Investigating the effect of aquifer water table variation on the subsidence phenomenon and balancing strategies of the aquifer (Case study: Ali Abad Plain, Qom)

Ali Abad Plain of Qom Province, located in the center of Iran, is among the areas recently affected by subsidence phenomenon due to water overexploitation. In this research, using the differential radar interferometry and Sentinel-1 images, vertical land deformation was monitored for an 18-month period from March 2015 to September 2016. The results showed a maximum subsidence of 240 mm. Moreover, it was found that subsidence in this plain is a progressive and continuous phenomenon with an almost constant spatial distribution. Next, groundwater table fluctuations were measured in Saveh Plain for a 14-years period ranging from September 2002 to September 2016. The results showed a maximum water table decline of -44 m. Comparing the ground deformation map with groundwater level fluctuation map revealed a direct relation between spatial distribution and ground deformation intensity and groundwater drop. In addition, comparing the alluvium thickness variations with ground deformation indicates that the alluvium thickness of the Ali Abad Plain varies from 20 m in its eastern part to 300 m in the western and central areas. The results do not show any significant relation between these two parameters in the study area. Moreover, it was found that layering type and the presence of thick fine-grained formations are among other factors affecting the intensity and rate of subsidence in the plain.