Asian and Pacific Coasts 2003

PREFACE.

CONTENTS.

This paper presents an overview for the current status of the impacts studies on climate change and sea-level rise focusing on the Asia and Pacific region. International research efforts such as IPCC have revealed the past trend of global warming and its future. Based on these estimates, climate change and sea-level rise could impose a wide range of impacts on the coastal zones; some of the typical impacts shown here are coastal erosion, increased flood risk, and impacts on infrastructure. A region-wide vulnerability assessment for the Asia and Pacific region is also introduced. The assessment consists of three steps; setting scenarios for sea-level rise and other external forces, assessing primary impacts in the coastal zones such as inundated and flooded areas, and assessing secondary impacts on natural and socioeconomic systems. The spatial distribution of affected areas and population are estimated using global databases. Low-lying areas in the region such as deltas of Mekong River, Ganges and Brahmaputra Rivers, and Yangtze River, and islands in the Pacific are most seriously inundated. The estimated amounts of inundated/flooded areas and population are quite large, indicating that the Asia and Pacific region is very vulnerable to sea-level rise and climate change. Lastly, countermeasures against these adverse effects will be examined as adaptation. Through such introduction, this paper tries to indicate new challenges to coastal science and engineering which are raised by climate change and sea-level rise.

In the 1983 Nihonkai-Chubu Earthquake tsunami causing serious damage including 100 casualties around Japan Sea, soliton-disintegrated wave was remarkably observed in shallow water, which amplifies by the waveform curvature, dispersion, effect more than a normal tsunami. Since a former numerical model widely used for a tsunami model excludes such an effect, soliton-disintegrated waves typed tsunami can not be simulated well. In this study, a new tsunami numerical simulation with Boussinesq-type equations is introduced for generation, propagation in deep and shallow water, and is applied to the 1983 Nihonkai-Chubu earthquake in order to discuss its applicability.

A tsunami generated by landslide is less studied than the more frequent tsunami generated by fault motion. From historical reports, it is clear that landslide-induced tsunamis killed many people and caused serious damage; about 1,500 casualties in the 1741 Oshima-oshima tsunami and 15,000 in the 1792 Ariake tsunami. This type of a tsunami can result in significant local wave amplification, energy concentration and/or radiation. A strong ground motion, failure of slope, volcanic activity and great societal impact, can trigger landslide-induced tsunami. The mechanisms of tsunami through hydraulic experiments and numerical simulation have been studied. For example Imamura and Lee (1998) and Matsumoto et al. (1998) proposed the two-layer model for interaction between landslide and tsunami, and computed the tsunami generation by using the numerical model to reproduce the historical tsunami in 1741([1] and [2]). Hermann et al. (2001) carried out the hydraulic experiment supposed rockslide impact of the Lituya bay tsunami in 1958, [3]. However, the mechanism of tsunami generation has not been clarified and modeled, since the physical mechanism when the sediment rushes into the water is still unknown and there are few examples of experimental researcidanalysis on the interaction between debris flow and tsunami. In this study, we carried out the hydraulic experiments in sloping one-dimensional open channels with the high-speed video camera and water gauges in order to measure the detail process and sequence of landslide motion and the generation of the tsunami by rushing into water and have clarified some processes of tsunami generation by landslides. Moreover, using the numerical model of two-layers with three kinds of shear stress, the tsunami by landslide try to be simulated and compared with the result from the hydraulic experiment.

The artificial coastal barriers such as seawalls and break waves have been constructed in Japan and have played an important role in protecting the city and coastal area from natural hazards such as tsunamis, tidal waves, high waves. However, the artificial coastal barriers need high cost of the construction and maintenance, change the present environment and have forced inconvenient to use the coastal area. Therefore, the countermeasures against tsunamis by using the artificial coastal barriers are not recommended for all coastal areas. It is required that a new countermeasures corresponding to every area is considering with the combination with artificial and natural functions for more appropriate management for natural disaster reduction and keeping good environment. One of a new way is to utilize a control forest along coast. However, the quantitative and concrete functions of coastal forest to reduce tsunamis are not established and formulated, so that no guidance to use control forest is available. Additionally, in order to take the countermeasures for the mitigation of tsunami damage, it is necessary to predict the situation at the time of a tsunami attack, which considering with tsunami control forest and other coastal structures. In order to use a coastal control forest positively and effectively as countermeasures against tsunamis, it is important to evaluate the hydrodynamic effect of tsunami control forest, and to clarify a disaster prevention function further. The present paper aims to provide the concrete functions of tsunami disaster prevention by control forest from old tsunami reports and other studies, and the quantitative guidance of tsunami reduction effect from numerical simulation including the resistance of tsunami control forest.

