Inundation and Potentials Hazard Analysis of Landslide Lake Attaabad-Hunza, Pakistan

Abstract

The landslides considered to be very perilous among the natural hazards and it become more destructive if it blocks the flow of river creating a landslide lake. On 4th January, 2010 landslide occurred close to the Attaabad village approximately 80 km upstream from Gilgit. The landslide blocked the flow of Hunza River and created Landslide Lake. The landslide occurred at the fault line and created highly crushed rock mass. The objectives of the study were to model and simulate Landslide Lake Dame break and map the potential area at risk downstream due to the flood inundation in case of dam breach. To achieve the objectives of the study a joint approach of GIS, remote sensing and hydrological modeling was used for flood simulation. Hydrologic Engineering Center‘s River Analysis System (HEC - RAS) with its GIS embedded extension HEC-GeoRAS was used. The data used include ASTER 30-m digital elevation model (DEM), peak flow discharge at landslide location, land use map (Manning‘s n values) and satellite imageries. HEC-GeoRAS was used to develop the RAS layers geometry including River Centerline, banks, flowpaths, inline structure and cross-sections from Triangulated Irregular Network (TIN). The data was then used as an input to HEC-RAS for unsteady flow simulation. Data input in the model include recoded monthly flow average, normal water depth, and inline structure breach parameters. The HEC-RAS generated water surface profile, velocity and flow hydrographs. The results of the HEC-RAS were finally mapped in ArcGIS for flood extent, flood water depth and flood wave velocity. The water depth, velocity and time to reach maximum discharge were calculated for all the inundated villages. The result of the study indicated that out of 26 villages 7, 10, and 9 villages were classified as at high, medium and low risk, respectively. This approach could be used for development of early warning and emergency preparedness plans to save the livelihood and property.