Detecting land subsidence using Sentinel 1 satellite images (Case study: Northern basin of Yazd-Ardakan plain)

Introduction:

Land subsidence occurs under several conditions, including subsidence due to excessive exploitation of groundwater, subsidence due to the construction of large dams, and subsidence due to the tectonics of salt domes (Omidvar, 2011). Excessive extraction of groundwater for various urban uses causes land subsidence. For example, in the Venetian Lagoon, the policy of intensive industrialization in the main part of the island led to excessive extraction of groundwater, which also contributed to the effective subsidence of the island cities. The growth and development of the city of Bangkok throughout the Chao Phraya Delta Plain has also been so rapid that the city's inadequate and inadequate water supply is forced and quite extensively carried out by the private sector through illegal extraction of groundwater. The pattern and extent of subsidence caused by pumping can be determined to some extent by the reactivation of faults in the delta's constituent materials (Zamardian, 2017).Meanwhile, the phenomenon of land subsidence, which is the result of the slow and gradual compression of subsurface deposits in the plains, occurs as a displacement of part of the earth's crust downward. This hazard has also raised many concerns, especially in sensitive and strategic centers, and is the result of anthropogenic activities such as various types of mining, water, oil and gas extraction, underground excavation and excavation, including tunnels, metros and dams, and environmental processes such as volcanic activities and lava eruptions, dissolution processes, melting and compaction of snow and glaciers, fault movements, and sometimes both. Human factors and land use change are the main drivers of subsidence, and there is a direct relationship between the increase in the rate of subsidence and the withdrawal of groundwater resources (Bagheri et al., 2021).Land subsidence is the gradual or sudden lowering of the earth's surface, which occurs due to various factors such as tectonic activities, mining, oil and gas fields, and excessive groundwater extraction, and is one of the issues that has put the country's plains at risk in recent years. The northern basin of the Yazd-Ardakan plain is also among the plains that are at risk of land subsidence. The Sentinel-1 satellite is capable of imaging in any atmospheric and ground conditions, and it makes it possible to provide high-quality images at night, in fog and dust, and even under clouds. This satellite provides useful information for remote monitoring of various areas such as agriculture, forests, climate, earthquakes, and land subsidence. It can be said that most researchers have calculated subsidence using various methods such as Sentinel satellite images and radar. And most of the reasons for land subsidence are due to human activities such as excessive extraction of groundwater, the effects of which are manifested in the form of rupture and tilting of well wall pipes, or even natural causes such as volcanic activity and drying of fine-grained sediments. In this study, subsidence and piezometric wells in the northern basin of the Yazd-Ardakan plain were analyzed using Sentinel 1 satellite images. The present study was conducted with the aim of analyzing land subsidence in the northern basin of the Yazd-Ardakan plain.



Objective:

This study investigates land subsidence due to excessive groundwater extraction in the northern basin of the Yazd-Ardakan plain.



Methodology:

The present study was conducted with the aim of investigating land subsidence due to excessive groundwater extraction in the northern basin of the Yazd-Ardakan plain. To achieve this goal, the Sentinel 1 radar satellite, the Landsat satellite, and data from piezometric wells were used in the period (2005-2020). The correlation index has also been used to examine the effect of groundwater level drop on land subsidence.

Discussion and Results:

The results show that the study area has subsided by 8 cm during the 15-year period, which is a significant figure. The spatial analysis of the subsidence indicates that the highest amount of subsidence has occurred in the areas of Meybod, Februieh, Ardakan and Ahmadabad (which are facing a decrease in groundwater levels). Accordingly, one of the reasons for the subsidence has been the decrease in groundwater resources, but the abnormal behavior of the deep Roknabad well not only has not decreased water, but also 81 cm of water rises every year to an extent that is in line with the slope of the land. Also, the correlation index has been used to investigate the effect of the decrease in groundwater levels on land subsidence, and the results obtained show that no significant correlation has been identified between these two variables. The lack of correlation between groundwater changes and land subsidence can be due to geological, hydrogeological factors or measurement methods and other cases.