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Accurate prediction of wave energy dissipation over mud is essential for understanding nearshore circulation, sediment transport processes, and design of engineering projects along muddy coasts. It is desirable to be able to simulate wave propagation over a wide range of mud behaviors as wave evolution is highly dependent on mud rheological characteristics. In this study, we develop a numerical model to simulate surface wave evolution over viscoelastic muds. This new wave-mud interaction model is comprised of a frequency-domain phase-resolving model for wave propagation that explicitly solves nonlinear wave-wave interactions, and a model for mud-induced surface wave dissipation and modulation. Model results show satisfactory agreement with laboratory measurements of wave height and attenuation rates over mud, and shows improvement over the model with a viscous mud mechanism. The model is then used to investigate the combined effect of mud viscoelasticity and nonlinear wave-wave interactions on surface wave evolution. Cnoidal and random wave simulations are conducted. In general, qualitative measures such as shape of cnoidal waves or pattern of variation in H r m s of random waves are dictated by direct mud-induced damping which due to resonance effects, has a substantially different structure over viscoelastic mud compared to viscous mud. Nonlinear interactions affect spectral shape and distribution of energy loss across the spectrum. Subharmonic interactions cause indirect damping of high frequencies but ameliorate damping of harmonics around mud's resonance frequency. Therefore, neglecting mud elasticity can result in significant errors in estimation of bulk wave characteristics and spectral shape. • A new phase-resolving model is developed to study wave evolution over viscoelastic mud. • Spectral shape is highly affected by relative magnitude of spectral peak and resonance frequency of mud. • High frequencies are attenuated due to subharmonic interactions regardless of the magnitude of mud shear modulus. • Subharmonic interactions can reduce damping of low frequencies over viscoelastic mud. [ABSTRACT FROM AUTHOR]

This paper presents the results of an experimental study on the scour development of a hydraulic-transparent offshore foundation exposed to combined waves and current. Irregular waves propagating perpendicular to a current were simulated in a wave-current basin. The physical model tests were conducted in a length scale of 1:30 while measurements of the scour development over time were achieved by echo sounding devices placed at several locations at the upstream and downstream side of the jacket structure. Insights were gained on the scour development and time scale of the scouring process around a complex jacket structure for different wave-current conditions. The results were presented with respect to the Keulegan-Carpenter KC number and the relative wave-current velocity. Wave conditions were adjusted so that KC numbers between 6.7 and 23.4 could be tested in a systematic wave-current test program with tests reaching from wave dominated conditions up to current dominated conditions. Measured scour depths were critically assessed by an extrapolation to expected equilibrium scour depths. With respect to the current flow direction, the experiments showed generally larger scour depths at the upstream side and lower scour depths on the downstream side for each pile of the jacket structure. The development of global scour around the structure intensified with increasing relative wave-current velocity. As a result, a practical formulation is proposed for the reliable prediction of local scour depths around a jacket foundation in combined wave-current conditions. Finally, dimensionless time scales and observed as well as predicted scour depths are compared to values for the scour development around monopiles. • Systematic laboratory tests on the scouring process around a jacket structure in combined waves and currents are presented. • The scour development over time was measured with eight echo sounding devices at the front and back side of the structure. • Scour depths and time scales are given as a function of the Keulegan-Carpenter number and the relative wave-current velocity. • Dimensionless time scales and observed as well as predicted scour depths are compared to those for monopiles. [ABSTRACT FROM AUTHOR]

