Comments on “Quantifying groundwater exploitation induced subsidence in the Rafsanjan plain, southeastern Iran, using InSAR time-series and in situ measurements” by Motagh, M., Shamshiri, R., Haghighi, M. H., Wetzel, H. U., Akbari, B., Nahavandchi, H., … & Arabi, S. [Engineering Geology, 218 (2017), 134–151

Abstract

In confined aquifers, there is a direct correspondence between changes in both hydraulic head and aquifer thickness as well as between changes in aquifer thickness and vertical land deformation. In fact, the vertical land deformation in confined aquifers incorporates changes in both compressibility of the aquifer skeleton and expansion of the pore water as main factors controlling the storage coefficient of the aquifers. This is not the case in unconfined aquifers where the water is predominantly drained by gravity from the pore spaces implying that it may not be possible to calculate the storage coefficient of unconfined aquifers using the land deformation data. In a paper published in this journal, Motagh et al. (2017) conducted a join of InSAR land deformation data and hydrogeological measurements to estimate the storage coefficient and the average volume storage loss of the Rafsanjan aquifer, southeast of Iran, from 2004 to 2010. The authors estimated the storage coefficient of the unconfined Rafsanjan aquifer using specific storage equations, but adopted for confined aquifers which led to an overestimation in the storage coefficient (~0.1) in comparison with the average value obtained from standard well-pumping tests (~0.05) reported by Zayandehroodi (2012). Likewise, this overestimation in the storage coefficient led to a deviation of ~116 million cubic meters per year (MCM/yr) of the average volume storage loss for the unconfined aquifer.