###### Abstract  
The intricate geological conditions of reservoir banks render them highly susceptible to destabilization and damage from fluctuations in water levels. The study area, the Cheyipin section of the Guangdong Hydroelectric Station, is characterized by numerous ancient landslides of varying scales and ages. In June 2019, during the reservoir filling process of the Guangdong Hydroelectric Station, a large-scale reactivation of ancient landslides occurred in this area, posing severe threats to riverside infrastructure and human safety, including ground cracking, house cracking, foundation settlement, and road collapse. The reactivation mechanism of ancient landslides at reservoir banks is highly complex due to fluid dynamics. This study conducted field investigations in the Cheyipin landslide area, monitored surface and subsurface deformations using GNSS and inclinometers, and analyzed the distribution characteristics, destruction features, and reactivation mechanisms of the landslides through correlation analysis and numerical calculations. The results indicate that the instability pattern of the slopes manifests as traction-type sliding failure. The slopes do not slide along the ancient sliding surface but along a newly formed arcuate sliding surface, with the direct impact area mainly concentrated near the waterline. The stability of the slopes in this project is closely related to the reservoir water level. It can be assumed that the lowering of the reservoir water level triggered the reactivation of the ancient landslides in the Cheyipin section, while the influence of rainfall can be ignored. To prevent the reactivation of ancient landslides, attention should be focused on the changes in reservoir water level, avoiding rapid adjustments in water level during the initial lowering and final raising of the water level. ancient landslide; reservoir water level; rainfall; reactivation; failure mechanism; forensic study; numerical modeling +
Footnote †: journal: Medical  
Research indicates that within 1 to 3 years after the reservoir reaches its maximum water level, ancient and old landslides are prone to reactivation, and new landslides may occur [9]. Since the impoundment of the Three Gorges Dam in 2008, the reservoir water level has risen from 75 m to 175 m, resulting in significant changes to the geological environment. Several ancient landslides have been reactivated, leading to numerous disastrous consequences [10]. These landslides include the Qianjiangping landslide, the Huangduipo landslide, and the Shuping landslide, among others [11; 12; 13]. In early June 2019, multiple landslide events occurred within the territory of Huangdeng Reservoir in Lanping County, Yunnan Province [14]. According to on-site investigations, there are 26 large-scale landslides developed on both sides of the reservoir. The landslides are mainly composed of gravel, boulder, gravelly sandy soil, and gravelly sandy loam, with volumes ranging from hundreds of thousands to millions of cubic meters. Fourteen of these landslides are located below the normal reservoir water level, and their stability is significantly affected by reservoir impoundment. During normal reservoir operation, the water level fluctuates by up to 33 m, and the geological conditions of the reservoir banks are extremely complex, with some sections exhibiting poor stability. Due to the influence of fluid dynamics, the mechanism of landslide reactivation along the reservoir banks appears to be more complex [15]. Existing studies have been unable to effectively elucidate the reactivation mechanism of ancient landslides along reservoir banks [16]. The Cheyiping ancient landslide area in the Guangdong Reservoir region is home to two villages with a total population of 268 people and currently has 1.18 \(\times\) 105 m\({}^{2}\) of cultivated land.