Document Type : Original Research Paper
Authors
1 Department of Civil and Surveying Engineering, North Tehran Branch, Islamic Azad University, Tehran, Iran
2 Department of Surveying Engineering, Imam Hossein University, Tehran, Iran
Abstract
Background and Objectives: Landslides, as one of the most destructive natural phenomena, pose a serious threat to engineering and environmental structures. The Siah Bisheh Pumped Storage Dam, the first concrete-faced pumped storage dam in Iran, is at risk of geological displacements due to its geographical location in the Alborz Mountains and complex geological conditions (including active faults, unstable rock masses, and steep slopes). This study aimed to monitor land surface changes and manage landslide hazards within the dam area, using ground surveying and interferometric radar (InSAR) methods. The main focus was on analyzing the impact of key factors such as rapid drawdown, water level fluctuations, and construction activities on the instability of the area.
Methods: In this study, two main methods were used. In the first method, called Ground surveying, changes in critical points such as Gully 5 and areas adjacent to Chalus Road have been monitored by installing concrete targets (small benchmarks) and periodically measuring planar and elevation displacements since 2011. In the second method, changes in the land surface were examined with millimeter accuracy using Sentinel-1 satellite data from 2015 to 2022 and image processing in SNAP software. The processing steps included image alignment, removal of topographic effects with a digital elevation model, Goldstein phase filtering, and phase-to-displacement conversion.
Findings: The results showed significant agreement between the two methods. The highest displacements occurred in areas close to dam basins (such as Gully 5 with more than 60 cm of elevation displacement) and areas adjacent to Chalus Road. Rapid reservoir subsidence was identified as the main cause of instability, as sudden changes in water level accelerate the saturation and rapid depletion of soil and rock masses. The InSAR method was confirmed as a low-cost and faster tool compared to traditional land surveying methods, with displacement estimates of 0.13 to 0.5 meters in identifying changes over large areas.
Conclusion: The combination of ground and satellite methods allows for more comprehensive and continuous monitoring of unstable areas. It is suggested that radar interferometry be used for periodic monitoring and crisis management in similar projects. Also, creating a satellite database and integrating the results with dam behavior models will help reduce landslide risk. This study emphasizes the role of modern technologies in increasing the accuracy and reducing the costs of monitoring sensitive structures.
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