As of 22 September, Stichting FloodControl IJkdijk will initiate a new field trial, in order to study the phenomenon of flow slide at September 22th.

Subsidence flow, which refers to the subsidence of banks, sandbanks or dikes, is one of the failure mechanisms for which dikes in the Netherlands are assessed. The trial will take place at the Walsoorden sandbank in the Westerschelde.

This flow slide trial will be created under the most natural circumstances possible. The method used will gradually steepen a section of the underwater bank by extracting sand using a dredging vessel. The large-scale trial will test traditional and new measuring and prediction systems. An image will be formed of the development of the sand surface over time, from gauging boats, from underground and from the air.

By monitoring what happens before, during and after the trial, valuable knowledge will be gained for more effective prediction of subsidence flow. A second aim is to gain knowledge on the sensor and data systems deployed. Accurate and high-frequency measurements, data processing, data visualisation and models of the participating companies all contribute to improved prediction of flow slide.

Flow slide is a naturally occurring mechanism, which occurs in the Netherlands in Zeeland, Zuid-Holland and the Wadden Sea. It is also a common failure mechanism in other regions, including the Lower Mississippi. It is a form of instability of underwater slopes (foreshores), in which a large volume of sand flows away in the form of sand sludge. If subsidence flow takes place close to the bank, it can result in erosion of the bank and subsequently serious damage to the dike (dike subsidence). This damage caused by subsidence flow is generally much more serious than that of 'normal' shifting.

All Dutch sea and river dikes are periodically tested in order to assess the risk of flow slide, among other factors. Dikes found to be unstable due to this factor will require very expensive improvements. Certain dike sections in the Netherlands are therefore already scheduled for such work. The know-how gained in the trial will enable the optimisation of these improvements.

The trial will not affect shipping in the Westerschelde, though skippers have been requested via a Notice to Skippers to pass the trial at reduced speed.
Ecologically speaking, the trial will disrupt the balance temporarily, but this will not harm the natural life in or around the Westerschelde. In fact, the know-how gained is expected to be useful in helping to repair the sandbanks, whose surface area is now gradually being lost.

This trial is a joint effort by Stichting FloodControl IJkdijk, the Department of Public Works, Scheldestromen water board, Hollandse Delta water board, the HWBP flood protection programme, the STOWA foundation for applied research into water management), NV NOM, Deltares, AGT, Fugro, Miramap, Nelen&Schuurmans and Target, University of Utrecht and TU Delft, the National Oceanography Centre (Great Britain), University of New Brunswick (Canada) and the University of Ghent (Belgium).

This experiment has been made possible in cooperation with the Ministry of Economic Affairs.

Watch data of the test in the Dijk Data Service Centre use the login data username: zettingsvloeiing and password: zettingvloeiing

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