The Country - Ashburton-Lyndhurst Irrigation scheme 'refreshed'

Irrigation is big business writes Toni Williams for The Country.

From the cost of its development and construction to the distribution of water, the return it offers to the rural community it serves and the urban community it ultimately feeds is priceless.

Many of the farms across Mid Canterbury thrive because of the area's irrigation schemes and the promise of reliable water supply.

The Ashburton Lyndhurst Irrigation Ltd (ALIL) Pipe Scheme was officially opened this month by Agriculture Minister Damien O'Connor at a ceremony attended by around 100 people - people with a vested interest, and those who laboured in different ways over its design or construction.

They were gathered to celebrate the successful modernisation of a scheme originally designed more than 75 years ago.

Ashburton Lyndhurst Irrigation Scheme Ltd board of directors chairman Colin Glass said the leap to spray irrigation and better water efficiency meant the scheme needed to be modernised.

It needed to be pressurised.

PIPE PROJECT

The stage one concept - completed in November 2008 - used the natural fall of the land within the open channel irrigation scheme to generate pressurised water. It then piped the water from the Rangitata Diversion Race (RDR) to each individual farm.

There was enough pressure to spray and irrigate without pumping.

The $8 million pressurised pipe system was a ground-breaking development in New Zealand at the time.

There was 30km of pipeline laid, supplying 37 properties to irrigate around 4000ha.

The design pressure allowed a minimum of 40m (58psi) to each property, sufficient for centre pivots, laterals, travelling irrigators and sprinklers to be used.

The advantages of the initial project included energy savings, improved water efficiency and minimum of 50 year design life with very low maintenance.

TURBINE SCHEME

In 2009 a turbine scheme was developed to allow five farmers just below the Rangitata race to access the water supply. It was too close to the race to build pressure, so powered turbines were used.

Two turbines were installed on the main race of the Lyndhurst scheme, 1km below the Rangitata race.

They became operational in December 2009, supplying water to more than 940ha.

One turbine drives a high pressure pump supplying water to five big gun irrigators and the other turbine drives a low pressure pump supplying seven centre pivots.

It cost around $580,000 but the annual power saving for the five farmers is about $125,000 annually.

The turbines operate high and low pressure pumps independently. The high pressure pump output is 110 litres/second (l/sec) at 80m head, low pressure 235 l/sec at 40m head.

MORE PIPES

The benefits of that initial stage encouraged the board to convert the rest of the scheme to pressurised water, with the stage two piping scheme upgrade.

It now covers around 30,000ha.

The original infrastructure and its technology stood the test of time, Mr Glass said at the official opening.

It just ''needed a refresh'' and ultimately the ALIL board members and its shareholders agreed, and the BNZ agreed to support them.

Efficiency gains meant the sale of around 2cumecs (2000 litres of water per second) allowed the scheme to self-fund, with the support of the bank.

It cost $110 million for piping, plus buffer ponds and telemetry.

And on-farm irrigation investment by scheme shareholders was around $150 million.

The completed scheme was delivered on time, within budget.

The board was happy, the shareholders were happy and the bank was happy.

The total $250 million investment improved the water delivery system already in place.

It was meant to improve water use efficiency, and since completion in February 2017 it has. Significant reductions in farm water use have been recorded.

The nutrient loss per hectare has also decreased and all farms are achieving A or B grades on their Environment Canterbury required Farm Environment Plans.

DEVELOPMENT

Getting enough water to farmers to cover just over half their properties was the thinking behind the development of the Government-funded Ashburton Lyndhurst Irrigation Scheme in the mid-1940s. It was eventually bought by the Ashburton Lyndhurst Irrigation Scheme Ltd (ALIL) in 1989 and is still a farmer-owned co-operative.

It was originally set up to a provide border-dyke irrigation supply to its co-operative farmers via a gravity-fed open channel system, taking water from the Rangitata Diversion Race.

It was built to deliver water to irrigate just 60% of a property, which at the time was thought to be more than enough.

It now delivers water through a network of races and pressurised pipe systems to 244 shareholder members who collectively farm nearly 30,000ha.

Over the years, ALIL land use has changed. It is now dairy 44%, dairy support 23%, arable 17%, sheep & beef 14% and other 2%.

The scheme has a water allocation of 12,041 litres per second.

The scheme itself runs from the northern bank of the north branch of the Ashburton River in the south to the RDR race in the west, down Ledgerwood Rd, Line Rd and Thompsons Track to Mitcham Rd in the north and Somerton and State Highway 1 in the east.

The irrigation season runs from September 10 to May 9.