Journal of Waterway, Port, Coastal, and Ocean Engineering

The accumulation of large quantities of sediments in the port of Kanazawa prevents smooth navigation every year. To find the directions of the sand movement and the sedimentary sources of littoral drift of sand in the port of Kanazawa, the methods of the ratio matching and gradients of kilo count number per second per weight of each element are applied after analyzing geochemical elements in sand samples. According to the correlation numbers obtained from the ratio matching, three kinds of sediments were found near the port, two of which were found in the port. The first kind of sediment is transported by the stationary, strong ocean current, which flows along the coast from the southwest to the northeast. These advected sediments accumulate near the tip of the breakwater because of the decrease of current velocities due to the blocking effect of the breakwater. During the winter season or during storms with incident waves of high amplitude, the accumulated sediments intrude into the port. The second and third kinds of sediment are conveyed into the port along the beach by the back flows of the ocean current. The back flows are caused by the interaction of the strong ocean current with the long breakwater. The historical coastal change near the port of Kanazawa following the construction of the long breakwater is estimated using the present results.

This paper presents an experimental study investigating the relevant characteristics of the flow field induced by a regular wave acting on a uniform steep slope. Due to their uniqueness, the experimental data are of paramount importance and give a contribution toward the rational definition of wave-structure interaction. In the first part of the paper, attention is focused on the flow field characteristics, i.e., temporal and spatial behavior of surface elevation and vertical distribution of the horizontal component of the local velocity. In the second part, it is shown that the main characteristics of the velocity distributions may be represented by the variance of the distribution itself. Furthermore, it has been verified that the temporal behavior of the variance is well reproduced by a Fourier series truncated to the first three even harmonics. Relationships are presented between the coefficients of the Fourier series and some global quantities of the wave motion. Due to the relationship between the variance of velocity distribution and the momentum flux correction coefficient, the proposed second-order model allows the actual shape of the velocity profiles to be accounted for in one-dimensional numerical models describing the flow field due to the action of a wave on a steep slope.

Massachusetts Bay is a shallow (35 m average depth) semienclosed embayment, roughly 100 × 50 km, which opens into the Gulf of Maine at its eastern boundary. Surface waves associated with winter storm winds from the northeast cause large sediment resuspension events, and wave and circulation fields during these events have a quasi-steady response to the wind stress. Coupled wave, circulation, and boundary layer models indicate that wave-enhanced bottom friction has a significant damping effect on storm-driven circulation in Massachusetts Bay. The simulated response exhibits significant three-dimensional structure, but still can be fundamentally understood using idealized models. The depth-integrated momentum balance is dominated by along-bay stress, pressure gradient, and bottom stress. The effective bottom drag coefficient during typical storm conditions is increased by a factor of 2–5 when wave effects are included, but the mean bottom stress is relatively unaffected by wave effects due to a reduction in bottom currents by 30–50. The vertical mixing is also relatively unaffected by the waves, and the result is that the increased drag causes a nearly depth-independent offset of the vertical current profiles. The alongshore transport in the bay is reduced 10–50, depending on wind direction.

A time-dependent model for obliquely incident shallow-water waves with small incident angles is developed to elucidate the dispersion effects due to the vertical variations of instantaneous horizontal fluid velocities on the cross-shore variations of the wave height, setup, and longshore current in surf zones. The three equations for the cross-shore continuity, momentum, and momentum flux correction are solved numerically to predict the water depth and the cross-shore depth-averaged and near-bottom velocities. The two equations for the alongshore momentum and momentum flux correction are derived and solved to predict the alongshore depth-averaged and near-bottom velocities. The developed model is compared with laboratory and field data for planar beaches. The dispersion effects on the wave height and setup are shown to be minor. The dispersion effects on the longshore current are significant for regular waves but secondary for irregular waves. The model is also shown to predict the vertical shape of the longshore current in the surf zone but not outside the surf zone.

Analysis of the change in the spectrum of wind waves over a 5-km reach just prior to the surf zone during a major extratropical storm indicates that significant shifts in the spectral distribution of wave energy occur. For both onshore and offshore winds, the midrange of the spectrum loses up to 40% of the energy content, while the lowand high-frequency ranges have an energy gain. In the onshore case, gain in the high-frequency range dominates, and in the offshore wind case (predominant wave energy propagation is still shoreward), gain in the low-frequency region dominates.

