The passage of migratory species has been the main focus of mitigation actions related to environmental impacts due to large barriers. Recently, smallest barriers have been found to be the cause of reduction on fish community. A culvert fishway can improve the fish passage in small streams and has been widely studied. In Belgium, the model known as stairs pipe culverts have been built in the field since 2008. This kind of culvert is an adaptation of the traditional drainage culvert that combines the baffles and the pools, which are based on Denil and the pool fish ladders. There are different baffles: the first (with an angle of 30° horizontal) working as a weir, raising the water level upstream and creating a small pool; the second (with an angle of 60° vertical) concentrating the flow, braking the water velocity and creating a counter current. The aim of this study was to obtain the velocity field and pool depth for two flowrates (40L/s and 60L/s) and two slopes (5% and 6%) with numerical models. The 3D volume of fluid (VOF) model was applied. An unstructured mesh was used to incorporate the baffles layout. According to the numerical results obtained, the flowrate increase (10 L/s) created increment in maximum vorticity (50%) in pools, water depth (around 10 to 50%) and maximum velocity (10 to 25%) along the entire culvert. The slope increase (1%) induced reduction in water depth (around 11 to 22%). The maximum velocity in the flow for tested flowrates and slope could be a barrier for European weak swimmer species, such as Abramis brama, and for small wide spread species in Brazil, such as Piabarchus stramineus.