Rangitata Diversion Race Management Ltd

The Rangitata Diversion Race was a dream in the minds of the pioneering farmers in Mid Canterbury when the 750,000 acre plain was first farmed in the mid-19th Century. Regarded as the largest area of nearly flat land in New Zealand, all development was closely linked to water problems – water races to supply stock on light soils and water courses to drain heavy swamp lands.

Despite high expectations of development, it took the massive unemployment of the 1930s depression to provide the catalyst for the work to start in what would become the RDR. The Minister of Public Works, Bob Semple the ebullient and colourful minister in the first Labour government wrote in a foreword to a government booklet ”Water put to work”; “We as a nation cannot afford the continued idleness of such extensive resources not only for our own good, but for the benefit of the world at large”. Work began on the scheme on April 2nd 1937 and was completed in November 1944. Race water first generated electric power at Highbank power station on June 8th 1945. Expected to cost £1.5 million pounds, the scheme costs grew to £2 million pounds.

Since 1945 there have been a number of amendments to refine the efficiency of the RDR. Montalto, the second hydroelectric power station was built in 1981 and started producing electricity a year later. The Sandtrap was designed and built at a similar time to remove much of the suspended sediment from the water by reducing the velocity of the flow. The sediment causes wear and tear on the hydro electric turbines and can cause gastric problems for sheep and lambs when washed out onto paddocks. Conversely the sediment is a good bonding agent that can help to plug microscopic holes in the race lining.

The RDR Resource Consents were renewed by Environment Canterbury in 2008. Part of the consent conditions required the RDR to install fish diversions to reduce the number of native and exotic fish from becoming entrained in the Race. 2Kms downstream from the Rangitata River intake a behaviourial screen called a Bioacoutic Fish Fence that uses bubbles and underwater sounds to divert fish to a channel returning them to the river, was installed in 2007. At the South Ashburton River, a physical rock gallery was installed in 2008 together with a bypass to return fish to the river.

Back to top of the page

Mayfield Hinds - Contract area 32,000 hectares | Scheme allocation 16.5 cubic m/sec.

Valetta - Contract area 7,300 hectares | Scheme allocation 4.4 cubic m/sec.

Ashburton Lyndhurst - Contract area 25,000 hectares | Scheme allocation 13.0 cubic m/sec.

Total Area Irrigated 64,380 hectares

Total Irrigation Water Demand 33.95 cubic m/sec.

Irrigation season 10th September to 9th May, Generation Season 10th May to 9th September

Back to top of the page

Montalto - Station capacity 1.8 MW | Operating head 7 metres | Average generation 12 GWh

Highbank - Station capacity 25.5 MW | Operating head 104 metres | Average generation 94 GWh

Back to top of the page

Ashburton District Ranges from 300 litres / sec to 1500 litres / sec depending on seasonal requirement

Back to top of the page

Scheme Location Diagram. See larger Diagram...

Back to top of the page

History

2 April 1937 - Construction commenced

1938-39 - Picks and Shovel replaced by modern mechanised equiptment

19th October 1940 - First pipe laid for the Surrey Hills high-pressure system

1944 - Race completed

8 June - First power generated from Highbank power station

1978-79 - Sand Trap installed

June 1982 - First power generated from Montalto power station

1 October 1990 - The government transfers the ownership of the RDR to a user owned limited liability company called Rangitata Diversion Race Management Ltd

Back to top of the page

• Rangitata Race is 67km long extending from an intake on the Rangitata River at Klondyke to a discharge at Highbank on the Rakaia River.
• Can carry a flow of approximately 30 cubic metres of water per second.
• A second intake on the South Ashburton River can also divert approx 7 cubic metres per second of water (when available) into the RDR.
• Three Community Irrigation Schemes, two hydroelectric power stations, Ashburton District Council stockwater race system and various private stockwater and irrigation schemes are supplied by the race.
• Irrigation has priority of supply during the irrigation season extending from September 10th to May 9th each year.
• During the rest of the year, Highbank power station located at the Rakaia end of the race. Has priority of supply.
• The other power station, Montalto, is located 1.5kms downstream from the Mayfield-Hinds Irrigation Scheme.
• Major control structures built along the race include the Rangitata intake and sandtrap, checkgates, spillways and siphons passing under rivers and streams which cross the race.
• In total the RDR supplies irrigation to approximately 66,000ha of land during the irrigation season.
• It was officially opened in 1945, but wasn't in its present form until 1982 when the Montalto Power station was built.
• It is New Zealand’s largest irrigation scheme.

Back to top of the page

View Larger Map

Back to top of the page

Ben Curry
CEO
C: 021 89 39 44
E: ben@rdrml.co.nz

Wendy Reith
Executive Assistant
C: 027 254 5550
E: office@rdrml.co.nz

Neill Stevens
Operations Manager
P: 03 3039703
C: 0274 398411
E: neill@rdrml.co.nz