Aquifer Mechanical Properties and Decelerated Compaction in Tucson, Arizona

In recent decades, high groundwater extraction rates, often coincident with periods of severe drought, result in the widespread decline of water levels. Overexploitation of aquifers also causes land subsidence, which poses a severe threat to infrastructure. Tucson, Arizona experiences land subsidence coupled with the depletion of groundwater, a critical water resource for the desert city. To understand the spatiotemporal evolution of land subsidence and its implications for aquifer properties, we examine long time series of surface deformation and head levels. Measurements at extensometer stations indicate rapid compaction of fine-grained material up to 8.5 mm/yr from 1990 to 2005, which results in permanent storage volume losses up to 4.1%. The analysis of densely populated sets of interferograms generated from Envisat and RadarSAT C band acquisitions yields multitemporal maps of surface deformation at unprecedented resolution. These maps reveal that subsidence significantly slows by the late 2000s, corresponding with the implementation of artificial recharge efforts. Subsequent to groundwater level recovery, we observe a brief 6.6 year interval of residual compaction, suggesting a high vertical hydraulic conductivity, which is then shown to be up to 9.8 × 10⁻⁴ m/d. We also estimate the average elastic and inelastic skeletal storage coefficients for the aquifer system to be 3.78 × 10⁻³ and 6.01 × 10⁻³, respectively. Interferometric synthetic aperture radar shows deformation nearly ceases by 2015, likely reducing hazards associated with Earth fissuring and infrastructure damage. This study highlights successful outcomes of water management and conservation plans that preserve existing groundwater reserves and increase artificial recharge.