Journal of Waterway, Port, Coastal, and Ocean Engineering

Bore impact on horizontal fixed decks of coastal structures is studied by use of the Level I Green–Naghdi (GN) equations and the Navier–Stokes (NS) equations. The bore is generated by the breaking of a water reservoir, and may represent the propagation of a tsunami on land or broken storm waves. The bore-induced horizontal and vertical forces are determined and their variation with the bore and deck conditions is studied in this work. Various conditions of deck location with respect to the water level are considered, including cases with the deck under or above the still-water level. Two types of bore are considered, namely (i) a bore generated by a dam break, where the reservoir water depth is substantially larger than the downstream depth, and (ii) a bore generated by an initial mound of water, where the reservoir water depth is comparable to the downstream depth. It is shown that these mechanisms result in the formation of significantly different bore shapes. It is also shown that the relative height of the reservoir and the downstream water depth play a significant role in the bore generation and its impact on coastal structures. It is also found that the bore-induced forces vary almost linearly with the change in amplitude of the reservoir, while a change in the length of the reservoir has little effect on the loads. The horizontal force on submerged decks is shown to be independent of the submergence depth of the deck; this is due to the uniform velocity distribution over the water column of the bore. Results of the GN and NS models are compared with each other for submerged cases and the limitations, accuracy, and efficiency of these models in studying this problem are discussed. Results of the GN equations are in close agreement with the NS equations, making them a computationally efficient alternative for the study of this problem.

Depth-induced breaking is the major wave transformation process in coastal waters that significantly influences the wave energy that eventually reaches the coastline. Most studies of depth-induced wave breaking focus on evaluating the wave breaking characteristics on a slope or reef in two dimensions, accounting for the reduction of water depth in the direction of wave propagation. This study investigated wave breaking on a three-dimensional submerged bar through experiments and numerical simulations. Propagation of nonbreaking and breaking waves in different water depths was studied and the energy transferred across the wavefront owing to the presence of a side slope and the nonsimultaneous breaking wavefront was analyzed. The results indicate that classification criteria that account for the local water depth can reasonably predict the type of breaking. The long period waves in the study that did not break over the structure were most affected by refraction. It was also found that the extent of the domain where a steep wave crest is seen increases from nonbreaking to spilling to plunging breaking waves. In the case of the nonbreaking waves, this steep crest propagates along the domain without breaking.

Scour holes around slender piles were measured in areas inundated during Hurricane Michael and were compared with scour hole depths estimated from existing scour prediction equations. Despite testing a wide range of feasible input parameters, some measured scour depths could not be predicted by five common scour prediction equations (one wave only, three current only, one wave and current equation). Current only equations yielded the best prediction rate despite the site being in a wave-dominated environment. The scour depths that were not accurately predicted by the equations tended to be underpredictions despite the range of input values. A range of factors were considered that might have caused these differences. Momentary liquefaction was investigated as one possible explanation to some of the discrepancies between observed and predicted scour depths using laboratory tests and field measurements. The results suggested that momentary liquefaction of the top layer of sediment is possible for wave heights of approximately 0.83 m in 1.3 m of water depth, indicating that momentary liquefaction of sediments was possible during Hurricane Michael with 2 m waves in 3.5 m of water and therefore presents one possible explanation for the observed mismatch between the scour predictions and observations.

Herein, a semianalytical model is presented for solitary wave diffraction by a surface-piercing concentric dual-arc thin wall. The two arc-shaped walls are porous and thin, and they are placed on a flat seafloor. As a key element, two imaginary closed cylindrical structures with two arc-shaped walls of different radii are introduced such that the entire computation domain can be partitioned into three subdomains, two bounded and one unbounded, based on common interfaces, within which the analytical solution is obtained using eigenfunction expression matching. Furthermore, a system of linear algebraic equations to determine the unknown coefficients is derived by satisfying the boundary and matching conditions. The numerical results obtained for the limiting cases are exactly the same as published results for a solid and porous cylindrical structure. Meanwhile, the effects of the wave incident angle, opening angle, annular spacing, and porous-effect parameter on wave loads and wave elevations are investigated. In addition, as a particular case, a concentric structure with an arc-shaped porous exterior wall is investigated as an alternative to the two-cylinder structure in practical engineering. It is discovered that the arc-shaped exterior wall can effectively reduce the wave force and wave height around the interior cylinder, compared with a single cylinder. By contrast, the wave forces and wave runup on the interior cylinder are similar to those of the interior cylinder of a concentric two-cylinder system.

