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The landslide lakes are temporary lakes in the river valleys formed by landslide debris and commonly form in mountains of high relief and mass movement activity such as Indian Himalayas. Breaching of such temporary lakes with huge amount of accumulated water and sediments can create devastating floods in the downstream areas. On 31 December 2014, a large landslide in the Zanskar Himalayas, India created a 50m high natural blockade on the Phuktal river, a tributary of Zanskar which is further a tributary of Indus river, resulting in formation of around 15 km long impounded lake upstream of blockade. nHPC has a hydroelectric power project, namely nimmo-Bazgo power station (45 MW) in the downstream on Indus river about 220 km from Phutkal and about 20 km d/s of Indus-Zanskar confluence. After the blockade a study was carried out for possible landslide breach to estimate the flood peak, its travel time and rise in river water level at various locations along the reach upto nimmo-Bazgo project. The landslide dam finally breached on 7th May 2015 and in this study, a comparison of simulated and actual event parameters have been presented. Results of the study indicate that parameters estimated through hydrodynamic simulation using river cross-sections from open source DEM provided a reasonable assessment of the situation which helped in formulation of effective reservoir operation plan for passing the flood safely in the downstream.
