Risk analysis of the 2018 Sedongpu glacial debris flows in the southeastern Tibet

Several high-magnitude glacial debris flows happened at Sedongpu, a tributary of Yarlung Tsangpo river in the southeastern Tibet in 2018. The hazards blocked the main river twice and inundated the road and bridge to Jiala village on the foot of Namche Barwa massif. The glacial dammed lake with an impounded water of 0.6 billion m³ broke out and caused an outburst flood of peak discharge ~ 30,000 m³/s on October 19. A comprehensive methodology was developed to assess the potential hazard of the glacial-debris-dammed lake before the outburst. Multi-temporal remote sensing image interpretation was used to obtain the frequency-magnitude relationship. The debris-flow deposition and dam height were estimated via numerical simulation of 2-D shallow water equations. Then, the impoundment area and potential inundation were analysed by GIS spatial analysis. We also test different hydrological empirical models of calculating the peak discharge of glacial-debris lake outburst floods. With regard to the Sedongpu event, the 1985 Costa’s model shows best agreement with the measured data.