Field measurements of wave interactions with a dike on a shallow foreshore using an “artificial dike” concept

Low-lying countries typically have mildly-sloping beaches as part of their coastal defence system. Many countries in north-western Europe have coastal urban areas that rely on this type of defence system, which consists of a lowcrested impermeable sea dike with a relatively short promenade, and a long (nourished) beach in front that acts as a very/extremely shallow foreshore as defined by Hofland (2017). Along the cross-section of this hybrid beach-dike coastal defence system, storm waves are forced to undergo many transformation processes before they finally overtop the dike. These hydrodynamic processes include shoaling, sea and swell wave energy transfer to sub- and superharmonics via nonlinear wavewave interactions, wave dissipation by breaking and bottom friction, reflection against the dike, wave run-up and overtopping on the dike, bore impact on a wall or building, and finally reflection back towards the sea interacting with incoming bores on the promenade. Field measurements of all these processes at the same time are very challenging but necessary since these suffer from neither scale nor model effects. Field data are therefore crucial to evaluate design methodologies, which rely on physical and numerical modelling. This paper presents the field setup and the design features of the innovative artificial dike, unique in the world.