Modeling historical subsidence due to groundwater withdrawal in the Alto Guadalentin aquifer-system (Spain)

Resumen

The Alto Guadalentin Basin (Spain) is widely recognized as an area of major anthropogenic land subsidence due to groundwater extraction. This paper presents a numerical methodology to quantify the severe subsidence of this basin over history. First, a 3D groundwater model is proposed to reproduce groundwater evolution in the regional Alto Guadalentin aquifer system since 1960, leading to an average piezometric level drop of 150 m. Secondly, a generalized plasticity state parameter-based model is calibrated to reproduce the mechanical behavior, observed in oedometer laboratory tests, of compressible materials extracted from a 300-m drilled borehole located in the area of maximum subsidence. The strength of this constitutive model is that a single set of material parameters can be used to reproduce the mechanical behavior of material located at different depths, hence having different confining pressures and void ratio states. Afterwards, subsidence is assessed through a partially saturated 1D vertical finite element model, solving Biot equations that reproduce the slow vertical drainage and vertical consolidation processes, taking into account the calibrated constitutive model and prescribing the previously computed groundwater evolution of the aquifer. Finally, the subsidence model is adjusted with different displacement data available from 1992: datasets acquired by ERS, ENVISAT, Cosmo-SkyMed satellites and the global positioning system GNSS. The proposed calibrated subsidence model reproduces the 3.1 m subsidence monitored in the period 1992-2018, and quantifies historical subsidence (since 1960) in the Alto Guadalentin Basin area at around 5.8 m. Moreover, the model predicts subsidence of up to 7.3 m by 2100 for an assumed constant hydraulic head from 2012 onward.