Flood hazard mapping in urban area using the hydrogeomorphological approach: case study of the Boumerzoug and Rhumel alluvial plains (Constantine city, NE Algeria)

In Algeria, flood hazard is among the most frequent and damaging natural hazards constituting, hence, a major constraint for the economic and social development of many cities. Constantine is one of the most populated cities of the country, located at the confluence of the alluvial plains of Boumerzoug and Rhumel and at the outlet of three watersheds: Rhumel, Rhumel Smendou and Boumerzoug. Therefore, it constitutes a flood hazardous area as may be suggested by the recurrent historical cases. In this work, we used the hydrogeomorphological approach to map the flood hazard in Boumerzoug and Rhumel river plains within the urban area of Constantine based on the interpretation and analysis of the floodplain's geomorphology. The obtained results allowed us: (i) to delineate the flood hazard areas, (ii) to identify the main overflow points and (iii) to determine the water levels for annual, frequent and exceptional floods. Our results show that the Rhumel and Boumerzoug plains exhibit a same hazard level. The obtained flood hazard map can be used as planning decision support tools to better consider flood risk in urban planning and economic development of the city of Constantine. [Display omitted] The flood hazard map of the alluvial plains of Boumerzoug and Rhumel rivers within Constantine city using the hydrogeomorphological approach on the Digital Elevation Modsel (DEM) showing cross-sections and the heights of water corresponding to 10 and 100 years return period according to the morphology of the functional units (minor, middle and major beds) of the Rhumel and Boumerzoug rivers valleys. •Constantine, located at the confluence of the alluvial plains rivers of Boumerzoug and Rhumel and at the outlet of three watersheds (Rhumel, Rhumel Smendou and Boumerzoug) is highly exposed to flood events generated by the cyclic floods of these rivers.•In this work, we used the hydrogeomorphological approach to map the flood hazard in Boumerzoug and Rhumel river plains within the urban area of Constantine (North East Algeria).•The methodology is based on the interpretation and analysis of the floodplain's geomorphology.•The obtained results allowed to delineate flood hazard areas, to identify the main overflow points and to determine the water levels for annual, frequent and exceptional floods.•The established maps may constitute a first tool for flood risk prevention and land use planning.