Delta Life 7

FROM SANDBAGS TO SOFTWARE: 20 W hen you think about dikes, you think first about the Netherlands. More than a century and a half after the heroism of Hansje Brinker, the boy who stuck his finger in the dike, Dutch flood prevention is still world famous. The approach has shifted from sandbags to software: computer models are used to put the policy on a sounder footing. Both houses of the Dutch Parliament recently approved major amendments to the Dutch Water Act, which sets out how the country manages flood risks. The new policy is intended to make dike management more efficient and more economical. That is still a big challenge: 7.4 billion euros have been earmarked until 2028 for the improvement of 1100 kilometres of dike in the country. What will change in practice? Fromwater level to dike strength The Dutch developed the previous flood policy in response to the floods in the south-west of the Netherlands in 1953. That policy was based on the idea that a dike needs to be high enough and strong enough to cope with extremely high water, a situation that occurs once in at least 250 years and no more than once every 10,000 years. This is known as the exceedance probability. This approach can be used only to assess measures that affect the height or strength of a dike, or the water level. Creating extra room for the river, for example. Some elements of the policy have now been amended. In the future, we will be assessing how probable failure is in a dike that is not high or strong enough: the flood probability. This approach makes it easier to factor in the different ways a dike can fail, and therefore to formulate better policies for strengthening dikes. It also allows you to assess the effect of risk-mitigation measures such as compartmentalising dikes and evacuation plans. The essence of this 'advanced dike mathematics' is that more precise and detailed knowledge can be used to reduce uncertainty margins. Tailored solutions can be applied everywhere, often cutting costs and reducing local disruption. There is also a stronger Even though dikes are being built throughout the world based on Dutch models, we are changing the rules of the game here. Dike management has to be more efficient and more economical. Three features of the new approach. BY JANNEKE IJMKER IMAGE ISTOCKPHOTO