International Journal of Emerging Technology and Advanced Engineering Website: www.ijetae.com (ISSN 2250-2459, Volume 2, Issue 9, September 2012) 389 Investigation of land subsidence in Southern Mahyar Plain in Isfahan province, Iran Salehi 1 , R. Ghafoori 1 M., Lashkaripour 1 , G.R. and Dehghani 2 , M. 1 Department of Geology, Faculty of Sciences, Ferdowsi University of Mashhad 2 Department of Civil and Environmental Engineering,School of Engineering, Shiraz University Abstract— Land subsidence is one of the environmental hazards in which various mechanisms take part in its formation and development. Excessive extraction of groundwater has caused severe land subsidence and earth fissures in the Southern Mahyar Plain located in Isfahan province in the peripheral part of Iran’s central desert. In the last decades, fast agricultural expansion coupled with rapid population growth has tremendously increased pressure on the ground water resources. This paper deals with the relation between declining of ground water level, land subsidence and earth-fissure based on the available data in Southern Mahyar Plain. Based on field data, the temporal and spatial distribution of land subsidence is investigated and the causes for earth fissures are analyzed. Collected data using peizometric wells on the plain surface shows that the mean drop of water level in the period of 12 water years was 6m. Moreover, investigation of groundwater level fluctuations and compiling iso-depth maps in the district of the plain confirmed sharp drop of groundwater level. The areal distribution of the land subsidence is closely related to the cones of depression in the main exploited aquifers. In addition, field surveys in the study area indicated that fissures and cracks due to subsidence occur in the peripheral part of plain that inflicted severe losses to the agricultural lands. In this study, Interferometric SAR technique with the aid of radar image of the satellite ENVISAT was used for the determination of the area affected by subsidence and investigation of surface undulation in short-term and long-term periods. Also by analysis of maximum time series, the mean rate of subsidence in the period of 2003-2006 was calculated to be 8.2 cm per year.. Keywords—subsidence, groundwater, Southern Mahyar Plain. I. INTRODUCTION Land subsidence is a gradual settling or sudden sinking of the earth surface associated with negligible horizontal displacements [2]. Subsidence due to the drop of groundwater level is a universal hazard that caught attention throughout the world. One of the most important factors of subsidence is the drop of groundwater level that caused subsidence in many plains inside Iran in the recent decades. There are a variety of methods available to monitor land subsidence. They include vertical extensometers, baseline and repeated surveys of benchmarks using Global Positioning System (GPS) or conventional survey methods, and Interferometric Synthetic Aperture Radar (InSAR). Interferometric SAR technique (InSAR) is the most modern technology for the subsidence surveys. The technique of (InSAR) is uniquely suited to monitor elastic and inelastic response of aquifer systems to changes in groundwater levels, providing new insight into the role of geological structures and lithological parameters in plain aquifers [1,7,3,8]. With its wide spatial coverage (∼ 104 km 2 ), fine spatial resolution (∼ 102 m 2 ), and high accuracy (∼ 1 cm), InSAR offers new capabilities to measure surface deformation caused by aquifer discharge and recharge at an unprecedented level of detail never before possible with techniques like GPS and leveling [7,3,9]. Also, new methods and techniques such as advanced geographic positioning and radar have been applied in some plains of the Iran including the Neyshbour plains in the Khorasan-e- Razavi province [5] and the Mashhad plains [6,9]. This paper focuses on the study area Southern Mahyar Plain SE of Isfahan, which bounded on the north by the southern part of the Kolah Ghazi Mountains, with trending NW-SE as shown in figure 1. It is a broad sedimentary basin composed primarily of Quaternary-Neogene alluvial deposits [10]. Annual rainfall in the area is estimated to range from 100 to 150 mm yr –1 , occurring mainly during spring and winter seasons.