Flood risk assessment of Attabad lake: adopting a scenario-based approach for disaster preparedness

Abstract

Attabad Lake is a debris-dammed lake formed due to a landslide disaster on 4th January 2010 in Gojal Valley. Multiple villages are located downstream of the lake along Hunza River. As this lake was formed by a massive landslide, there always remain questions about dam’s stability. The lake is in an active seismic zone which makes it prone to future earthquake and landslide disasters. Considering the sensitivity of region and ambiguities about dam’s structural integrity, this study adopts scenario-based approach for flood risk assessment and identification of potential inundation hotspots downstream. Seven hypothetical flow scenarios ranging from 5 to 50% flow were hydrologically modeled using HEC-RAS 6.5. Based on unsteady flow analysis, inundation boundary, depth, velocity, and product of depth and velocity were computed for all scenarios. The inundation boundary was highest (26.1 km²) in 50% flow scenario followed by 35% (19.6 km²), 25% (8.5 km²), 20% (5.1 km²), 15% (3.5 km²), 10% (3.1 km²), and 5% (2.5 km²). Threshold value of depth i.e., 0.35 m surpassed in all scenarios, whereas threshold velocity (1.5 m/s) was exceeded only in 50% flow scenario. In all flow scenarios, mean value of depth times velocity was higher than the threshold value of 0.52 m²/s. Based on analysis of flood critical parameters, flooding hotspots were mapped, and socio-economic impacts were evaluated. Using risk assessment maps, strategies for infrastructure development downstream, timely evacuation of villages in high-risk zones, and extensive disaster management plans can be prepared by administrative authorities to avoid casualties and economic loss.

Graphical Abstract