Observations in the field suggest that the existing guidelines for bed protection design may lead to overly conservative protections at berthing structures of inland vessels. In this study, physical scale model tests have been performed using particle image velocimetry to assess the near-bed velocity and the velocity decay of jets generated by transverse bow thrusters. The effect of the bed roughness, under-keel clearance (UKC) and quay wall clearance on the resulting near-bed velocities are discussed here. The results show that the maximum near-bed velocity occurs in the vicinity of the quay wall and results from an interplay between jet diffusion and the blockage effect of the nearby boundaries (e.g., quay wall, bed, and vessel), where the roughness of the confining boundary plays a role. The existing design guidelines predict fairly well the maximum near-bed velocity for smooth beds and for relatively large UKC's. However, the guidelines tend to overestimate the maximum near-bed velocities for rough beds and for small UKC's. This study proposes a new method based on measurement data to estimate the maximum near-bed velocity for confined bow thruster jets.

Vortices are a very common phenomenon to consider in many hydraulic engineering problems, e.g. when designing pump sumps or intake works for turbines. Until now, the focus is on avoiding the development of vortices because of induction of cavitation and air entrainment by a fully developed air core. However, vortices may also be used in a more positive manner e.g. by taking advantage of the capacity to transport (floating) particles to avoid the built up of scum layers in wastewater pump sumps. To the authors’ knowledge only little literature is available in this specific field of research. In order to obtain state-of-the art data on the dynamics of large particles in a free-surface vortex flow field and to examine the vortex transport capacity, a simple but novel 3D-PTV (Particle Tracking Velocimetry) method using 6 iPhones was designed, built, tested and employed to measure the 3D-motion of a large particle in the vortex flow. The experimental set-up, particle detection method and the post-processing of the raw data are described in detail along with some first experimental results. The presented 3D-PTV method showed to be able to obtain data that can be used for detailed analysis of the dynamics of large particles in the vortex flow. The overall standard uncertainty of the particle centre position is in the order of magnitude of 0.1 mm in each direction in a volume of a diameter of 0.6 m and a height of about 1 m, while recording at 240 fps.