Dense avalanches made of dry snow were studied as granular flows, through the development and use of a numerical model based on the shallow water theory. Friction was represented by a phenomenological law resulting from the recent progress in the field of snow avalanche constitutive laws. Using this friction formulation and assumptions similar to those employed in the shallow water theory, a simple model describing erosion and deposition was formulated and tested. The system of equations obtained was solved using a numerical scheme of finite volumes. The model was then tested on experimental data obtained in the laboratory. Relative good agreement was observed between the simulated and experimental data. An avalanche path where 153 avalanches were observed over the last century was chosen. The dry friction values have been determined providing the coincidence of the calculated and observed distances. We analysed the statistical distribution of the obtained dry friction coefficient and compared the obtained range to the range obtained by Cassassa et al. [Cassassa, G., Narita, H. Maeno, N., Shear cell experiments of snow and ice friction, J. Appl. Phys., 69 (1991), pp. 3745-3755]. Afterwards, we studied the effect of a dam of different heights placed at two locations in the path and analysed its effectiveness in terms of volume reduction and run-out distance, demonstrating that the friction coefficient has a prevailing role on both the dynamics of the avalanche and the effectiveness of the dam.