Water storage: options for maintaining and growing resilience

Irrigation water supplies have been under pressure this summer, with the government classifying Canterbury and a number of other regions as being under drought conditions.

That pressure has also been felt by irrigation systems that include storage: we’ve seen several headlines accompanied by images of dams with very low water levels. In the face of a changing climate, it’s going to be increasingly important to ensure that water storage systems – including those that are already in place – are adequately designed to deliver the required levels of water supply security alongside other co-benefits such as environmental flows and recreational opportunities.


Previous long, dry summers have prompted thinking (both within farming circles, and in local and central government) about water storage as a means of maintaining the long-term resilience of existing irrigated land uses and enabling growth or land-use change. Investing in a reliable water supply is crucial for new developments seeking external capital, especially where high-value land uses are being considered. However, securing adequate water sources has become increasingly challenging due to various factors, including existing water allocations being at or near limits in many areas, and uncertainty around future regulations.

The significance of water storage, particularly for high-value horticulture, has been consistently underscored by governments past and present. The first critical step in the process of developing water storage is accurately sizing the storage capacity, which requires a comprehensive understanding of several key factors. These include the variability of the water supply over time, the specific water demands the intended crops, and the desired level of water supply reliability.

There are two primary options for water storage: community schemes and on-farm storage:

Community schemes

Community schemes offer economies of scale and centralised management, making them potentially more cost-effective per unit of water stored or hectare irrigated. However, establishing community schemes can be challenging, requiring broad community support, and navigating complex regulatory processes to obtain necessary resource consents. Once operational, these schemes handle ongoing operation and maintenance tasks, and in several cases the water supply entities have also been handling land-use consenting on behalf of farmers.

On-farm storage

Conversely, on-farm storage places decision-making and responsibility solely in the hands of individual landowners. While this option may offer more flexibility and autonomy, it also requires significant effort to obtain consents and construct necessary infrastructure. On-farm storage systems can be tailored to meet the specific needs of individual farmers, but may be less cost-efficient, including the opportunity cost of land that is taken out of production.

Hybrid approach

A combination of community schemes and on-farm storage presents an attractive option for balancing flexibility and reliability in water supply. By leveraging the benefits of both approaches, farmers can customise their water supply solutions while benefiting from the reliability and economies of scale offered by community schemes. This hybrid approach may be particularly appealing for mitigating risk and attracting investment, as it provides a baseline level of reliability while allowing for individualised adjustments based on farmers' specific needs and risk tolerances. It could also be an economically and hydrologically feasible approach for bolstering the supply reliability of existing systems without the need for major dam remediation projects.

Whichever storage option is chosen, accurately sizing water storage facilities through hydrological modelling studies is crucial for ensuring an adequate and reliable water supply while balancing cost and consenting considerations. 

These studies utilise historical climate data and projected future climate scenarios to predict water availability and demand. While commissioning a modelling study for an on-farm storage project may seem excessive, the potential consequences of insufficient water supply during critical growing periods make the effort worthwhile.

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