The re-examination of the 1983 tsunami in Korea especially at Imwon Port was carried out by Hong and Imamura (2002). Although they have good agreement with the measured, the low accuracy of the simulation for run-up is found at 3 locations with the complex land-use and geometry. One of the reasons is considered to be related with the run-up simulation on the land with houses, building and so on. From those results, we need the advanced model for run-up on a complex land-use to represent appropriate friction coefficient of the bottom. In recent years, the Equivalent Roughness Model (ER-model) based on shallow water theory, which is utilized to obtain appropriate friction coefficient at the bottom following the percentage of the structures, is proposed by Aburaya and Imamura (2002). However, the quantitative verification about the ER-model has not thoroughly been clarified yet. Therefore, in this study, the accuracy of ER-model is studied through comparing with measured data, and its applicability is also discussed.

In February 2002, Jakarta experienced one of the most severe floods in history, which caused widespread damage and affected more than 75% of the total population of the city. Duration of the flood was from the end of January to the beginning of February 2002. Jakarta City is frequently affected by floods; a third of northern Jakarta is flooded on average twice a year…

Predicting 3-D nearshore current in wide area is important to management for the coastal sand and the water-quality in coastal area. We need a 3-D nearshore current model being able to predict efficiently and accurately in shallow coastal and deep offshore area. Nobuoka et al. (1998) have shown that the driving force of 3-D nearshore currents is the vertical distribution of radiation stress, and have developed the time-mean current model based on this principle. However, using the level method of the Cartesian coordinates, this model was not practical, i.e., the vertical distribution of the current can not be predicted sufficiently in a shallow region, a simulating CPU time is very long because grid points increase as a water depth becomes deep. If the sigma coordinate is used in the model, an equal number of grid points can be set in shallow coastal and deep offshore areas…

A riverine-type mangrove (R-type mangal), which is observed in most mangrove forests in Japan, is composed of meandering creeks and fringing mangrove swamps with a densely vegetated mangrove trees and roots. The ratio of the swamp area to the creek area appears to be typically of order 2-10 and then the horizontal scale of the swamp is quite different with that of the creek. To accurately predict water environments and sedimentary processes in a R-type mangal, it is desirable to conduct current simulations in which the morphological feature of R-type mangals as mentioned above are taken into consideration. For this purpose, it may be expected to employ a nesting procedure, in which the computational results in a larger-scale domain are successively reflected on a smaller-scale computation. From these reasons, in the present study, we have attempted to apply a nesting procedure to the highly-resolved current simulation in Fukido River estuary, one of typical R-type mangals, located in the north-west part in Ishigaki Island, Okinawa, Japan.

The wave conditions in the water aera of Yangtze River Estuary are of significance for the design of deep-water channel regulated works for Yangtze Estuary (Fig 1). The regulated structures of the works are laid out in very large scope of the sea area. The wave parameter of the structure must be defined through analysis and calculation depending on the observed information. The parabolic approximation of mild-slope equation is one of the most useful methods in simulating the wave transformation for wave refraction and diffraction. In our research some key parameters are discussed of how to define the friction coefficient, how to use the measuring data, and how the structures influence the propagation of the wave…

Taiwan situates right on the rim of the Asia Continental Shelf. A typical profile of the shelf bathymetry around the coast of Taiwan is shown as Figure 1. Due to the topographical effect of the shelf (Lin, et al., 2001), the oscillation patterns of a partially standing tides appeared in the Taiwan Strait are investigated firstly by using the theory of co-oscillation, Figure 2. To further identify the oscillation patterns, a two-dimensional depth-averaged shallow water wave model: MIKE21_HD, developed by Danish Hydraulic Institute (DHI, 1996), is applied to compute the regional tidal characteristics (Juang, et al., 2001). By extracting the computed variations of water surface elevation from sections along the coast of China and around Taiwan, Figure 3, the visualizations of tides oscillating in the Taiwan Strait are finally produced as animations and shown statically as Figures 4 and 5, respectively. From Figure 4 of the tidal oscillation along the coast of China, one can visualize a Kelvin wave equipped with nearly constant amplitude propagating from north to south, and accompanied with a partially standing tides oscillating adjacent to the southern end. From Figure 5 of the tidal oscillation around the coast of Taiwan, it is easily to identify that a partially standing tides oscillating on a topographical shelf with the anti-node appeared almost at the central part of the shelf and the nodes located adjacent to the rims. With the aids of the visualizations associated with the animations, the oscillation appearances as well as the characteristics of tides in the Taiwan Strait are illustrated completely…

