Areas of the soil of Santiago sink up to 25 mm a year due to the exploitation of groundwater and drought

A soil deformation monitoring study in Santiago shows that, despite the fact that the capital basin is relatively stable, there are areas that present anomalous subsidence, especially to the north and south of the city. The sectors with continuous drops in the ground level, of up to 25 millimeters per year, coincide with areas of underground water exploitation for agriculture and human consumption, and due to drought; which has made the water level drop in the last 10 years between 1 and 0.3 meters per year.

“In Quilicura, Chicureo, Colina, Polpaico and Lampa, the exploitation and compaction of the aquifer is more evident and criticality is noted. For Paine and Huelquén, the deformations have been evident in recent years, influenced by intensive agriculture in the area”, explains the research “DInSAR high-resolution deformation monitoring: implications for geological hazards and ground stability in the metropolitan area of ​​the Santiago, Chile”. The study was carried out by Felipe Orellana, from the Department of Civil Engineering, Building and Environment of La Sapienza University, in Rome; Marcos Moreno, from the Department of Geophysics of the University of Concepción; and Gonzalo Yáñez, from the Department of Structural and Geotechnical Engineering of the Catholic University of Chile.

One of the conclusions is that the soil deformations did not occur at a certain time, but are continuous, which indicates that water extractions have continued to affect soil stability during the period investigated.

The deformations of the earth’s surface are slow processes, so they do not imply immediate risk situations since their effects are observed after several years; however, during that period its effects can change the topography of the earth’s surface, causing damage to the population and civil infrastructure.

Furthermore, the study states that there is no evidence of large deformations influenced by tectonic movements, particularly linked to the activity of the San Ramón fault. A general uplift of the area of ​​about 10 millimeters a year does occur, which is very normal because it is on the plate subducted by tectonics between the Nazca and South American plates. “However, we do not rule out that the fault is active and that more observation time is needed to estimate the possible deformations along it,” the scientific article indicates.

The investigation recorded the ground deformations using a multi-temporal differential interferometric synthetic aperture radar (DInSAR) from the Sentinel 1A and 1B satellites, obtaining a high-resolution ground motion map. These satellites are part of the Copernicus mission of the European Space Agency. Multitemporal satellite radar interferometry is based on the analysis of a series of images, in this case acquired between May 2018 and May 2021.

The results highlight that knowing the behavior of the Santiago basin is a key factor for the management and overexploitation of groundwater. “This is fundamental for decisions related to territorial planning and demonstrate the importance of satellite geodetic measurements in assessing the impact of climate change and how it affects the deformation of the soil surface and the storage of groundwater,” highlight the authors.

In addition, there is a clear relationship between the stability of the Santiago soil and the thickness of its basin, with less thickness being the areas most affected by subsidence. “This work demonstrates the great utility of satellite data to determine soil stability, data necessary for good urban planning,” they conclude.