Recharge mechanism and groundwater age in the Ti‐Tree Basin, Northern Territory

Groundwaters in Cainozoic sand and gravel aquifers in the arid Ti‐Tree Basin are becoming intensively used for irrigation. Carbon isotope chemistry indicates that most of the groundwaters in this basin were recharged in the Holocene. Estimated 14C ages of the groundwaters range from modern to 8910 years bp. The modern ages correlate with flood‐out recharge situations. Elsewhere in the basin, groundwater age correlates with the depth to aquifer suggesting that diffuse recharge by direct infiltration may have occurred episodically from 1730 to 8910 years BP. Stable isotope parameters indicate that recharge took place during exceptionally heavy rainfall events, and that the recharging groundwaters were subject to evaporation prior to infiltration. Only limited recharge takes place in the modern climatic regime, and this needs to be considered in groundwater resource management.