If the extraordinary sea-level rising caused by strong wind or sudden change of air pressure meets the high water of astronomical spring tides, the interaction of the two will probably result in the sudden and sharp rising of water level as well as some damages such as dams, lands, ports and villages being flooded. This kind of damage is usually called damages caused by storm surge. Chinese coastal areas, especially the areas south to the River Changjiang’s Mouth in East China Sea, are one of the high frequency storm surge occurrence areas in the world. Because the water of our offshore areas is often relatively shallow, when the strong wind power of typhoon acts on sea surface, the water body will be fully mixed vertically and be transported horizontally in a great extension. Therefore it can be assumed that the upper and lower layers of seawater are symmetrical so that it is proper to adopt the depth-concerned integral 2-D overall storm surge numerical model…

As waves enter into open shallow water, shoaling and refraction occur due to water depth variations. The presence of various currents in the ocean makes wave motion much more complicated. Isobe (1994) considered variation method to derive a set of equations, which can be simplified to different physical equations according different water depth distributions; however, he did not include the current effects. In this paper, we consider a much more realistic problem, which includes wave condition and current effects simultaneously. A set of governing equations was derived based on dynamic boundary condition with the method of calculus of variation, that the order of current velocity is much smaller than the order of wave phase velocity and group velocity, i.e.O(|U|²/CC_g)<<1…

In view of practical concerns for pollutants, oil spill dispersal, search and rescue operations at sea, and navigation, demands for accurate tidal predictions in both time and space are increasing. The current tide prediction system for regional seas neighboring to Korean peninsula comprised of the modeling systems with finite element mesh based model, addresses the necessity of resolving the detailed estuarine and continental shelf tidal system and timely prediction for operational forecast. Design strategy of predictive modeling system is to provide accurate water level prediction including tidal prediction and meteorologically induced surge prediction. To meet this requirement, fine-resolution relocatable FEM based model is developed during recent years and presented in this paper. Application of the modeling system for estimating the effects on tides due to construction of barriers at Saemangeum area, west coast of Korea and Isahaya Bay in the Ariake Sea, Japan are described Some of results showing the changes in tidal regime including the detailed flow patterns and variations in drying-boundaries are presented and discussions are also make for further modeling studies.

Breaking waves are dominant phenomena in the surf zone. However long waves with periods of a few minutes may be more important near the shoreline, as the wave steepness of the long waves is too small to break…

The bottom shear stress estimation under saw-tooth wave is the crucial step, which is required as an input to most of sediment transport model under rapid acceleration and the relative contribution of pre-suspended sediment to the onshore sediment transport in swash zone. Suntoyo et al. (2002) had shown that the bottom shear stress variation under saw-tooth wave was dependent on high acceleration and deceleration. However, investigation of a more reliable estimation method to estimate the time-variation bottom shear stress under saw-tooth wave over rough bed has not deeply done yet. Turbulent bottom boundary layer flow under saw-tooth wave is investigated with the experiments in oscillating wind tunnel over rough bed by Laser Doppler Velocimeter (LDV) to measure velocity distribution. Bottom shear stress will be estimated by fitting the logarithmic velocity profile to the measured velocity. Furthermore, the experimental results will be examined with the bottom shear stress estimation method based on both the consideration of the friction coefficient for sinusoidal wave motion and that of the acceleration effect for saw-tooth wave…

The Boussinesq equations have been developed as one of the most useful mathematical models for coastal hydrodynamics in the last decade. The distinguished work by Madsen and his colleagues (e.g., Masen et al, 1991) and by Nowgu (1993) extended the classical Boussinesq equations (Peregrine, 1967) to be valid beyond the deepwater limit of water waves. Enhancements by other researchers further generalized the applicability of the mathematical model to various coastal hydrodynamic phenomena including wave breaking (e.g., Madsen et al., 1997, Skotner, 1999). When compared with the extensive efforts in the development of the Boussinesq equation theory, study on the numerical method, however, does not seem to have been enough. The present paper is to present a high-resolution numerical scheme for accurate solution of the Boussinesq equations…

The ability to predict wave transformation from deep to shallow water accurately is vital to the numerical models of water wave in coastal waters. During the wave transformation, shoaling is one of the most important processes on the changing of wave profile in intermediate and shallow water zone. In the estuary, wave-current interaction will change the wave significantly as well. The moving shorelines generate complicated wave phenomena on beaches. It is our common interest to develop an integrated mathematical model for simulation of all these water wave processes. In the present work, some aspects mentioned above are discussed in the scope of the higher order Boussinesq equations…

A Boussinesq equation is practical depth-averaged flow model. The original one, however, has some problems, for example, the dispersion relation of water waves does not agree with the Airy waves theory in high wave number range…

