Investigating the effect of aquifer type and groundwater level drop on subsidence rate using radar interference technique and field data (Case study: Tehran-Karaj-Shahriar aquifer area)

In the last decade, the phenomenon of subsidence has occurred in a large part of the plains of Iran due to excessive harvesting of groundwater and climatic drought. This has caused a great deal of environmental, economic and social damage. In this study, the effect of fine-grained layer thickness and groundwater level drop on the Tehran-Karaj-Shahriar aquifer is investigated. In the first step, fine-layer thickness maps, groundwater level changes, bedrock level, permeability and hydrodynamic coefficients (storage coefficient and transferability) were prepared in GIS. Subsequently, the extent and location of the subsidence map was prepared using differential interferometry and ENVISAT ASAR satellite imagery from 2004 to 2009. The results of this study show a maximum subsidence rate of about 17 cm in the central part of the aquifer and an average groundwater level reduction of 0.42 m / year. Comparison of the subsidence map with the groundwater change map shows that the amount of subsidence in the northwestern aquifer with the greatest decrease in water level (27 m) is low (less than 0.5 cm / year) in contrast to the maximum subsidence (17 Cm/ year) occurred in central areas showing a 5 to 10 m drop in groundwater level. To interpret these results, fine-grained layer thickness maps, permeability, hydrodynamic coefficients and bed scales were used. The results confirm that the areas with maximum subsidence are in accordance with the thickness map of the fine-grained layers.