Effects of groundwater withdrawal on land subsidence in Kashan Plain, Iran

Kashan Plain is located in an arid area on the west side of central desert of Iran in north of Isfahan province. In recent decades, increasing population, industrial and agricultural developments in the region that require water withdrawal have resulted in the decline of groundwater and the occurrence of subsidence in this plain. Since 1991, earth fissures that have caused many damages to buildings, farmlands and roads have been observed in many parts of Kashan Plain. The lengths of some of these fissures are more than 2 km long. In this study, after determining the location and direction of fissures, the probable influential causes of earth fissuring were investigated. The results indicated that the main causes of this phenomenon are basically the decline of groundwater head, variation in sediment thickness due to bedrock anomalies and differential vertical compaction. In order to investigate the rate of land subsidence in the Kashan Plain, the Envisat ASAR data from 2003 to 2008 were used. The displacement maps were generated by InSAR time series analysis. The maximum rate of subsidence in this period was determined to be about 3.5 cm/year.