The importance of collecting water has always represented an interesting topic for all the populations throughout years. The possibility to catch and store it has represented a necessary thing for different reasons: crops, fauna, flood control and in the last century a valid alternative for the generation of electricity and recreational uses. The most common way to store it are the dams, from small to the bigger ones. This work deals with the study of the behaviour in case of failure of dams, and in particular focusing on the smaller. What is interesting in this is that for big dams the wave generated by the collapse of the weir does not take into account the presence or not of elements in the valley area.