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Sasan Zangenehtabar 
, Mojtaba Yamani * , Mohammad Sharifikia , Seyed Mosa Hossieni , Masoomeh Amighpey
, Mojtaba Yamani * , Mohammad Sharifikia , Seyed Mosa Hossieni , Masoomeh Amighpey
Faculty of Geography, University of Tehran, Tehran, Iran , myamani@ut.ac.ir
Abstract: (8 Views)
1- Introduction
Land Subsidence, as the downward movement of the land surface, plays an important role in shaping geomorphological features in different landscapes. Subsidence significantly affects the formation of river geomorphology by changing sediment distribution patterns, channel morphology, and basin evolution. Studies have shown that subsidence can lead to channel deviation, creating head-changing deviations, and increasing river gradients. In addition, subsidence affects sediment distribution, shoreline patterns, and channel mobility. The Tehran Plain aquifer has been subsiding over the past three decades, and the magnitude of this subsidence does not show a uniform distribution. Previous studies have attributed excessive groundwater extraction to the subsidence phenomenon in recent years. It seems that geomorphological diversity with different sedimentary characteristics can play a different role in the speed of expansion and secondary consequences of subsidence in this area. In order to directly observe the geomorphological effects of subsidence in the Tehran Plain, a field visit was conducted to about 20 points in areas affected by significant subsidence.
2- Methodology
This area is part of the Tehran-Karaj aquifer and includes the cities of Islam Shahr, Shahriar, Qods and Baharestan, Tehran city and parts of the cities of Malard, Fardis, Robat Karim and Rey. The northern border of this area is limited to the slopes of the Alborz mountain range and includes the Tehran and Karaj alluvial fans and alluvial plain. In this study, Sentinel 1 satellite radar images in VV polarization were used in the period of 2022 with a time interval of 12 days. The number of selected images is 27 pieces. The small baseline radar interferometry technique (SBAS) and GMTSAR software were used to study Land subsidence. In order to directly observe the geomorphological effects of subsidence in the plain of Tehran, a field visit was conducted for about 20 points of areas affected by high subsidence.
3- Results
The final results show a displacement rate of -163.338 mm to +38.3 mm per year along the satellite line of sight. According to the obtained displacement map, most of the subsidence of the Tehran Plain is seen in the central and western parts of the plain, with its maximum in the center and east of Shahriar County and northwest of Eslam Shahr County. The margin of the subsidence zone also extends to the southwestern part of Tehran City, showing a rate of up to 25 mm per year. The graph of the standardized cumulative groundwater level confirms periods of severe groundwater decline for all wells, although in some wells the water level continues to decline, while in others it has increased after a while, which may be due to groundwater consumption management or other possible changes such as sewage leakage into the aquifer. Photographs taken from the Karaj Riverside areas between the cities of Shahriar and Islamshahr, which are located in an area with high subsidence (between 80 and 150 mm per year), show the creation and expansion of gullies and the separation of the riverbed wall in the form of cracks in the wall and on its surface due to subsidence.
4- Discussion & Conclusions
A large part of the area affected by subsidence is located in Shahriar County, but due to the expansion of construction and agricultural lands, it is not possible to study its geomorphological changes in this area, and we can only focus on the effects of subsidence on human structures and ground cracks. The graph of the standardized cumulative value of the groundwater level confirms the periods of severe groundwater decline for all wells. Considering the dispersion of the selected well locations and the spatial and sedimentary differences, a different behavior of groundwater level changes compared to subsidence is evident and it can be concluded that the decrease in groundwater level is not the only reason for the dispersion of subsidence in the Tehran plain aquifer and that other different contributing factors such as sedimentary structure and soil type and human impacts such as possible sewage leakage are involved. Field visits to the maximum subsidence areas show geomorphological changes caused by subsidence in the form of cracks in the ground and river walls, as well as the creation of gullies in the walls of old river embankments.
Received: 2025/01/21
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