In recent year’s groundwater pomping in the Mashhad plain and decreasing of rainfall in the Mashhad, plain is cause subsidence and creat damage to province infrastructure. This problem is causing more application for deep well water in agriculture, industries, and drinking water. Follow by this demand the number of illegal wells dicking by customers is increasing, therefore the water level of groundwater in Mashhad plain decreasing and the subsidence rate is growing. Mashhad plain is one of the significant plains in the Khorasan Razavi province which is the main water source to support the cropland and industries. High pressure in Groundwater pumping and rainfall is decreasing it causes aquifer recharge reduction. Groundwater depletion induced a variety of inadequate in the Mashhad plain such as reducing well discharge, Qanat destructive, Water quality decreasing and land subsidence, etc. In this research, the rate of land subsidence by satellite radar data of ALOS-1 and Sentinel-1 and its relationship with groundwater depletion are investigated. For this purpose the time-series InSAR with multiple SAR data in L and C- bands are used for land subsidence analysis for ten years from 2007 to 2018.
The main goal of this research is to find the land subsidence rate in relationship with groundwater depletion of the Mashhad plain for a period of 2007-2018 using the InSAR technique. For achieving the research goal the three pairs of SAR images of ALOS data and three pairs of Sentinel-1 data are used. For analyzing the water delation with land subsidence the ten years piezometric well data for a period of 2006-2017 are modeled to create the groundwater table contour line. This map is used for finding the relationship with land subsidence. The final result of the subsidence map was assessed with field observation and previous work.
InSAR result of ALOS-1 data in this research is shown the subsidence maximum rate of 5.2 cm in the period of 2007.10.16 to 2008.10.16 for 92 days, subsidence maximum rate of 3.8 cm in the period of 2008.01.16 to 2008.03.02 for 46 days, and subsidence maximum rate of 4.7 cm in the period of 2008.03.02 to 2008.06.02 for 92 days. In addition, the Sentinel-1 data processing for InSAR analysis has shown the subsidence maximum rate of 16.1 cm between 2015.05.28 to 2016.05.22 for a year, subsidence maximum rate of 17.4 cm from 2016.05.22 to 2017.05.29 for 372 days, and subsidence maximum rate of 20.3 cm from 2017.05.29 to 2018.05.24 in a year. The spatial distribution of the subsidence area is mostly in the central and southeast of Mashhad plain. The subsidence area is extended in the area with a 39 km length and 8 km wide. The Mashhad plain does not have a permanent river therefore most of the water demand in agriculture, industries, and drink water is supplying by groundwater pumping. The correlation between the subsidence map and groundwater level contour map obviously has shown that groundwater depletion affects land subsidence. Field observation was also confirmed the subsidence by wall and building crack, wellhead uplifting in the test site.
The result showed that the area with the maximum rate of subsidence is the counterpart to cropland and garden which have more influence on groundwater pumping. In addition, the piezometric well date is shown the groundwater table continuously decreasing. According to the result of this research, the main reason for subsidence is a force to groundwater pumping. The field observation approved that the subsidence is happening in the Mashhad plain by some cracks in the wall, bridge, road, well destructive.
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