Spatial analysis, assessment and mapping of flood hazard in the alluvial plains of Boumerzoug and Rhumel (city of Constantine, north-eastern Algeria): application to development and urban planning projects

This paper proposes an operational methodology for flood hazard assessment and mapping based on the use of two complementary methods: a geomorphologic analysis and a hydrological modelling method under GIS. The methodology has been applied to the urban and peri-urban areas of Constantine, extended over the flood plains of the Boumerzoug and Rhumel river catchment areas highly exposed to frequent flooding. The spatial analysis of the hazard factors revealed the natural predisposition of the two rivers plains of Rhumel and Boumerzoug to flooding. The hydrological modelling of flood phenomena by adjusting the time series of maximum daily rainfall and flow data of the five stations of the catchment areas to log-normal and normal laws allowed to obtain values of maximum daily rainfall and flows for different return periods of 5, 10, 50, 100 and 200 years. The obtained values are close to the recorded ones during the historical floods, which show the reliability of the used adjustment models. The obtained flood hazard map obtained on the basis of the identification of geomorphological units allowed to define the flood extension areas, the main overflow points and the degrees of hazard. This map can be useful for risk for decision about risk reduction and land use planning in the urban area of Constantine.