Coastal Engineering Journal

The rate of sediment pickup for suspension by breaking waves is shown to be proportional to the dissipation rate of wave energy flux within the surf zone. A database of mean concentration of suspended sediment has been compiled by collecting various data of field measurements and large-scale laboratory tests and by calculating the depth-averaged mean concentration. The wave energy flux dissipation rate is computed with the PEGBIS model for random wave breaking on beaches of arbitrary profile. By comparing the mean sediment concentration and the energy flux dissipation rate, a sediment pickup coefficient is assessed at a value of 0.0045 on the average. Use of this coefficient makes it possible to estimate the cross-shore variation of mean sediment concentration. Peak values of mean sediment concentration within measured cross-shore profiles agree well with the prediction based on the wave energy flux dissipation rate.

Extensive laboratory experiments were carried out to investigate the efficiency of low (vertical) crown-walls on the reduction of wave overtopping on sea-dikes. It is shown that the reduction of wave overtopping discharge by crown-walls is inadequately described in the TAW-2002 guidelines. A new approach for the wall influence has therefore been developed, explicitly taking into account both the wall height and the promenade width. The approach can straightforwardly be incorporated in the original formulations of TAW-2002 to significantly improve the prediction of wave overtopping on sea-dikes crowned with this type of walls.

The nonlinear shallow water equations and Boussinesq equations have been widely used for analyzing the solitary wave runup phenomenon. In order to quantitatively assess the merits and limitations of these two approaches, a shock-capturing scheme has been applied to numerically solve both sets of equations for predicting the runup processes over plane beaches. The analytical and experimental data available in the literature have been used as references in the assessment. In this study, the uniform sloping beach is preceded by a length of flat seafloor. When incident solitary waves are specified close to the slope, the two approaches are found to produce almost identical results for nonbreaking waves. For breaking waves, the Boussinesq equations give a better representation of the wave evolution prior to the breaking point, whereas they overestimate the short undulations accompanying the breaking process. If incoming solitary waves need to travel a long distance over a flat bed before reaching the slope, the shallow water equations cannot capture the correct waveform transformation, and the predicted runup depends heavily on the length of the flat-bed section. As this length approaches zero, however, the shallow water equations somehow give roughly the same maximum runup heights as those predicted by the Boussinesq model. The bed friction has little effect on the runup for small waves, but becomes important for large waves. The roughness coefficient needs to be calibrated to reproduce the measured runup heights of breaking waves.

Estimating the settling velocity of organic settling matter (OSM) under the effects of organic properties is necessary for developing a pelagic-benthic coupled ecosystem model to evaluate the coastal environment, where OSM deposits on the sea bottom. In this study, laboratory experiments were performed with several materials, such as bentonite, OSM and suspended matter, using a particle distribution analyzer to reveal the effects of organic properties on the settling factors (e.g. effective density, fractal dimension). From the experimental results, it was found that the effective density of each material decreased in association with the increase in particle size from a certain size. Comparing these results to the organic properties of materials, it is evident that the organic properties, such as the absorption amount and the decomposition degree of organic matter, strongly affect the physical properties, such as the fractal dimension and the effective density. Furthermore, a model formula of the settling velocity, in which the effects of the organic properties are considered, has been suggested.

The 2010 Chile tsunami had different effects along the Chilean coast. Seawater surged hundred meters into many rivers, though field surveys showed that the 2 km wide Biobio River did not experience any flooding. In a similar manner, the coastal zones south of the river had an inundation height of less than 2 m. To ascertain why these areas were not greatly affected by the event, the behavior of tsunami waves propagating over a submarine canyon was investigated by means of numerical simulations over a simplified and idealized bathymetry. The main variables which define the size of the canyon were varied, and three different tsunami wave lengths were tested. The results show that submarine canyons have a strong influence on tsunami propagation and run-up such that there is a spatial variation of wave amplitude along the coast and this behavior is very sensitive to the canyon size. The run-up directly behind the canyon is lower than in the case without the canyon, while there are zones of wave amplification at both sides of the canyon. These idealized results compare well with what happened during the 2010 Chile tsunami, and provide a useful insight into the behavior of tsunamis around other submarine canyons in other regions of the world.