Debris flows are wide spread phenomena in mountain areas and due to their high velocity and kinetic energy, are very destructive processes in terms of human life and structures. Several studies have been dedicated to both triggering and propagation phases of a mass movement but there is still a lack of knowledge about the behavior of the flow during its impact against an obstacle. In particular, the crucial point is the definition of the impact action, fundamental to design protection barriers, that depends on the flow nature and propagation characteristics (velocity and thickness). These entities are difficult to be determined by means of experimental measurement and consequently several empirical and theoretical relations were proposed in literature. Laboratory tests on scaled channel are also available but they are often affected by the limitation of the scale effects. The aim of this paper is to analyze in detail the impact of a debris flow against an obstacle and present a new method to design these protection structures: this method combines the numerical method DAN and the Brighenti’s method in order to evaluate the flow characteristics and quantify the action applied to the barrier. Laboratory tests have allowed for model calibration and for the validation of the hypothesis about the nature of the impact.