GAB | An integrated remote-sensing mapping method for groundwater dependent ecosystems associated with diffuse discharge in the Great Artesian Basin, Australia

• Vjekoslav Matic
• Justin Costelloe
• Andrew Western

Vertical leakage (discharge to upper aquifers) is an important but poorly constrained component of water balance in the Great Artesian Basin (GAB), Australia. It ranges from negligible discharge where the GAB is overlain by aquitards, to high discharge where artesian water feeds the shallow unconfined aquifer (thereby raising the water table) causing elevated surface soil moisture and extensive surface salinisation. Adequately representing the temporal and spatial variability of vertical leakage is difficult due to the large scale over which the discharge occurs. An innovative method is presented that integrates a supervised classification of high-discharge zones using time-series Landsat data with landform mapping information to improve classification results. ‘Wetness persistence’ and ‘salt persistence’ classes, determined from the time series data, are related to groundwater discharge processes through a discharge framework that allows scaling up of field-based discharge estimates. The results show that using multi-image classification integrated with landform data will significantly reduce uncertainty by reducing false positives. No significant temporal trends were found in a time series assessment, with results featuring high variability, most likely due to image normalisation issues. The lack of a clear temporal signal suggests that an assumption of steady-state discharge is valid for estimating annual fluxes of vertical leakage. Supervised classification and landform outputs provide updated knowledge on GAB vertical leakage rates by providing useful lower and upper bounds of discharge rates respectively. Additionally, groundwater-dependent ecosystem classification, covering the full extent of the basin margins, is a new source of information resulting from the work.

Matic V, Costelloe JF & Western AW (2020), An integrated remote-sensing mapping method for groundwater dependent ecosystems associated with diffuse discharge in the Great Artesian Basin, Australia, Hydrogeology Journal, vol 28 (1), pp 325-342. https://doi.org/10.1007/s10040-019-02062-4