Introduction

The landscape of the earth's surface as a complex system is the result of the interaction of factors such as geographical, climatic, temporal processes and human activities. The physical development of cities, without observing the principles of urban planning and taking into account the potential of their natural hazards, leads to the high vulnerability of cities. One of the most important dangers in the plains and plains of our country is the dangers caused by land subsidence, which for various reasons, such as over-harvesting of underground water resources and climate changes, causes many problems for agricultural lands, roads, and transmission lines. has become power and energy; Therefore, it is very necessary to investigate the causes and to control and reduce its risks (Abedini et al., 1402). Groundwater is one of the most important sources of water needed by the agricultural, drinking and industrial sectors, especially in the dry areas of the central plateau of Iran. Therefore, investigating the process of its qualitative changes is very important in the sustainable management of water resources (Arshad Hosseini et al., 1400). . Yilaghi city of Shandiz, which is a part of Targaba Shandiz city, is 1400 meters above sea level and is located at 59 degrees and 17 minutes of latitude and 36 degrees and 23 minutes of latitude. This city is adjacent to the central part of Mashhad from the north, Targaba city from the south, Neishabur from the east and Golbahar from the west, and has an area of about 37,825 square kilometers. Since Shandiz Mashhad is known as one of the holiday areas of Khorasan and is surrounded by thick and dense vegetation of towering sycamore trees and flowing rivers and tourist attractions (Karizno Aqueduct, Shandiz Historical Tower, Shandiz Padideh, Cozy Cottage Garden, Panjan Nama, Park It is mountainous and...), has a cool and summery climate and is one of the main centers of travelers and tourists in Mashhad and all over Iran. All over the south of this city are the heights of the Binalud mountain range of Khorasan, and Shirbad peak in the Zashk region of Shandiz is also considered the highest point of this mountain range and Khorasan province.

Methodology

In order to investigate the subsidence rate of Shandiz city and its relationship with the drop in the underground water level, first the rate of land subsidence in the period of 2016-2023 was calculated annually by radar interferometric method and then the trend of changes in the water level of piezometric wells during 29 years was investigated. took Finally, the research results were verified by field surveys. In order to process by radar interferometric method, SNAP software was selected to obtain the final results of the subsidence rate based on the phase difference between the images taken on different dates. In order to study the latest status of the groundwater level in the study area, the statistical information of piezometric wells from 1370 to 1399 was obtained from Razavi Khorasan regional water, which was then prepared in the GIS software after annual averaging using the IDW interpolation model to prepare the groundwater level map. and was evaluated.





Results and Discussion

In the investigations carried out with SLC radar images of Sentil 1 satellite in relation to the city of Shandiz, 8 images were processed two by two in the Snap software, the image of the year 2016 with 2017, 2017 with 2018, 2018 with 2019, 2019 with 2020 and 2020-2021, 2021-2022 and 2022-2023 images were checked and the amount of subsidence recorded for each period was 2 cm for 2016-2017, 6 cm for 2017-2018, 2 cm for 2018-2019, 5 cm for 2019-2020, for The 2020-2021 period was about 2 cm, 4 cm for the 2021-2022 period and about 1 cm for the 2022-2023 period. In the survey of the water level of Shandiz city from 1370 to 1399, the number of 2 main wells, Hassan Abad and Qasim Abad, which are located in the northeast and east of the city at a distance from it, were obtained with the same data, which information was obtained from the Khorasan Razavi Regional Water Organization. and was investigated. The data were averaged every 5 years and its maps were prepared using the IDW tool in the GIS environment for the study area. In the east of the region, the villages of Hesarsokh and Sarassiab were located in the area of high risk. The minimum and maximum water level drop in the 30-year period from 1370 to 1399 was calculated as 57.86 and 76.84 meters.



Conclusion

The results of interferometric studies showed that the amount of subsidence during 5 statistical periods in the studied area was 22 cm. The amount of subsidence recorded for each period is 2 cm for 2016-2017, 6 cm for 2017-2018, 2 cm for 2018-2019, 5 cm for 2019-2020, and 2 cm for 2020-2021. 4 cm for the 2021-2022 period and about 1 cm for the 2022-2023 period. According to the obtained results, the highest amount of subsidence has happened in the east, north and south of Shandiz from east to west. The water levels of the wells have reached their maximum decrease in the period from 1370 to 1399. The water level drop in this time period is at least 57.86 meters and the maximum is 76.84 meters, and all areas of Shandiz city have water level drops and are at risk. The subsidence has also covered most of the city areas. Shandiz city is a tourist area and all its geosites (Carizno Aqueduct, Shandiz Historical Tower, Shandiz Phenomenon, Cozy Cottage Garden, Finjan Nama, Mountain Park, etc.) are vulnerable to damage, therefore it needs special attention.



Key words: interferometric technique, subsidence, geosite, Snap, Shandiz city.