Sand transport processes and net transport rates are studied in a large-scale laboratory swash zone. Bichromatic waves with a phase modulation were generated, producing two continuously alternating swash events that have similar offshore wave statistics but which differ in terms of wave-swash interactions. Measured sand suspension and sheet flow dynamics show strong temporal and spatial variability, related to variations in flow velocity and locations of wave capture and wave-backwash interactions. Suspended and sheet flow layer transport rates in the lower swash zone are generally of same magnitude, but sheet flow exceeds the suspended load transport by up to a factor four during the early uprush. The bed level near the inner surf zone is relatively steady during a swash cycle, but changes of O (cm/s) are measured near the mid swash zone where wave-swash interactions lead to strongly non-uniform flows. The two alternating swash events produce a dynamic equilibrium, with bed level changes up to a few mm induced by single swash events, but with net morphodynamic change over multiple events that is two orders of magnitude lower. Most of the intra-swash and the single-event-averaged bed level changes in the swash zone are caused by a redistribution of sediment within the swash. The transport of sediment across the surf-swash boundary is minor at intra-swash time scale, but becomes increasingly significant at swash-averaged time scales or longer (i.e., averaged over multiple swash events). •Large-scale wave flume experiments involving two alternating bichromatic wave induced swash events. •Sediment mobilization as sheet load and suspended load increases substantially from inner surf to lower swash zone. •Sheet flow transport dominates the total transport during the early uprush and during instants of strong wave-backwash interactions. •Single swash events can produce much greater net transport rates and bed level changes than the overall trend over multiple events. •The sediment exchange across the surf-swash boundary becomes increasingly significant when integrated over larger time scales. [ABSTRACT FROM AUTHOR]

A new methodology capable of concurrently resolving free surface wave field, bottom boundary layer, and sediment transport processes throughout the entire water column was recently developed in the OpenFOAM framework, called SedWaveFoam. In this study, SedWaveFoam is validated with large wave flume data for sheet flow driven by near-breaking waves. Good agreements are obtained for free surface elevation, flow velocity, turbulence kinetic energy, sediment concentration, and sheet flow sediment fluxes. Model results are used to investigate the joint effects of velocity skewness, acceleration skewness, and progressive wave streaming on sheet flow sediment transport. SedWaveFoam results are contrasted with rigid-lid one-dimensional-vertical model results to isolate the effect of the free surface. Onshore directed near-bed flow velocity and sediment flux are enhanced due to the presence of the free surface via progressive wave streaming. However, the enhancement of net onshore sediment transport for the near-breaking condition with both high velocity and acceleration skewness is several factors greater than that found in the nonbreaking condition with only high velocity skewness. Model results suggest that the large horizontal pressure gradient, which has a Sleath parameter exceeding 0.2, may play a key role. Momentary bed failure is identified via near-bed instability of the sheet flow layer, associated with a large bed shear stress and horizontal pressure gradient. Instantaneous near-bed vortices due to the near-bed instability correspond to the increase of horizontal pore pressure gradient during the wave crest, consistent with measured data. Model inter-comparison suggests that a two-dimensional model is crucial to capture the effect of momentary bed failure that increases sediment suspension during wave crest passage and net onshore sediment transport. • A free surface resolving Eulerian two-phase flow model is validated for sheet flow driven by near-breaking waves on a sandbar. • Onshore-directed sediment flux is enhanced due to progressive wave streaming effect for both velocity and acceleration skewed waves. • The enhancement of onshore transport is more significant for acceleration-skewed waves due to momentary bed failure. [ABSTRACT FROM AUTHOR]

For many coastal communities, dunes serve as the primary defense against tropical and extratropical events. Vegetation is believed to increase the stability of dunes during wave attack, but limited data is available. A physical model study was performed to evaluate changes in the dune stability with and without biomass, both above and belowground. The above and belowground biomass was modeled using wooden dowels and coir fibers, respectively. For both the collision and overwash storm impact regimes, the results of this study clearly demonstrate that the inclusion of biomass in the model dune reduces the erosion and overwash. The combination of both above and belowground biomass was the most effective at reducing erosion followed by belowground biomass, with aboveground biomass providing the smallest benefit regardless of the wave condition and water level. Additionally, the overwash of sediment and water was decreased with the inclusion of biomass, following the same trends as the erosion. As the dune eroded, the storm impact regime transitioned from collision to overwash. The inclusion of biomass delays this transition in storm impact regime, providing greater protection to coastal communities. This study highlights the need to consider dune vegetation for dune construction and coastal planning. • Physical model study to evaluate dune stability with and without biomass. • A novel approach to modeling belowground biomass in dunes. • Vegetation biomass is demonstrated to provide dune stability during wave attack. • Biomass delays the transition in the storm impact regime. [ABSTRACT FROM AUTHOR]

