Water storage solutions for irrigation schemes

The issue

The demand for water in New Zealand has intensified over the past two decades at a phenomenal rate. The majority of easily abstractable run-of-stream resources (using flow without modification by upstream storage) are highly allocated in many regions. With the availability of further run-of-stream resources decreasing, famers identify that water storage is critical for achieving security of reliable irrigation water supply to realise economic benefits. This reliability can be achieved by making water available at times when it’s required and by enhancing the consistency of supply.

There are many factors that need to be considered in water storage development such as the environment, economics, social aspects, culture, potential employment, and farmer and community well-being. Due to high uncertainty and contentions associated with storage development, getting stakeholder support to undertake a robust assessment can be challenging. The uncertainties include identifying suitable locations for storage, size of storage, irrigation demand and uptake, water availability, irrigation reliability and likely cost. Many of these uncertainties arise due to a lack of available information at the early stage of the storage development concept. Stakeholders generally would like to have better information and availability of multiple options for consideration. The social, economic and technical uncertainties of this work can be complex, and it can be extremely expensive and time-consuming to carry out a detailed study to determine the potential of water storage. It is therefore important to devise a cost-effective but sufficiently accurate approach to assess the pre-feasibility of storage development to pave the way for more detailed investigations.

The approach and tools

NIWA has developed a software tool to undertake preliminary assessments to inform the stakeholders on feasibility of water storage. This tool uses catchment irrigation demand, which is estimated based on topography, climate and soil information, along with flow data for a catchment to optimise the potential capacity of a reservoir and irrigable area with the available water resources to achieve the required irrigation reliability under regional allocation rules. The runtime of this software is short (less than one minute),  which means multiple options such as different allocation rules and reliability criteria can be considered.

This software tool can be used in conjunction with NIWA’s NZ Water Model – Hydrology and TopNet to assess the viability of irrigation storage development for any catchment in New Zealand, including where measured flow data is unavailable or ungauged to obtain preliminary understanding of the feasibility of a storage development.

The project is funded through the Strategic Science Investment Fund from the Ministry of Business, Innovation and Employment.