Floods are defined as hazards caused by water flow abnormal behavior. In the present work, we evaluated a platform to study hydrological disasters caused by water flood in urban regions. MOHID (Modelagem Hidrodinâmica -Hydrological Modelling) computational platform is presented as a system to simulation the models of water flow and runoff in mountainous urban watersheds, allowing simulation of different scenarios. The importance of computational modeling and simulation as auxiliary tools for disaster risk reduction is discussed, showing MOHID as a system to decision support. Simulations results are presented for a real case-study with data from the Bengalas River watershed, in Nova Friburgo region.