Integrated HEC-RAS 2D and GIS mapping for flood risk assessment in ungauged urban watershed: a case study of Saïda Wadi, northwestern Algeria

Algeria, like many Mediterranean regions, is highly vulnerable to flooding, which often occurs in catastrophic forms. The control and management of such events represent major challenges to both economic and social development. Since 2012, the rehabilitation of 8 km of the Saïda Wadi in northwestern Algeria has played a significant role in controlling recurrent floods. This study aims to analyze and compare hydraulic conditions before and after the rehabilitation of the Saïda Wadi. Flood simulation is essential for predicting wave arrival times and delineating flood-prone areas, particularly in ungauged catchments. HEC-RAS 2D, coupled with a Geographic Information System (GIS), is applied to model unsteady flows governed by the Saint-Venant equations. The results demonstrate a notable improvement following the rehabilitation works, with reductions of 29.4% in water depth, 8.97% in floodplain extent, and 43.9% in maximum flow velocity.