In the prediction of shallow water tidal current field, numerical method becomes the most effective tool. As a practical numerical model, the governing equations used in the model should be as more general as possible to cover various practical engineering situations under the limit of computational capacity. The numerical method should also be good in terms of numerical effectiveness, accuracy and flexibility to various boundary shape. Verification of the model by field data is essential. Although quite a lot of research work has been carried out on the development of numerical shallow water flow model, our purpose is to use the most effective numerical method to solve the quasi-3d shallow water equations to establish a practical numerical model…

Since the mild-slope equation was originally derived by Berkhoff [1], various numerical models have been developed to solve it, see [8]. However, an analytic solution is very difficult to obtain although the mild-slope equation is only a simple linear equation. Up to date, only a few analytic solutions have been obtained in two limiting cases, i.e., for long waves and short waves. Examples include the solution of the Helmholtz equation for a cylindrical island standing in an open ocean with constant water depth [4], solutions of the linear shallow-water equation for a circular cylinder mounted on a parabolic or conical shoal [2, 5, 7] and the solution of the linear shallow-water equation for a conical island [6]…

The evolution of free-surface waves due to a suddenly stopping body submerged in an incompressible fluid of infinite depth is analytically investigated. The body is assumed to stop suddenly from a steady translational motion. In order to investigate the effect of viscosity on the evolution of waves, the linearized Oseen equations are employed for the disturbed flow. The kinematic and dynamic boundary conditions are linearized for small-amplitude waves, and the initial values of the flow are taken to be those of the corresponding steady-state solutions. By means of integral transforms, exact solutions for the transient waves are obtained. The asymptotic representations for the far-field transient waves are derived by applying Lighthill’s two-stage scheme. The results show that although the inviscid waves will keep their profiles due to the conservation of energy, the viscous waves will eventually die out due to the presence of viscosity, which is consistent with the physical reality. The energy dissipation rates for the viscous ship waves are analytically expressed and the evolution of the transient viscous waves is explicitly shown…

Methods for wave height and direction measurements vary throughout the world, depending on wave climate and local traditions. In Japan, bottom mounted systems have long been the standard for coastal areas (water depth less than 50m ) and extensive studies in the 80s and 90s refined their systems to a level where the full wave directional spectrum could be measured. These systems take a multi-parameter approach to the problem by taking into account both pressure fluctuation, orbital particle velocity, and surface elevation to generate a spectrum that covers the full range from 1 second wind waves to 1000 seconds Tsunami. In this study, we are looking at the results from 3 different bottom mounted systems, all using acoustic techniques in combination with pressure. The detailed implementation is different in each system and the purpose is to analyze how the differences impact the characteristics of the wave spectrum…

When a wind speed is higher than 3 m/s, it is well known that numerous streaks nearly parallel to the wind direction sometimes appear on the sea surface of lakes, open oceans and coastal area Langmuir (1938) showed that these streaks are the visible manifestations of a parallel series of counter-rotating vortices developing below the surface with axes nearly parallel to the wind. Today this kind of flow pattern is well known as Langmuir cells or circulations LCs). They play an important role in the study of coastal process such as collection of plankton, generation of blue tide in Tokyo Bay, and so on…

A number of random wave propagation models which can be classified into the mild-slope equation model, have been developed. The models of Kubo et al. (1992) and Lee et al. (2001) were developed by using the Taylor series expansion technique, while the models of Radder and Dingemans (1985) and Suh et al. (1998) were developed by using the Hamiltonian theory of surface waves. In the numerical models for wave propagation, the incident waves along the open boundary should be specified. Recently, for the Boussinesq wave model, Wei et al. (1999) developed a source function method, which can be used for arbitrary grid systems. In this study, we derive two source functions by applying the method of Wei et al. to the mild–slope equation models for random waves: One is for Kubo et al.'s (1992) and Lee et al.'s (2001) models, and the other is for Radder and Dingemans' (1985) and Suh et al.'s (1997) models…

The Smoothed Particle Hydrodynamics (SPH) method, coupled with a Large Eddy Simulation (LES) sub-particle scale turbulence model, is proposed to simulate wave overtopping a curtain breakwater. The SPH model solves the Navier-Stokes (N-S) equations by Lagrangian approaches and no grid is needed in the computations. Thus free surfaces can be easily and accurately tracked by particles without numerical diffusion. Classical SPH kernel functions are reviewed and the N-S equation solver is developed based on a semi-implicit algorithm of pressure projection. The accuracy of the SPH model is validated through available data from a wave flume experiment conducted in the Kansai Electric Power Incorporation. The agreement between experimental and numerical wave profiles is quite satisfactory. The efficiency of the incorporated LES model is further demonstrated by the computed velocity and turbulence eddy viscosity distributions of the overtopping flow. The findings in the paper will provide a good understanding on wave mechanics in coastal areas…

