ASSESSING FLOOD RISK THROUGH INTEGRATED HAZARD AND VULNERABILITY MAPPING: THE UPPER TUNISIA MEDJERDA VALLEY CASE STUDY

This paper summarizes the hydrological modeling research results of the national CPR flood project developed by the National Center for Cartography and Remote Sensing to create a warning system for predicting and combating future floods. The watershed studied is located in northwest Tunisia, characterized by an elongated shape and bordered on one side by high reliefs that favor the convergence of flowing streams towards the Medjerdawadi. In terms of pedology, the soil texture is mainly characterized by a dominance of complex soil units and poorly evolved alluvial deposits. Following the flooding phenomenon that affected several towns around the Medjerda during the last century, our study aimed to map and delineate risk areas using hydraulic modeling methods. Flood risk analysis is performed using the HEC-RAS 2D hydraulic model and geographic information systems (GIS), based on several rainfall events. The exceptional floods that occurred in 2003, 2012, and 2015 brought a very large volume of water upstream of the Sidi Salem dam. Inflows from the intermediate basins on both banks, as well as the volumes released from the Mellègue and Bouhertma dams, caused spectacular flooding along the region between Ghardimaou and the Sidi Salem dam. We focused on very high-risk areas located in sectors with medium or low slopes, with varying degrees of cover. The "floodability" method is used to quantify vulnerability. Finally, risk mapping is obtained by cross-referencing the flood hazard map and the vulnerability map of the exposed issues. The aim was to determine the extent of the flooding and identify flood-prone areas. The mapping results enabled the identification of areas affected by flooding during the February 2015 flood. The flooded areas are located mainly in the town of Jendouba.