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Infragravity waves are a common feature in the nearshore wave field and have a significant impact on numerous coastal processes. It is therefore important to accurately predict infragravity wave conditions at a given location. However, analytical relations do not exist with which to make such predictions and one has to rely on numerical models. In this study infragravity waves are simulated with a linear 1D surf beat model (IDSB) and a non-hydrostatic model (SWASH). The aim of this study is to perform a detailed numerical investigation into the nearshore behaviour of infragravity waves. Specific attention is paid to the generation, propagation and reflection of IG-waves.

The swash zone is the part of the beach that reaches from the limit of wave run-up until the limit of wave run-down. It is recognized as being a dynamic area of the nearshore region, characterized by strong and unsteady flows, high turbulence levels, large sediment transport rates and morphological changes on a small timescale. Due to the complexity of the processes taking place in the swash zone, there are still great uncertainties about the driving forces for sediment transport. Morphodynamic process-based numerical models tend to overestimate the seaward directed sediment transport in the swash zone, especially for mild wave conditions. The main objective of this thesis is to obtain insight in the hydrodynamic processes responsible for sediment transport in the swash zone, and to use this knowledge to optimize a morphodynamic numerical model (XBeach) for simulating swash zone physics. First, an extensive literature review is carried out to provide the physical base. Second, a number of (theoretical) linear profile simulations are conducted to provide insight into the simulated swash characteristics for different beach states, and to assess the effect of including a number of swash processes (e.g. turbulence or groundwater flow) in the simulations. Third, measurements obtained during a field experiment in Le Truc Vert (France) are used to verify three hydrodynamic modelling approaches and two sediment transport models.

Novel observations of surface grain-size distributions are used in combination with intra-wave modeling to examine the processes responsible for the sorting of sediment grains on a relatively steep beach (slope = 1:7.5). The field observations of the mean grain size collected with a digital camera system at consecutive low and high tides for a 2 week period show significant temporal and spatial variation. This variation is reproduced by the modeling approach when the surf zone flow-circulation is relatively weak, showing coarse grain sizes at the location of the shore break and finer sediment onshore and offshore of the shore break. The model results suggest that grain size sorting is dominated by the wave-breaking-related suspended sediment transport which removes finer sediment from the shore break and transports it both on-shore and offshore. The transport capacity of wave-breaking-related suspended sediment is controlled by the sediment response time scale in the advection-diffusion equation, where small (large) values promote onshore (offshore) transport. Comparisons with the observed beach profile evolution suggest a relatively short time scale for the suspended sediment response which could be explained by the vigorous breaking of the waves at the shore break.

In this study the focus is on modelling turbulence anisotropy in open channel flows with the SWASH model. Turbulence anisotropy significantly influences the flow features of: channel flows with heterogeneous roughness conditions, curved open channel flows, compound channel flows with different floodplain depths, etc. The SWASH model is a non-hydrostatic wave-flow model, mainly used to predict the transformation of surface waves from offshore to the beach. For this study, adaptations were made to this SWASH model, in order to model turbulence anisotropy. Two different modelling approaches were used: RANS modelling and Large Eddy Simulation (LES). The SWASH model is extended with a non-linear k-ε closure to the RANS equations, since the standard linear closure does not take turbulence anisotropy into account. A 3D subgrid model is implemented to perform LES. The performance of the LES code and the RANS model with the non-linear k-ε closure is tested on two flow geometries: an open channel flow with homogeneous bottom roughness conditions and an open channel flow with parallel smooth to rough bed sections. Results of the RANS computations, for both horizontal homogeneous and non-homogeneous open channel flow, show good agreement with laboratory measurements of Muller and Studerus [13], Nezu and Rodi [17] and Wang and Cheng [32]. Although there is a number of closure constants involved with the non-linear k-ε model, additional tuning of these coefficients was not necessary for this study: both the homogeneous and non-homogenous test case were simulated successfully using the standard values proposed by Speziale [25]. With its low computational costs and robustness, the non-linear k-ε model appears to be a useful extension to the SWASH wave-flow model. LES results for horizontal uniform flow are validated with DNS data of Moser, Kim and Mansour [12]. Especially near the bed the LES results deviate from the DNS data. The mean velocity, as well as the transverse and vertical turbulence intensities, is seriously underestimated. The deviation from the DNS data is related to the use of non- periodic boundary conditions, the coarse grid resolution, the size of the computational domain and the amount of numerical dissipation that is involved. Since it is the bottom region where secondary currents are generated, the use of the present LES code for problems involving heterogeneous roughness is not appropriate.

