•The paper presents the effects of water on obstacles in the dam break flow problem are investigated numerically.•It is solved by the Navier–Stokes and multiphase flow equations for incompressible fluid.•The numerical solution based on the PISO algorithm (Pressure-Implicit with Splitting of Operators).•Various forms of obstacles were examined, by which the pressure distributions were reduced three times on the dam surface. In this paper, the effects of water on obstacles in the dam break flow problem are investigated numerically. The numerical method is based on the Navier–Stokes equations describing the flow of an incompressible viscous fluid and the equation for the phase. As a numerical method for solving equations, the numerical algorithm PISO (Pressure-Implicit with Splitting of Operators) was chosen. The water surface movement is captured by using the volume of fluid (VOF) method, which leads to a strict mass conservation. Moreover the accuracy and reliability of the 2D and 3D models were tested using several small and large-scale laboratory experiments on dam destruction problem. The obtained free surface dynamics was compared with the experimental data and numerical results of other authors. These numerical results gave good agreement with the experimental data. Comparison of simulation results with experimental data for various turbulent models was also performed. By dam break flow problem simulation, the best turbulent models were chosen, which describe almost the same pressure distribution as in the experiment. Finally, various forms of obstacles were examined, by which the pressure distributions were reduced three times on the dam surface.