Barrier lake bursting and flood routing in the Yarlung Tsangpo Grand Canyon in October 2018

Abstract

Ice-soil mixture landslide dams formed frequently in the Tibetan Plateau in response to global warming, which pose great threats to both upstream and downstream areas due to inundation and lake bursting. On 17 October 2018, a large landslide, induced by an ice-avalanche at the Sedongpu Basin of the Yarlung Tsangpo, blocked the main course of the river near Gyalha. The barrier lake level rose quickly and the dam was overtopped naturally at 13:30 on 19 October 2018, generating a dam-breaching flood with a peak flow rate of 32,000 m3/s. This paper presents a comprehensive study of the disaster chain of landslide-barrier lake-dam breaching-river flooding in the Yarlung Tsangpo Grand Canyon, detailed geological and hydrological characteristics of the study region, rapid prediction of the dam breaching hydrograph using an erosion-based numerical model, and analysis of the flood routing in a 460 km canyon reach along the Yarlung Tsangpo. The simulated peak discharge at the dam site is over 30,000 m3/s and the corresponding dam-breaching and flood routing hydrographs agree well with the observations. Two additional scenarios with larger inflow rates are also considered. Results show that with a larger inflow into the barrier lake, the erosion of the dam body becomes more rapid. When the inflow rate is increased by six times, the peak dam-breaching discharge can be doubled. The study serves as basis to manage the flood risks due to landslide dam bursting on the Yarlung Tsangpo or similar rivers.