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COMPACT

The project “Remote Characterization of groundwater storage changes using geophysical Observations and Modelling of Poroelastic processes in Aquifers, under Compaction and Transient groundwater flow conditions” (COMPACT - PID2019-104571RA-I00) aims to develop new methods to estimate groundwater storage changes in aquifers using non-invasive geophysical methods.

Currently, it is estimated that over 2 billion people rely on groundwater as their dominant water supply source. Our dependence will increase due to growing demand and climate change limiting access to surface waters. Aquifer systems are porous and permeable systems that store water. Groundwater systems respond to natural and anthropogenic recharge and discharge fluxes by changes in water storage and fluid pore-pressure (head), affecting complex fluid flow. Monitoring and understanding of the changes in groundwater storage is essential to manage this vital natural resource.

However, estimating groundwater resource changes, at smaller scale (<10km), is notoriously difficult and improvements are needed. Traditional methods involve limited data (e.g., costly phreatic level monitoring wells) and a complex physical modeling process, with large uncertainties due to high heterogeneity in aquifer systems. Alternatively, geodetic and geophysical methods can provide useful constrains. Surface displacements can track fluid pore-pressure change in shallow compacting aquifers, and gravity can provide key information of mass-changes. Therefore, we are limited on the type of aquifers and spatial resolution, at an affordable cost, on which we can estimate groundwater resource changes with non-invasive geophysical measurements. We need new physical constrains to estimate aquifer groundwater storage changes in any type of aquifer.

This project will overcome past limitations by implementing the necessary experimental and theoretical understanding to estimate groundwater storage changes using non-invasive surface geophysical measurements. We will establish the quantitative relationships to physically model storage change using variations in seismic ambient wavefield (natural occurring ground vibrations). We will use gravity and surface displacements, along with the necessary physical and mechanical rock sample laboratory experiments to separate 1) the effects of time-dependent aquifer internal deformation (compaction), 2) fluid flow in the aquifer non-saturated zone, from 3) the actual water content change. We will use the exceptional hydrogeological conditions of the Tenerife Island, to record seismic ambient wavefield, to confirm our predictions and calibrate our models.

This project addresses important questions in groundwater resource management; and will contribute to our understanding of how to use geophysical signals can illuminate groundwater dynamics. This will, in turn, improve monitoring and detection changes in aquifer systems. The feasibility of using geophysical (gravity, seismic and surface displacements) as a continuous, passive, non-invasive, remote tool to detect and characterize groundwater storage changes will be scrupulously evaluated. We anticipate that our research will influence the development of new strategies to monitor and forecast groundwater natural resources in near real-time and high-spatiotemporal resolution.

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