Journal of Waterway, Port, Coastal, and Ocean Engineering

Video footage from the 2004 Indian Ocean and 2011 Tohoku tsunamis showed large quantities of debris entrained within the inundating flows. Such extreme debris conditions can lead to a high probability for multiple impacts on structures particularly in built-in coastal communities. In the current North American design guidelines and standards, common methods of addressing debris impact loads have focused on a single debris impacting a structure. Hence, the study presented herein examines the mechanisms and consequences of multiple debris impacting a structure simultaneously. The experiments consisted of examining several impact conditions for free-floating debris in a dam-break wave, similar to a broken tsunami wave advancing inland, and classifying each impact based on the debris configuration as well as the number of debris impacting the structure. The debris were modeled as scaled-down (1:40 scale) shipping containers. The number of debris and hydrodynamic forcing conditions were varied to investigate a wide range of impact conditions. The results of this study showed that an increase in the number of impacting debris resulted in an increase in the measured impact load. To aid in the consideration of multiple debris impact in future design standards, a methodology that would complement the framework of the single-degree-of-freedom impact model is proposed.

This paper discusses the floatation of a buried pipe in association with wave-induced liquefaction of sand beds. Centrifuge wave tests in a drum channel were performed with viscous scaling introduced such that the time-scaling laws for fluid wave propagation and consolidation of the soil were matched. The characteristics of liquefaction under irregular waves as well as regular waves were investigated. Under severe wave conditions, the loose sand beds underwent liquefaction, and the liquefied zone propagated downward in the course of wave loading. It was found that the floatation of the buried pipe was a consequence of progressive liquefaction. With the occurrence of liquefaction at a shallow soil depth, the buried pipe started moving upward and the motion of the pipe increased markedly in association with the downward progress of liquefaction during wave loading. Finally, the pipe reached the soil surface. The effects of a gravel layer replacement over a sand bed on wave-induced liquefaction and pipe floatation were also examined. A gravel cover over the sand bed with a range of 120° above the pipe prevented significant vibratory motion of the liquefied soil and floatation of the pipe.

The lateral separation ratio ($S/D$) between the twin pontoons of a floating breakwater (TPFB) is one of the prominent factors that attenuate wave energy transmission and reflection. In fact, a numerical investigation of optimum TPFB $S/D$ is inevitably required. To accommodate such a requirement, a numerical optimization model of a genetic algorithm (GA) was developed to assess the optimum $S/D$ primarily through minimizing wave transmission ($K_t$) and reflection coefficients ($K_r$) while maximizing the energy dissipation coefficient ($K_d$). Several parameters, such as wavelengths and $S/D$ ratios including a set of optimization criteria, were taken into account in the simulation, where the optimum solution was then selected from various populations. In addition to the current GA simulation, the optimum $S/D$ was evaluated and quantified by the values of $K_t$, $K_r$, and $K_d$, in which the reduction of some flow parameters was visualized via computational fluid dynamics. The results revealed that the GA simulation is effectively capable of determining global trade-offs between $K_t$, $K_r$, and $K_d$. As compared with the existing model, $K_t$ and $K_r$ decreased to less than 0.3 and 0.4, respectively, whereas $K_d$ increased up to 0.9, resulting in optimum TPFB hydrodynamic performance. Hence, the elaboration of this optimization algorithm can serve as a conceptual design to find an optimum $S/D$ for the twin pontoons of a floating breakwater.

The erosion processes of consolidated cohesive sediment under irregular breaking waves were formulated to predict the profile evolution of a cohesive sediment beach with a layer of sand. The cohesive sediment is eroded by turbulence generated by wave energy dissipation caused by wave breaking and bottom friction. Sand released from the eroded sediment is transported onshore or offshore by wave action. The cohesive sediment erosion rate is increased by a thin mobile layer of sand and decreased by a thick sand layer. The complicated interactions of waves, sand and cohesive bottom were simplified and incorporated into an existing cross-shore numerical model. The model was compared with flume experiment data with measured till erosion rates on the order of $0.05\mathrm{cm}/\mathrm{h}$. The calibrated model was used to simulate the temporal change of the till erosion rate for a duration of 100 h. The scale effect was examined in hypothetical prototype tests of the same till with a length ratio of 1/4. The prototype 200-h simulations predicted much larger till erosion near the shoreline and sand deposition in the surf zone. The model will need to be compared with actual field data.

