WATER RESOURCES AS A LIMIT ON HUMAN SYSTEMS IN THE HYPERARID CALAMA BASIN OF NORTHERN CHILE: INVESTIGATING RECHARGE USING BASIN-SCALE GROUNDWATER MODELING

The Calama Basin lies west of the Andean volcanic range and high Altiplano plateau in the hyperarid Atacama Desert of northern Chile. Here water is a scarce, valued, and contentious resource that limits multiple human systems. Water from the Calama Basin is used in the mining of about 1/3 of Chile’s copper, an important national economic resource. Water use within the basin also includes irrigation, municipal services, traditional uses in rural indigenous communities, and maintenance of sensitive ecosystems. Additionally, water is transported outside of the basin for municipal use by the city of Antofagasta. While demand for water is expected to continue to grow, the effects of increased groundwater and surface water extraction are uncertain.

The effective, basin-wide management of the Calama Basin’s water resources requires understanding of the water balance, including the quantity of available water and the rates at which water is entering and exiting the basin. Chilean water management laws are based on the concept of sustainability, in which consumptive water use must be balanced annually by recharge. Unfortunately, the magnitude and geographical distribution of recharge is not well understood. Most researchers believe that the aquifers are at least partially fed by subsurface inflow from the less-arid Altiplano to the east. However, the magnitude of the flux is unknown. Evapotranspiration rates in the hyperarid basin floor and the arid uplands are also not well understood, adding greater uncertainty to the recharge component of any water balance.

To investigate the magnitude and geographic distribution of recharge to the Calama Basin, we construct a groundwater model of the Calama basin using Visual MODFLOW. This model is constrained by available stratigraphic data from boreholes, seismic reflection profiles and outcrop observations, limited groundwater monitoring wells and historic records of stream flow rates. We will test a range of recharge hypotheses, varying the magnitudes, locations and durations, and test the hydrologic outcomes. By comparing the model results with known hydrologic characteristics of the basin, we work to constrain the magnitude and geographic distribution of recharge within the basin.