Abstract
Overexploited aquifers in drylands require a thorough assessment in order to get the best insight possible of theirhydrogeological behavior and groundwater resource. With this aim we develop an integrated methodology,using the northern part of the Pampa del Tamarugal Aquifer (PTA), at the Atacama Desert, Northern Chile, astesting site. This multidisciplinary assessment was completed including 34 direct piezometric measurements inboreholes, 92 geophysical soundings (TDEM) and 9 stream gauging. Main results show strong correlation betweena well-defined contrast of resistivity and the water-table of the unconfined aquifer (dry unsaturatedzone≥100 Ω.m vs saline groundwater in the saturated zone≈10 Ω.m). TDEM results helped to map the piezometriclevels and reassess the limits of the PTA. The eastern limit of the aquifer, delimited up to now by thebasin floor, is repositioned from 10 to 50 km eastward in the Andean Piedmont, indicating larger groundwaterreserves than those described previously. A high-resistivity anomaly (∼200 Ω.m) in the apex of alluvial fansreveals that frequent flood events cause rapid flows through the coarse permeable deposits leaching the vadosezone and contributing to recharge the aquifer (temporary recharge process). However, the updated piezometricmap indicates the piedmont as the area where most of the aquifer recharge takes place. In the piedmont, at thedownstream of tectonic structures or substratum outcrops, stream discharge changes reveal perennial river lossescontributing to a located and permanent recharge of the PTA. This groundwater recharge process would be themain contribution to the aquifer recharge. By taking into account the regional geology, the results are summarizedin a new conceptual model redefining the geometry, the spatial distribution of groundwater levels, theboundary conditions and the complex recharge processes (different flow magnitudes) in the northern part of thePTA. Finally, this study indicates an integrated and efficient methodology, providing original results that areuseful for the characterization of other aquifers located in arid piedmonts and hillslopes.