The Grand Algiers was built on the Sahel foothills. Like other Mediterranean metropolises, it fits in a context of strong cyclogenetic instability, which manifests by floods and the surface runoffs. However, the Grand Algiers makes the exception with the scale which takes the damages after the passage of one of these meteorological events. The event of November 9-10th, 2001, which affected the western part of Grand Algiers, reflects perfectly this situation. Floods activated by this event caused damage to the property and loss of life, which are unequalled in the Mediterranean Basin. In this work, by using classic tools and numerical simulation, we tried to understand the behaviour of the whole hydrosystem (meteorological, geomorphological, and anthropogenic factors). Then we have classified the predisposing, triggering, and aggravating factors of flooding and surface runoff. The results of all the anal-yses serve for quantifying and mapping the risk. To conclude, we made various management proposals (combination of structural and non structural measures), in order to reduce the im-portant level of present risk
