The Baige Barrier Lake in the Upper Changjiang River and its Dam-Breach Flood Simulation

Devastating disasters may occur in case of breaching of a barrier lake, which therefore have to be rapidly assessed and urgently treated in order to reduce the potential risk. A giant and dangerous barrier lake was formed in the upper reach of the Changjiang River (known as the Jinsha River) by a landslide close to the Baige Village in Tibet, China, on the 3^rd Nov. 2018. The landslide dam is about 273m long along the river direction, and 322m wide in the cross river direction. The dam crest is about 2966m above the reference mean sea level and 58.24m above the water level of the upstream barrier lake when formed. The upstream inflow is 700m³/s, implying an increase of roughly 2.5×10⁶m³ water volume per hour in the lake. Should the water level rise to the dam crest of 2966m, the lake capacity would come to 770×10⁶ m³. According to the continuous accumulated and updated measured or conjectured data transmitted from the site which is very remote and quite inaccessible, simulation of a large number of possible scenarios of the dam-breach flood of the Baige barrier lake was conducted to predict the flood peak outflow and hydrograph, and help to evaluate the severity of the threat to the downstream area, providing basis for the emergency evacuation of the population at risk. To reduce the water volume of the barrier lake and the flood peak outflow, and consequently the flood risk to the downstream area, ten days later after formation the Baige landslide dam was artificially breached by a manual excavated drainage channel, and the lake was successfully drained. No human lives were lost in this dam failure. After that back analysis of the draining process of the Baige barrier lake was also conducted to reproduce the well-monitored outflow hydrograph obtained during the dam breaching process of the barrier lake. This paper will present a detailed description of the formation, channel excavation, and breaching of the barrier lake; summarize the simulation of the dam-breach flood and back analysis of the draining process; and give a few experiences in barrier lake emergency treatment.