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Delta-Zuiderzee Works
The Delta Works 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.
Netherlands, Europe
Modern Wonders of the World
Delta Works
Dated Started: 1950
Date Finished: 5/10/1997
Zuiderzee Works
From 1920 to 1975
7 Modern Wonders of the World
Construction of Afsluitdijk[1]


The Zuiderzee Works

The Zuiderzee Works (Dutch: Zuiderzeewerken) are a human-made system of dams, land reclamation and water drainage works, and the largest hydraulic engineering project undertaken by the Netherlands during the twentieth century. The project involved the damming of the Zuiderzee, a large, shallow inlet of the North Sea, and the reclamation of land in the newly enclosed water body by means of polders. Its main purposes were to improve flood protection and create additional land for agriculture.

The American Society of Civil Engineers has declared the works to be one of the Seven Wonders of the Modern World together with the Delta Works.[2]

The Delta Works

The Delta Works 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.

Along with the Zuiderzee Works, they have been declared one of the Seven Wonders of the Modern World by the American Society of Civil Engineers.

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 400 miles (640 km). 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.

Delta law and Conceptual framework
According to the Discovery Channel 15% of the total budget for the Delta Works was spent on fundamental research. An important part of this was a new tool to help solve the flooding problem once and for all. Instead of analysing past floods and building protection sufficient to deal with those the Delta Works commission has pioneered a conceptual framework to use as norm for investment in flood defences.

The framework is called the 'Delta norm' and works as follows: Major areas to be protected from flooding are identified these are called "dyke ring areas" because they are protected by a ring of primary sea defences. The cost of flooding is assessed using a statistical model involving damage to property, lost production and given amount per human life lost. For the purpose of this model a human life is valued at € 2.2 million (2008 data). The chances of a significant flood within the given area are calculated. This is done using data from a purpose build flood simulation lab as well as empirical statistical data regarding water wave properties and distribution. Storm behaviour and spring tide distribution are also taken into account.

The most important "dyke ring area" is the South Holland coast region. It is home to 4 million people, most of whom live below normal sea level. The loss of human life in a catastrophic flood here can be very large, because there is very little warning time with North Sea storms, so comprehensive evacuation is not a realistic option for the Holland coastal region.

The commission initially set the acceptable risk for complete failure of every "dyke ring" in the country at 1 in 125,000 years.
However the cost of building this level of protection was deemed too high, so the acceptable risk was set according to region as follows:

North and South Holland (excluding wieringermeer): 1 per 10,000 years
Other areas at risk from sea flooding: 1 per 4,000 years
Transition areas between high land and low land: 1 per 2,000 years
River flooding causes less damage than salt water flooding so areas at risk from river flooding have a higher acceptable risk. River flooding also has a longer warning time, making for a lower estimated death toll.

South Holland at risk from river flooding: 1 per 1,250 years
Other areas at risk from river flooding: 1 per 250 years.
These acceptable risks were put down in the Delta law, requiring the government to keep risks of catastrophic flooding within these limits and to upgrade defences should new insights into risks require this. These limits are also put down in the new Water Law to be effected in May 2009.

The Delta Project (of which the Delta Works are a part) has been designed with these guidelines in mind. All other primary defences have been upgraded to meet the norm.

New data elevating the risk assessment on expected sea level rise due to global warming has brought 10 'weak points' to the fore. These are currently being upgraded. This work is expected to be completed in 2015. For rivers an upgrade is underway, which is expected to be finished in 2017.

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.

Oosterscheldekering, the largest of 13 Delta Works' dams.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 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.[3]




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1. Flickr-Public Domain-retrieved 7/20/2009
2. Wikipedia-Zuiderzee Works-retrieved 7/20/2009  
3. Wikipedia-Delta Works-retrieved 7/20/2009 
 Wikipedia  text is available under the Creative Commons Attribution/Share-Alike License


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