The floods in Tunisia pose a major risk to the environment, particularly soil and water resources. The country experienced several catastrophic events and that affected several regions, including the Maknassy Basin. Located in the communes that belong to Maknassy and Mazzouna, the basin of Maknassy (more than 1020 km2) is drained from east to west by the Wadi Lban that represents itself a part of the watershed of the Lban- Ouadran wadi. The Maknassy Basin is a compact catchment area characterized by low slopes in the center and fairly steep slopes (always more than 15%) on the slopes that delimit it with a belt, often impermeable rock outcrops and relatively high drainage density. Thus, the physical characteristics of the Maknassy Basin make it an environment vulnerable to flood risk. This has led to a profound change in geomorphology of the interfluves and a change in the hydrological behaviour of wadis. These only increases the risk of flooding which can reach the disaster phase just like the situation in 1969 and 1989.In addition to material and infrastructure damage, hundreds of victims were also caused. This increases the risk (The danger or possibility of the occurrence of a hazard, affecting the human population, and the damage to the material and the environment) of flooding that can reach the disaster (It is the realization of increasing the risk of man-made losses on the basis of material and environmental losses) phase as was the case in 1969 and in1989 which have made a few hundred victims in addition to the material damage and in the infrastructure. This chapter focuses on the use and contribution of the GIS to the study and management of flood hazards in the Maknassy basin (the Lban-Ouadran wadi watershed, Tunisia) as part of a hydro-geomorphological study and with the aim of mapping to flooding hazard. The research methodology is based, in particular, on the analysis of the morphometric characteristics of the alluvial deposits, those of the river system and the terrain (slope and permeability) to identify the flood-hazard. The research methodology is based in particular on the analysis of the morphometric characteristics of alluvial deposits, those of the hydrographic network and the terrain (slope and permeability) to identify flood risks. Therefore, this analyse on the one hand shows the natural tendency of the Maknassy Basin to flood risk. On the other hand, the solution to this hazard is to protect the bottom of the cultivated basin (30% of the basin surface area), which is the most important agglomerations (such is the case of the Maknassy city, home to 4,215 people according to INS (National Institute of Statistics, Tunisia) estimates for 2024).