Coastal Engineering Journal

A huge tsunami caused by the giant earthquake occurred off Sumatra in Indonesia, on 26th December 2004, attacked the coastal regions of many countries facing the Indian Ocean. This paper describes evaluation methods of structural damage in order to mitigate the damage by huge tsunamis. First, the damage by this tsunami at Patong Beach in Phuket province of Thailand is explained. Next, diagrams to get critical inundation heights which break buildings are shown by using a rigid frame model as functions of inundation heights. Then, how to get the inundation height empirically is explained. Moreover, a numerical model to simulate the inundation height is also used, because the method described previously will give inundation heights of low accuracy as geographical feature becomes complicated. Furthermore, there were some structural collapses (a masonry wall and so on) by tsunami back-flow; the stability of a concrete wall against the back-flow is also discussed.

The influence of tidal currents is a very important factor in port planning. The normal orientation of harbor facilities is usually designed to be parallel with the main direction of tidal currents to accommodate larger-sized vessels. However, there are still many ports that do not necessarily satisfy this fundamental rule, especially in small ferry berths. This study describes the present situation of Japanese ports under strong tidal currents. First, meteorological and oceanographic parameters have been observed to understand the properties of seawater and tidal currents. This observation revealed the existence of a complicated water density environment with strong tidal currents around OK Island in Japan. To evaluate a difficulty of ferry berthing, it is essential to take ship motion into consideration. This new numerical simulator makes it possible to reproduce motions of a berthing ship in tidal currents and winds while applying maneuvering forces. With this system, ship motions can be accurately reproduced, which makes it possible to quantify berthing criteria. The analytical methods presented here could be used for the planning of ports with strong tidal currents.

For land creation regarding coastal structures, large mounds of soil, sand, and blocks are emplaced for mound formation, while accurate prediction of sedimentation deposition steps is necessary for cost reduction of construction work. In this study, high-resolution calculations using computational grids as fine as one to several tens with regard to typical block size are performed to ascertain details of flow fields around the blocks. The Smagorinsky model is introduced to investigate a turbulence field under high particle Reynolds number conditions. The deposition steps of block groups thrown into the water and the flow fields surrounding blocks that are difficult for measurements are presented in detail. Complex turbulent flow is formed in the sedimentation process and the influence of turbulence is not negligible.

This paper refers to the laboratory testing carried out on model caissons embedded in marine clay and the results of ultimate lateral loads. Ground level deflection of a caisson was measured for various embedment depth ratios (L/D) of caisson, load eccentricity ratio (e/D), and various undrained strength (s_u) of clay. At a given lateral load, the deflection levels are increased as the e/D increases and decreased as L/D, s_u, and D increases. The ground level deflection (y) and the lateral load (P) data obtained in the testing have been expressed in the rectangular hyperbolic formulation. The agreement ratio obtained by comparing the actual ultimate lateral loads with the ultimate lateral loads of transformed hyperbolic representation showed narrow variation, hardly 2–14% and the average agreement ratio is 8%. The estimated lateral loads are observed to be slightly greater than the test values. Also the test data of lateral load–ground level deflection has been further analyzed using nondimensional plots to arrive at lateral capacity of caissons. The published results of previous researchers based on the tests conducted on field prototype models were compared with the trend of the test data and these are found to be quite satisfactory.

Numerical experiments with Monte Carlo simulations have confirmed that large size samples of annual maximum (AM) wave data belong to the family of generalized extreme-value (GEV) distributions, regardless of their parent distributions of GEV, generalized Pareto (GPA), and Weibull. Evolution of the shape, scale, and location parameters of the GEV-fitted AM distribution from those of the parent distributions has been clarified. When the sample size of AM data is less than a few hundreds, however, its statistical characteristics deviate from the GEV significantly with the sample skewness taking a smaller value. The distribution best-fitting to a small size AM sample is not confined to the GEV but scattered among the GEV, GPA, and Weibull. The best-fit distribution yields negative bias of several percent of the wave heights corresponding to the return period longer than several dozen years. Empirical formulations have been derived for the coefficient of variation of the estimated return wave heights.

A high-resolution or complete bathymetric map of shallow water based on sparse point measurements (depth soundings) is often needed. One possible approach to such maps is passive remote sensing of water depth by using multispectral imagery in the popular method proposed by Lyzenga et al. [2006]; however, its application has been limited due to insufficient accuracy. To improve accuracy, we have developed 3 extensions of Lyzenga's method by addressing unrealistic optical and statistical assumptions in the method. The purpose of this paper is to compare the accuracy of Lyzenga's method, the 3 extensions, and the combination of the 3 extensions. The accuracy comparison test was performed for 2 coral reef sites by using cross validation.

