Closure of the New Waterway

Abstract

The Netherlands are protected against extreme high waters from the sea by an ingenious system of barriers. One of the most famous ones is the Maeslant barrier in the New Waterway near the port of Rotterdam. This barrier however, is subject to discussion, as it might not function as intended, because of the following reasons. It has a very low reliability regarding closing. Furthermore, because of the sea level rise, it is expected that the barrier should close much more frequently, causing more nuisance for navigation. Therefore a different solution is put forward by Spaargaren c.s. Namely to close off the New Waterway permanently by means of a barrier, consisting out of a pumping station, dewatering sluice and a lock complex. The latter one is further elaborated on by making a feasibility study for it. First of all, the best location is chosen for the barrier, which in this report is the location near Rozenburg, just east of the Maeslant barrier. Because of the high demands regarding both navigation and flood safety in combination with the uncertainty in these demands for the future, there is a need for a sophisticated design for the lock complex. This is done by first considering the boundary conditions for different (initial and adaptive) scenarios for both sets of requirements (navigation and flood safety). For navigation a larger vessel is taken into account in the adaptive boundary conditions. For flood safety, the adaptive boundary conditions results in a higher water level of about 1 meter to be retained, mostly due to a larger sea level rise. It turns out that the boundary conditions regarding navigation have a way larger impact in the design choices of the lock complex than the boundary conditions regarding flood safety. The above boundary conditions are used to create an overall solution for the barrier. 4 locks are needed (in case of an initial design): one large lock for large seagoing vessels, one mid-sized lock for smaller seagoing vessels and two for inland going vessels. When looking at the adaptive requirements, another mid-sized lock should be added. For the large lock, different principal solutions are developed that also take the adaptive boundary conditions into account. First of all, an adaptive design of a lock head is considered by making the head modular. This makes it possible to place a larger gate in the head later on. It turns out that this is probably not cost-efficient. The second proposed solution is to use a retaining wall in combination with a relieving floor for the chamber walls of the large lock for seagoing vessels. The relieving floor will decrease the horizontal soil loads on the soil retaining wall beneath it, which is structurally beneficial. This relieving floor will be combined with a longitudinal filling system. A longitudinal culvert over the length of the lock is placed on top of the relieving floor. Filling and emptying will be done using openings in the floor of the superstructure. The load on vessels during levelling of the lock are determined for this system, which is the main requirement that determines the filling time. It turns out that this option results in much faster levelling times compared to other levelling systems. Levelling could be done a factor 3 faster than filling through the head. It is concluded that the longitudinal culvert in combination with the relieving floor can compete with conventional filling systems. Furthermore, it fits in an adaptive design approach, because even with a wider lock, faster levelling times are possible. However, there are still some considerations to be made regarding this solution. A thorough cost-benefit analysis should be made. Besides of this, the hydraulic computations should be validated by means of a scale model or computational fluid dynamics.