Characterization of land deformation, hydraulic head, and aquifer properties of the Gorgan confined aquifer, Iran, from InSAR observations

摘要

In this study, Interferometric Synthetic Aperture Radar (InSAR) is applied to analyze the land deformation across the Gorgan Plain, Iran, where recent droughts and over-exploitation of groundwater leading to widespread subsidence. Having significant long-term and seasonal signals in head measurements, analysis of TOPS S1 month-scaled images from October 2014 to October 2016 exhibits significant inelastic (70 mm/yr on average) and seasonal elastic (ranging from about 20 to 132 mm) vertical land deformation over the Gorgan confined aquifer system (GCAS), according to the decomposed vertical displacement map. The investigations indicate that these significant deformations are due to both severe head decline (up to similar to 2 m/yr) and the presence of thick aquitards intervening aquifers. To obtain elastic land deformation (totally recoverable) and static head components, the inelastic (partially recoverable) and long-term head decline trends are removed by lines fitted to the land deformation and head time series, respectively. Having a high cross-correlation coefficient between the seasonal components of head and land deformation time series (ranging from 0.60 to 0.93; similar to 0.78 on average), we use a joint well-InSAR data analysis to estimate bulk aquifer parameters of the elastic skeletal storativity (0.0035 to 0.0142; 0.0085 on average), specific storage (1.54 x 10(-5) to 7.68 x 10(-5) m(-1); 4.35 x 10(-5) m(-1) on average), and compressibility (1.50 x 10(-10) to 7.40 x 10(-10) N/m(2); 4.20 x 10(-10) N/m(2) on average) at 14 piezometer locations. InSAR-derived aquifer storage properties are reasonably correlated with the hydrogeological setting of GCAS. Moreover, the elastic land deformation data are acceptably transformed to head fluctuations at 14 piezometers and several arbitrary point locations. It is observed that the heads reconstructed from InSAR and measured in piezometers are consistent over a broad portion of GCAS. Seasonal elastic land deformations occurred between wet and dry seasons in 2015 are also used to map the confining degree across GCAS. The higher confining degree has been observed in those areas of higher subsidence signatures, implying that the subsidence potential in confined aquifers is higher than that of unconfined aquifers. In this study, we have demonstrated more benefits of the InSAR observations in estimating aquifer storage properties and predicting head in confined aquifers of significant subsidence signatures with better temporal and spatial resolution than that can be retrieved from hydrogeological data alone.