One of the key factors of computation of wave breaking is the improvement of water surface tracking. The Lagrangian particle method has the advantage in the description of complicated behavior of water surface including a splashing, over the Eulerian grid-base models. Another significant factor of wave breaking is a turbulence. To describe a turbulence, being in the same way as the SGS(=Sub-Grid-Scale) model of turbulence, such as the LES in Eulerian approaches, the SPS(=Sub-Particle-Scale) model is required in the particle method. The analysis of wave breaking by the particle method has just begun, hence there is no studies of numerical simulation by the particle method with the SPS-turbulence model. In this study, the SPSturbulence model, which had been proposed by the authors, is applied to the wave breaking on the uniform slope…

When obliquely incident waves with a small incident angle reflect h m a vertical wall, a wave propagating along the wall (Mach–stem) can be generated. Such a reflection pattem is called as Mach–reflection. Many researchers have investigated the characteristics of Mach–stem waves experimentally and numerically. To evaluate wave overtopping and the stability of wave dissipating blocks, the influence of Mach–stem waves is significant. There is possibility that Mach–stem neglected at the conventional design is relevant to the damage of coastal structure…

This paper will present the development of models for predictions of near-shore wave characteristics and the evolution of surface rollers. The wave model is based on the concept of an equivalent linear wave, but nonlinear wave characteristics may also be reconstructed from the prediction of the equivalent linear wave characteristics. The surface roller model is based on the energy conservation equation which is ideally consistent with the proposed breaking wave energy dissipation model. Because both models are based on simple energy conservation equations, the entire model retains flexibility and computational efficiency for practical applications. The waves may be periodic or narrow-banded random waves, the beach profile may be plane, barred, or movable bed with natural sand grains. Model predictions are compared and show excellent agreement with experimental observations…

A three-dimensional σ-coordinate LES model is proposed to simulate hydrodynamic behavior of free surface turbulent flows with vegetation. Vegetation is considered as an internal source of resistant force and a phenomenon model is employed to express the performance of vegetation in the flows. The model is modified from the σ-coordinate LES model developed by Lin and Li (2002, International Journal for Numerical Methods in Fluids, Vol 38, Page 1045-1068). The governing equations of the modified model include additional terms for drag force produced by vegetation and the modified model is distinctive in that not only compound channel flow can be solved but also wave motion through vegetation in coastal region can be taken into account. An operator splitting method, which splits the solution procedure into advection, diffusion and pressure correction steps, is employed so that different numerical schemes can be used for the solution of different physical processes. The model has firstly been applied to simulate the hydrodynamic behavior of turbulent flow in compound open channel with partly vegetated region. Then by using the model the attenuation of wave movement due to vegetation in coastal region is simulated. The results reveal that the present model has the capacity of describing three-dimensional structure of large eddy appearing in free surface turbulent flows with vegetation. It is believed that the model will become a useful tool to pursue further study of wave hydrodynamics in coastal region with the presence of aquatic vegetation.

Various theories and wave transformation models have been devised to describe nearshore wave fields. Each of the theories and models has certain advantages and limitations with respect to its applicability. In order to estimate the wave conditions, the appropriate model has to be selected depending on the relative importance of the various physical processes and the target coastal area…

All waves acting on a breakwater during its design lifetime (for example, 50 years), represented by their frequency of occurrences according to wave scale, are defined as the fatigue limit state design waves. In Japan, wave heights with a frequency of occurrence equal to 10⁴ are adopted as the serviceability limit state design wave for the purpose of controlling cracks in concrete structure…

In Taiwan, coastal giant waves, nicknamed rabid wave due to their unpredictable and violent nature, are responsible for at least several deaths each year. It is urgent to understand these waves so that human lives can be protected…

