Predictability of Hydraulic Head Changes and Characterization of Aquifer-System and Fault Properties from InSAR-Derived Ground Deformation
Abstract:Space geodesy has demonstrated its potential in detecting ground deformation associated with exploitation of aquifers. However, because geodetic data remain rarely integrated with hydrologic data, ground deformation observations are not typically used for water management purposes. Here, we characterize ground deformation of the Santa Clara Valley in the southern San Franciso Bay Area, an aquifer undergoing water extraction and recharge with over 50 multi-decadal monitoring wells. We perform Interferometric Synthetic Aperture Radar (InSAR) time-series analysis of ERS, Envisat, and ALOS SAR data to resolve the 1992-2011 ground deformation.
Using T-mode Principal Component Analysis we isolate temporally and spatially variable deformation signals embedded in multi-decadal InSAR time series. The longer-term signal reveals uplift at 0.4 cm/yr between 1992-2000 and < 0.1 cm/yr during 2000-2011, illustrating the end of the aquifer system's poroelastic rebound following recovery of hydraulic heads after the 1960s low stand. In addition, seasonal elastic deformation with amplitude of up to 3 cm, in phase with head fluctuations, is observed over the confined aquifer sharply partitioned by the Silver Creek Fault (SCF).
We integrate the deformation with hydraulic head data to characterize the aquifer-system properties at the scale of the basin, and show that after calibration we can accurately predict hydraulic head levels from deformation alone. Finally, by modeling the deformation partitioning across the SCF we constrain the time of the fault's last tectonic activity, hydraulic conductivity, and material composition. The SCF cuts the shallow confining clays and was last active since ~140 ka, it has a horizontal hydraulic conductivity several orders of magnitude lower than the surrounding aquifer system, and it is likely composed of clays, making it an effective barrier to across-fault fluid flow.
Our results demonstrate that space-derived ground deformation, when combined with hydrological data, enables characterization of basin-wide aquifer-system and fault properties and could help characterize hydraulic heads in areas with sparse temporal well monitoring.