Episode 26…this means we’re hitting 6 months of Wonderment! Thanks to all of you wonderful readers, whose interest and comments have kept me on track with this, the longest running feature of my blog.
Today’s post is rather special, as there is one thing that growing up in the Netherlands teaches you at an early age: the power of water! When you live in a country, where water is at every turn, you know that you have to be aware and mindful of what water can do. The power of water can never be ignored in the Netherlands, as a significant portion of the country is below sea level, and storms in the North Sea can drive up the water level, thus testing dikes to their breaking point, as last happened in 1953.
Hence, my appreciation and wonderment for the Power of Water…
Delta Works (Deltawerken)
The estuaries of the rivers Rhine, Meuse and Scheldt have been subject to flooding over the centuries. After building the Afsluitdijk, the Dutch started studying the damming of the Rhine-Meuse Delta. Plans were developed to shorten the coastline and turn the delta into a group of freshwater lakes. By shortening the coastline, fewer dikes would have to be reinforced.
Due to indecision and the Second World War, 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 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”.
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 700 kilometres (430 mi). The mouths of the Nieuwe Waterweg and the Westerschelde were to remain open because of the important 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 ports of Rotterdam and Antwerp.
Delta law and conceptual framework
An important part of this project was fundamental research to help solve the flooding problem. 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. 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, 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 are currently being upgraded to meet the future demands. This work is expected to be completed in 2015. An upgrade to river flooding defences is underway, which is expected to be finished in 2017.
The Delta Works can be visited across the province of Zeeland, and, if you find yourself on the island of Schouwen-Duiveland, be sure to visit the Watersnood museum (Flood disaster museum) in Ouwekerk.
Technical Details
This image was captured with a Canon EOS 5D Mk III using an EF 24-105mm f/4L lens. Exposure settings were at 1/10 second at f/16 and 100 ISO.
