Dynamic landslides susceptibility evaluation in Baihetan Dam area during extensive impoundment by integrating geological model and InSAR observations

On April 6, 2021, the Baihetan dam launched impoundment, and the reservoir water surface elevation dramatically increased from 660 m to 812 m until October 2021, which may induce large-scale landslides in reservoir bank. Accurate landslides susceptibility evaluation during impoundment is crucial for controlling the possible disasters and taking early evacuation or disaster prevention measures. Although many traditional geological models can accurately evaluate the landslides susceptibility of the reservoir area, they are inadequate to make the prompt response to the quick condition changes of reservoir bank induced by impoundment, while InSAR technology can provide a dynamic observation to monitor the small displacement occurring in the reservoir bank. Thus, this study proposes a new approach to dynamically evaluate the landslides susceptibility on reservoir banks during impoundment integrating geological evaluation model and InSAR observation. The approach combined stability coefficient of the reservoir area calculated from Scoops 3D model and geotechnical parameters, with slope displacement from InSAR technology to evaluate the susceptibility of landslides. The comparison between before and during impoundment shows that when the reservoir water elevation increased by 150 m, the high risk area of geohazards increases by 14.26 km2. The field validation confirms that the approach provides an effective and accurate dynamic landslide susceptibility evaluation, which forms a timely response to the geoenvironment changes in reservoir bank caused by the 150-m water level increment during impoundment.