Discovering confined zones and land deformation characteristics across an aquifer system in Iran using GNSS and InSAR techniques

Aquifer characteristics provide important information for hydrogeological studies such as groundwater simulations and development of an effective water management strategy. This work shows how long-term and seasonal land deformations can help to understand an aquifer system in the absence of sufficient hydrogeological data. The land deformations over the Abhar aquifer in Iran were analyzed using interferometric synthetic aperture radar (InSAR) spanning 2014–2019 and the Khorramdarreh GNSS (Global Navigation Satellite System) station data acquired during 2006–2020, in tandem with drilling logs and groundwater hydraulic head measurements, to identify which parts of the plain are composed of a confined aquifer system. The confined aquifer extent is mapped by independent component analysis (ICA) without prior conditions and then verified against hydrogeological observations. Besides the maximum long-term subsidence (up to 80 mm/year), the confined parts of the aquifer system also have the largest seasonal land deformation amplitude (up to 80 mm), which is typical of confined groundwater systems and not the case in unconfined aquifers. There is strong correlation between the seasonal heads and land deformations ( R 2 of 0.60–0.80) at five piezometer locations, which coincide with the determined confined aquifer. This study leveraged the InSAR technique to improve hydrogeological knowledge for aquifer characterization by discovering the confined portions of a complex groundwater system without requiring detailed hydrogeological observations or significant disruption of water use practices, making the technique convenient for developing countries and elsewhere where hydrogeological data are rarely available.