Hazard Assessment due to Dam Break Flood: A Case Study of Attabad Landslide Dam

Abstract

Floods are the most disastrous and recurring natural hazards which causes widespread destruction to human life, to public and private property, devastation of crops, livestock fatalities, pollution of water sources and harmful influence on health due to stagnant flood water. Flood modeling and risk mapping is very helpful in flood management and hazard mitigation. Flood simulation models provide the flood extent, depth and velocity which are the very basic ingredients that go into generation of flood hazard maps. The objective of this research was to carry out flood modelling resulting due to landslide dam breach of the Attabad dam on river Hunza, a tributary of Gilgit river in Gilgit- Baltistan (GB), Pakistan. The river reach from Attabad to Gilgit of about 100 km on Hunza River was modeled based on likely breach scenarios. The river flow was modelled using the BASEMENT model which solves the 2D Saint Venant equations. For this purpose, three breach scenarios were considered, namely, 1/4, 1/3 and 1/2 breach corresponding to peak discharges of 10379 m3/s, 19076 m3/s and 40057 m3/s respectively. The simulated flow depths were compared with values in literature. The model showed good performance as regards to the maximum flood depth for the upper and middle river reaches. However, the results were in disagreement at Gilgit city. The simulated depth of water was 19.76 m, 27.87 m and 34.86 m for 1/4, 1/3 and 1/2 dam breach scenarios. It is concluded that BASEMENT model can be utilized for dam break flood modelling. Moreover, areas susceptible to most hazardous flood were identified and measures were suggested to mitigate the damages.