The Alagou Reservoir was officially closed for water storage in November 2014. Since September 2016, gradual slope collapse and deformation have been observed at elevations ranging from 600 to 1050 m upstream of the left bank of the Alagou Reservoir dam site. The increasing annual deformation raises significant concerns about a potential landslide, which could lead to surge waves, posing a threat to both the dam and the surrounding environment. Owing to difficult access and worsening conditions, thorough exploration of the site was challenging. Consequently, after emptying the reservoir, we conducted on-site investigations using satellite D-InSAR analysis, numerical modelling and post-event monitoring. This multidisciplinary approach aimed to investigate the relationship between deformation behaviour, triggering conditions and reservoir water-level changes. Our study provides valuable insights into the complex geological processes involved in slope deformation and failure mechanisms induced by water-level fluctuations. We elucidated the interplay between deformation behaviour and triggering conditions, which is essential for designing effective reinforcement treatments for deformed slopes. Although InSAR has proven to be a cost-effective tool for monitoring surface deformation, it offers limited insights alone. Therefore, we recommend a multi-technique approach incorporating geophysical, geotechnical and remote sensing data for a comprehensive understanding of slope stability.

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