This paper deals with coastal storm-induced hazards i.e. mainly coastline retreat and erosion. Coastal managers and councillors we met during this study largely expressed the need to prevent erosion and flooding events in order to keep beaches and back barrier environments in a healthy state. The main problem they encounter is about storms: most of them do not have impacts and only few of them are followed by erosion. In other terms, they want to anticipate which storm has to be cared for and which one is not dangerous. Defending a pragmatic point of view, we propose a new method to sort erosive storm from non erosive ones. It consists of a beach behaviour model resting on the graphical combination of three essential parameters assessed at a very local level: strong onshore winds, high swells and high sea levels (spring tide). The results obtained on the beach of Marennes (Gascony, France) are very good. In order to fine tune the model for other sites, where local conditions are slightly different, new local observations should be done and could then feed an other version of the model.