construction docks needed to fabricate the massive pylons. Commenced in April 1979, the first was finished early in 1983. In the meantime, work began on the sliding gates. Fifty-foot-deep foundations were prepared to support the pylons, and a special dredge was designed to secure the estuary floor against uneven scouring. By the end of 1982, the river bottom was secured by vast mats laid by purpose-designed vessels. All was ready for placing the pylons.

The construction docks were flooded and the pylons, each weighing 21,600 tons (18,300 tonnes) and between 100 and 135 feet (30 and 40 meters) high, were floated into position, then sunk to the prepared floor. Sixty-five pylons formed the spine of the barrier: sixteen in the northern opening, seventeen in the central, and thirty-two in the southern. They were connected by prefabricated elements, and the sliding gates, each 150 feet (45 meters) long and weighing 1,440 tons (1,220 tonnes), were then installed, a task that took a little under two years to complete. Then followed the fixing of each of the sixty-two 3,000-ton (2,270-tonne) precast concrete elements that carried the roadway across the barrier. The Stormvloedkering Oosterschelde was officially opened on 4 October 1986. It cost about a sixth of the 11 billion guilder (U.S.$5.5 billion) total of the Deltaworks.

The danger of overflowing rivers in the winter and early spring also threatens large parts of the Netherlands. Several inland engineering works—the Philipsdam (1976–1987); the Oesterdam (1977–1988); the Markiezaatskade (1980–1983); and the Bathse Spuikanaal and Spuisluis (1980–1987)—were adjuncts to the primary dams of the Deltaworks.

Holland’s struggle against the water continues. Despite the pleas of regional and local water authorities for river dike reinforcement, the national government concentrated its funding for forty years upon the Deltaworks. Moreover, conservationists oppose any dike improvements that would spoil the landscape. The Boertien Commission was established early in the 1990s to address potential problems, and it produced the Great Rivers Delta Plan, which involved reinforcing nearly 190 miles (300 kilometers) of river dikes and embankments. The first phase was completed by the end of 1996; the second, covering another 280 miles (450 kilometers), was finished by 2001. But that will not solve the problem; if nothing else is done, the next generation of Hollanders will have to raise the dikes again. Climate changes, deforestation, urbanization, and drainage in their upper reaches mean that the river systems will carry increasingly large peak volumes. Cooperative policy and water management must be integrated internationally, from the sources to the deltas.

See also

Afsluitdijk; Storm Surge Barrier

Further reading

Boermans, Anne, and Herman Hoeneveld. 1984. English summary of Tussen land en water: Het wisselende beeld van de Deltawerken. Amsterdam: Meulenhoff.

Haan, Hilde de, and Ids Haagsma. 1984. English summary of De Dettawerken: Teckniek, politiek, achtergronden. Delft: Waltman.

Meijer, Henk, ed. 1998. Het Deltaplan in beeld. Utrecht: IDG.

Ditherington Flax Mill

Shrewsbury, England

The Industrial Revolution gave rise to a new building type: the factory, where a managed workforce could operate machines that were driven by steam power. The advent of machines also created a demand for iron to be produced on a large scale; in addition to being used to build machines, it soon became apparent that iron could be used to construct industrial buildings. The forerunner was the prefabricated cast-iron bridge at Coalbrookdale, England, of 1775–1779. But the factories, especially textile mills, involved problems other than the structural ones. Because they handled large quantities of cotton, flax, and wool, and because their wooden floors were quickly saturated with the oil used to lubricate the machines, they presented a fire hazard. The earliest textile mills had timber floor and roof framing and solid masonry external walls. Cast iron was non-combustible, and it was believed that it offered, as well as greater strength, a measure of fire resistance. Designed in 1795 and built the following year by the