they didn't even inspect it and the train went over it half an hour later. It was a pretty quick job really."
When full, the storage pond will hold four weeks of storage. Farmers are also required to put in their own ponds, enough for a week's storage but most have provided for twice that, giving them about six weeks of irrigation water up their sleeves.
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