TheDelta Works (Dutch:Deltawerken) is a series of construction projects in the southwest of theNetherlands to protect a large area of land around theRhine–Meuse–Scheldt delta from the sea. Constructed between 1954 and 1997, the works consist ofdams,sluices,locks,dykes,levees, andstorm surge barriers located in theprovinces ofSouth Holland andZeeland.
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 theZuiderzee Works, the Delta Works have been declared one of theSeven Wonders of the Modern World by theAmerican Society of Civil Engineers.
Due to indecision and theSecond World War, little action was taken. In 1950 two small estuary mouths, the Brielse Gat nearBrielle and the Botlek nearVlaardingen were dammed. After theNorth Sea flood of 1953, a Delta Works Commission was installed to research the causes and develop measures to prevent such disasters in future. They revised some of the old plans and came up with the "Deltaplan".
An important part of this project was fundamental research to come up with long-term solutions, protecting the Netherlands against future floods. Instead of analysing past floods and building protection sufficient to deal with those, the Delta Works commission pioneered a conceptual framework to use as norm for investment in flood defences.
The framework is called the 'Delta norm'; it includes the following principles:
The most important "dike ring area" is the South Holland coast region. It is home to four 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 typically little warning time with North Sea storms. Comprehensive evacuation is not a realistic option for the Holland coastal region.
The commission initially set the acceptable risk for complete failure of every "dike ring" in the country at 1 in 125,000 years. But, it found that the cost of building to this level of protection could not be supported. It set "acceptable" risks by region as follows:
River flooding causes less damage than salt water flooding, which causes long-term damage to agricultural lands. Areas at risk from river flooding were assigned a higher acceptable risk. River flooding also has a longer warning time, producing a lower estimated death toll per event.
These acceptable risks were enshrined in the Delta Law (Dutch:Deltawet). This required the government to keep risks of catastrophic flooding within these limits and to upgrade defences should new insights into risks require this. The limits have also been incorporated into the new Water Law (Waterwet), effective from 22 December 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 expectedsea level rise due to global warming has identified ten 'weak points.' These have been upgraded to meet future demands. The latest upgrades are made under the High Water Protection Program.
During the execution of the works, changes were made in response to public pressure. In the Nieuwe Waterweg, the heightening and the associated widening of the dikes proved very difficult because of public opposition to the planned destruction of important historic buildings to achieve this. The plan was changed to the construction of a storm surge barrier (theMaeslantkering) and dikes were only partly built up.
The Delta Plan originally intended to create a large freshwater lake, theZeeuwse Meer (Zeeland Lake).[1] This would have caused major environmental destruction in Oosterschelde, with the total loss of the saltwater ecosystem and, consequently, the harvesting of oysters. Environmentalists and fishermen combined their efforts to prevent the closure; they persuaded parliament to amend the original plan. Instead of completely damming the estuary, the government agreed to build a storm surge barrier. This essentially is a long collection of very large valves that can be closed against storm surges.
The storm surge barrier closes only when the sea-level is expected to rise 3 metres above mean sea level. Under normal conditions, the estuary's mouth is open, and salt water flows in and out with the tide. As a result of the change, the weak dikes along the Oosterschelde needed to be strengthened. Over 200 km of the dike needed new revetments. The connections between the Eastern Scheldt and the neighboringHaringvliet 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. Since operating the barrier has an effect on the environment, fisheries and the water management system, decisions made on opening or closing the gate are carefully considered. Also the safety of the surrounding dykes are affected by barrier operations.
In an attempt to restore and preserve the natural system surrounded by the dykes and storm-surge barrier, the concept 'building with nature' was introduced in revised Delta Program updates after 2008. The new integrated water management plan not only takes into account protection against flooding, but also covers water quality,leisure industry, economic activities, shipping, environment and nature. Whenever possible, existing engineering constructions would be replaced by more 'nature friendly' options in an attempt to restore natural estuary and tides, while still protecting against flooding.[2] In addition, building components of the reinforcements are designed in a way that they support formation of entire ecosystems.[3] As part of the revision, theRoom for the River projects, enabled nature to occupy space by lowering or widening the river bed.[4] In order to establish this, agricultural flood plains are turned into natural parks, excavated farmland is used for wild vegetation and newly excavated lakes and bypasses create habitats for fish and birds.[5] Along the coast, natural sand is added each year to allow sand to blow freely through the dunes instead of having the dunes held in place by planted vegetation or revetments.[6] Although the new plan brought along additional cost, it was received favourably.[citation needed] The re-considerations of the Delta Project indicated the growing importance of integrate environmental impact assessments in policy-making.
The Delta Project of which the Delta Works are part of was originally designed in a period of time when environmental awareness and ecological effects of engineering projects were barely taken into consideration.[7] Although the level of awareness for the environment grew throughout the years, the Delta Project has caused numerous irreversible[citation needed] effects on the environment in the past. Blocking theestuary mouths did reduce the length of dykes that otherwise would have to be built to protect against floods, but it also led to major changes in the water systems. For example, the tides disappeared, which resulted in a less smooth transition from sea water into fresh water. Flora and fauna suffered from this noticeable change.[8] In addition, rivers experienced an increase in sedimentation by polluted sludge, since there was no longer an open passage to the sea.
The projects of the Delta Plan are financed with the Delta Fund. In 1958, when the Delta law was accepted under the Delta Works Commission, the total costs were estimated at 3.3 billionguilder. This was at that time equal to 20% of national GDP. This amount was spread out over the 25 years that it would take to complete the massive engineering project. The Delta works were mostly financed by the national budget, with a contribution of theMarshall Plan of 400 million guilder. In addition, the Dutch natural gas discovery contributed massively to the finance of the project. At completion in 1997, costs were set on 8.2 billion guilder.[9] Nevertheless, in 2012 the total costs were already set on[clarification needed] around $13 billion.[10]
The original plan was completed by theEuropoortkering which required the construction of theMaeslantkering in theNieuwe Waterweg betweenMaassluis andHook of Holland and theHartelkering in the Hartel Canal nearSpijkenisse. The works were declared finished after almost forty years in 1997.
Due to climate change and relative sea-level rise, the 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, and involve a complicated decision-making process. In 1995 it was agreed in the Delta Plan Large Rivers andRoom for the River projects that about 500 kilometres of insufficient dyke revetments were reinforced and replaced along the Oosterschelde and Westerschelde between 1995 and 2015. After 2015, under the High Water Protection Program, additional upgrades are made.[11]
In September 2008, the Delta Commission presided by politicianCees Veerman advised in a report that the Netherlands would need a massive new building program to strengthen the country's water defenses against the anticipated effects of global warming for the next 190 years. The plans included drawing up worst-case scenarios for evacuations and included more than €100 billion, or $144 billion, in new spending through the year 2100 for measures, such as broadening coastaldunes and strengthening sea and riverdikes.The commission said the country must plan for a rise in the North Sea of 1.3 meters by 2100 and 4 meters by 2200.[12]
The works that are part of the Delta Works are listed in chronological order with their year of completion:
