Coastal Engineering Journal

The relationships between medium-term shoreline fluctuations, offshore wave energy flux and longshore current velocity were investigated on the basis of data sets from 1987 to 2001 (15 years). In this analysis, the spectral density of the data was calculated, and the frequency components from the investigated period (15 years) to 1000 days were recomposed and defined as the medium-term fluctuation. A multiple linear regression analysis was performed to evaluate the associations between the medium-term fluctuations of shoreline change rate and that of the major dependent variables, which are the offshore wave energy flux and the longshore current velocity. The results suggested that a medium-term fluctuation of the shoreline change rate at the field was affected by both the medium-term fluctuations of the offshore wave energy flux and the longshore current velocity at approximately the same rate. The fluctuation range of the medium-term shoreline fluctuation was nearly the same range of the seasonal shoreline fluctuation, i.e. approximately 20 m. This indicates that for beach management, not only seasonal shoreline fluctuation but also medium-term shoreline fluctuation is needed to be considered.

Dredging to maintain channels and berths produces large volumes of sand that need to be appropriately disposed of or used. The construction of artificial shallows and tidal flats has attracted attention as a way of effectively using dredged sand. However, there is still an issue to be resolved in that dredged sand with its fine sediments is vulnerable to wave action. In this study, the wave-induced topographic change in artificial shallows composed of fine sand was examined experimentally for bottom flow velocity on its surface and pore-water pressure on its surface layer. Experimental results showed that the relative vertical effective normal stress ratio calculated from pore-water pressure was negatively correlated with the signed Shields parameter defined as positive landward. Its relationship was unchanged despite a change in the surface profile of the shallows, implying an acceleration in seaward sediment transport and a reduction in landward sediment transport, regardless of the topographic change in the shallows. Furthermore, a signed Shields parameter modified to consider the effects of pore-water pressure gave a reasonable evaluation of the trend in the sediment transport. From these results, it was demonstrated that the effects of pore-water pressure must be considered when discussing the sediment transport.

Nonuniform vertical discretization is investigated for use with a previously developed numerical model that solves the incompressible, nonhydrostatic, Navier–Stokes equations for free surface flow. The equations are vertically transformed to the sigma coordinate system and solved in a fractional step manner in which the pressure is computed implicitly by correcting the hydrostatic flow field to be divergence free. A specific discretization is proposed to attain greater accuracy and/or minimize computational effort when compared to a uniform vertical discretization. Numerical accuracy is assessed by comparison with experimental data for spilling and plunging breakers.

This paper presents validation comparisons between field and laboratory measurements and a new probabilistic model for predicting ship underkeel clearance (UKC). Prototype ship motions and environmental data were obtained in May 1999 in the deep-draft entrance channel at Barbers Point, HI. These field measurements were reproduced in controlled laboratory studies in 2000 and 2002 with a model of the World Utility (WU) bulk carrier. These measurements constitute some of the data being used to validate the Corps's Channel Analysis and Design Evaluation Tool (CADET), a suite of programs to determine the optimum dredge depth for entrance channels. In general, the CADET predictions matched the field and laboratory measurements within cm-accuracy for wave heights that ranged from 45 cm to 75 cm.

This study presents a model which takes flocculation, sedimentation and turbulent diffusion into account, to analyze the vertical transport of cohesive fine sediment. A good agreement between simulation results and published experimental data shows the model can be used to describe vertical transport of cohesive fine sediment. We discuss the influence factors through simulation experiments. The results indicate sedimentation dominates in upper regions and later stage, flocculation plays more important role in lower regions and early stage, while the effect of turbulent diffusion is remarkable in whole region, especially in high turbulence energy dissipation rate.