Feasibility assessment of MAR

This presentation gives an overview of an investigation of the potential for managed aquifer recharge (MAR) in three established or emerging irrigated cotton-growing regions in Australia: the Lower Murrumbidgee and Lower Namoi basins in western NSW and the Gilbert River catchment in far northern Queensland. Ongoing interest in MAR as a strategy to support irrigated agriculture has not translated into much investment in Australia. The aim was to evaluate how MAR might be feasible for irrigated cotton production and associated cropping systems in the focus regions and make recommendations on next-step actions that could incrementally develop the knowledge, confidence and expertise needed to invest in MAR. The broad approach taken was to draw on evidence from a holistic feasibility assessment to scope a set of plausible scenarios for MAR, to test and refine these scenarios with local and state government stakeholders and researchers, and to develop recommendations to support any efforts to proceed with MAR by the funder (the Cotton Research and Development Corporation) or other parties.

The scenarios varied in their scale (e.g. single farm, irrigation schemes), purpose (e.g. managing drawdown, reducing evaporative losses), infrastructure and governance arrangements. Together they highlighted the critical need to improve knowledge on local hydrogeological conditions and develop MAR policy and regulations that enhance the strengths of MAR whilst minimising risks. A water accounting grade estimate of recharge is critical to being confident that MAR provides an advantage over investing in reducing infiltration “losses”, allowing an allocation to be issued. As an initial step, MAR pilot studies could work with state government to test water accounting of recharge quantification methods in dedicated trial infiltration basins and test injection wells. Reducing uncertainty about evaporation and recharge rates is critical to comparing MAR as a low loss water storage solution to other evaporation or infiltration reduction alternatives. If land managers invest in improving understanding of aquifers under their land and quantifying seepage and evaporation over time, this will incrementally reduce uncertainty on the effectiveness and viability of MAR.