Development of a numerical model to predict the erosion of a dike after the failure of the revetment using time dependent boundary conditions

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Dorothea Kaste, Mark Klein Breteler, Yvo Provoost

Thursday 2 july 2015

16:15 - 16:30h at Mississippi (level 1)

Themes: (T) Water engineering, (ST) Computational methods

Parallel session: 13E. Engineering - Computational

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The presented work was carried out for WTI2017 (“Research and development of safety assessment tools of Dutch flood defences”) and Projectbureau Zeeweringen (PBZ). The WTI2017 programme is commissioned by the Dutch government to set up new rules and tools for the assessment of the flood protection structures. The goal is to enhance the safety standards in The Netherlands in case of flooding. The PBZ was founded under Rijkswaterstaat (the executive organisation of the Dutch Ministry of Infrastructure and Environment) and Waterschap Scheldestromen (the local water board) almost 20 years ago to take care of the coastal protection systems in Zeeland, in the South of The Netherlands. In the scope of WTI2017, in the subgroup for revetments, a model was set up by Kaste and Klein Breteler (2014) to predict dike erosion under wave attack. The dike erosion model was used to calculate the residual strength of a dike after the failure of the block revetment. It is programmed in Matlab and can also be used in probabilistic calculations. The model was based on erosion formulas by Klein Breteler et. al. (2012), which were derived from large scale physical model tests on the erosion of a dike with a clay layer and a sand core. The erosion during a storm is calculated divided in time steps. The formula for the erosion rate in clay was later enhanced by numerous numerical simulations by Mourik (2014). In close cooperation with PBZ, this numerical model was recently extended by the ability to include a varying water level, such as a storm surge in a tidal area. With the varying water level the wave loading acts on different levels of the dike slope. The challenge hereby was to consider the fact that the erosion of a certain time step depends on the present erosion volume from the previous time steps and it has to be determined what part of the erosion counts into that. The numerical model is especially useful in probabilistic calculations, because it is much faster than an erosion simulation with a numerical model, as e.g. XBeach or ComFlow. Probabilistic calculations with the model were already successfully applied within the WTI2017 project. At the conference, the dike erosion model will be presented with the focus on the recent extension for a varying water level. Furthermore its performance and practical implementation is presented based on a number of test cases.