Modeling Flood Propagation and Risk Mapping Using HEC-RAS, Simulation of Wadi Kaam Dam Collapse in Libya

Abstract

Floods resulting from dam failures lead to severe losses in lives and properties, especially in river deltas and valleys, as was the case in the city of Derna in September 2023. The extent of losses is determined by the flood area, flood wave propagation, available warning time, and the population at risk. Despite significant improvements in dam design and construction, their collapse due to natural or human causes remains a persistent issue. One of the current natural hazards contributing to this is rainfall anomalies resulting from global climate change, particularly in arid and semi-arid regions, coupled with inadequate maintenance. Therefore, flood modeling is a crucial process in providing information on flood extents, characteristics, and mitigation strategies.

A simulation model was developed to simulate the collapse of Wadi Kaam Dam using the HEC-RAS application along with Geographic Information System (GIS) models and satellite imagery processed in the ArcGIS environment to generate flood inundation maps and identify flood risk maps in the event of dam failure.

The study has concluded that in the event of a catastrophic failure resulting in the collapse of the Kaam Valley Dam, the ensuing flood would reach the residential area in Kaam at the valley outlet in less than an hour. This flood would submerge the area to depths ranging from 4.1 to 9.1 m, with a high flow velocity estimated at approximately 15 m/s at the dam's forefront, and around 2 to 4 m/s upon reaching the residential neighborhoods located at the valley outlet. Where, the floodwaters will continue to flow for about 17 to 19 hours, assuming the dam reservoir is at 50 to 60 million m³. such circumstances could lead to catastrophic damages in the area. Therefore, the study results highlight the severity of this situation and aim to assist decision-makers in Libya in taking necessary measures and developing plans to address such a potential scenario.

Keywords: Kaam