This study demonstrates the use of a multiyear country-scale automatic identification system (AIS) data set to partition a nationwide portfolio of navigation structures managed by the US Army Corps of Engineers (USACE) into affinity groups based on emergent vessel traffic characteristics. The marine vessel AIS was originally intended to prevent the collision of ships at sea. As a remote sensing technology, it provides continuous monitoring for marine vessel traffic and has enabled a variety of unforeseen applications. The methodology presented uses spatial distance criteria to identify vessel traffic local to each structure. Metrics characterizing traffic behavior including traffic composition, spatial position, trip frequency, and traffic seasonality are derived from vessel data. AIS-derived metrics are combined into feature vectors describing each structure. Pearson correlation of feature vectors with r-neighborhood pruning of the affinity matrix is used to identify similar structure pairs. Semisynchronous label propagation is used to partition the structure portfolio graph into prototype groups with strong similarity in underlying traffic characteristics that may be further refined to align maintenance activity with organizational goals.

Due to seawater intrusion, submarine sediments and slide masses routinely evolve into fluidized mudflows during long-distance migration and seriously endanger marine engineering facilities. However, few studies of the rheological properties of mudflows have considered the low-temperature seafloor environment and natural sediment properties. Hence, a series of rheology experiments of sediment samples from the northern South China Sea were performed. The apparent viscosity and shear stress of mudflows at 0.5°C were 36.3% higher than those at 22°C. In addition, at a given temperature, the apparent viscosity and shear stress of mudflows with a 90% water content are on average 24 times greater than those of mudflows with a 151.2% water content. The internal variation mechanism of mudflow rheological behaviors was well analyzed on the basis of Brownian motion and interparticle interactions. The Herschel-Bulkley model was employed to fit the test results, and equations of the yield stress and consistency factor were established by considering the temperature. Furthermore, the relationships between rheological parameters and water content conditions are thoroughly discussed. A rheological model that considers the temperature and water content is proposed, and the results provide scientific support for the assessment of mudflow migration ranges, sediment transport, and marine engineering design.

As an essential coastal structure, a breakwater is generally designed to be stable and reliable during its lifetime. With respect to stability, failure modes usually are statistically independent. However, the interaction of different failure modes can produce extra effects for the calculation of the total cost. Considering interactions of failure modes, this paper presents an analysis and verification of an optimal design solution for rubble mound breakwaters to minimize the total cost, including construction and repair costs. The three main failure modes, overtopping, armor instability, and crown wall sliding, are involved in the solution. An auxiliary coefficient representing the extent to which the failure mode (or interaction) affects the structure was used to calculate the extra repair cost along with the failure probability in the cost optimization. The aforementioned solution was applied to a real breakwater example, and a sensitivity analysis of the total cost of the design variables was carried out. The total expected cost using the optimal design solution was 19.1% less than the cost before optimization. Other coastal structures under wave impact loads can have the same failure modes and also could be optimized by the solution. The solution in this study can provide economical design recommendations.

Harbor siltation is a problem that will exist as long as harbors exist and it is intrinsically linked to their primary function: providing shelter for anchorage and operative conditions for loading and unloading ships. In these semienclosed basins, flow characteristics are one of the main factors influencing siltation and water quality. One of the largest recreational ports of Europe, La Rochelle Marina (southwestern France), is not spared by siltation, which requires serious dredging operations during a major part of the year. In this context, a three-dimensional model has been used to investigate its hydrodynamics. Using a simplified approach, floating structures were implemented in the model. Comparison with observations has demonstrated the need to consider these structures in our study. They significantly reduce velocity in the inner parts of the marina and concentrate current on access channels. Numerical results also highlight the joint role of the macrotidal regime and wind stress in the movement of water masses and their residual circulation.

An ever-increasing need to develop coastal infrastructure as well as continuously rising coastal population calls for a rigorous assessment of coastal vulnerability in many parts of the world. This study emphasized the need to use projected climate and socioeconomic data in place of historical information to evaluate the vulnerability of a given coast. A coastal vulnerability index was determined using historical as well as projected climate and socioeconomic conditions for two periods, one in the past (1979–2017) and one in the future (2017–2052). Projected wind, wave, and shoreline changes were simulated under a moderate global warming scenario, representative concentration pathway (RCP) 4.5. The methodology was implemented for three different types of coastline, namely uninterrupted, naturally discontinuous, and artificially interrupted coastlines, located along the central west coast of India. The coastal vulnerability index was calculated with seven physical-geomorphologic and four socioeconomic indicators using an analytical hierarchical process. A comparison of the two periods showed that the vulnerability at all three coastal segments will increase in the future, calling for changed strategies by coastal ecosystem planners, stakeholders, and port authorities. The increasing vulnerability to physical and socioeconomic hazards points to adoption of a more serious approach to plan the coastal ecosystem in the future.