Journal of Waterway, Port, Coastal, and Ocean Engineering

Mangroves have demonstrated the potential to provide engineering services to shorelines through wave attenuation, inland load reduction, and erosion mitigation. However, to confidently leverage these and other natural and nature-based features as coastal protection alternatives, their performance must be quantified over a broad range of environmental conditions that may interact with these systems in nature, ranging from daily stressors to extreme events. This paper examines the attenuation of 236 vessel-generated wakes through red mangroves (Rhizophora mangle) using high-frequency pressure sensors positioned at the fringe (X = 0 m), middle (X = 6.8 m), and sheltered edge (rear, X = 12.6 m) of a narrow mangrove stand near Key West, FL. We observed average characteristic wave height reductions of 38% and 65% at the middle and rear positions, respectively. At the rear of the mangrove stand, wave height attenuation increased with increasing incident relative wave height and increasing incident wave steepness for the range of characteristic wave heights, periods, and water depths observed. A subset of wake events for which water particle velocity measurements were available suggests proportionality between wave height and water particle velocity, which may indicate that transmission coefficients calculated for wave heights may be representative of water particle velocity attenuation as well. This work provides quantitative data to expand the parameter space assessing the performance of natural and nature-based infrastructure in mitigating chronic stressors such as vessel-generated wakes, which may be major drivers of erosion in developed coastal and estuarine regions.

In the present work, different types of resonance associated with the flexural gravity wave motion in the presence of current are discussed. Trapping is one important class of resonance and is studied in the presence of ocean current and ice compression. The existence of a resonant wave below the cutoff value is observed and analyzed in the presence of a submerged cylinder by using the multipole expansion method. It is observed that the inclusion of the ocean current enhances the search for locating the trapped waves. Trapped mode frequency increases up to the cutoff value with an increase in the current speed and, hence, ceases to exist. Therefore, the boundary value problem has a unique solution near the upper surface for higher values of the current speed. The effect of the compressive force on trapped mode behavior is also observed. It is shown numerically that trapped waves fail to exist when the group velocity is negative for specific values of the compressive force which is a very interesting result that is obtained. Significant effects of flexural rigidity, radius, and submergence depth of the cylinder on trapped waves are also observed. On the other hand, the Bragg resonance, which is used for efficient utilization of wave energy, is analyzed in the presence of current and an undulating bottom topography by using methods of perturbation and Fourier transform. The condition for Bragg resonance in the presence of current is derived in the case of a small undulating bottom topography.

In order to study the influence of friction wheel parameters and loading eccentricities on the horizontal bearing characteristics of pile-wheel hybrid foundations, the numerical calculation models of pile-wheel hybrid foundations of offshore wind turbines in heterogeneous soil were established by using ABAQUS finite-element software. The results show that with the increase of the diameter, height, density of the friction wheel and the decrease of the loading eccentricity, the horizontal bearing capacity of hybrid foundations increases. With the increase of the diameter and height of the friction wheel, the change amplitude of load gradually weakens, indicating that there is an optimal friction wheel size that could give full play to the bearing performance of the hybrid foundation. Compared with other influencing factors, the friction wheel density has less influence on the horizontal bearing capacity, pile shear force, and bending moment of hybrid foundations. The closer the position of the horizontal load is to the mud surface, the better the friction wheel can improve the bearing capacity of the pile foundation.

Wave climate studies mainly focus on the wave climatology in the open ocean. There is currently a limited understanding of trends and changes in the wave climatology of coastal waters. This study quantifies climate-induced trends in winter wind-generated wave heights in Jamaica Bay, a back-barrier bay in the western North Atlantic Ocean. A high-resolution hydrodynamic-wave model, forced by pressure and wind fields from a local weather station and the ERA5 reanalysis, is utilized to generate a 30-year (1990–2019) hindcast of wave heights. The model accuracy is evaluated using existing wave height measurements, and the bias in model results is calculated and subtracted from the simulated wave heights. The bias-corrected hindcast is then utilized to determine the wave height climatology and the trends in the mean and extreme (95th percentile) significant wave heights. The study shows that the winter mean and extreme wave heights in Jamaica Bay are 0.12 and 0.5 m, respectively. Based on the trends detected using a linear regression method, the mean and extreme wave heights, averaged in the study area, have increased, respectively, up to 1 and 3 mm/year. The rates of increase in extreme wave heights are generally larger than that in the mean wave height. A decadal trend analysis indicates that the rates of change in wave heights vary in different decades, suggesting that the wave climate change in Jamaica Bay is nonstationary. The increasing waves could cause adverse effects on salt marsh ecosystems in Jamaica Bay, which have already experienced marsh losses since the past century.

Geotextile sand containers (GSCs) gained popularity recently as a modern age coastal protection measure. Its usability as an ecofriendly alternative for traditional breakwaters overcomes issues such as scarcity and quarrying prohibition of natural rocks. The current work involves a 1:30 scaled physical experimentation on the hydraulic performance of an emerged, nonovertopping breakwater model with GSCs. Four configurations of GSC structures are analyzed for their runup, rundown, and reflection characteristics confining to wave parameters of Mangaluru. The study revealed that the reflection coefficient (K_r) for GSC structures could range from 0.26 to 0.69. In addition, reducing GSC fill percentage from 100 to 80 is found to be more effective (up to 64%) in reducing reflection, runup, and rundown rates, than altering GSC size. These results can serve as a practical guideline for designing GSC breakwaters.