Investigating river-aquifer interactions using heat as a tracer in the Silala river transboundary basin

Abstract

This article reviews scientific studies in which heat was used as a natural tracer to investigate stream-aquifer interactions in the Silala River in Chile and provide evidence that was used to support a legal dispute between Chile and Bolivia over the status and use of the waters of this watercourse. Streambed temperature time series at various locations downstream of the Chile-Bolivia international border showed that water flows downwards through the streambed sediments, from the river towards the fluvial aquifer. These findings are consistent with hydraulic head measurements performed at the study site. Additionally, fiber-optic distributed temperature sensing (FO-DTS) methods were employed to observe river temperatures with a spatial resolution of the order of 0.5 m in a river reach of similar to 1.3 km. FO-DTS technology allowed detection of various warm springs that discharged their waters into the Silala River, as well as the location of an artesian well that supplies the river with similar to 90 L/s of deep groundwater at similar to 20 degrees C. The results provided improved understanding of the Silala River hydrogeology, and were used to calibrate and validate a groundwater model of the system, reported elsewhere. Both methodologies demonstrated that the river is indeed a system of surface waters and groundwaters interacting as a unitary whole, a key aspect of the definition of an international watercourse, and generated valuable scientific evidence to support a major international legal dispute.nThis article is categorized under: Science of Water > Hydrological Processes Science of Water > Methods