Abstract
A GIS-based one-dimensional flood simulation model is presented and applied to the centre of the city of Nîmes (Gard, France), for mapping flow depths or velocities in the streets network. the geometry of the one-dimensional elements is derived from the Digital Elevation Model (DEm). The flow is routed from one element to the next using the kinematic wave approximation. At the crossroadqs, the flows in the downstream branches are computed using a conceptual scheme. This scheme was prior designed to fit Y-shaped pipes junctions and has been here modified to fit X-shaped crossroads.The results were compared with the results of a two-dimensional hydrodynamic model based on teh full shallow water equations. The comparison shows that good agreements can be found in the steepest streets of the study zone, but differeces may be important in the other streets. Some reasons that can explain the differences between the two models are given and some research possibilities are proposed.