Groundwater recharge through internally drained basins in a semiarid climate, Western Australia

Abstract

Study regionThe study site, the Mount Bruce Flats, is located in the Pilbara, a semiarid region of northern Western Australia. Study focusSemiarid climates are characterised by an extreme water deficit, with evaporation exceeding precipitation several-fold. Groundwater recharge is episodical and occurs only after infrequent but very large volume precipitation, while all other precipitation events are quickly lost to evaporation. We investigated the contribution of an internally drained basin to localised groundwater recharge by combining the results of calculations from various tracer methods. We developed a new mobile-immobile recharge transport model coupled with a probability model based on Markov Chain Monte Carlo simulations that combines several age and hydrochemical tracers to estimate localised infiltration. New hydrological insights for the regionThe actual recharge varied greatly across the basin, being 4–5 times higher in the central part compared to the margins. The highest probability for recharge was calculated for 2.5 mm×y−1 and 12.6 mm×y−1, with a median value of 6.8 mm×y−1 while the median mobile effective porosity was low at ∼0.5 %. The flood plains overlying freshwater aquifers may contribute several times more to localised recharge than the upper parts of the catchments, which are characterised by fast runoff and a lower water retention time. Therefore, these endorheic basins could be a valuable source of water for groundwater recharge or constitute an additional hydrological challenge for mining.