46 | Reliable water crucial during El Nino Hugh de Lacy Facing the threat of El Nino droughts, farmers on Central Plains Water Ltd’s (CPWL’s) irrigation scheme in the South Island’s Selwyn and Waihora districts can take comfort in its underpinning of Canterbury’s agricultural productivity and regional resilience. Farmers have been warned that a significant El Nino event is expected to develop this winter in the central South Island – in Canterbury and North Otago in particular – with drier, windier and colder conditions the likely outcome. “The CPWL scheme’s storage and delivery infrastructure, including a stored water contract with Manawa Energy at Lake Coleridge, provides farmers with greater certainty through increasingly volatile climate cycles, helping safeguard food production and rural communities,” says CPWL Chief Executive Susan Goodfellow. “The scheme captures run-of-river water when flows in the Rakaia River are high, and supplements supplies during low flows with water stored in Lake Coleridge, which is released back into the river. “Enabled by the Rakaia Water Conservation Order (RWCO), this approach offers an elegant and sustainable alternative to large-scale water storage development, which otherwise faces significant challenges in central Canterbury. “Our labyrinth weir is another example of an asset that we’ve built to increase operational resilience during flood events, and ensure delivery down-times to water users are reduced,” she says. This is reflected in the $390m that CPWL shareholders totaled in expenditure in 2025, with a $399m contribution to Canterbury’s gross domestic product, supporting 2203 full-time jobs in the region directly or indirectly. These figures come from the CPWL 2025 annual report, supported by Business and Economic Research Ltd (BERL). There’s often high demand for water during nor-west winds such as experienced during El Nino weather patterns when the river is at high flows. The labyrinth weir has boosted the resilience of the irrigation scheme by reducing the frequency and duration of flood events, allowing it to withstand floods ranging in volume from around 1200 cumecs to 3000 cumecs in a controlled manner, then returning the water safely back to the river. CPWL has also made progress in nitrate leaching mitigation. “For more than 13 years CPWL has monitored groundwater and surface water quality and levels, building a strong and reliable dataset,” Susan says. RURAL SERVICES » Central Plains Water “Recent results are encouraging, with the past five years showing that 60% of our monitored groundwater bores are recording improving nitrate trends, with levels decreasing. “Independent expert reviews indicate that a 32% reduction in nitrate losses below the root zone is likely being driven by shareholders through the adoption and achievement of high-standard on-farm practices since 2015. “While it’s still early, the trends are promising, demonstrating how good management practices are working at scale through the scheme’s collective management.” Such results highlight the value of CPWL’s collective approach to water management and farm practices in delivering better environmental outcomes. “By combining robust data, long-term monitoring and one-on-one engagement with farmers, CPWL can track progress, identify areas for improvement, and support meaningful, ongoing change – something that would be far more difficult to achieve without a coordinated approach,” Susan says. Rakaia Intake Labyrinth Weir. The Rakaia labyrinth weir increases the resilience of water delivery by reducing the frequency and duration of flood events impacting operations.
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