44 | Rangitata Diversion Race Management Limited REGIONAL DEVELOPMENT T T Rosa Watson RDR repairs improve canal design Repairing the damage has been a major project for operators RDR Management Ltd (RDRML). Four years on from the devastating floods that hit mid-Canterbury, major repair works to the Rangitata Diversion Race water-supply scheme, costing $6.5 million, have been successfully completed. Seven sites along the 67-kilometre canal – known as the “lifeblood of Canterbury” – were damaged by floodwaters in 2021, and again in 2022. Repairing the damage has been a major project for operators RDR Management Ltd (RDRML). The canal crosses under eight rivers on its course between the Rangitata and Rakaia rivers – each with protective head walls made from heavy concrete tiles. These tiles were “hammered” in the flooding by water and gravel, with some completely washed away, RDRML chief executive officer Tony McCormick says. “It looked like someone that’d had their teeth knocked out.” Accessing the damage required excavation down into the riverbed, and extensive temporary protection works were required before contractors could get started to ensure the safety of the crew and the integrity of the race. Tony says local civil contractors Grant Hood Contracting were outstanding in their contribution to the project, both at the design and planning stage, and then for the site works, providing and installing precast concrete panels, concreting complicated-shaped retaining structures, and successfully completing the work safely. He was thrilled with the final results. “We’ve built something that’s stronger, and an improved design on what we had.” Interestingly, he says the repair design was very similar to structures put in place 80 years ago. “We cannot believe how resourceful and onthe-mark those guys were, and how they did it. The repair is basically a modern-day version of what they did in the 1930s.” The 80-year-old scheme built during WWII has stood up remarkably well to what Mother Nature has thrown at it. While the head walls were damaged in the 2021 flood event, the syphons under the rivers remained intact, Tony says. This meant there was no disruption to supply while repairs were carried out. “Fortunately, we didn’t miss a beat. We continued to operate every day of the year at full capacity.” The work at each site began with machinery mobilised to redirect the rivers away from the structures to make it safe for work to be carried out. The rivers themselves had been significantly changed by the flood events. “We’re very conscious that the rivers are different now than they were before the floods,” Tony says. The RDR supplies 547 landholdings via the three irrigation schemes, irrigating just over 100,000 hectares, and also powers the Montalto and Highbank hydro stations. The repaired structures are now stronger than they have ever been, with design and construction improvements, but there is further ongoing work to ensure resilience, Tony says. “While the floods of 2021 revealed some frailties from age, it was also a reminder of the need for us to be reviewing the condition and design in light of future forecasts of climate change, in particular.” Climate change meant similar flooding events would be more frequent. “It’s prudent to be thinking about making our system more resilient to even higher flows.” The company may look at rebuilding some of the river crossings in the future, with Taylors Stream high on the list. However, Tony is confident the repairs are enough at this stage with ongoing monitoring. The RDR remains vital to the region’s economy, highlighted by a recent study carried out by RDRML on the economic benefit of the RDR to the Mid-Canterbury region, which confirmed an estimated $614 million per annum of economic value. Going forward, electricity producer Manawa Energy is investing approximately $30 million in the upgrade of their Highbank Power Station at the Rakaia River end of the RDR. And landowners in the region continue to invest in improving their operations, based on a secure supply of water from the RDR into the foreseeable future. Industrial Controls are proud to support Rangitata Diversion Race Management Limited Electrical Design, Install & Maintenance Complete electrical engineering from design to servicing. End-to-end Project Management From concept to commissioning — delivered on time, every time. Instrumentation, Calibration & Safety Precision measurement and certified functional safety. IT Networks & Fibre Infrastructure Reliable and secure networking & fibre solutions. Custom Software & Smart Data Analytics Turn your data into decisions with custom software, real-time insights, and intelligent reporting. Process Automation & Control Systems Smarter, faster production with integrated automation.
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