Identifying the influence of episodic events on groundwater recharge in semi-arid environments using environmental tracers

Informing groundwater recharge in arid environments is both challenging and necessary for understanding complex and changing water systems, and for making well-informed aquifer management decisions. The difficulty with interpreting aquifer recharge in arid environments lies in the sporadic and often unpredictable recharge opportunities. There is a gap between theoretical groundwater age distributions based on the physics of groundwater flow and the interpretation of real groundwater age tracer data. This gap is amplified in transient environments. This study uses a deconvolution approach constrained by probable recharge events to interpret variable groundwater recharge in the Weeli Wolli Creek alluvial fan, in the semi-arid Pilbara region. This approach is paired with spatial correlation to establish relationships between wells, making space a proxy for time in the recharge interpretation. Spatial correlation also helps address the data density requirement of deconvolution. The resulting model was able to identify specific events in the last 100 years as contributors to recharge, as well as highlighting effects of mine dewatering in the catchment. In addition, spatial interpretations showed water recharging along specific channels in the fan, and showed active channels varying over time. This level of detail in groundwater recharge studies is a move toward more meaningful environmental interpretation and aquifer planning.