Analyzing hydraulic risk involves simulating a high number of scenarios from which to draw statistical information about flood extent and depth in relation to variations in the defence conditions and the entity of the event. With the aim of keeping the computational times of simulations within reasonable values while maintaining a sufficient reliability of the results, rapid models enabling flooded areas to be delimited using a DEM have been introduced into the scientific literature. These models, called Rapid Flood Spreading Models (RFSMs), are based on highly simplifying hypotheses that are analyzed and discussed in this paper thus arriving to a new formulation. A comparison of the results produced by this new formulation versus those of other RFSMs in a test case largely characterized by flat land shows it to be superior and reliable, while maintaining the computational times to within a few seconds. The new formulation thus lends itself to being used to support hydraulic risk assessment and management procedures requiring a reliable simulation of numerous flood scenarios. Copyright Springer Science+Business Media Dordrecht 2013
