The Netherlands and the North Sea have long struggled over territorial rights. After flood waters ravaged the country around the Zuiderzee, several attempts at controlling the waters were made. The Delta Project was an ambitious 3.2-billion dollar barrier across the Eastern Scheldt estuaries. The first three estuaries are spanned by solid dams and dikes. The fourth estuary, however, is spanned by a structure called a storm surge barrier. It links the banks of the estuary with massive gates mounted between huge prestressed concrete piers. It is designed to remain open unless a surge of tidal or storm-driven water is anticipated. The design allows seawater to cycle normally within the estuary, maintaining the saltwater ecology and providing security for the lowlands.
The 18,000-ton piers were constructed in dry docks. Each pier was built in seven sections, starting with the top of the slab and ending with the superstructure. To prepare for placing the piers, the sea floor was first leveled and cleared. A floating vessel was constructed that vibrated and compacted the sand and silt of the sea floor. Another specialty vessel leveled the floor to final elevation and deposited the first of three foundation mattresses. A huge vessel called the Ostrea was used to lift, transport, and place the massive piers with 8 inches of each specified position during the 1.5-hour period at the turning of the tides. Once the piers were set, a box girder across the piers, a sill beam, a steel gate unit, and an upper beam were built to fit between each pair of piers. The barrier was completed in 1986.