Primary and potential secondary risks of landslide outburst floods

Outburst floods triggered by breaching of landslide dams may cause severe loss of life and property downstream. Accurate identification and assessment of such floods, especially when they leading to secondary impacts, is critical. In 2018, the Baige landslide in the Tibetan Plateau twice blocked the Jinsha River, eventually resulting in a severe outburst flood. The Baige landslide remains active and it is possible that a breach happens again. Based on numerical simulation using a hydrodynamic model, remote sensing, and field investigation, we reproduce the outburst flood process and assess the hazard associated with future floods. The results show that the hydrodynamic model could accurately simulate the outburst flood process, with overall accuracy and kappa accuracy for the flood extent of 0.956 and 0.911. Three future dam break scenarios were considered with landslide dams of heights 30m, 35m, and 51m. The potential storage capacity / back-flow reaches 142x10 6 m 3 /32km, 182x10 6 m 3 /40km, and 331x10 6 m 3 /50km in the valley upstream. Failure of these three dams leads to maximum inundation in the downstream of study reach of 1.674 km 2 , 1.833 km 2 , and 1.927 km 2 . These results demonstrate the serious secondary hazard associated with this region.