Author(s): Tomohiro Suzuki; Jasper Dijkstra
Linked Author(s):
Keywords: Wave attenuation; Cliff; Irregular topography; Salt marsh; Vegetation; VOF model
Abstract: Salt marshes are valuable and vulnerable features of the coastal system, but the dynamics of salt marsh formation and erosion are inadequately understood. A particular aspect, central in this contribution, is their potential to attenuate waves. The quantification of these processes in models is difficult, due to the combination of irregular topography, vegetation and cohesive sediments. In this paper, the applicability of a volume of fluid (VOF) model (CADMASSURF) to study the wave dynamics on strongly varying beds with vegetation is tested by comparing the results of numerical simulations to the results of two experiments. The first experiment used rigid artificial vegetation on a slope: cylinders with a diameter of D=0. 5 cm and a density of 325 units/m2. By using the appropriate porosity and directional permeability that match the vegetation properties, the model can reproduce the wave height quite well. Simultaneously, it is possible to obtain wave profiles and orbital velocities. The second experiment used flexible artificial vegetation similar to kelp, made of plastic with a density of 1200 units/m2, on a flat bed. Here, since the shape and flexibility of the vegetation prohibit a straightforward choice of the drag coefficient CD, this coefficient had to be calibrated. The model can reproduce the wave heights quite well with CD=1. 0 to 2. 0, which are standard values for a rigid cylinder and a flat plate, respectively. It can be concluded that the VOF model can be applied to simulate wave attenuation over strongly varying beds and vegetation fields. Furthermore, the VOF model not only gives information about wave heights, but it also calculates velocities and pressures in each cell, which are very relevant for studies of erosion and vegetation development in salt marshes.
Year: 2007