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Violante-Carvalho, N.; D'Avila, V.; Heringer Villena, H.H., and Mendonça Filippo, A.M., 2020. The Flying Anchor: An original technique for beach profile measurements in the surf zone. Journal of Coastal Research, 36(3), 654–660. Coconut Creek (Florida), ISSN 0749-0208. An original method is proposed to measure beach profiles in the surf zone. Surveying this dynamic and energetic region is usually a challenge when waves are large, which is exactly when the nearshore processes are more intense. The lack of bathymetry and wave data is indisputably a limiting factor hindering the understanding of the physics involved. Countless techniques have been proposed in the last decades to increase the temporal and spatial density of such measurements, with different degrees of success. Seeking to bring new approaches to address these issues, the proposed operation consists of launching a specially designed anchor from the beach face over the surf zone, carrying a graduated cable. When the cable is drawn taut, a pressure sensor is hand towed along the sea floor measuring the profile, as well as yielding the wave energy spectrum. The technique is efficient and fast and employs a small team at a very low cost. Some of the main limitations of the known in situ techniques, such as sea state dependency, high cost per profile, and longshore drift, are mitigated. [ABSTRACT FROM AUTHOR]

Atkin, E.A.; Mead, S.T., and Phillips, D., 2019. Investigations of offshore wave preconditioning. In: Bryan, K.R. and Atkin, E.A. (eds.), Surf Break Management in Aotearoa New Zealand. Journal of Coastal Research, Special Issue No. 87, pp. 78–90. Coconut Creek (Florida), ISSN 0749-0208. The way in which a wave breaks is largely a function of the path wave orthogonals and the bathymetry that wave orbitals encounter as the wave propagates shoreward. This effect is commonly referred to in surf science literature as preconditioning and occurs at a range of scales. This work considers seabed features that do not cause wave breaking but influence the way in which they break. An assessment first quantifies the dimensions of a number of known wave preconditioning features, and then involves iterative numerical model simulations of heuristic seabed features. The impact of an offshore feature is descried in terms of the wave propagation in the lee of the feature and breaking patterns, or surf zone plan-shape, near the shoreline. It is proposed that offshore features be considered as either disruptive or focus preconditioners. The former results in complex and chaotic interference patterns resulting in multiple peaks at the shoreline, with the latter creating a more singular or defined peak with less widespread disruption. A key component for surfing wave quality to be influenced by offshore preconditioning is the establishment of longshore wave height gradients, which are often associated with the bifurcation, or "snapping" of wave crests. The degree to which a feature sets up longshore wave height gradients and bifurcates wave crests is shown to be influenced by the size of the preconditioning feature relative to the incident wave conditions. [ABSTRACT FROM AUTHOR]

Atkin, E.A.; Mead, S.T., and Phillips, D., 2019. Investigations of offshore wave preconditioning. In: Bryan, K.R. and Atkin, E.A. (eds.), Surf Break Management in Aotearoa New Zealand. Journal of Coastal Research, Special Issue No. 87, pp. 78–90. Coconut Creek (Florida), ISSN 0749-0208. The way in which a wave breaks is largely a function of the path wave orthogonals and the bathymetry that wave orbitals encounter as the wave propagates shoreward. This effect is commonly referred to in surf science literature as preconditioning and occurs at a range of scales. This work considers seabed features that do not cause wave breaking but influence the way in which they break. An assessment first quantifies the dimensions of a number of known wave preconditioning features, and then involves iterative numerical model simulations of heuristic seabed features. The impact of an offshore feature is descried in terms of the wave propagation in the lee of the feature and breaking patterns, or surf zone plan-shape, near the shoreline. It is proposed that offshore features be considered as either disruptive or focus preconditioners. The former results in complex and chaotic interference patterns resulting in multiple peaks at the shoreline, with the latter creating a more singular or defined peak with less widespread disruption. A key component for surfing wave quality to be influenced by offshore preconditioning is the establishment of longshore wave height gradients, which are often associated with the bifurcation, or "snapping" of wave crests. The degree to which a feature sets up longshore wave height gradients and bifurcates wave crests is shown to be influenced by the size of the preconditioning feature relative to the incident wave conditions. [ABSTRACT FROM AUTHOR]

