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Delta Works

The Deltaworks are a series of constructions built between 1950 and 1997 in the southwest of the Netherlands to protect a large area of land around the Rhine-Meuse-Scheldt delta from the sea. The works consist of dams, sluices, locks, dikes, and storm surge barriers. The aim of the dams, sluices, and storm surge barriers was to shorten the Dutch coastline, thus reducing the number of dikes that had to be raised.

The American Society of Civil Engineers has declared the works to be one of the Seven Wonders of the Modern World together with the Zuiderzee Works.

History

The estuaries of the rivers Rhine, Meuse and Scheldt have been subject to many floodings over the centuries. After building the Afsluitdijk, the Dutch started studying the damming of the Rhine-Meuse Delta. Plans were developed for shortening the coastline and turning the estuary into freshwater lakes. By shortening the coastline fewer dikes would have to be reinforced.

Due to indecision and the Second World War, these plans remained studies and little action was taken. In 1950 two small estuary mouths, the Brielse Gat near Brielle and the Botlek near Vlaardingen were dammed. After the North Sea flood of 1953, a commission was installed which had to come up with a plan to research the causes and seek measures to prevent such disasters in future. They revised some of the old plans and came up with the so called "Deltaplan".

The plan consisted of blocking the estuary-mouths of the Oosterschelde, the Haringvliet and the Grevelingen. This reduced the length of the dikes exposed to the sea by approximately . The estuary-mouths of the Nieuwe Waterweg and the Westerschelde were to remain open because of the shipping routes to the ports of Rotterdam and Antwerp. The dikes along these waterways were to be heightened and strengthened. The works would be combined with road and waterway infrastructure to stimulate the economy of the province of Zeeland and improve the connection between the port of Rotterdam and Antwerp.

Alterations to the plan during the execution of the Works

During the execution of the works alterations were made due to pressure from society. In the Nieuwe Waterweg heightening and the associated widening of the dikes proved very difficult because of many historic buildings that would have to be destroyed. Therefore, a storm surge barrier would be built (the Maeslantkering) and dikes were only partly built up.

The Oosterschelde was originally to be dammed and turned into a fresh water lake, leading to the loss of the saltwater nature and, consequently, the fishing of oysters. Environmentalists and fishermen combined their efforts to prevent the closure and successfully pressed parliament to make amendments to the original plan. Instead of completely damming the estuary mouth, a storm surge barrier would be built. This exists today as a collection of very large valves.

The storm surge barrier only closes when the sea-level is expected to rise above 3 meters above mean sea-level. Under normal conditions the estuary mouth is open and salt water flows in and out with the tide. Consequently, the weak dikes along the Oosterschelde needed to be strengthened. This strengthening had not been done yet because the Oosterschelde would be dammed. Over 200 km of dike needed new revetments. The connections between the Eastern Scheldt and the neighboring Haringvliet had to be dammed to limit the effect of the salt water. Extra dams and locks were needed at the east part of the Oosterschelde to create a shipping route between the ports of Rotterdam and Antwerp.

Current status

The works were finished after almost fifty years in 1997 with the completion of the Maeslantkering and the Hartelkering. The Dutch government often cites the Delta Works project as the world's largest flood protection project. With over of dikes (1,500 miles designated as primary dikes and as secondary dikes) and 300 structures, the project is one of the most extensive engineering projects in the world.

Due to climate change and relative sea-level rise dikes will eventually have to be made higher and wider. This is a long term uphill battle against the sea. The needed level of flood-protection and the resulting costs are a recurring subject of debate. Currently reinforcement of the dike revetments along the Oosterschelde and Westerschelde is underway. The revetments have proven to be insufficient and need to be replaced. These works started in 1996 and should be finished in 2015. In that period the Ministry of Public Works and Water Management in cooperation with the waterboards will have reinforced over 400 km of dikes.