The probability density distribution of a random event depends on the experimental constraint conditions, there are diversified distributions for the given constraint conditions, the so called MEP distribution is to choose such a distribution whose information entropy is the maximum value among the diversified distributions. In order to find the best fitting method for the wave climate statistical distributions, the Maximum Entropy Principle (MEP) method is introduced, and the corresponding probability density evaluation method for the random fluctuation system is elaborated. According to the MEP method, the probability density evaluation steps can be described as follows: given the random fluctuation signals, then the moments of different orders can be obtained from a sample function, thus the analytical probability density function, then the entropy function, is also obtained according to the MEP concept, in accordance with the constraint conditions, regulating the probability density function in order that the entropy reaches the maximum value, then the corresponding probability distribution function is the MEP distribution. In this article, the constraint conditions are limited to the second order moment, a kind of new MEP distribution expression is obtained for the first time, this expression means that the relationship between the probability density of the random fluctuation signals and the second order moment of the variable has been found. Deferent with all the fitting methods in the past, this kind of MEP distribution can compute the probability distribution of a random fluctuation system conveniently and exactly, so long as the second order moment of the random signal is known, that is, the ratio of the root-mean-square value to the mean value of the random variable is obtained from the random sample, the corresponding MEP distribution expression can be computed according to the deduced expression in this essay. The concept of the wave climate is introduced here, by using the deduced MEP distribution, this article focuses on finding the best method in fitting the significant wave height and spectral peak period probability distributions. Take the Mexico Gulf as an example, three stations at different locations, depths and wind wave strengths are chosen in the half-closed gulf, the significant wave height and spectral peak period distributions at each station are fitted with the MEP distribution, the Weibull distribution and the Log-normal distribution respectively, the fitted results are compared with the field observations, differences between the three distribution fitting methods have been analyzed, the results show that the MEP distribution deduced in this article is the best method, and the Weibull distribution is the worst method when fitting the significant wave height and spectral peak period distributions at different locations, water depths and wind wave strengths in the half closed Gulf, this conclusion shows the reasonability and feasibility of the deduced MEP distribution expression in describing wave climate statistical properties, and it also proves the great potential of applying the MEP method to the study of wave statistical characteristics…

In the statistical analysis for extreme wave data proposed by Goda (1988, 2000), the Fisher-Tippett distributions of type I and II (hereafter, abbrebiated as FT-I and FT-II) and the Weibull distribution are employed as candidates for the population function. The reason of employing the Weibull distribution is the flexiblity for fitting to sample. The extreme value distributions are obtained theoretically by the asymptotic process and the extreme value distributions can not be always applied to the samples of wave heights collected by the annual maximum series as well as by the peak-over-threshold series. Besides, the Fisher-Tippett distribution of type III (hereafter, abbrebiated as FT-III) is not employed as a candidate, even though FT-III is an extreme value distribution as well as FT-I and FT-II. Because the FT-III has the upper bound, it is taken into consideration to avoid the possibility of underestimating the return wave height if the FT-III is selected by mistake as the best-fitting function. In these points of view, it can be said that the conventional method is only a means of fitting the empirically supposed populations and that it is not based on the rigorous extreme value theory. Recently in the field of the theoretical statistics, the asymptotic process to the extreme values are being modeled by employing the generalized Pareto distribution (abbrebiated GPD) for the tail-part of the population functions of the peak-over-threshold series. In the model by GPD, the excess by an appropriate threshold in the sample follows asymptotically the GPD, and the asymptotic process can be practically confirmed by changing thresholds and estimating the slope of mean residual lifes and the shape parameters, which is independent from threshold value, for different thresholds…

Almost all the existing ports in Vietnam are located in rivers, inner bays or lagoons. Coastal ports exposed to the open sea are now under construction such as Danang Port and Dung Quat Port. In such coastal ports, sea waves constitute one of the most fundamental and important natural conditions for planning, design and construction of protective facilities such as breakwaters and seawalls…

The empirical relationship between minimum central pressures and maximum wind speeds for Northeast Asian tropical cyclones was obtained by analyzing typhoon parameters and sea-surface winds observed at the East China Sea, the South Sea and the East (Japan) Sea for 20 years (1979 - 1999). The resulting empirical equation, V_max = C(P_∞ − P₀)^γ was compared with various relationships obtained from previous studies. The result shows a very close agreement with SPM′s(1984) relation. However, it was much lower in wind intensity compared with other relations, and the differences in the maximum wind speed were increased as the minimum central pressures were decreased. The main cause of these differences may lie in the quality of observation data obtained by either direct measurement or indirect estimation of sea-surface winds…

It is difficult to evaluate the deformation of beach profile due to the wave excitation for long duration of time in terms of a single representative wave because the beach deformation is a result of dynamic interaction with unsteady wave excitation. The wave observation stations are not enough to cover whole the coastal line, numerical estimation of waves in time and space domains is necessary to estimate the waves where the observed waves are not available. In the wave generation process, wind plays primary roles on it, and therefore developing a wind simulation technique and analysis of a wind-wave interaction problem seem to be very significant…

