Salt Intrusion Prevention in Locks

Designing a Movable Sill in the Existing Krammer Commercial Navigation Lock

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Salt intrusion is undesired because it has negative effects for drinking water and agricultural water intakes. At the Krammer locks (Zeeland, the Netherlands) a complex system is integrated in the design of the lock which prevents salt intrusion very accurate. This effective reduction of salt intrusion is regrettably accompanied with high energy consumption, high operational costs and high maintenance costs. On top of that, the entire system needs big maintenance in 2 years (20 M euro) and an extensive expansion in 10 years (300 M euro). Since retaining the current system is very expensive, other options have been elaborated. A pilot project is carried out in the smallest lock of the complex. The pilot has as main objective to get insight in possibilities for a design in the much larger commercial locks. The objective of this study is to present a feasible design for a salt intrusion prevention system in the commercial locks. It should be comparably effective as the current system, while having lower energy consumption, lower construction costs, lower maintenance costs, lower operational costs and a higher lock capacity. After an analysis it became clear that this is possible by including a movable sill in the structure. A comparison with the design of the pilot and the current system must prove the abilities of the new design. The presence of a movable sill results in a height reduction of the air bubble- and water screens in the new design. The screens are both integrated in the movable sill. In operation, the sill moves vertically up and down once every tidal cycle of 12 hours. It allows ships to sail over it, while being positioned as high as possible. Above the top level of the sill, the integrated screens reduce the negative effects. In this way, the optimum reduction of water exchange is obtained. The design of the screens is partly based on the design of the pilot. It’s optimised by using other dimensions and reducing the required air pressure for the air bubble screens. After determining the governing loads on the structure, a dimensioning has led to the final design. The driving mechanism is located above water and controls the height of the sill via vertical steel tubes. The structure is integrated in the existing lock chamber, in which a guiding rail distributes the forces of the sill to the lock chamber. The design is first compared to the current situation. In this comparison it becomes clear that salt intrusion prevention of the current system can be matched closely. The reduction of fresh water loss by the system improves considerably and the capacity of the lock increases by a third. A comparison of the design with the design of the pilot is quantified as being approximately 20% more effective, consuming 50% less energy and being 30% cheaper than a configuration with air bubble- and water screens only. The expected improvements of the design in this study show that it is an interesting design. The quantifications are obtained by calculations based on various assumptions. Before the design can be realised, there are quite a few important recommendations which need to be elaborated. The assumptions in the used calculation methods need attention especially. Nevertheless, the presented design shows that a movable sill is an interesting option, to which further studies seem worthwhile. Apart from a realisation in the Krammer locks, the design has a broader potential; the benefits hold for all locks with salt intrusion countermeasures installed. It’s especially interesting in deep locks or locks with an increasing mean water level. In that case the effectiveness may increase even more.