ABSTRACT:- The oryxlake, was once a lake designed to recharge the groundwater in Dakar. But, nowadays, because of anarchic and raging urbanizationit is confronted with serious modifications involving imbalance on ecosystem and causing devastating floods. In that area, flooding becomes more and more catastrophic, worrying for Senegal government. Progressive urbanization leads a waterproofing surfaces thus reducing the infiltration of rainwater. This reduction has as a corollary increased amounts of runoff. The object of this present article is, through numerical modeling, to assess the risk of flooding linked to the excesses of the waters of the lake representing the outlet of the catchments areas of Grand Yoff, Castors and Front de Terre. To do this, we used the software Storm Water Management Model (SWMM) to simulate dripping rainwater and make forecasts to horizon 2025. The results show that in 2025, an amount of water estimated at 371 149 m3 could overflow from the lake if a ten years return period for rainfall, like a Kiefer one, is recorded. This result shows that accompaniment measures are necessary to prevent flooding.

Keywords -Urbanization, rain water, Overflowing risk, Oryx lake, Dakar