Modeling the contribution of infragravity and incident band swash on wave run-up on East coast South-Korean beaches

Abstract

The maximum wave run-up on a beach is an important factor in the design of coastal protection measures. Therefore, it is desired to predict this run-up based on numerical models. In this thesis, this is done with the use of the model XBeach. Wave run-up consists of multiple components: a swash height, S, and a wave set-up, . The swash height can be divided in a high frequency (incident) and low frequency (infragravity) part. Which of these two frequencies prevail depends on multiple factors such as offshore wave energy and local bathymetry. In general, it is expected that on low sloping beaches or dissipative coasts, low frequency swash is dominant. Steep beaches or reflective coasts experience a dominance of high frequency swash motions. Intermediate beaches experience both high and low frequency motions, and thus lie somewhere between these two extremes. This report uses a case study, which is such an intermediate beach, with an alongshore varying bathymetry and topography: Anmok beach in South-Korea. This report also shows that the prevailing frequency band determines what type of (simplified) model can be used. This is done with the use of both 1D and 2DH models. As no data are available, all conclusions are made based on the model results only. The main part of this thesis consists of 1D results, as this required less computational time. Therefore, many synthetic storms could be analysed. Their analysis showed that low frequency motions prevail in the wave run-up and that the use of a simplified model is allowed. Even though a 1D model requires less computational demand, the question can arise whether it is valid to use it, since the case study showed a strongly alongshore varying coast. To research this, a 2DH model of the case study site has been analysed as well. The analysis is limited to one storm condition, which was also used in the 1D model, due to time constraints. The results showed differences between the 1D and 2DH model in the generation of low frequency motions, which lead to differences in the maximum wave run-up as well. The low frequency motions do not prevail as was seen in the 1D model. Contrary to the 1D model, very low frequency motions could also be found in the wave run-up of the 2DH model. As the 2DH model results are assumed to be closest to reality, the results suggest that a more simplified approach in the determination of wave run-up is not allowed for this particular case study. However, since the results are based on a single stormcondition, further research is necessary to provide more insight and better conclusions.