HYDROLOGIC RESPONSE OF THE SALAR DE ATACAMA TRANSITION ZONE TO THE EXTREME MARCH 2015 PLUVIAL FLOOD

The Salar de Atacama (SdA) is a 3,000 km² salt playa on the eastern side of the Central Andes in northern Chile. The Transition Zone (TZ) is located on the southeastern edge of the halite nucleus of the SdA at 2300 m.s.l. The TZ hosts perennial lagoon complexes and open pools fed by internal, down-gradient drainage of high elevation precipitation on the adjacent Andean plateau (Boutt et al. 2016). There are outstanding questions as to the origin of water in the lagoon complexes and this work seeks to investigate the impact of an extreme precipitation event on the hydrologic functioning and source of water to the lagoons. In March 2015, a la Niña episode fueled a rare precipitation event directly on the salar surface and in the adjacent up-gradient recharge area. The basis of this study is hourly water level data collected by pressure transducers installed in 26 wells across the TZ. In response to the event, rapid increase in groundwater level was observed in all monitoring wells, with the greatest change of over 0.7 meters recorded in the brine-hosted halite aquifer. The elevated water levels display a general exponential decay following the event that continues past the end of the 6-month study period, with the exceptions of two wells along the TZ-halite nucleus margin, which experienced minimal decay. The groundwater response is mirrored by remotely-sensed surface water extent from Landsat 8 satellite imagery of the SdA. The perennial lagoons did not incur a significant or lasting surface extent increase, compared to the Open Pools 1100% growth and negligible decay. We conclude that the influx of the March 2015 precipitation event flowed downgradient along the established flow paths, and discharged at the dense brine interface, evident in the longevity of the open pools and maintenance in the high groundwater level observed in wells at the TZ-halite nucleus margin.