Accurate calculation of wave overtopping is important for determining the required crest height and geometry of a dike. Berms and roughness elements are widely used to reduce the average overtopping discharge at dikes while the reductive effects of berm and roughness are still not fully understood. Several empirical formulae are available to predict the overtopping rate at coastal structures. However, the extrapolation of these empirical formulae is not always applicable for complex structures (e.g. a dike that has a berm and/or roughness elements on the waterside slopes) or wave conditions that are outside the applicability of the empirical predictors. A 2D numerical model based on OpenFOAM® is set up in this study for predicting wave overtopping at dikes that have complex configurations with berms and roughness elements. The validation results show that this OpenFOAM® model is capable of reproducing the incident waves accurately and predicting the wave overtopping discharge with good accuracy. Subsequently, the numerical model is applied to study the reductive influence of a berm and protruding blocks on the mean overtopping discharge at dikes. The roughness of protruding blocks is incorporated by explicitly modelling the protrusions using refined mesh. The model shows reasonable behaviour of the reduction of wave overtopping influenced by a berm and roughness. This indicates the capabilities of the numerical model in the design and safety assessment of dikes.

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A reliable estimation of average wave overtopping discharge is important for dike design and safety assessment. Berms and roughness elements are widely applied to reduce the overtopping discharge over dikes. In this study, the effects of a berm and roughness on the wave overtopping discharge are investigated by means of physical model tests. New empirical formulae are derived from the analysis of the experimental data in order to provide more accurate estimations of reductive influence of berms and roughness on the wave overtopping discharge. Additionally, a new formula is developed to estimate the reductive influence of varying roughness along the waterside slopes with a berm. The new equations show a significantly better performance within the tested range when compared with existing formulae for the average overtopping discharge.

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In 2014, a project, Living Lab Land Subsidence, is established to find a sustainable solution for land subsidence problem in Gouda. Being a part of the project, this research focuses on building a high-resolution groundwater model (2m*2m) by describing the model (such as recharge, leaky sewerage pipes) in local details. Water management strategies can be tested in the model to observe their effects on the groundwater levels. Then this model can be linked to a land subsidence model for further study on land subsidence under different (ground)water management scenarios.

Jakarta is a city which suffers from the problem of urban flooding and inundation. It is urgent to figure out solutions on how to manage the storm water in its urban area. Jakarta locates at the downstream of the catchment; the peak runoff generated in the city can occur earlier than the peak discharge coming from upstream, potentially leading to a ‘collision’ of both peaks. Since the storm water detention methods have both the runoff reduction and delay functions, whether adopting storm water detention methods in Jakarta is able to limiting the discharge magnitude because of its discharge reduction function or even increase the discharge because of the peak delay function is studied. In this article, there are 4 storm water detention methods, green roofs, household storage tanks, pervious pavements and on-site detention tanks, tested with a precipitation event with 100-year return period in a segment in the Jakarta City. The result of the example in this research shows that the delay functions of these 4 solutions are negligible, and the runoff reduction functions of all the solutions are almost lost in this extreme rainfall event when the discharge from the upstream reaches the peak value. So these 4 storm water detention methods in the example have no influence on the peak discharge in the downstream in this precipitation event. However, because the fast runoff is still contributing to the runoff at the exit of the segment when the peak discharge from the upstream comes, these storm water management methods are still possible to reduce the peak discharge during other precipitation events with smaller total precipitation amount or earlier peak intensity. An off-line detention tanks could have positive effects on reducing the peak discharge in the river to the downstream if they start to collect storm water certain period later so that they are capable to store the runoff when the peak discharge from the upstream comes.