The Delta waters north of the Volkerak dam will continue to be in open communication with the sea through the Rotterdam Waterway, so the area will still be tidal, although the tidal movements will be greatly moderated. The waters from the Rhine and Meuse will also continue to flow to the sea through this area. Formerly the water coming down these rivers could reach the sea along three different routes, viz. through the Rotterdam Waterway, the Haringvliet and the Volkerak. The dams across the Volkerak and the Haringvliet will bar the latter two escape routes, so if no other measures were taken all the water would have to pass through the Rotterdam Waterway. This sets no problem when the discharge ofthe rivers is smalI, but this waterway alone would not be able to cope with fairly large quantities. Consequently, at least one more outlet to the sea must be provided. This is why a row of sluice gates has been incorporated in the Haringvliet dam of great enough capacity when they are wide open to handle, together with the Rotterdam Waterway, the largest conceivable river-water discharge during ebb tides. This report describes the sluices, the design, the gate systems and the operating system.