The Potential for Water Banking in Australia's Murray-Darling Basin to Increase Drought Resilience

Banking water in aquifers during wet years for long-term storage then recovering it in drought is an application of managed aquifer recharge (MAR) that minimises evaporation losses. This requires a suitable aquifer for long-term storage of banked water and occasional periods when entitlements to surface water are available and affordable. This has been widely practised in Arizona and California but thus far not in Australia, in spite of severe impacts on agriculture, society, and the environment during recent droughts in the Murray-Darling Basin. This preliminary study based on a simple area exclusion analysis using six variables, some on a 90 m grid, over the 1 million km(2) basin produced a first estimate of the order of 2-4 x 10(9) m(3) of additional aquifer storage potential in surficial aquifers close to rivers. For 6 of the 23 catchments evaluated, banking capacity exceeded an average water depth of 0.3 m for the irrigated area. At one prospective site in the Macquarie River catchment in New South Wales, water banking operations at various scales were simulated using 55 years of historical monthly hydrologic data, with recharge and recovery triggered by dam storage levels. This showed that the estimated 300 x 10(6) m(3) additional local aquifer capacity could be fully utilised with a recharge and recovery capacity of 6 x 10(6) m(3)/month, and recharge occurred in 67% of months and recovery in 7% of months. A novel simulation of water banking with recharge and recovery triggered by water trading prices using 11 years of data gave a benefit cost ratio of approximate to 2. Data showed that water availability for recharge was a tighter constraint on water banking than aquifer storage capacity at this location. The analysis reveals that water banking merits further consideration in the Murray-Darling Basin. Firstly, management across hydrologically connected systems requires accounting for surface water and groundwater entitlements and allocations at the appropriate scale, as well as developing equitable economic and regulatory arrangements. Of course, site-specific assessment of water availability and hydrogeological suitability would be needed prior to construction of demonstration projects to support full-scale implementation.