Work to begin on $17m fish screen for Rangitata Diversion Race

A massive $17 million fish screen project is underway for New Zealand's biggest irrigation scheme that starts in the Rangitata River.
Rangitata Diversion Race Management Ltd (RDRML) chief executive Tony McCormick said the project was in response to concerns from anglers and runanga about fish, particularly sports fish such as salmon, and native fish such as galaxiids, getting caught into the 67-kilometre long irrigation race which extends from an intake on the Rangitata River at Klondyke to a discharge at Highbank on the Rakaia River.

Its a proper collaborative project, McCormick said of the fish screen work for a scheme which takes up to 30 cubic metres of water per second (cumecs) and irrigates more than 100,000 hectares of land during the irrigation season.

Were hopeful it will go some way to address everyones concerns.


Construction of the screen, which will cost about $17.2m, will begin in March and is expected to be completed by May 2022.

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* Salmon anglers settle appeal with Rangitata River irrigation company

McCormick said the main fish screen structure will be 105 metres long and 5m high, but the amount of actual screen area is over 370 square metres which is enough to wrap a 1-metre-high barrier right around a rugby field.

This will certainly be the largest of its type in New Zealand.

"It will be among the largest fish screen facilities globally and comparable with the ones (we) visited in 2017 in the USA.''

Supplied
One of the sections of a new fish screen for a Rangitata River irrigation scheme arrive for installation.

McCormick said it would replace the Bio-Acoustic Fish Fence (BAFF) screen installed in 2006 that created a wall of sound and air bubbles rather than a physical barrier.

The BAFF was state of the art for its time, but it also proved inconsistent when it came to diverting fish from the scheme back out to the Rangitata River.

Were confident that the new fish screen will divert 100 per cent of fish back into the river.

There are more than 900 consented fish screens installed in Canterbury, with about half of them in South Canterbury.

Tony McCormick/Supplied
Part of the new fish screen's components gets moved on site at Rangitata Diversion Race Management Ltd

A report in 2020 into fish screens in South Canterbury found major non-compliance issues with the majority of them.

McCormick said there would be thousands of fish in the area of the RDRML scheme and part of the project involved testing the effectiveness of it on a yearly basis.

Theres a lot of research that goes into a project like this, its not just a matter of commissioning it.''

It will comprise a series of seven large cylindrical screens and a series of vertical flat screens that have wedgewire grills with a slot spacing of just two millimetres.

Tony McCormick/Supplied
Components of the Rangitata Diversion Race Management Ltd (RDRML)'s new fish screen have been sourced from Australia.

Water can pass through the slots and continue on down the race, but fish will be excluded and will return to the river through the fish bypass channel.

It promises to be the most effective and efficient one of its kind in the Southern Hemisphere.

Were sourcing the key components from Australia. We also went to the United States in 2017 to look at what has been done there, and how it can be applied to our conditions.

McCormick said it had initially hoped to commission the project by the end of September 2020, but the design process took longer than expected.

Bejon Haswell/Stuff
Rangitata Diversion Race Management Ltd says the fish screen will take up to 36 cumecs of water through its system.

We just want to be very confident that what we build will work, so weve taken extra time to ensure we have the best conditions.

New Zealand Salmon Anglers Association spokesman Paul Hodgson said his organisation had been working with RDRML ever since they settled their appeal with the company in 2019 over its consent to take an extra 10 cumecs from the river in high flows.

Part of our settlement was the development of a world-class fish screen, Hodgson said.

Quite plainly the old methods, such as the BAFF, didnt work the way they should.

Hodgson said there were two components to any successful fish screen.

The first is that any fish removed from the river need to be returned to the river, he said.

The second is that no fish should be damaged by the scheme. If the fish screen can achieve those two things, then anglers will be very happy.

Bejon Haswell/Stuff
The start of the Rangitata civersion race canal fed from the Rangitata River.

Arowhenua Marae chairman John Henry said it had been working closely with RDRML on the development of the screen.

From our point of view, its got to protect native fish as well as salmon and trout, Henry said.

Sports fish are bred, but native fish have to survive in the waterways on their own. We simply want this fish screen to work, the vast majority of them in Canterbury dont do anything.

Central South Island Fish and Game resource officer Angela Christensen said it was optimistic about the project.

At the end of this, we should have a fish screen that is 100 per cent effective, Christensen said.

We appreciate the system will be quite complex, as its dealing with massive volumes of water.

KEY RDR POINTS:

  • Three community irrigation schemes, two hydro electric 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 10 to May 9 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 1.5km 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.
  • It was officially opened in 1945, but wasn't in its present form until 1982 when the Montalto power station was built.

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