Potential for a Ganhaizi landslide-generated surge in Xiluodu Reservoir, Jinsha River, China

Xiluodu hydropower station is located on the Jinsha River, the upper course of the Yangtze River, and is the third largest hydropower station in the world. In May 2013, impoundment of the Xiluodu Reservoir started and preliminarily operation began, and the reservoir area was subject to frequent landslides and collapses. On 23rd July 2013, Huangping landslide, with a volume of 20 × 10⁴ m³, slid into the Xiluodu Reservoir and generated an impulse water wave that killed 12 people on the opposite bank. The reservoir water level will fluctuate by 60 m each year, between the elevations of 540 and 600 m, so any impulse wave generated by a landslide in the reservoir is a major concern in the preliminary impoundment phase. Ganhaizi landslide is the biggest landslide in Xiluodu Reservoir, with a volume of about 7,800 × 10⁴ m³. This landslide is only 14 km upstream from the Xiluodu Dam. In particular, the landslide deformation has obviously intensified after impounding. This paper analyzes the terrain and deformation features of Ganhaizi landslide, and we propose that sliding on the Ganhaizi slope may occur at the front part of the landslide. The front part of landslide has a volume of around 300 × 10⁴ m³; the elevation of the barycenter of this part is 510 m. The sliding mass is thus largely underwater, and can pose a threat mainly in the form of surges. Based on the underwater landslide terrain in the mountain reservoir area, the authors have modified the seabed landslide-generated surge source model of Grilli and Watts (2005) to form an initial source model for an underwater landslide-generated surge. Using this model, the authors predicted possible surge disasters that can be caused by a Ganhaizi landslide at both the dead water level of 540 m and the normal water level of 600 m in Xiluodu Reservoir. The surge disaster might mainly strike the area within 5 km along the river channel both upstream and downstream of the landslide area, but generally poses no threat to Xiluodu Dam. This paper aims to provide technical support for the safety of Xiluodu Dam and the reservoir area. The newly established underwater landslide-generated surge initial source model for mountain reservoir areas may serve as reference for calculation of underwater landslide in other reservoir areas around the world.