Editing Delta Works (section)

=== Delta law and conceptual framework ===
[[File:Colijnsplaat - Zeelandbrücke.jpg|thumb|[[Zeeland Bridge]]]]
[[File:Oosterscheldekering-pohled.jpg|thumb|[[Oosterscheldekering]]]]

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:
* Major areas to be protected from flooding are identified. These are called "dike 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 a 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-built 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 "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:

* 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, 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.

* 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 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 expected [[sea 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.