The results indicated that for both sites, the extended methods were more accurate than Lyzenga's method when sufficient training data were available. The most accurate extension was the one derived by modeling the spatial autocorrelation in the error term of the regression model used in Lyzenga's method. The combination of the 3 extensions was even more accurate than the extensions.

The implementations of the extended methods are not difficult in terms of software availability and computational cost.

A set of theoretical models is deduced for computing suspended sediment concentration in coastal waters under the influence of suspension on the bottom boundary layer due to turbulent motion over full-scale sand ripples and sheet-flow, following on from the work of Jayaratne and Shibayama [2007]. Dimensional analysis and best-fit technique are the main methods for the formulation of reference concentrations and vertical distribution of diffusion coefficients of the models. Model parameters (e.g. calibration coefficients) are calibrated with the help of full-scale measured data. Time-averaged concentration profiles are derived from the steady diffusion equation. Two distinct suspension layers (i.e., lower and upper) were identified within the suspension over rippled bed, therefore predictive models were given separately for each layer. In the case of sheet-flow regime, predictive models were given for suspension and upper-sheet-flow layers. Published experimental data from 4 different data sources in the SANTOSS database (75 and 80 full-scale experiments for rippled bed and sheet-flow regimes respectively) from 1994 to 2007 [Van der Werf et al., 2009] are better explained by the proposed formulae, however different sets of calibration coefficients were assigned in each data set primarily due to the flow type (regular or irregular flows) and nature of the laboratory experiments (wave flume and wave tunnel).

Some harbors constructed on sandy shore have interrupted littoral drift, resulting in updrift beach accretion, siltation in navigation channel, or downdrift erosion. Conventional harbor design procedures have focused on water tranquility in the basin and prevention of sediment into the harbor, using scaled hydraulic experiments or numerical modeling which could not precisely determine the effect of breakwater orientation and its tip on adjacent beaches. After having discussed a wide range of field cases of harbors in Japan, Korea, and Taiwan, this paper then demonstrates the potential of a quantitative approach based on the static bay beach concept for mitigating the impact of harbors on sandy beaches. With this alternative, the most preferred location of a breakwater tip to minimize the adverse effect on adjacent shorelines can be readily devised with a freeware MEPBAY on a computer screen. This approach could benefit the work of experimentalists and numerical modelers on planning a new harbor or improving an existing one in many countries.

The Bragg scattering of water waves by multiply composite artificial bars was investigated both theoretically and experimentally. Miles' theory is first employed to derive general formulae to calculate Bragg reflection coefficients for multiply composite artificial bars with different shapes, spacings, bar heights, bar footprint, and the number of bars. The theory provides explicit expressions in estimating Bragg reflections over multiply composite bars in practical engineering applications. The undulating oscillation components expanded with respect to the bottom slope and curvature components in the numerical model can increase the accuracy for the simulation of Bragg scattering. Experiments of Bragg reflection over multiply rectangular artificial bars were also conducted in a wave flume. Analytical solutions are in good agreement with numerical simulations of evolution equation of mild-slope equation (EEMSE) and laboratory experiments. Influence parameters that may lead to the optimal combination of a multiple artificial bar to increase the bandwidth of Bragg resonance were studied.

A novel imaging technique for identifying the locations of free-surface shapes was applied to three-dimensional hydraulic tests of coastal structures. Three-dimensional wave fields, consisting of superposed local reflected and diffracted waves, were measured around a breakwater and the mouth of a model harbor in a laboratory wave basin, and the results are consistent with the predictions of a Boussinesq-type equation model. The new technique was applied to surf zone waves to describe the organized deformation of breaking wave faces that evolve during wave propagation. Typical finger-shaped jets form in the wake of plunging jets, and a local depression trails behind a breaking wave front.

According to Goda [2011], the annual maximum series data of extreme statistics yields inherent negative bias in quantile estimates owing to decrease in the skewness of small samples. Small sample derived from asymmetric distributions are examined for their skewness through simple calculation and numerical experiments with Monte Carlo simulations. For the distribution functions of algebraic, Weibull, and generalized Pareto (GPA) types tested, the sample skewness is confirmed to monotonically decrease as the sample size becomes small. It is found that the decrease of skewness is associated with a decrease of the expected value of the largest data in a sample with lessening of its size.