Currently, approximately 2,000 m² of our halls is occupied by a specially designed scale model of the port of Zeebrugge for long-term trials.
In recent years, the Government of Flanders has invested heavily in dredging to deepen the access for large vessels to the port of Zeebrugge. This currently enables ships with a draft of 15.5 to 16.0 m to reach the port. However, the navigation window, which is the access time in and out of the port, of such vessels and LNG carriers is limited to approximately 4 to 6 hours per day. This is because of the large cross flow at the port mouth and difficulties associated with dredging the sludge layer in the outer port. Furthermore, the port of Zeebrugge faces the issue of siltation in which the silt present on the seabed flows inwards during the twice daily flood stage.
Problems with tidal flow
The current along the Flemish coast is generally parallel to the coastline. During the flood stage, water from the Strait of Calais flows along the Flemish coast towards the Western Scheldt and during ebb stage flows away from the Western Scheldt in the opposite direction. Near the port of Zeebrugge, the flow parallel to the coast concentrates in front of the port mouth, creating a strong cross flow in the fairway. During the period around the high tide, this current is so strong that large ships cannot safely enter or leave the port. This is a significant limitation for the port of Zeebrugge since at that moment, the water depth is the greatest and provides the best access for the largest ships.
Flanders Hydraulics Research is studying this issue using 3 different research tools: detailed numerical models, ship simulators and a large scale model. The cross flow at the port mouth and in the fairway are studied in detail, for both the current situation and potential modified layouts. The large scale model and accompanying steering software were designed completely in-house. The model includes a 15 km coastline (from Blankenberge to Knokke) and extends 10 km into the sea, past the ‘Scheur’ fairway. The scale model simulates a complete spring tide, including the correct variation in the changing water level and current throughout the entire tidal cycle. The current velocities and flow patterns are measured and analysed in detail.
Velocity measurements with PTV engineering
PTV means ‘Particle Tracking Velocimetry’. The PTV system captures video images of floats (white particles of 15 mm) drifting along with the moving water, follows the trajectory of every single float and calculates the current pattern. This technique is suitable for measuring surface velocities in a large area. Additionally the current velocity is also registered in detail by electromagnetic velocity sensors.
Features of the scale model of Zeebrugge:
- horizontal scale: 1/300;
- vertical scale: 1/100;
- velocity scale: 1/10;
- time scale: 1/30;
- discharge scale: 1/300,000;
- tidal cycle: 25 minutes (= 12.5 hours in reality);
- amplitude at mean spring tide: 4.3 cm (= 4.3 m in reality).