Estimation of subsidence rate using radar interferometry technique and groundwater parameters and land use (Case study: Ardabil plain)

Estimation of subsidence rate using radar interferometry technique and groundwater parameters and land use (Case study: Ardabil plain)IntroductionThe phenomenon of subsidence has affected many parts of the world, including Iran, and in recent years has been raised as one of the main issues and challenges. This phenomenon has developed in different regions under the influence of different factors. In Iranian subsidence, groundwater loss has been suggested as the main factor. Because there is a direct relationship between subsidence of areas and the rate of groundwater loss in different areas. In fact, the prevailing dry climate in most parts of Iran and the concentration of industrial, agricultural and drinking water consumption on groundwater resources, has provided a good infrastructure for the occurrence of this phenomenon. Due to the importance of the issue in recent years, various studies have been conducted in the field of subsidence and advances in the field of remote sensing have led to monitoring the phenomenon of subsidence with greater accuracy and speed than in the past. . Which has received a lot of attention in recent years Radar interference method that has high accuracy and speed in processing information and monitoring land surface changes. Therefore, in this study, this method has been used to monitor the subsidence of Ardabil plain.MethodologyIn this study, First, radar interferometry method has been used to investigate and measure the amount of subsidence. One of the powerful tools for monitoring the subsidence phenomenon is the radar interferometry method. This method is able to determine the changes in the earth's surface in that time period by comparing the phases of two radar images taken from an area at two different times. Sentinel 1 satellite images from 2016 and 2020 were used for this purpose. Considering the direct effect of groundwater decline and increasing its utilization rate on subsidence, in the present study, the status of piezometric wells in the Ardabil plain was evaluated by intriguing method (kriging). Kriging interpolation requires zero mean estimation error. Absolute estimation in interpolation is one of the main features of Kriging model. Also, This means that the estimated value of the quantity at the sampling points is equal to the measured value and the variance of the estimate is zero. Object-oriented method was used to classify the images in the land use map in this study. This is because the method uses information from other pixels (size, shape, texture, etc.) for classification in addition to spectral information. Image objects are created based on parameters such as scale, object shape, color, compression ratio that are determined during interpretation.ResultsThe study of subsidence according to Figure 3 in the last 5 years from 2016 to 2020 in the study area shows that the amount of subsidence is 4 mm per year and 22 mm during 5 years. In order to reconcile the results of radar interferometry with other supplementary data, land use map as well as piezometric wells in Ardabil plain were used. By reviewing and analyzing the land use map and subsidence of Ardabil and field studies confirm the maximum occurrence of subsidence in agricultural areas and good rangelands or 0.22 mm, medium rangelands 0.21 mm and 0.20 mm It provides unsafe and risky living conditions for the residents of Ardabil plain and indirectly has reduced the quality of environmental conditions and life of the residents of Ardabil plain. Land subsidence is a pervasive phenomenon in the world, which has had a significant quantitative and qualitative manifestation in recent years, mainly due to the improper exploitation of groundwater resources and the intensification of its surface decline. To investigate the situation and the effect of groundwater level decline and its effect on the subsidence of Ardabil plain from the information of 39 piezometric wells (obtained from Ardabil Regional Water Organization) during the years 1987 to 2020 that the results of the analysis of a decrease of 48% Shows the water level in 2020 compared to 1987. The maximum water level of piezometric wells has increased from 45 meters to more than 70 meters in 2020, which indicates the deterioration of the Ardabil plain aquifer. Which requires the identification of effective factors, mitigation measures and adaptation measures, including the restriction or prohibition of groundwater extraction in areas subject to subsidence and the implementation of strict regulations for extractors of groundwater resources in areas subject to subsidence and continuous monitoring Indicators of subsidence.ConclusionsIn this study, the extent and distribution of subsidence in Ardabil plain and the effect of groundwater level decline and land use on land subsidence were investigated by radar interferometry, interpolation and object-oriented methods. Studies show subsidence of 22 mm over a period of 5 years. The results of data analysis of 39 piezometric wells in Ardabil plain in a period of 33 years show an average groundwater drop of about 9.5 meters. Co-institutionalization of subsidence maps with land use layers also confirms the maximum occurrence of the settlement area, which has the highest rate related to good pastures and agricultural areas0 / 22. Mm, medium rangelands 0/21 mm and man-made areas0 /20 mm.