As part of the European project CADZIE, the interaction between powder avalanches and dams has been studied. First, we simulated a powder avalanche using a heavy salt solution in a water tank. These experiments showed that (1) the ratio between the maximum velocity parallel to the slope and the front velocity is greater than 1 (up to 1.5), and that (2) the velocity normal to the slope can rise to 74% of the front velocity. The presence of a dam leads to a reduction of front velocity. The ratio between the maximum horizontal velocity and the front velocity increases with the dam height and reaches a maximum value of 1.9. As we did not have access to the density distribution in our experimental set-up, we calibrated a numerical model thanks to the experiments and we deduced the dynamic pressure. Our results showed that, for an avalanche without obstacle, AVAER (Rapin, 1995) and Beghin and Closet's hypothesis (1990) lead to an overestimation of the dynamic pressure in the lower part of the flow as well as in the upper part, and that the use of front velocity for estimating the loss of kinetic energy leads to an overestimation of the dam's effectiveness.