Enhancing knowledge of the evacuation process is still a challenging topic. Hard to exercise in real conditions, we aim to propose a numerical simulation of an entirely pedestrian evacuation at the scale of a city. The main interest of this study is to render realistic pedestrian mobility in an evacuation context. To that end, a multi-agent system framework is used, allowing intelligent agents implementation mixed with an adapted social force model (Helbing and Molnár, 1995). The simulation is applied to Alès and its agglomeration (ten municipalities), subject to a dam failure that could cause a flood wave. Evacuation times for the ten municipalities were thus calculated and analyzed.