Hazard assessment of the formation and failure of the Sunkoshi landslide dam in Nepal

Abstract

A massive landslide occurred at Jure village of Nepal on August 2, 2014. The landslide mass blocked the Sunkoshi River and created a landslide dam. Thirty-seven days after the formation, the Sunkoshi landslide dam breached on September 7, 2014. In this study, flood hazards due to the formation and failure of the Sunkoshi landslide dam were analyzed. Flood inundation due to impounded water in the upstream river valley of the dam was also analyzed. The outburst discharge from the dam breach on September 7, 2014 and flood characteristics along the downstream river valley were computed by using an erosion-based dam breach and flow model. Flood inundation maps were prepared by using the results obtained from the numerical simulations and geographical information system tools. The peak flow discharge of the Sunkoshi landslide dam outburst at the dam outlet was found to be 6436 m3/s, and the estimated time of the dam breach was found to be about 26 min. The estimated volume of water released from the impounded water in the upstream river valley of the dam was approximately 4.5 million m3. The calculated peak flow velocity and maximum flow depth along the river ranged mostly from 3 to 11 m/s and from 4 to 10 m, respectively. The dam breach had considerable impact on areas more than 30 km downstream from the dam.