The lock complex at Terneuzen in the Netherlands is the link between the Port of Ghent in Belgium and the Western Scheldt. The current lock complex consists of three locks: the Eastern Lock, the Middle lock and the West Lock. The West lock is the largest and was constructed in the 1960s. It is sufficiently large to accommodate the Panamax class of sea-going vessels. The Flemish –Dutch Scheldt Commission (VNSC), a cooperation between the Dutch and the Belgian governments, is executing its plan to build a new large lock at this complex, which will replace the Middle lock (see Paper 126 PIANC SMART RIVERS 2015). When completed, the New lock will rank among the 10 largest locks in the world and will be sufficiently large to accommodate the Neo Panamax class of sea-going vessels.
Recent hydraulic research at the scale model facility in Deltares, Delft, The Netherlands, on the levelling system of the new lock has shown that a system of openings in the gate, as is being employed in the new sea lock of IJmuiden near Amsterdam, was not appropriate for the new lock at Terneuzen. This conclusion is due to the large mooring forces that the density currents can cause on the moored vessel during levelling (this research is presented in a separate presentation at PIANC World Congress). Instead the choice was made for a longitudinal filling system, similar to the one present at the West lock in Terneuzen. The principle behind this choice is that the density currents are generated at both the bow and the stern and that the forces will therefore be reduced.
The final design of the lock is to be made by the contractor who will build the lock. Prior to the tender process, completed in the summer of 2017, additional hydraulic research was conducted at Deltares for VNSC to investigate the hydraulic dimensions of the longitudinal filling system of the new lock. This research, conducted solely with numerical techniques, was used to define the hydraulic specifications of the filling system in the tender process. A combination of 3D Computational Fluid Dynamics (CFD) of different components of the culvert system and dynamic 1D culvert simulations with WANDA were used to simulate the levelling process. This approach cannot account for density flows in the lock.
The research studied two alternatives for the longitudinal filling system. One where the lock is filled via bottom grids in the lock floor at ¼ and ¾ of the length of the lock and one where the lock is filled via openings in the wall at both sides of the lock and at both heads. The first system is similar to that at the current West lock, the second system does not have direct antecedents, except a scale model investigation of the filling and emptying system of the Baalhoek lock, which was never constructed.
For both alternative filling systems detailed flow patterns and hydraulic resistances of the various elements were calculated with 3D steady state CFD simulations. Only those for the system with bottom grids are presented here as the constructor who won the tender has chosen for this system. Emptying and filling situations were considered owing to the asymmetry of the system. Consideration was also made of the flow patterns in the approach harbour for the design of the intake openings. Subsequently, the calculated hydraulic resistances were used in the 1D dynamic model to simulate a levelling process in the lock. The water level slope in the lock chamber could be calculated during the simulation to give a first estimate of mooring forces and achievable levelling times. This model was also used to assess the inertia effects of the large culvert system, such as overtravel. This is the phenomenon whereby the water level in the lock can overshoot that in the approach harbour and can affect the force on the gates during opening at the end of the levelling process. Similarly the time-dependent asymmetry of the system was also studied. Unequal discharges through different branches of the culvert system can lead to large forces on the moored vessel.
The simulations showed that this type of longitudinal filling systems is feasible for achieving the desired levelling times whilst maintaining a safe levelling process. The final verification, taking into account density currents will be made in a physical scale model after the final design has been completed by the constructor.