Submarine landslide-generated waves have been responsible for significant damage to coastal communities worldwide. Despite this, the existing knowledge on the mechanism of the phenomenon is limited that can be partly attributed to the absence of adequate validated numerical models. In this study, we applied and validated a Computational Fluid Dynamics numerical model (FLOW3D-Hydro) and used it for investigating the sensitivity of landslide-generated waves to the variations of different parameters. This study is limited to solid-block submarine landslides moving downward at a fixed slope angle of 45°. We conducted 177 simulations applying the validated model by using three different sliding block sizes (small, medium, and large). The experiments revealed an inverse exponential relationship between maximum initial landslide amplitude and both initial submergence depth and travel distance. We observed that the dominant wave period generated by the large block was 0.7 s whereas it was 1.1 s for the small block; this unexpected result could be attributed to the relatively lower velocity of the sliding mass for the case of the smaller block.

The United States Army Corps of Engineers (USACE) maintains the Mississippi River, Baton Rouge, Louisiana, to the Gulf of Mexico Project as part of its Navigation mission to enable safe, reliable, and cost-effective marine transportation throughout the country. The entrance channel for this vast inland port system is known as Southwest Pass (SWP) and is the most highly utilized commercial deep-draft waterway in the nation. In recent years, the SWP has been prone to rapid-onset shoaling, with predictive lead times based on upstream river discharge rates of only about 14 days. The daily survey frequency in combination with the Dredging Quality Management (DQM) dredging records now available provide the framework for better understanding the dynamic shoaling conditions and the relative role of USACE dredging activity toward restoring full channel navigability.

The traditional conceptual model of freshwater-dominated estuarine hydrodynamics states that long-term average within-estuary water level is elevated over long-term average sea level at the sea inlet(s) in order to push freshwater inflows seaward. At low freshwater inflows, other factors, including nonlinear tidal propagation, can cause either setup or setdown in the average estuary water level. The Cumberland Sound estuary straddles the Georgia–Florida state line. Deepening and widening of the Cumberland Sound entrance and interior channels from 1984 through 1988 increased channel dimensions by 25%–66%. A weight of evidence approach considering analytic, physical, and numerical models’ results, plus statistical analysis of observed MTL from 1953 through 2019 leads to the conclusion that the channel enlargements reduced a pre-existing Fernandina Beach MTL setdown of up to 0.02–0.05 m.

A comprehensive case study of the coastal processes for Fortescue Inlet (New Jersey, USA) is presented with the objective of minimizing maintenance dredging of the navigational channel. This study compares the effectiveness of both traditional sedimentation control structures and modified dredging templates, including construction of a new jetty, modification of the length and orientation of an existing jetty, and the use of upland and offshore deposition basins. The alternatives were analyzed using Deflt3D Flexible Mesh. The results indicate that sediment transport near Fortescue Inlet is dominated by wave action with pronounced seasonal variations in wave direction. The site exhibits relatively shallow depths above the depth of closure and pronounced offshore bars. Consequently, much of the sediment transport occurs well offshore (approximately 300 m offshore) and beyond the existing jetty. The results indicate that structural modifications (i.e., relocation or lengthening) of the existing jetty do not improve the sedimentation rate within the channel. Instead, use of offshore deposition basins delivers the most promising improvement, with potential cost savings over 10% over existing strategies.

The mechanisms controlling sediment transport at river mouths and estuaries nearby ports are complicated interactions among waves, tidal currents, and river flows over complex bathymetry. Episodic river discharge triggered by large rainfall may contribute to significant sediment into the ocean. Over the last decade, the exposed riverine sediment from the Zhuoshui River, north of Mailiao Port, is one of the major sources of sediment supply in this region. Previous field observations shortly after the passage of a typhoon suggested fine-grained sediments settled rapidly near the river mouth, and tidal currents and strong wind-driven waves during winter were the mechanisms that transported sediment toward the navigational channel. Numerical simulations provide insights into the patterns of residual circulations for a range of spring-neap tidal forces and wave conditions. Model results show that extending North Jetty could be one of the engineering countermeasures to modify the circulation system between the port and the river mouth to mitigate the siltation problem.