Monitoring landslide associated with reservoir impoundment using synthetic aperture radar interferometry: A case study of the Yalong reservoir

The construction of large reservoirs can address the problem of uneven distribution of rivers in time and space, thereby meeting the needs of human production and living. However, the huge elevation of the water level in some areas may modify the distribution of the groundwater level, causing geological disasters, such as surface deformation and landslides. The Yalong reservoir supplies water to the downstream area of Shannan, Tibet; however, since the reservoir started storing water in 2017, the government has discovered two ancient landslides. In this study, to monitor the deformation of the Yalong reservoir since its construction in 2014, we first used synthetic aperture radar (SAR) data and the multidimensional small baseline subset (MSBAS) method to obtain the deformation in the east–west and vertical directions. The result indicated the presence of three large, slow-moving landslides: Landslides I and II, located on the right bank of the Yalong reservoir, which are consistent with the results obtained by the actual survey, and a new discovery, Landslide III, located on the left side of the reservoir. Meanwhile, the experimental results indicated that the dam had undergone obvious deformation after impoundment, which should not be ignored. The global positioning system and interferometric SAR (InSAR) time-series deformation residual data were used to verify the accuracy of the InSAR method. The results also showed that the deformation caused by the three landslides had tended to accelerate after the reservoir's impoundment, and that the failure mode was retrogressive landslide. We found that InSAR plays a vital role in landslide detection and failure mode research around reservoirs, and assists in providing early warning for subsequent landslide disasters.