Construction of drainage network topology using Digital Elevation Model: case of Dakar ; Utilisation d’un MNT pour la construction de la topologie de drainage de l’agglomération de Dakar

International audience ; In Dakar, floods have been recurring since 2005 with negative social and economic impacts. These flooding are caused by: (1) physical environment (nearly 4,800 ha of wetlands in Dakar) on which (2) increased urbanization without proper management and (3) frequency of heavy rainfall intensities. The recurrence of these floods in the context of rainfall recovery requires monitoring tools to reduce risks. This study aims to develop a methodology, capable of providing, in real or deferred time, a fine-scale representation (5m) of the flowflux over the entire Dakar metropolitan area and of identifying areas presenting overflow during a rainy episode. Two key steps are followed to achieve this objective: (a) reconstitute the trajectories of the flows by taking into account the terrain and the modifications induced by urban objects; (b) define and validate the flow models, by coupling a hydrological model for calculating flows at the outlet of small urbanized watersheds with a hydraulic network propagation model. This article mainly deals with the first phase of the study. It is based on a 5m resolution DEM from which we extract a first drainage model which is then modified in order to integrate urban conditions and thus spatialize the new directions of flow flux. The processing chain has been implemented in the ATHYS software. ; A Dakar, les inondations sont récurrentes depuis 2005 avec de lourds impacts sur les actifs sociaux comme économiques. Trois facteurs permettent d'expliquer les causes : (1) le milieu physique (composé de près 4 800 ha de zones humides) sur lequel s'est opéré (2) un étalement urbain rapide sans aménagements adéquats et (3) la fréquence de fortes intensités pluviométriques. La récurrence de ces inondations dans un contexte de reprise pluviométrique nécessite de développer des outils de monitoring permettant de réduire le risque. Cette étude vise à développer une méthodologie originale et performante, capable de fournir, en temps réel ou différé, une représentation à ...