Numerical coastal erosion models are used by engineers to predict the magnitude of storm erosion at the coastline. In particular, the 'dry' region of the beach, extending landwards from the waterline to include the beach face, berm and dunes, is a particular focus of interest to managers, planners and other coastal practitioners. However, the choice of the most appropriate numerical model to predict subaerial beach erosion requires careful consideration of the strengths and limitations of each model, and the quality and quantity of field data available for both model calibration and prediction. While no model can perfectly replicate observed upper beach erosion, this study specifically assesses the quantity of field calibration data required to achieve optimum model performance for coastal storm erosion modelling applications. Two of the most commonly used, but differently formulated, coastal erosion profile models are compared: the process-based and more complex model XBeach, and the semi-empirical and significantly simpler model SBEACH. A rigorous calibration technique (the Generalised Likelihood Uncertainty Estimation) is applied to both models, using a comprehensive dataset of pre- and post-storm topographic measurements collected over four differing storm events at Narrabeen-Collaroy Beach in southeast Australia, as well as at two adjacent embayed beaches. When applying the two numerical models using their default parameters (i.e., with no model calibration), SBEACH was found to be the more skilful model and XBeach default parameters were found to have no predictive skill along this stretch of coastline. Once calibrated with detailed field observations obtained before and after a single storm event, XBeach validation skill rose considerably and provided predictions of subaerial beach profile change with greater skill (87% better Brier Skill Score on average for the same calibration data) than SBEACH. Overall XBeach model performance was found to marginally improve when field observations obtained from additional storm events were included in the calibration process, whereas SBEACH showed negligible improvement. A comparison was made of the options available for transferring previously-calibrated parameters to adjacent locations, finding spatial proximity to be the most sensitive indicator of model performance for a transferred parameter set. Due to the alongshore variability in pre-storm topography as well as wave exposure at the sites tested, the spatial coverage of data was more important for the calibration process than the magnitude of the individual storm(s) used for a specific calibration. The results of this study underscore the need for careful consideration of the available calibration field data when choosing and optimising coastal erosion models. • Default XBeach parameters were found to be non-skilful at coastal sites in southeast Australia. • The XBeach model outperformed the SBEACH model when one or more calibration storm event field datasets were available. • Collection of calibration pre- and post-storm field data at specific locations of interest was important. • Spatial proximity was found to be a good performance indicator of calibrated parameter values transferred to new locations. [ABSTRACT FROM AUTHOR]

Abstract: This paper is a discussion of Turner et al. “Measurement of wave-by-wave bed-levels in the swash zone”. The discussion highlights previous work on the same topic that in fact demonstrated swash-by-swash measurements of total net sediment transport, but which was not presented by Turner et al. The discussion highlights the advantages and disadvantages of the two measurement methods, and the problem of longshore sediment motion which can introduce errors. [Copyright &y& Elsevier]

Abstract: The authors are grateful to the derivation and correction addressed by Shi and Kirby (2008) for the calculation of the wave setup and setdown induced by obliquely incident waves. The mathematical equations for the expression of setup and setdown are rederived in which the velocity potential is expanded to the second-order on the still water lever. The correct form of setdown presented by Shi and Kirby is confirmed in the present paper. [Copyright &y& Elsevier]

Abstract: This brief comment of Roos et al.''s [Roos, P.C., Hulscher, S.J.M.H. & de Vriend, H.J., 2008. Modelling the morphodynamic impact of offshore sandpit geometries. Coast. Eng. doi:10.1016/j.coastaleng.2008.02.019] paper is aimed at supporting the validity of idealized process-based models as a valuable tool for the design of sand pits. The discussion moves from a brief description of the capabilities of an already existing idealized process-based model [Blondeaux, P. and Vittori, G. 2005a Morphological development of shallow sand pits. Proceedings 29th International Conference Coastal Engineering 2004, World Scientific (Jane McKee Smith ed) ISBN 981-256-995-2 pp. 2581–2593; Blondeaux, P. and Vittori, G., 2005b. Flow and sediment transport induced by tide propagation: part 2: the wavy bottom case. J. Geophys. Res., Vol. 110, No. C8, C08003] which can predict the morphological time development of sand pits. Then, the differences between Blondeaux & Vittori''s model and Roos et al.''s model are analysed to give to the potential user an idea of the range of applicability of the different models, also in relation to practical applications. [Copyright &y& Elsevier]