Natural or induced floods are of increasing concern to watermanagers and civil protection services for three main reasons.Firstly, a continuous and 'unconscious' increase of socialpressure in the flooding valleys amplifies flood vulnerabilitiesand consequently natural or induced flood risk. Secondly, thealarming forecasts of the impact of potential climate changes onwater resources, in spite of the high uncertainty associated tothese forecasts, points out to larger flood hazards. Thirdly,dam-break induced accidents may occur more frequently due toinfrastructure aging.Emergency Planning is a non-structural measure to minimise floodimpacts playing an important role in crisis management. In fact,if a disaster cannot be avoided, individual and social structurepreparedness may be of great help in risk reduction.An Internet-based system that supports flood emergencymanagement is presented in this article. This application is partof a more complete system, developed with the goal of endowingthe Portuguese water authorities, dam owners and the civilprotection system, with adequate tools to store and easilyretrieve information on dams and their downstream valleys, tomodel the flood wave induced by a dam break and, eventually, tomanage the response to flood-induced catastrophes.