Journal of Waterway, Port, Coastal, and Ocean Engineering

A new two-phase box model is developed in this study for the prediction of a spatially varying turbidity current with sediments on a horizontal bottom. The turbidity current is segmented into small subvolumes to account for the spatial variation with nonuniform spreading, while a two-phase formulation computes the differential settling of the suspended sediments inside the turbidity current, which form deposits onto the seabed. In addition, the new model is capable of simulating the transition from constant flux to fixed volume propagation, which is typical for both natural submarine landslides and engineered barged sediment disposal. The computation is terminated when most of the total sediment volume is deposited, yielding the final deposition pattern. Following the model development, a detailed experimental study was carried out in the laboratory to validate the model predictions by releasing large but finite amounts of sediments through a rectangular opening on the water surface. The agreement between the model predictions and experimental measurements was found to be satisfactory. Finally, this model is integrated into the Barged Sediments Disposal Model (BSDM) software for the assessment of open-water barged sediment disposal. A practical application of the integrated BSDM is demonstrated using a field study reported in the literature.

Probabilistic models to evaluate the vulnerability of aboveground storage tanks (ASTs) subjected to waterborne debris impacts during storm surge events are currently lacking, despite evidence of debris-induced damage during past severe storms. This paper addresses a gap in understanding the vulnerability of ASTs subjected to waterborne debris, such as shipping containers, by deriving simulation-based fragility models and an associated risk assessment framework for probabilistic performance assessment. First, finite-element models of ASTs and a shipping container are developed to perform debris impact analyses and assess the potential for damage; the shipping container model is also validated against experimental results. Parametrized fragility models are derived using a statistical sampling method, results of debris impact analyses, and logistic regression. Fragility models are derived for two damage mechanisms: inelastic damage of the tank shell and sliding. Next, this study presents a risk assessment framework to evaluate the probability of an AST being impacted by debris and to demonstrate how the derived fragility models can be employed to evaluate and mitigate the vulnerability of ASTs located in industrial areas. The framework is illustrated for a case study storage tank terminal. Insights obtained from the fragility and risk assessments reveal that large ASTs are less vulnerable than are small ASTs to debris impacts, and that neglecting debris impacts for ASTs located near potential debris sources can significantly underestimate the vulnerability of ASTs during storm surge events.

The mechanisms of fluid mud formation and its characteristics are far from clear in the deep-dredged waterway in Xiamen estuarine bay. Some experiments were conducted in the muddy estuarine bay of Xiamen when Super Typhoon Meranti, which was the strongest typhoon to have affected the area over the last 70 years, struck and after it passed. Contrary to expectation, results reveal that typhoon-induced waves are not the main hydrodynamic forcing that transport sediment. The influence of fluvial flooding and ebb tidal flow results in high concentrations (greater than 14 kg/m³) of suspended sediment in a layer near the bed, which may either deposit or be released directly into the waterway to form fluid mud. Further, new indicators are proposed, namely, river discharge and fluvial flood duration, to describe quantitatively the conditions under which fluid mud forms; it is in fact likely to form in the waterway when a discharge greater than 1,000 m³/s lasts for more than one day. The new indicators may be applied as reference by waterway administrators in their operations.

A new prediction formula is proposed to determine wave-induced pore pressure height distribution inside the core of rubble-mound breakwaters. Existing observed field and experimental data in the literature have been examined, and a valuable database has been obtained. Using dimensional analysis, a new wave damping parameter has been derived. In comparison with the existing empirical Biesel's formula, the proposed prediction formula directly takes into account the influence of the mean diameter of the core material, water depth, and important wave parameters such as incident wave height and wavelength, and there is no more necessity to assume appropriate values for the seepage coefficient and the material coefficient that are essentially needed for Biesel's formula. The new prediction formula presented here has its merits in providing an alternative form and insight into the physics of phenomena.