3. The Delta Works
3.1 The Delta Commission
The Delta commission was initiated twenty days after the North Sea flood, on the 21st of February 1953. This commission gave advice on improving safety. This was a challenging task, as the Nieuwe Waterweg and Westerschelde had to stay open for economical concerns of the Rotterdam and Antwerpen harbor. The Delta commission finally gave five counsels which resulted in the Delta plan, on the 18th of October 1955. The plan would be carried out for 25 years whereby the costs were devised for an estimated 1.5 to 2 billion Dutch guilders (approximately 680 to 900 million Euros). To ensure the high quality building of the dams, the Delta law was accepted in 1959.
As, the diverse parts of the Delta Works could not be completed simultaneously, the Department of Waterways and Public Works chose to follow a logical order: from small to large and from simple to complicated. The Department of Waterways and Public Works also took into account that protection from storm floods should be gained as soon as possible.
3.2 The dams
The building of dams in the gullies was extremely problematic, due to the fast speed of the fluxing water. The sand and the stones which should shape the dam were washed away. Therefore a new technique was devised: Phoenix unity caissons. These are prefabricated hollow concrete boxes, which could be placed adjacent to each other in the water gully. In this way they could group together and form a dam. During transportation to the gully the caisson was temporarily blocked with wooden boards. Once at the destination the caissons were submerged and the wooden boards were removed. This way, all the caissons ended up next to each other, and became part of the permanent works. The dam initially had an open disposition whereby the sea water ebb and floodtide could almost flow back and forth through the hollow caissons unhindered. Once in place, the top part of the caisson was filled up with sand and gravel. Stones and sand were also added to the base of the caissons before gates embedded in the caissons were closed. Through lowering the gates, the sea arm was closed, and the dam could be completed. The Veersegatdam and parts of the Grevelingendam, Volkerakdam, and Brouwersdam were completed using this technique.
3.2.2 Funicular railway
For some parts of the dams the caissons turned out not to be the best method for closing the gully. Hence, a revolutionary technique was used. Via a funicular railway, large concrete blocks, weighing about 2.5 tons each, were dumped into the water. A gondola was built that could carry 15 tons of material. With the help of pincers, the concrete blocks could be hung under the cabin. After dumping the huge concrete blocks into the sea, the dam was filled up with sand, so no water could flow through any longer. This technique was applied to the Grevelingendam, Haringvlietdam and Brouwersdam.
3.3 From salty to fresh
Where at first the sea water streamed in and out unhindered, the sea water was now sealed up behind the dams. The tide disappeared and the salt water turned fresh. This had major consequences for the nature. Saltwater fish and plants died and birds went away. Particular parts of the country which were originally always flooded were now dry. Other parts that were normally dry at ebb were now continuously under water.
3.4 Oosterscheldedam becomes a ‘kering’
Originally it was planned to dam the Oosterschelde. This meant that the water behind the dam would slowly turn to fresh water. Resistance quickly arose against this interference, as the unique salt water environment in the Oosterschelde would be the next ‘victim’ of the extra safety regulations. In 1976 people came up with an alternative: the Oosterscheldedam would become a barrier, where the doors would only be closed under extreme weather conditions. This way, the unique saltwater environment, the mussel and oyster cultivation and the working of the tides would remain natural. The storm surge barrier with a total length of 3 km would consist of 65 prefabricated concrete pillars, in between which 62 steel slides would be installed.
The soil on which the barrier would initially be placed was too weak. To strengthen the soil, a number of proceedings were carried out, for example, the placement of gravel filled synthetic mats, on which the pillars were placed.
The pillars were the most important elements of the dam. Each pillar is between 30.25 and 38.75 meters high and weighs 18,000 tons. The placement of the pillars was precision work and could only take place when the flux was as small as possible, that is, at the turn of the tide. The pillars were heightened with pieces between which the barrier gates subsequently would be assembled.
The Oosterscheldekering became the largest barrier in the world. The costs of a barrier were considerably higher than those of a dam: 2.5 billion Euros were needed to complete the barrier. The Oosterscheldekering received a celebratory opening, by Queen Beatrix, on the 4th of October 1986.
At first, people thought that with the Oosterscheldekering, the Delta Works were complete. However, the enhancement of the levees along the Nieuwe Waterweg would not sufficiently protect the surrounding areas, including Rotterdam. Therefore the Ministry of Waterways and Public Works organised a competition for the construction of a storm surge barrier. This barrier would be placed in the Nieuwe Waterweg. Due to the fact that this waterway is the main route into the harbor of Rotterdam, the barrier was not allowed to block the shipping route; and only in exceptional cases should the barrier be able to be closed. The winning design consisted of two curved steel doors that would be submerged to the bottom of the waterway on a threshold. The Maeslantkering is the only storm surge barrier in the world with such large movable parts; the storm surge barrier doors are both 240 meters long. Under normal weather conditions the two doors are fully open, stored away in a dock alongside the water. This allows ships access to the harbor of Rotterdam without any inconvenience. At storm tide the storm surge barrier doors are closed. The round shape of the doors ensures it can resist the power of the water during the storm. On Saturday the 10th of May 1997 the official opening of the storm surge barrier Nieuwe Waterweg at the Hoek van Holland took place. Thanks to this storm surge barrier, one million people are protected from the sea.
3.6 Importance of the Delta Works
Finally, the Delta Works were complete. However, the massive project cost more than the expected 680-900 million Euros. Altogether the Delta Works cost nearly 5 billion Euros.
On top of the diminution of the total length of the sea averting levees by 700 km, the Delta Works have many more advantages. Firstly, the freshwater supply for agriculture is much better regulated. Additionally, the entire water management within the Delta area has been improved. The installation of the Delta Works has been beneficial for the mobility and the inland waterways. Finally, the Delta Works influenced developments in the fields of economics, recreation and nature. Some nature areas were irrecoverably affected, but in other places nature values have been created or maintained.
The Delta Works are a global model for technological development whereby the safety of humans and nature play the central part. Thereby, the Netherlands have widened its look on safety and water. The Delta Works compose an unique compromise between safety, economy, recreation and nature.
Nonetheless, the accomplishment of the Delta Works does not mean a remission of consideration for water management in the Netherlands. The Netherlands face new challenges. Climate changes ask for a fundamental reflection on a permanent livable design of the Netherlands, for future generations.
Also, dried land turning brackish, land subsidence, and demands on water quality and ecology ask for new treatments. To care for these challenges responsibly the Netherlands will in the future invest in an enduring delta system, in change for socially acceptable expenses.