In the Netherlands, we have strict requirements for the strength of our primary water defences. The Dutch Water Act sets out what needs to be done by managers of water defences to determine whether those requirements are being met. For the purposes of these assessments, the Dutch Ministry of Infrastructure and the Environment provides the Statutory Assessment Instrument (WTI), for which Deltares supplies the technical content and the software. The standards will be amended with effect from 1 January 2017. The current standards require dikes to cope safely with a particular water level. The new standards are based on a maximum permissible probability of flooding. The change means that an overhaul will be required for the entire assessment instrument. In addition, we need to know more about the process: from the start of any damage up to and including the actual failure of the water defences. Uncertainties relating to the loads and to strength are included in a standardised way. Deltares is studying the loads on water defences and the strength of the defences, for example on the basis of large-scale field trials. The results are used to produce design rules that we implement in user-friendly software for the assessment of water defences. The knowledge we develop is also used for other areas of flood risk management, such as policy studies and the design, management & maintenance of water defences.
The final studies were completed in 2014 and the emphasis was on developing design rules. An important moment was the delivery of the first version of the software that management authorities will have to use to make assessments. To check whether all dike sections comply with the standards, the hydraulic loads, soil data and formulas for the relevant failure mechanisms are needed. Important intermediate products have been produced in all three of these areas. Deltares has conducted the first 'trial assessment' with the end users, looking at the procedure and various specific components.
The setting of the WTI programme is exceptionally dynamic. Furthermore, it involves new knowledge that needs to be well founded. We are proud of the fact that Deltares has played such an important supplier role in this entire process.
This programme brings together a range of disciplines, including physics, probabilistics and software development. The challenge was to merge all that knowledge and to produce a single practical instrument.
Frans Hamer (left) and Han Knoeff (right). Copyright Guus Schoonewille