|Paper title||Mapping land subsidence and aquifer system properties of the Willcox Basin, Arizona, from InSAR observations and hydraulic head data|
|Form of presentation||Poster|
The Willcox Basin, located in southeast of Arizona, USA, covers an area of approximately 4,950 km2 and is essentially a closed broad alluvial valley basin. The basin measures approximately 15 km to 45 km in width and is 160 km long. Long-term excessive groundwater exploitation for agricultural, domestic and stock applications has resulted in substantial ground subsidence in the Willcox Groundwater Basin. The land subsidence rate of the Willcox Basin has not declined but has rather increased in recent years, posing a threat to infrastructure, aquifer systems, and ecological environments.
In this study, spatiotemporal characteristics of land subsidence in the Willcox Groundwater Basin was first investigated using an interferometric synthetic aperture radar (InSAR) time series analytical approach with L-band ALOS and C-band Sentinel-1 SAR data acquired from 2006 to 2020. The overall deformation patterns are characterized by two major zones of subsidence, with the mean subsidence rate increasing with time from 2006 to 2020. The trend of the InSAR time series is in accordance with that of the groundwater level, producing a strong positive correlation (≥0.93) between the subsidence and groundwater level drawdown, which suggests that subsidence is a result of human-induced compaction of sediments due to massive pumping in the deep aquifer system and groundwater depletion.
In addition, the relationship between the observed land subsidence variations and the hydraulic head changes in a confined aquifer in accordance with the principle of effective stress and hydromechanical consolidation theory. Therefore, integrating the InSAR deformation and groundwater level data, the response of the aquifer skeletal system to the change in hydraulic head was quantified, and the hydromechanical properties of the aquifer system were characterized. The estimated storage coefficients, ranging from 〖6.0×10〗^(-4) to 0.02 during 2006-2011 and from 〖2.3×10〗^(-5) to 0.087 during 2015-2020, signify an irreversible and unrecoverable deformation of the aquifer system in the Willcox Basin. The reduced average storage coefficient (from 0.008 to 0.005) indicates that long-term overdraft has already degraded the storage ability of the aquifer system and that groundwater pumping activities are unsustainable in the Willcox Basin. Historical spatiotemporal storage loss from 1990 to 2020 was also estimated using InSAR measurements, hydraulic head and estimated skeletal storativity. The estimated cumulative groundwater storage depletion was 〖3.7×10〗^8 m3 from 1990 to 2006.
Understanding the characteristics of land surface deformation and quantifying the response of aquifer systems in the Willcox Basin and other groundwater basins elsewhere are important in managing groundwater exploitation to sustain the mechanical health and integrity of aquifer systems.