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By John Keast - Efficiency gains within the Rangitata Diversion Race system and an agreement with Environment Canterbury could boost irrigation in Mid Canterbury by 13,295 hectares.

Rangitata Diversion Race Management Ltd  (RDRML) chief executive Ben Curry said an agreement from Ecan to allow the three schemes within the RDR scheme to expand was a “red letter day for us and the community”.
The expansion, driven by efficiencies within schemes, could take place over the next decade, placing Mid Canterbury at the forefront of irrigation development in New Zealand. Any expansion decisions would be made by management of the schemes, Valetta, Ashburton-Lyndhurst and Mayfield-Hinds.
RDR holds the consents to the water used by the schemes. No more water would be taken from rivers.
Efficiencies and the expansion of existing schemes could be bolstered in the long-term by a massive storage pond RDR management hopes to built on land it has bought in the Montalto area at the head of the RDR system. The RDR draws water from the Rangitata and the South Ashburton for the irrigation schemes, and water is also used for the Montalto and Highbank hydro schemes.
Once developed – and this is a long-term project – that “pond” could cover 100ha and contain 20 million cubic metres of water. It would be the biggest water storage “pond” in Canterbury and boost irrigation reliability..
Mr Curry said efficient use of consented water – a key plank of the Canterbury Water Management Strategy – was a central part of the company's strategy.
Changes in the way water has been delivered to farmers over the past 10 years has altered irrigation demand to such an extent that in recent years there has been a net increase in the seasonal flow of water going to the TrustPower hydro plant at Highbank, the end point of the RDR system. More efficiencies were possible as farmers moved to variable-flow technology, which allowed an irrigator to deliver different amounts of water to different parts of a paddock.
Some of the increase in flow to Highbank during the irrigation season is due to climatic conditions, some due to farm conversion, and some to less irrigation demand because of efficient irrigation application.
Now, more than 60 per cent of RDR water is applied through spray irrigation.
Efficiencies in irrigation practice were foreseen by commissioners John Milligan and Cliff Tipler when RDR consents were renewed in 2003, a process that took “nine years and $5m”.
They said: “ Additionally, it is our view that the efficient use of land, their soils and physical structures and systems for irrigation contained in them is best achieved by permitting a supply of water to continue at present. If it is the case – as some submitters argue – the more efficient methods of water irrigation would enable the same land to remain equally productive with less water then it is plain that there are already processes in contemplation by which the 'excess' could be applied to land presently unirrigated. If this happens the result could be seen (in land terms) as an efficiency bonus.”
Mr Curry said RDRML had been in discussion with Ecan since the re-consenting process regarding the implications of the commissioners' decision.
The basis of RDRML argument was that the decision allowed for scheme expansion without review of consents.
Recently, Ecan agreed that an additional 500m boundary around the three schemes within the RDR would be granted.
RDRML contended that a 500m strip around each scheme, while an expansion, offered little in terms of distribution efficiency and it would be more efficient to aggregate up the boundary and substitute it for new block areas that the schemes could deliver water to when water efficiency becomes available.
Ecan has now agreed to that proposition, meaning the schemes, through efficiencies, including piping of water, can potentially irrigate an extra 13,295ha of land.
The management of the new areas is up to the boards of the three schemes within the RDR, which now waters 64,000ha of Mid Canterbury.
Mr Curry said the agreement was a major win for Mid Canterbury.
He said RDR storage, when developed, would bring more water reliability, a key element in farmer investment.
RDRML was also doing all it could to alleviate leakage in the RDR's races, and a liner had been fitted in one area.
The RDR was built during The Depression, much of it with rudimentary tools and machinery.
It is regarded as one of the great engineering feats of New Zealand.
The RDR now waters 64,000ha, and that could now expand to 80,000ha, making it far and away New Zealand's biggest irrigation scheme.

 

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