The need for economic diversification in northern Western Australia has been recognised in multiple national and state policy documents. Irrigated agriculture has been identified as a key growth industry in northern WA, with the state government aiming to double the value of agricultural output in the Pilbara by 2025.
The first challenge for irrigation is the provision of a reliable water supply. Most rivers in the Pilbara only flow for a few weeks each year, and annual evaporation is 10 times the volume of rainfall. To overcome the severe water deficit, this study examined the conjunctive use of river flows and groundwater with augmentation through managed aquifer recharge to provide a viable water supply for irrigation.
River flows, aquifer parameters, and the connection between the river and groundwater availability were assessed through fieldwork and modelling. We found that the river was strongly connected to the aquifer, and recharged a large volume of water into the aquifer each year. To leverage off this recharge process, an irrigation concept was developed which utilised watertable drawdown to maximise the volume of water captured from river flows.
Modelling of conceptual irrigation schemes showed that with groundwater extraction that lowered watertables, the river flows could contribute up to 140 GL/ year to aquifer recharge, and provide a long-term sustainable irrigation supply. Further, low-level weirs can be used to increase the volume of river flow captured by another 20%.
This presentation illustrates the use of river flows and groundwater in providing a sustainable water supply for irrigation. We show the economic benefits of such an irrigation scheme for different crop types in the Pilbara, demonstrating how conjunctively harnessing these water sources provides an opportunity to transform agriculture in the Pilbara.