Coastal Engineering Journal

An experimental study was performed to examine multiple debris entrainment and transport in tsunami-like flow conditions. The study was performed in the Tsunami Wave Basin at Waseda University. The wave basin used a falling-head driven elongated solitary wave that broke at the edge of a horizontal apron to generate a tsunami-like surge. The debris, modeled as scaled-down (1:40 length scale) 20-foot standard shipping containers, was placed on the horizontal apron. The debris was tracked using a camera-based object tracking algorithm. The study examined the effect of the debris configuration, the number of debris, and orientation of debris on the entrainment and transport within the inundating surge. In examining the transport of multiple debris, the debris tended to be transported within the surge as an agglomeration. Using a previously derived model of debris transport, the study determined experimentally derived coefficients to explain the difference in debris transport between various configurations.

According to the main recommendations and technical criteria along the world, the design project of a breakwater must address the verification of the different failure modes that can affect the breakwater stability. This research focuses on the estimation of the statistical characteristics of the wind waves interacting with different breakwater types and their evolution from the toe of the structure to the toe of the crown. This knowledge is essential to calculate the reliability of the structure in its useful life. Partial standing wave patterns are likely to occur in front and along the section of the breakwater depending on their typology. Based on Rice’s theory of envelope amplitude, we present an approximate solution of the total wave height distribution in front of the breakwater. The experimental results in 2D confirmed that the incident, the reflected and the total wave height in front of the breakwater followed a Rayleigh distribution in which the parameter is the root-mean-square total wave height. Its value depends on the modulus and phase of the reflection coefficient. The probability density function of the total wave height evolves from a Rayleigh to a Weibull distribution, whose scale and shape parameters vary from the toe to the crown of the structure, and depend on the breakwater type, the relative grain diameter, and the relative water depth. The largest deviation from the Rayleigh distribution occurs at the toe of the crown. These findings are weakly dependent on the incident wave steepness, and are valid for narrow-banded incident wave trains, impinging perpendicularly on nonovertopped breakwaters with a steep frontface, which ensures the rapid evolution of the wave train. Then, each mode of failure that might occur in the breakwater section can be formally checked against the same incident wave height, but verified (calculated) with the actual wave height, locally transformed by the specific typology.

Previous studies have applied various methods to analyze the wave runup on fixed columns, including linear and higher order diffraction theories and semi-empirical correlations. However, none of them seems to be adequate to accurately predict the wave runup over a full range of wave steepness and cylinder sizes when further compared with experimental data from the literature. The focus of this study is on a better semi-empirical formula for wave runup on a circular cylinder. We: (i) report on a set of experimental results obtained for a circular cylinder with various diameters in regular waves; (ii) evaluate the performance of existing theories or empirical equations using a full data set comprising new experimental results and results reported in the literature; and (iii) propose a new equation for predicting the wave runup on a fixed circular cylinder in regular waves. The proposed semi-empirical equation considers both the effects of wave scattering and wave nonlinearity and is able to estimate the runup of regular waves on a circular cylinder with significantly improved accuracy when tested with the full experimental data set.

This study proposes a safety evaluation process for a prevention structure against tsunamis, in which the most updated guideline (i.e. FEMA P-646) is used as the deterministic analysis and a probabilistic approach is adopted to consider uncertainties involved. To overcome the incomplete data on Tsunamis, a Markov chain Monte Carlo (MCMC) simulation is developed to increase the quantity of historical data from Taiwan followed by the use of the least squares support vector machine (LS-SVM) to estimate the probability density function (PDF) of random variables. Based on the fragility analyses of the superstructure, substructure and entire system, if the wall thickness is below 4.45m, the wall thickness is more likely to be the governing factor compared with the pile diameter. Conversely, the pile diameter would more likely be the dominating factor. When the pile size decreases from 75cm to 65cm, the threshold value will shift from 4.45m to 3.85m. In addition, when the wall thickness and height are greater, there is a greater likelihood of the failure probability being governed by the substructure. Based on historical records only, the probability of failure of the seawall is extremely low. Nevertheless, results shown here are in line with the engineering judgement and the computation procedure established in the present study can be used as a reference for performing safety analysis on tsunami structures with insufficient data.

The proposed formula for modeling sedimentation is based on a concept of hydrodynamic equilibrium in sediment transport. Hydrodynamic equilibrium occurs when the sediment transport is in a form of grain jumps with the distance traveled $dx$ smaller than the one established in the numerical modeling. A first-order upwind scheme FDM is applied. It provides the solution to equations describing changes in bathymetry in time and space coupled with simultaneous changes of bed sediment distribution. A clear-cut division of sediment transport into those during wave crest and wave trough is proposed. The results of bathymetry modeling coincided satisfactorily with the laboratory data. Moreover, the longer the experiments run, the more the results of measurements are compliant with the calculations. A certain time is needed for sediment transport to reach the hydrodynamic equilibrium, especially when the suspended load is significant. It is reached after going through the initial stages of bed level changes coupled with simultaneous changes of grain size distribution. The application of the model to field conditions shows its ability to predict sedimentation of dredged channels. Furthermore, the calculations show a good agreement with measured bed grain size distributions of sediment samples taken from the sites within the navigational channel of Łeba Port in Poland.

Hamanako is an economically and culturally important tidal lake on the Pacific coast of Honshu, Japan. Between 1954 and 1973, entrance works were constructed to regulate the channel to the lake. In a previous paper, the tidal records from Maisaka just inside the lake, prior to regulation, were analyzed to explain the responses of the lake to the ocean tide and other water level changes. The present paper compares water level responses with those following regulation of the entrance. The principal differences are that at Maisaka the tidal range increased up to 1965, following the first stages of regulation, but it has been constant since then. In the inner part of the lake, regulation has increased the tidal range but reduced its variability and has reduced the mean water level in the lake. The southern sand shoal divides the lake into two tidal basins, with Maisaka lying in the smaller outer basin. Studies of the inner basin have shown that its tidal range continues to increase. A hydrodynamic model has been used to show that this increase is primarily due to scouring of the inner channel through the southern shoal. The model has also shown that the constancy of the Maisaka tidal amplitude since 1965 is not a static equilibrium, but is a balance between the effects of the outer entrance channel scouring and increasing the Maisaka tide, offset by the inner channel scouring and reducing the Maisaka tide.

The forces and loading resulting from shallow water breaking waves are one of the most important drivers in coastal engineering design and morphological change. The importance of accurately and precisely predicting breaking wave conditions cannot be overstated. Using a novel dataset of laboratory and field scale breaking wave conditions, this study assesses the performance of widely applied empirical relationships for breaking waves and uses newly available artificial neural networks and gene expression programming (GEP) numerical methods to develop an accurate and easily applied predictor of breaking conditions for coastal engineers and planners. A novel GEP model is developed and shown to: provide excellent predictive ability at all scales, greatly improve prediction compared with previous works at laboratory scale, and clearly identify the relevant importance of seafloor slope and the water depth to wavelength ratio.