Understanding hydrogeological processes at a volcanic headwater in Central Chile.

Abstract:

This article presents a research at the Diguillín River headwaters, at central Chile. The Diguillín river drains a volcano through two watersheds: the Renegado creek and the Alto Diguillín, where flows per unit area in the Renegado creek are markedly lower than those of the Diguillín. This research aims to understand the hydrogeological processes that produce the dissimilarity between both watersheds.

The methodology consisted of integrating approaches: i) analysis of basin metrics (land cover, geological, topographic and climatological); ii) analysis of hydrometeorological data; iii) study the water balance model; and iv) analysis of environmental isotopes. All methods contribute to explain the hydrogeological processes in the system where soils, topography and geology favor infiltration and groundwater movements from the sub-basin of the Renegado creek to the Diguillín River.

Renegado soils are predominantly sands over a basement composed of fractured rocks. Infiltration of rain and snowmelt predominates over surface runoff, resulting in about 5 m³/s of depth groundwater that flows to the Diguillín River. At the lower part of the Renegado watershed, exist a geological control that maintain a constant level of groundwater, forcing the discharge of the aquifer by two clusters of springs. The upper cluster of springs, located at the level of the control, drains excess of water to the Renegado creek. A lower cluster of springs located at the Diguillin river, 3 km downstream of the surface connection, is feed by groundwaters that flows through fracture rocks beneath the geological control.

The results highlight the complexity of hydrological processes in volcanic mountain systems. Therefore, when issues such as water availability or the vulnerability of mountain ecosystems need to be addressed, site-specific studies are needed. Drinking water availability for the communities located at the Renegado watershed is limited to some springs that are located around the valley. There is a significant expansion of second home construction in the area of the Renegado watershed because with its skiing and hot springs it is a major tourism center. Due to the extensive use of septic tanks, located above the highly permeable soils that overlie the fractured rock aquifer, there is concern about how water quality may be affected.