Journal of Waterway, Port, Coastal, and Ocean Engineering

This work presents a theoretical discussion and experimental results about the directional bound waves generated by second-order nonlinear interaction between two noncollinear wave trains. Research focus is set on presence, characteristics, and effects of the angle difference between the primary wave trains on the generation of super- and subharmonic bound wave components as well as propagation direction, orbital velocity, and the resulting radiation stress field. An analytical model is derived, and computations thereof conducted for different conditions of wave height, period, and depth. Laboratory tests, systematically conducted in a wave basin, confirm computational results from analytical formulation and indicate that (i) the magnitude of all second-order properties (setup and setdown of the mean water level, orbital velocities) are strongly dependent on the individual combination of periods and directions of the primary wave trains, (ii) the direction of the bound wave differs from those of the primary waves, and (iii) the radiation stress components show a spatial and temporal oscillatory pattern outside the surf zone.

Forensic engineering field surveys conducted in the aftermath of large-scale tsunamis documented the presence of deep local scour holes around structures caused by extreme inundation occurring during such events. The mechanisms leading to scour in extreme flows are still not well understood, as several physical phenomena influencing the spatiotemporal extent of scour have not been adequately investigated. The authors have conducted an experimental test program that has employed a large square column in the Large Wave Flume of the Coastal Research Center, Germany, while they also used a state-of-the-art numerical model (FLOW-3D) to numerically reproduce the experimental results. An investigation of the turbulent flow structures observed around the impacted structure showed that these flow structures are largely responsible for the sediment transport during the runup phase, but the turbulent energy was far less intense during the drawdown phase. The weakness of the turbulent structures observed during drawdown indicates that a different physical phenomenon than the one corresponding to the inflow phase is responsible for the sediment transport experienced during inundation drawdown. Due to the rapid lowering of the flow depth during the drawdown phase of tsunami inundations, a loss of excess pressure occurs because of the upward pressure gradient forming within the soil. However, the pore pressure measurements taken inside the soil in the physical experiment indicate no sign of upward pressure gradient on the inshore side of the column, which is an observation that is incongruent with previous similar studies and previous theoretical concepts. This difference was explained by a layer of soil that remained with a low water content throughout the test because the column was installed on dry sand with low permeability, a condition never tested before for pore pressure change caused by tsunami-like waves.

Dredging is an important measure for maintaining sufficiently high water depths in waterways. However, previous dredging studies have rarely focused on modeling the transient effects of dredging activities on bed evolutions. Here, the transient dredging effects are parameterized as source terms in the mass conservations of bed materials. The parameterization is implemented into an existing depth-averaged hydrosediment–morphodynamic model. This facilitates detailed numerical case studies of dredging effects in the multiple-branched Dongliu waterway in the Lower Yangtze River. The dredging volume of the Dongliu waterway is estimated using the present method and two traditional methods. It is shown that consideration of the transient dredging effects can considerably reduce uncertainty. By systematic parametric studies, a dredging timing before the low water stage is recommended. It is shown that this dredging timing has the advantage of not only avoiding operation difficulties related to high water level as well as intense back-siltation for an earlier dredging but also avoiding the risk of sudden water level drop for a later dredging.

Oysters are hypothesized to affect the shear strength of nearby surficial seafloor sediment as fragments of oyster shells (shell hash) are typically more angular relative to sand particles alone, among other differences. Resistance to shearing is well characterized by the friction angle, which is estimated in this study from vacuum triaxial laboratory and portable free-fall penetrometer field tests. Friction angles of sediment with shell hash were higher relative to those of sediment without shell hash (via hydrochloric acid treatment) on average by about 19% (36.0°–30.2°, respectively). Triaxial confining pressures ranged between 2.1 and 49.0 kPa to simulate subtidal and intertidal aquatic conditions. Regularity (average of particle roundness and sphericity) values of sediment samples with shell hash were found to be less than those of samples without by about 6% (0.66 and 0.70, respectively), which indicates the particle shapes of the former are, overall, more angular and less spherical. Further study and methodology improvements are needed to decrease the approximate 9° friction angle discrepancy estimated from field- and laboratory-based tests. Knowing oysters have the potential to increase sediment shearing resistance helps establish a pathway of how shellfish colonies may contribute to mitigating surficial erosion around coastal infrastructure.

An analytical model for the horizontal multilayer porous plates has been developed based on linear potential theory. Energy dissipation across the horizontal porous plates is considered with an equivalent linearized porous boundary condition, and porosity-dependent drag coefficient estimated by CFD solutions. The hydrodynamic performance of the horizontal multilayer porous plates is assessed by estimating the reflection, transmission, energy loss coefficients, as well as wave force on each porous plate. The developed analytical model is verified by comparing with experimental and CFD-based numerical results. The parametric study with several key parameters such as porosity, submergence depth, number of plates, and their combination is performed in detail to search for the optimal design of the horizontal multilayer plates suitable for the development of eco-friendly wave barrier. It is concluded that a significant reduction in the wave transmission and high energy dissipation can be achieved by the dual-plate configuration with appropriate porosities and submergence depths, compared to the single- and triple-plate configurations.

Wave overtopping needs to be estimated in the design of rubble mound breakwaters, because a high overtopping rate could reduce the capacity and functionality of the structure. The existing formulas, among others, provide estimation of the mean overtopping rate, depending on the hydraulic and structural characteristics. This paper investigates the role of the armor roughness coefficient in the prediction of overtopping. Different rubble mound configurations have been tested by means of two-dimensional physical models. The novelty of the present research lies in providing values of the roughness coefficient for unconventional rubble mound breakwaters. Considering the existing trend and future projections of the sea level and wave climate, there is a need to find upgraded solutions for existing breakwaters, where these structures become more exposed to overtopping risk. Among the possible upgraded solutions, here we consider the case of adding an extra armor layer.

In the 1980s, a coastal defense plan was prepared for a 110-km long stretch of the northwest Portuguese coast, from the Leixões harbor to Cape Mondego. This paper revisits the plan for the location of the Espinho beach and compares the original plan predictions with the postconstruction evolution. In addition, coastal evolution prediction is reassessed with present-day models: the one-line model LITMOD and the parabolic model (using the Mepbay software) for headland-bay beaches. In reality, one-line evolution models give overall good predictions when applied to domains of the order of 10 km, whereas empirical equilibrium-beach models are better in predicting coastal configurations close to structures in headland-bay situations. The main conclusion is that the Espinho beach is in a dynamic equilibrium, fluctuating over time but still maintaining its average position, which is in agreement with the original project predictions of the 1980s.