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Rangitata Diversion Race fish screen
Rangitata Diversion Race Management Limited (RDRML) recently hosted an open day before the fish screen became operational, giving the community the opportunity to have a look.
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RDRML hosted open days for local school groups in the week prior to the public open day, allowing the younger generation to have a look and learn about the process.
After eight years of planning, and over a year of construction, the new Rangitata Diversion Race (RDR) fish screen is in action, and many people took the opportunity to take a glimpse before it was underwater.
The $18 million (M) hightech screen installed on the side of the Rangitata River just below the RDR irrigation intake is specifically designed to keep young salmon, trout, and native fish from being trapped in the main irrigation diversion race. Young fish that are swept into the intake will be diverted by the fish screen back into the river where they can continue their life journey. The screen is the first of its kind in New Zealand.
The fish screen has been built in a new section of race which has been excavated in an area of scrubland about 1600 metres downstream of the main RDR intake. The RDR is a 67kilometrelong canal scheme that has been in operation since 1945, diverting water from the Rangitata River for multiple uses. It delivers water to three community irrigation schemes covering 100,000 hectares of farmland, two hydroelectric power stations, and it supplies stock water. Over time, technologies have continuously been improved. Tony McCormick, Rangitata Diversion Race Management Limited (RDRML) Chief Executive, said the new fish screen was developed due to the previous one no longer being adequate and a need to futureproof the system. “The RDR diverts a significant amount of water from the Rangitata River, so it is important to ensure this does not impact the fish species that reside in the water, and is an essential part of the consent to take water.”
Almost 500 people from far and wide attended the open day in early April and took the opportunity to look at the screen. Tony McCormick said interest exceeded expectations. “The RDR truly is the lifeblood of MidCanterbury, and I am always keen to provide opportunities for members of our community to see for themselves what a fabulous legacy my predecessors have provided us, and how we take our responsibility very seriously to ensure the RDR continues to provide sustainable water delivery to our region.”
On ANZAC Day the RDR was shut down completely for the first time in five years. Grant Hood Contracting began the excavation of the remaining section between the existing RDR canal and the new facility.
Tony said it was great to host four key representatives from AWMA Water Control Solutions, the Australian company that manufactured the fish screens. The COVID pandemic had prevented them from visiting the site throughout the construction phase. “They were keen to get over and check out the installation of their equipment. They were
thrilled with what they saw, and the two days with them onsite were extremely valuable for us all.”
The actual screen covers 370 square metres; enough to wrap a onemetrehigh barrier around a rugby field.
Once the water has entered the canal it passes through the fish screen, which consists of seven finemeshcovered cylindrical Tscreens that divert young fish away from the irrigation race and channel them back into the river. Downstream of the Tscreens are a series of flat panel screens made of the same 2mm spaced wedge wire. All of the screens have control baffles to regulate the flows through the screens and ensure an even flow across the screen area. “The screens are designed such that the flow velocity through them is very low, to ensure small fish do not get sucked onto the screens, while the sweep velocity downstream remains high to enable fish to continue to swim downstream and back to the river via the fish bypass channel.” The screen is also an essential part of the consent to take water, which is vital for the region’s economy, as well as the ecosystem of the river. The consent specified key design aspects of the facility, including having it located as close as practical to the Rangitata River.
The total project cost is about $18M; $5.5M for the fish screen, $9.5M for construction, and $3M for engineering, design, and management costs. The project is funded entirely by RDRML shareholders, and water users whose contribution is based on their proportion of water delivered. MHV Water Ltd, Ashburton Lyndhurst Irrigation Ltd, Manawa Energy Ltd (formerly Trustpower), and the Ashburton District Council are the shareholding owners of RDRML.
Tony said the real test will be how the screen performs over the coming months. The National Institute of Water and Atmospheric Research (NIWA) is carrying out hydraulic testing in June, and live fish trials are scheduled for October.
