Investigating land subsidence due to groundwater over-exploitation in Kerdi-Shirazi plain, Hormozgan Province

Over-exploitation of the groundwater resources causes many environmental hazards among which land subsidence is more important. The main aim of this study is to evaluate the effect of groundwater level drawdown on land subsidence and fissure occurrence in the Kerdi- Shirazi plain, Hormozgan Province. For this reason, the groundwater level changes and distribution of the surface and subsurface sediments in the plain were investigated. Water level data from piezometers during the last 16 years from 1999 to 2015 indicate cumulative drawdown of about 40.6 m with an average annual declining rate of about 2.2 m. The groundwater level drawdown caused considerable stress loading on the aquifer forming sediments, resulted in compaction and settlement of aquifer materials. Consequently, a large fissure with a length of about 567.6 meters appeared at the northwest part of the plain in 1394. The results of this study indicate that two main factors including groundwater level drop down and changes in the thickness of the fine-grained clay layer caused unequal subsidence, creation of the tensile stress, and consequently occurrences of the fissure. Based on these factors, hazard map of fissure occurrence due to land subsidence was prepared for the plain with three categories including the high, moderate and low hazard areas.