The design formula for rubble mound breakwaters by Van der Meer has an unclear Notional Permeability term. This term causes a lot of confusion for designers. In the past many people have tried to derive a better formulation for that term by experimental and analytical research. The goal of this study was to obtain a better formulation along a numerical way. This study explores the numerical possibilities and tries to define which direction has to be taken in future research. As a first step, a very simplified case is taken with a vertical homogeneous breakwater which interact with monochromatic waves. In total six different blocks were made of epoxy and elastocoast. Only 4 out of the 6 blocks were tested. Also the porosity (n), laminar friction (α) and turbulent friction constant (β) of the blocks were determined experimentally. This way the experimental results could be compared with computations. These experiments have been done in the large flume of the Environmental Fluid Mechanics Laboratory of the TU Delft. Two types of data were collected: pore pressures and water levels in front and behind the block. The water levels seemed to be the most reliable data. The main deficit of the setup was the wave absorber at the end of the flume. The wave absorber is not able to sufficiently absorb long waves. So the dataset had to be corrected for that effect. The created dataset was in line with results from earlier experiments. Results were compared with an analytical solution and the numerical SWASH model. Comparisons with the analytical solution showed a reasonable fit without any calibration. The SWASH model showed in first instance large deviations using the same dataset. By calibrating the turbulent flow resistance β, it was possible to generate a decent fit. However, the used β constants are 6-10 times higher than the measured β constants. This is physically unrealistic high. Therefore the most likely explanation is an error in the transition between the water and the porous medium. During the experiment discontinuities can occur on this transition while SWASH uses an continuity requirement. Numerical tests were performed on some multi-layered combinations of the different blocks in order to derive a "Vertical P" value in a similar way as Van der Meer determined his P=0.4 structure. The results showed, nevertheless, quite some different patterns as the computations done by Van der Meer. However, taking into account all the problems with calibrating the SWASH model the results for the notional permeability seemed very promising. This numerical method shows the possibility of numerically calculating a notional permeability and should be investigated further in the future.

This paper presents numerical modelling of the nearshore transformation of infragravity waves induced by bichromatic wave groups over a horizontal and a sloping bottom. The non-hydrostatic model SWASH is assessed by comparing model predictions with analytical solutions over a horizontal bottom and with detailed laboratory observations for a sloping bottom. Good agreement between model predictions and data is found throughout the domain for bound infragravity waves. Furthermore the model predicts greater outgoing free infragravity wave-heights for steeper slope regimes which is consistent with the measurements. The model however tends to overestimate the magnitude of the outgoing infragravity waves.

This paper presents the application of the open source non-hydrostatic wave-flow model SWASH to wave propagation over a fringing reef, and the results are discussed and compared with observations obtained from a laboratory experiment subjected to various incident wave conditions. This study focus not only on wave breaking, bottom friction, and wave-induced setup and runup, but also on the generation and propagation of infragravity waves beyond the reef crest. Present simulations demonstrate the overall predictive capabilities of the model for a typical coral reef with steep slopes and extended reef flats.

This paper presents the application of the open source non-hydrostatic wave-flow model SWASH to wave propagation over a fringing reef, and the results are discussed and compared with observations obtained from a laboratory experiment subjected to various incident wave conditions. This study focus not only on wave breaking, bottom friction, and wave-induced setup and runup, but also on the generation and propagation of infragravity waves beyond the reef crest. Present simulations demonstrate the overall predictive capabilities of the model for a typical coral reef with steep slopes and extended reef flats.