In studying the instability of sensitive jets Rayleigh suggested an improvement in the theory by supposing a gradual change in velocity and thus proceeded to derive an equation which is known today as the Rayleigh equation. Miles (1957) proposed a model for the growth of wind waves on the basis of Rayleigh's equation. Later, Conte and Miles (1959) gave accurate computations of wave growth rates by numerical solution of Rayleigh's equation for a logarithmic wind profile. This work first considers a different approach of solving the Rayleigh equation for arbitrary mean wind profiles by implementing the ideas of Rayleigh, which render the equation analytically solvable in the immediate vicinity of the singular point hence providing the initial values for the numerical integration. Furthermore, the wave growth rate is obtained from the dispersion relation of the air-water interface, which involves the vertical integration of the disturbed vertical velocity. The growth rates obtained are then compared with those of Conte and Miles (1959) and found to be in excellent agreement. In closing, approximations to the vertical profile of the disturbed vertical velocity are suggested as a basis for the development of a vertically integrated model of coupled air-water system…

Isobe’s (1994) nonlinear mild slope equations have been utilized by employing ADI method in the discretization to build up a numerical model to study the harbor oscillation problem by using regular waves over constant water depth. Line boundary method together with a sponge layer has been used as a wave maker condition to prevent the reflections at the wave generation point. At first, for a rectangular harbor (30*150cm) (“I” shaped) amplification factors have been found then by assembling new square basins (50*50cm) to the existing “I” shaped harbor, “L”, “T”, “F” and “Y” shaped harbors have been obtained and amplification factors have been calculated for each basin’s end point. Coupling basins with dimensions of 25*50cm and 75*50cm have also been used to make up “Y” shaped harbors. Amplification factors have been determined by taking the square root of the ratio of peak frequency spectrum values for the wave height inside the harbor to the incident wave height outside the harbor, thus amplification factor curves can give information about the wave energy phenomenon. Comparison among the obtained amplification factor curves, revealed out that complicated harbors generate less oscillation than simpler models due to their efficiency in energy dissipation…

A numerical irregular wave model based on the Extended Mild-Slope Equation is established to simulate wave propagation in harbours. The main wave phenomena occurred in harbours are involved in the model, such as refraction, diffraction, reflection, dissipation due to bottom friction and energy input due to wind. The time-dependent Extended Mild-Slope Equation can be written as.

The scattering of water waves for the various configurations of thin barriers has been studied extensively over the past century, despite the mathematical difficulties encountered within the framework of linearized potential theory. In this paper, a mathematical solution for the trapping waves on a circular basin surrounded by a thin vertical barrier with gaps is obtained by using wide-spacing approximate method. In the presence of the barrier, it is expected that part of the incident waves is trapped in the basin, and part scattered to infinity. The approximation is only applied in treating with boundary condition along the barrier: It is assumed that the ratio of basin radius to depth of barrier immersion is large enough so that local effects are negligible. The solution demonstrates the resonant interaction between the barrier and incident waves. Numerical results are also obtained using both an eigenfunction expansion method (Cho, 2002) and the finite difference method by a mild-slope equation as described in Lee and Lee (2001) and are compared with the approximate solution…

Bohai Bay locates in the west part of Bohai Sea, which is a semi-enclosed internal sea in the North-East China (see Fig.1). Bohai Bay is a shallow sea bay with wide mild slope mud beach and receives large amount of wastewater from Beijing, Tianjin and Hebei province. Due to the development of the economy along the BoHai Sea in recent decades, the water quality and ecological environment in Bohai Bay has been becoming very poor, especially in the coastal area. In this paper, the numerical models for simulating tidal flow, residual tidal current and advection-dispersion of pollutant are setup for Bohai Bay, and verified with the field measured and monitoring data. The models for simulating wave propagation and wave-current interaction are also developed and setup for Bohai Bay. Then the hydrodynamic characters of Bohai Bay are studied by using these numerical models, and the significative results are obtained by analyzing the numerical results…

Recently, by including second order bottom variation effects, Suh et al. (1997) extended the timedependent mild-slope equations of Smith and Sprinks (1975) and Radder and Dingemans (1985), and Lee et al. (2001) also extended Kubo et al.'s (1992) equation so that the extended equations can predict the water wave transformation over a rapidly varying topography. Numerical results of the models showed better accuracy of the extended models compared to the previous models especially for the cases of waves on a steep slope and the Bragg reflection of waves on a ripple patch. In this study, in view of random wave transformations, comparisons are made between the extended mild-slope equations of Suh et al. and Lee et al. by both analytical methods and numerical simulations…

In most existing wave propagation researches it is usually assumed that the seabed is impervious. But in shallow water area seepage phenomenon in porous seabed has a certain effect on wave propagation. It can cause wave damping. Wave seepage in porous seabed can also induce seabed deformation, sliding, and even liquefaction. When the elasticity of seabed is small and porosity is large, the interaction between waves and seabed is more significant…

