Journal of Waterway, Port, Coastal, and Ocean Engineering

A series of experiments were conducted to study shoreline changes caused by the presence of a detached breakwater under the influence of pure wave action. The breakwater length, B, and its distance from the initial shoreline, X, were the two main parameters investigated. The study analyzes the effect of these two factors on shoreline changes. The experimental data show that (1) the size of a salient, X_s, increases with B, but decreases with X; and (2) the deposition area of the salient, A, increases with both B and X for X ≤ B. However, further increase in X (X > B) will lead to a reduction in A. Based on the experimental results, the study proposes a criterion to demarcate the formation of a tombolo from that of a salient. The data also show that the width of the tombolo is directly proportional to B and inversely proportional to X. Finally, a new relationship for estimating the sand deposition area is obtained, and published data from the literature are used to verify the new relationship.

Traditional elliptic harbor wave models are based on the assumptions that the region outside the computational grid is of constant depth and that the exterior coastlines are collinear and fully reflecting. These assumptions, which are associated with the open boundary, are generally not met in practice. This paper demonstrates that the effects of exterior depth variations on model results can be substantial, leading to unreliable simulations even with sophisticated modern wave models. A technique is developed to overcome these limitations. It is based on a one-dimensional representation to better simulate the effects of the exterior bathymetry. The results of the one-dimensional model are then interfaced along the open boundary of a two-dimensional finite-element harbor wave model. The new model is tested against analytical solutions for the case of wave propagation on a sloping beach, which is a difficult problem for harbor models in use today. Excellent results are obtained, suggesting that improved representation of the cross-shore slopes while treating the open boundaries may enhance the usefulness of these models.

It is well known that water waves tend to be higher or lower as they propagate onto an opposing or following current, respectively. This is also true for wind waves generated on currents. In the equilibrium range of wind waves, however, the spectral densities for the waves generated on a following or opposing current are larger and smaller, respectively, than those for the waves generated on quiescent water. To see this, a series of laboratory experiments was carried out in a wind-wave and current flume for various conditions of water depth, current, and wind. The experimental results qualitatively confirm the theoretical equations proposed by Gadzhiyev et al. in 1978 and Suh et al. in 1994, with the former performing marginally better for following currents and the latter doing better for opposing currents. It is also shown that the partially developed laboratory waves fall under gravity waves so that the laboratory regime represents the open ocean situation.

Active wave absorption in a physical wave flume or basin requires a wavemaker, a hydrodynamic feedback, and an absorption control system. The feedback provides the information on the waves to be absorbed, and the control system ensures that the paddle of a wavemaker moves accordingly. Different ways of viewing the principle of active absorption are discussed, and basic concepts are examined for the simple case of shallow water waves, starting with the flume case and subsequently including wave obliqueness. A brief review is given of existing 2D systems for active absorption in wave flumes. Quasi-3D systems for multidirectional waves constituted by an array of independent flume systems are discussed, and fully 3D systems, including a coupling between neighboring feedback signals, are reviewed. The diverse appearance of these systems is mainly due to different ideas of accounting for wave obliqueness. An attempt is made to unify the different approaches using the notion of a 2D filter giving the relation between the paddle control and the feedback, regarding each of the two signals as one function of time and space (along the wavemaker), instead of as an array of 1D functions of time. So far, active absorption relies on linear systems. Suggestions are made for the direction of future research, including the prospects for nonlinear extensions.

Over the last several decades, there has been a conspicuous increase in the coastal engineering literature in the use of the fall velocity as a variable to characterize sediment. The increasing interest in fall velocity reflects acknowledgment of the fundamental physical importance of this variable in littoral sedimentation processes. One difficulty in using the fall velocity has been that there was no continuous equation to calculate fall velocity over a wide range of conditions. An equation is developed to calculate sediment fall velocities and is shown to fit a large data set well over a wide range of conditions. The equation was carefully calibrated to the quartz sand subset of the data and found to fit that subset very well; rms error was about 8%. The equation also approaches logical limiting values for laminar and turbulent flow regimes. Simple equations to calculate the kinematic viscosity of sea water and freshwater are also given.

A model is developed for estimating the applied power of a tow as a function of tow speed through water, tow size, tow integration, local depth, channel size, and whether the towboat has Kort nozzles or open wheel propellers. The model computes the total resistance of the tow by considering friction resistance, resistance due to water level drawdown, form (pressure) resistance, and the effects of shallow water and size of the channel cross section. The effective push of the towboat is equated to the resistance, and the applied power is determined from empirical relations developed for typical towboats. Comparison with observed tows shows that the model provides a reasonable estimate of the applied power.