Assessing groundwater recharge in an Andean closed basin using isotopic characterization and a rainfall-runoff model: Salar del Huasco basin, Chile

Abstract

Closed basins are catchments whose drainagenetworks converge to lakes, salt flats or alluvial plains.Salt flats in the closed basins in arid northern Chile areextremely important ecological niches. The Salar delHuasco, one of these salt flats located in the high plateau(Altiplano), is a Ramsar site located in a national park andis composed of a wetland ecosystem rich in biodiversity.The proper management of the groundwater, which isessential for the wetland function, requires accurateestimates of recharge in the Salar del Huasco basin. Thisstudy quantifies the spatio-temporal distribution of therecharge, through combined use of isotopic characterizationof the different components of the water cycle and arainfall-runoff model. The use of both methodologies aidsthe understanding of hydrological behavior of the basinand enabled estimation of a long-term average recharge of22 mm/yr (i.e., 15 % of the annual rainfall). Recharge hasa high spatial variability, controlled by the geological andhydrometeorological characteristics of the basin, and ahigh interannual variability, with values ranging from 18to 26 mm/yr. The isotopic approach allowed not only thedefinition of the conceptual model used in the hydrologicalmodel, but also eliminated the possibility of ahydrogeological connection between the aquifer of theSalar del Huasco basin and the aquifer that feeds thesprings of the nearby town of Pica. This potentialconnection has been an issue of great interest toagriculture and tourism activities in the region.