The port of Antwerp in Belgium is located along the river Scheldt which gives access to the North Sea some 80km downstream. As a result of three capital dredging programs on the river and the estuary, completed in the periods 1970–1975, 1997–1998, and 2010–2011, Antwerp can now accommodate vessels with a draught up to 16 m sailing up-river and 15.2 m down-river on a tide-dependent basis. The tide-independent draught is 13.1 m.
The Scheldt river is a tidal river with a tidal range (low tide vs. high tide) of 3.5m near the northern part of the port and 5.7m near the city center. Large parts of the port area have historically been developed in dock systems behind locks in order to provide a constant water depth to the berthed vessels and facilitate cargo handling operations.
Some of the largest sea locks in the world are found in the port: the Zandvlietlock opened in 1967, and the Berendrechtlock opened in 1989. The Kieldrechtlock is the latest addition: the large lock was opened in 2016 and provided a second nautical access to the left bank port area, next to the smaller Kallolock. Construction of the Kieldrechtlock required nearly three times the amount of steel used to build the Eiffel Tower. The main works included:
- Construction of a bentonite slurry wall: 90.000m²
- Groundworks: 5.5 million m³
- Excavation works: 9.1 million m³
- Concrete works: 0.75 million m³
- Metal fabrication (lock doors): 8,700 tons
- Steel bridges: 3,000 tons
- Electromechanical structures: 113 tons
In the 1990s, the port of Antwerp decided to start developing terminals on the river (tidal terminals Europe Terminal and Noordzeeterminal and the tidal Deurganckdock), as container ships are time-sensitive and lock operations take time and form a risk (collision). Today all major container terminals in Antwerp have direct access to the river without sea locks (including the planned open tidal Saeftinghe dock). In this way, container vessels are not subjected to lock operations, reducing risks and port turnaround time. The tidal difference at the container terminals implies that the vessels go up and or down several meters when handled. To cope with that the systems/ropes used to fix the ship to the quay are adjusted continuously. The height of quay cranes is calculated for high tide.
Note that the port of Rotterdam has a tidal range of only 1m, so locks were not needed. The tidal range near the Channel (French ports) can reach more than 10m, such as in St-Malo in France. The English Channel is like a funnel that intensifies high and low tides.