Wave observations made during an October 1990 storm on the North Carolina coast are used to investigate the evolution of wind waves as they propagate from about 48 m to 8.5 m of water. The observations include height, period, and direction as well as frequency and directional spectra. The wave measurements are separated by 90 km with simple bathymetry. During the active wind-sea growth (winds of 25 m/s), spatial and temporal changes in the wave field indicate that a quasi-steady-state assumption is no longer valid. Later, the wave field becomes a mixture of two wave systems: swell out of the northeast and a wind-sea system from the northwest. It is concluded that even for a relatively simple storm, evaluation of the physical mechanisms and prediction require a time-dependent numerical model.

A strain-based criterion for sediment fluidization under transient pressure loading is presented. The criterion predicts that fluidization can be spontaneous, as opposed to incremental, and that it is triggered by a lowering—rather than a buildup—of the pore pressure. The criterion is examined and verified experimentally. A dam break is simulated in a laboratory flume, and a sediment bed is included in the half of the flume initially containing water. Both visual observation and extensive pressure measurements within the bed indicate the occurrence of a massive fluidization failure throughout the entire depth and length of the bed. The fluidization failure is shown to occur on an extremely short timescale. The results from several successive runs, allowing the bed to consolidate overnight between runs, demonstrate the tendency of a bed to repeatedly refluidize.

The Shore Protection Manual (SPM) method for estimating the volume rate of wave overtopping under irregular waves is reviewed and extended. This article presents an improved method of applying a monochromatic wave overtopping equation to irregular waves. The improvement is to remove an assumption made by the current SPM method. Numerical study shows that the current SPM method may underestimate overtopping rates by as much as 40% or overestimate rates by more than 100%, depending on freeboard and the ratio of significant wave runup to significant wave height. Comparing numerical results between the improved method and Monte Carlo simulations, one concludes that the improved method is analytically correct. The physical correctness of the newly developed method is examined by an empirical method that was derived directly from the overtopping experiments under irregular wave conditions.

The cross-shore variation of the local reflection coefficient R is examined under the assumptions of normally incident wind waves on beaches with alongshore uniform bathymetry. The existing three-gauge method is modified to estimate R for the sloping bottom. A new method is developed to estimate the incident and reflected root-mean-square (RMS) wave heights from the measured RMS wave height and wave setup. These methods are used to analyze six runs from the large-scale SUPERTANK data set. The estimated values of R are affected little by the formation of a bar and increase shoreward with the increased percentage of breaking waves. One set of the DELILAH field data on a barred beach is also analyzed using collocated pressure and velocity measurements. This data set confirms the negligible effect of the bar on the variation of R over the bar in the absence of wave-breaking on the bar crest. These crude estimates of R suggest that the reflected wind waves may not be negligibly small in comparison to the incident wind waves, especially inside the surf zone.

An alternative derivation of the extended refraction-diffraction equation is presented. The bottom curvature and slope-squared terms ignored in the mild-slope equation are included to account for relatively steep and rapidly undulating bathymetry. The linear elliptic partial differential equation is solved by the hybrid element method and applied to three-dimensional bedforms. Quadratic triangular elements are used in the model so that the curvature can be calculated directly from the water depth defined at the nodes. The model is illustrated by simulating wave reflection from a ripple bed and wave transformation over a circular shoal in which previous experimental and numerical results exist. The relative effects of the additional terms and their significance in the model prediction are examined in a numerical experiment.

Nonlinear responses of a submerged moored structure are investigated taking into account the presence of environment random noise. Sources of nonlinearity of the system include a quadratic Morison hydrodynamic damping and a geometrically nonlinear restoring force. The random perturbations are modeled by a white-noise process to examine their effects on nonlinear responses analytically and numerically. The analysis procedure includes a generalized Melnikov process to study response stabilities in a global sense and the Fokker-Planck equation to demonstrate response characteristics from a probabilistic perspective. Rich nonlinear phenomena including bifurcations, coexistence of attractors, and chaos are identified and demonstrated. Probability density functions solved from the Fokker-Planck equation are used to depict (co)existing response attractors on the Poincaré section and demonstrate their probabilistic properties. Noise effects on responses are shown via a generalized Melnikov criterion and the probability density function. It is found that the presence of noise may expand the chaotic domain in the parameter space and also cause transitions between coexisting responses.

As part of a study on wind effects on runup and overtopping of coastal structures, advection distances for water droplets of various sizes were measured in a wind/wave flume. The study found that advection distances were considerably greater than would be expected from wind forces acting on spherical droplets. Flattening of the windward face of water droplets from splash and spray in the presence of strong wind was found to increase the drag of droplets in this study and possibly add a lifting force, thereby increasing the distances droplets were carried. Results of this study indicate that splash and spray may be carried over a coastal structure considerably farther than may be expected, which in turn may contribute to higher overtopping rates.