This paper presents numerical modelling of the nearshore transformation of infragravity waves induced by bichromatic wave groups over a horizontal and a sloping bottom. The non-hydrostatic model SWASH is assessed by comparing model predictions with analytical solutions over a horizontal bottom and with detailed laboratory observations for a sloping bottom. Good agreement between model predictions and data is found throughout the domain for bound infragravity waves. Furthermore the model predicts greater outgoing free infragravity wave-heights for steeper slope regimes which is consistent with the measurements. The model however tends to overestimate the magnitude of the outgoing infragravity waves.

A large multi-institutional nearshore field experiment was conducted at Truc Vert, on the Atlantic coast of France in early 2008. Truc Vert’08 was designed to measure beach change on a long, sandy stretch of coast without engineering works with emphasis on large winter waves (offshore significant wave height up to 8 m), a three-dimensional morphology, and macro-tidal conditions. Nearshore wave transformation, circulation and bathymetric changes involve coupled processes at many spatial and temporal scales thus implying the need to improve our knowledge for the full spectrum of scales to achieve a comprehensive view of the natural system. This experiment is unique when compared with existing experiments because of the simultaneous investigation of processes at different scales, both spatially (from ripples to sand banks) and temporally (from single swash events to several spring-neap tidal cycles, including a major storm event). The purpose of this paper is to provide background information on the experiment by providing detailed presentation of the instrument layout and snapshots of preliminary results.

The hydrodynamics and sediment transport in the swash zone is currently outside the domain of coastal-area models, which is a significant limitation in obtaining littoral sediment-transport estimates, especially on steep reflective beaches where the waves practically break on the beachface. In this study, an existing process-based coastal model (MIKE 21) is combined with a theoretical derivation of swash processes, resulting in an innovative hybrid modelling approach that is capable of estimating longshore sediment transport in the swash zone. The method relies upon estimation of swash hydrodynamics from an extended ballistic swash model with friction included. The terminal bore and other incident wave properties were computed from the output of a spectral-wave model (MIKE 21 SW). The Bagnold-type equation was applied to estimate gross transport volumes and the longshore component was computed for the sand volume displaced during the up-rush. The newly developed hybrid modelling approach was applied to Jimmys beach, a steep reflective beach (D50 = 0.3 mm, gradient=0.1) along the northern shoreline of Port Stephens, Australia. The model results yield the alongshore swash transport pathways and the indicative transport volumes. A point of divergence is identified at the beach erosion area, which is of critical importance in terms of shoreline erosion and management. The preliminary results suggest that swash-zone transport can account for a large percentage of the total littoral drift for such beaches. However, further field or laboratory data are required to test model utility, as well as to tune calibration parameters based on the site-specific conditions

A one-dimensional hydrostatic version of the XBeach model (Roelvink et al., 2009) is applied to hindcast swash morphodynamics measured during an accretive, and an erosive tide at Le Truc Vert beach (France) in early spring 2008 (Masselink et. al, 2009; Blenkinsopp et al., 2011). Swash hydrodynamics are solved by applying the nonlinear shallow water equations, and sediment transport rates are obtained from a combined intra-wave Nielsen and Bagnold type transport model. Reasonable predictions of morphological change in the swash were obtained. Nevertheless, the model underpredicts the water level setup and/or wave run-up during the accretive tide, which is hypothesized to be related to 2D-effects.

In this paper, the effect of beach nourishment on wave overtopping in shallow foreshores is investigated with the nonhydrostatic wave-flow model SWASH. Firstly, the applicability of SWASH to model wave overtopping is tested by comparing results with a physical model setup with different storm wall heights on top of an impermeable sea dike. The numerical results show good agreement with the physical model. After validation, sensitivity analysis of the effect of beach nourishment on wave overtopping is conducted by changing bottom configurations with the SWASH model. From the sensitivity analysis, it becomes clear that wave overtopping discharge in shallow foreshores is characterized by the bores generated in surf zone due to wave breaking. To reduce wave overtopping discharge in shallow foreshore, it is important to reduce the horizontal momentum of the bores.