The preliminary designs of the new weirs in the river Meuse have at least three openings because of the required redundancy during large-scale maintenance or calamities. However, considering two openings of 40 m and one of 20 m, the question arises whether these 40 m openings are wide enough to be navigable during river floods. To answer this question, first,
the characteristics of the Dutch navigable weirs in the Lower Rhine and Meuse have been analyzed. Then, CFD simulations of the flow through the weir openings during a river flood have been carried out, to determine flow velocities and the eddies generated at the weir abutments and behind the pillars. The passage of the vessel through the weir opening may be greatly hindered by flow patterns with changing transversal velocities along the sailing line. The flow simulations showed that the size of the eddies near the bank and the amplitudes of the transversal velocity depend on the hydraulic design of the weir and the roughness of the bed behind the weir sill. When a realistic bed roughness is applied the influence of the horizontal eddies reduces. In the last step, for a preliminary weir design with an assumed bed roughness, the calculated flow pattern has been put into the real-time nautical simulator and simulations were carried out with a design vessel. It showed that it depends both on the hydraulic design of the weir and the wind conditions whether a new weir with a 40 m wide opening will be navigable.@en