Zhang, J.; Sun, K.; Zhai, Y.; Zhang, H., and Zhang, C., 2016. Physical study on interactions between waves and a well-mixed seabed. In: Vila-Concejo, A.; Bruce, E.; Kennedy, D.M., and McCarroll, R.J. (eds.), Proceedings of the 14th International Coastal Symposium (Sydney, Australia). Journal of Coastal Research, Special Issue, No. 75, pp. 198-202. Coconut Creek (Florida), ISSN 0749-0208. The problem of wave-seabed interaction has attracted more and more attention of coastal researchers and engineers, as it plays an important role in the estimations of seabed stability and foundation design of offshore structures. Much effort has been made by many investigators to study the wave-seabed interaction in the past decades. However, most of them focus on the wave-induced response within a seabed with single/uniform soil particle, ignoring the mixed seabed consisting of different soil particles in the real environment. A series of laboratory experiments are carried out in a wave flume to study the wave-driven pore-water pressure in a well-mixed seabed (consisting of sand and silt) and the attenuation of wave height. Waves propagating over a mixed seabed lead to oscillatory excess pore-water pressures within the porous seabed. Maximum amplitude of the ratio of pore-water pressure within the seabed to pressure on seabed surface decreases within a deeper layer. A phase lag of pore-water pressure is clearly observed, and it contributes to net upward pressure related to seabed instability. The impacts of mixture percentage of sand/silt on pore-water pressure are also analyzed and discussed. [ABSTRACT FROM AUTHOR]

In the present study, a new, simple method for determining the slip velocity (also called the bed velocity) at the solid-fluid interface in the wave boundary layer is proposed. Based on experimental and numerical results, when waves travel over a rigid permeable seabed, a nonzero slip velocity exists at the interface. The defect of a small slip velocity has been found to occur in previous studies and is usually encountered in fluid-porous layer problems. In the wave-rigid permeable seabed problem, the slip effect depends on the properties of the seabed. The slip velocity boundary condition (SVBC) is one specification of the slip conditions and is usually applied to explain the slip phenomenon in a fluid-porous layer problem. However, the traditional SVBC or the slip velocity is only considered in a single flow, and application of SVBC in harmonic motion is still an open problem that necessitates a simple formula for determining the slip velocity in realistic cases. The Stokes' second problem and the slip length model (SLM) are applied to derive a new slip velocity and a slip factor in this paper. Both the permeability and the roughness of the seabed are chosen as the slip length. The analytical solution shows that the new slip velocity depends on the wave period and the pressure gradient, and the slip factor is related to the wave Reynolds number, the permeability, and the roughness of the seabed. The resultant slip velocity exhibits good agreement with the experimental results, and the slip factor formula obtained by this present study can be applied to a real seabed. [ABSTRACT FROM AUTHOR]

Seabed accretion, formation of a local irregular shoal as the result of disposal of dredged sediment, and modifications of the coastline configuration from anthropogenic action have introduced significant changes in the physical processes involved in wave propagation, and consequently on the wave climate, in the nearshore area of Hac-Sá Bay, Macau. Statistical analysis of the wave data recorded at a wave-rider station located offshore the study area revealed seasonal, energetic, and directional variation tendencies of the wave regime and facilitated schematization of a representative offshore wave regime. Numerical modelling of propagation and transformation of the components of the representative offshore wave regime, including processes of shoaling, refraction, diffraction, reflection, and breaking, was applied to assess the nearshore wave climate before and after the major coastline and seabed morphological changes. An advanced and accurate numerical model, suitable for the case study, was applied. Comparison of the results obtained for both situations showed that significant changes occurred in the wave climate due to the morphological evolution. [ABSTRACT FROM AUTHOR]

A two-dimensional wave flume investigation was conducted to examine the effect of multiple steps on the form of breaking waves. The study was initiated to gain a better appreciation of the design tolerances for artificial surfing reefs. The geotextile bags used to form an artificial surfing reef create multiple steps in the seabed; reducing the size of these steps improves the quality of waves for recreational surfing but comes at considerable economic cost. Sets of steps were placed on a 1 : 15 slope, and image analysis methods were used to quantify the effects of increasing step size on the form and intensity of the breaking waves. The vortex area, angle, and length-to-width ratio were quantified for various step sizes. It is shown that breaking intensity decreases with increasing step size. Variations in wave reflection were measured using a three-element surface-piercing wave gauge. Wave reflection coefficients were found to be unchanged for all step sizes implemented in this experiment, and reflection was not found to significantly affect the form of the breaking waves in the current tests. The quality of the surfing waves for recreational surfing was seen to degrade measurably with increasing step size, with a higher degree of variability and irregularity in the vortices of the plunging breakers. A qualitative assessment of the quality of the breaking waves suggests that step size should be limited to approximately 23% of the design wave height. [ABSTRACT FROM AUTHOR]