Author(s): Joost Kranenborg; Jebbe Van Der Werf; Geert Campmans; Robert Mccall; Niels Jacobsen; Ad Reniers; Suzanne Hulscher

Linked Author(s): Joost Kranenborg, Jebbe van der Werf, Robert McCall

Keywords: Sediment transport; Numerical model; Swash-zone

Abstract: The dynamics in the swash zone play an important role in the overall morphodynamics of the coast. However, numerical models still have difficulties predicting sediment transport and morphodynamics in this dynamic and turbulent region. Most models that are applied to the swash zone use a depth-averaged approach, where model quantities such as flow velocities and sediment concentrations are integrated in the depth direction. This approach, being comparatively cheap, enables longer simulations. However, certain important processes that influence sediment transport are not well understood in a depth-averaged framework. For this reason, depth-resolving models are developed. These models are comparatively expensive and as such are not suitable for simulating longer time series. However, they can give insight into the depth dependency of parameters such as flow velocity, turbulence and sediment concentrations, and as such can be used to improve depth-averaged models. In this study, we investigate numerically how sediment in suspension is picked up, transported and deposited, on a beach consisting of fine sand (D50 = 0.2 mm). To do this, we use a depth-resolving model, based on the open-source OpenFOAM framework. This model implements the RANS equations, coupled with a turbulence model, and implements formulations for bedload and suspended load transport, and uses the mass balance equation for morphodynamics. The model is applied to experiments from the RESIST data campaign. Specifically, we use the bichromatic wave experiments with an effective wave height of H=0.6 m. We choose to use bichromatic waves, since this gives the possibility to analyse transport on a wave-averaged framework. At the conference, we will present the results produced by the model. Firstly, we will show how the model performs compared with the measured data. This will be done in terms of hydrodynamics as well as morphodynamics. Furthermore, we show the vertical suspended sediment concentration profiles behave at different locations and points in time in the swash, and how this can be related to hydrodynamical parameters such as flow velocities and turbulence. These findings can then be used to identify important processes to consider when implementing depth-averaged models for sediment transport.

DOI: https://doi.org/10.3850/IAHR-39WC2521711920221011

Year: 2022