Recently, third generation models, e.g. WAM (WAMDI Group, 1988) or SWAN (Booij et al., 1996), are used to evaluate wave fields. These models take nonlinear wave-wave interaction into account explicitly, and therefore the wave field evaluation is highly accurate. The boundary conditions for these models are usually open boundaries, which are difficult to evaluate with the existent models. Since the boundary conditions affect the wave field evaluation, they should be accurately computed. In this model we include the data assimilation model in the wave model, and assimilate field data in the wave field evaluations with open boundaries. Because this model computes the wave fields and evaluates open boundary conditions at the same time, an improved wave fields evaluation is obtained…

Practical applications in coastal engineering usually demand the solutions of governing equations in geometrically complicated areas. Therefore, a circulation or a wave model expressed in boundary-fitted coordinates is much preferable. Earlier attempts were directed to transformation of the governing equations alone, keeping the Cartesian velocity components unchanged as dependent variables. Later, it was recognized that transforming both the governing equations and the velocity components would be much better for accuracy and numerical stability (see Muin and Spaulding, 1996). In this work, one-component form of the nonlinear dispersive wave equations of Nadaoka et al. (1997) along with the Cartesian velocities are transformed to a curvilinear coordinate system, which is not necessarily orthogonal. Thus, the resulting equations are expressed in terms of the contravariant velocity components, which render the specification of the lateral boundary conditions as simple as possible…

The dispersion effect plays an important role in wave propagation and transformation. Thus, many studies have been conducted on the characteristics of wave dispersion, and some numerical models are proposed. In the present paper, the truncation error of numerical simulation using linear dispersive wave theory is discussed on a basis of exact solutions of the difference equations…

Orissa is a maritime state along the east coast of India and has a coastline of 480km in length. The coastline is bestowed with six major estuaries besides many small rivers which debouch into the Bay of Bengal (Figure 1). During the last 109 years (1804-2000), Orissa coast experienced 128 cyclones of which six were most notable (29 October, 1999; 23-27 May, 1989; 13-1 7 October, 1985; 1-5 June, 1982; 29-30 October, 1971 and 9-11 October, 1967) and caused unprecedented loss of life and property in the state of Orissa. The frequency of tropical cyclones along the six coastal districts of Orissa (Figure 2) is very high and is responsible for shoreline changes and vegetation loss in addition to its other damaging effects. Topography of the coastline, strong littoral drift and longshore current also contribute significantly to the shoreline changes. The changes in the areas of deposition and erosion near Mahanadi delta region were estimated for the periods 1972 to 1986 and 1986 to 1993. The areas of deposition and erosion were respectively 16.52 Km² and 13.39 Km² during the former period while the depositional and erosional trend changed to 1 1.61 Km² and 6.44 Km² during the latter period…

Several studies have been conducted on shoreline change in a lake. These studies described interesting characteristics, and are effective for understanding basic processes of sand movement, because the external forces acting on lake shoreline is relatively simplified compared with those on coastal shores. In addition, these studies are useful for investigating similarity law of coastal sediment, because the scale of topographical change and external forces are smaller in a lake than those encountered along seashore, but much larger than laboratory flume. In this study, the process of longshore sediment transport around the mouth of Nagase River and the Shidahama Beach, which is located to northeast of the Lake Inawashiro, is investigated based on aerial photographs and field measurement data…

To predict topographic changes is indispensable for developing a long-term coastal management plan, in particular for the coasts where sandy beaches are dominant. A number of models have been developed so far to predict beach topographic changes, based on the physical principles associated with the interaction between waves and sediment movements. However, these models cannot be applied directly to large-scale coastal areas with a length of more than several tens kilometers, for they cannot represent all the local conditions and need a huge computational capacity. On the other hand, the correlations between incident waves and long-term topographic changes are relatively easy to obtain by a statistical analysis. The correlations can be used to predict future coastal topographic changes. For the prediction, predominant patterns of the topographic changes must be analysed in details at first…

There are many sand banks in the Seto Inland Sea. These sand banks are generally located behind islands or peninsulas. However, a large amount of sand was dredged from the sand banks in order to get an aggregate for concrete structures such as highway roads or buildings during high economic growth age. It is estimated that totally 600 million m3 of sand was dredged from the Seto Inland Sea for last 40 years. Due to the disappearance of the sand banks from the sea bottom, several environmental impacts on fishes andlor seaweeds habitats were reported. Especially, the most serious problem influenced by the sand mining is that a number of sand eel decreased greatly in the western part of the Seto Inland Sea…

An extension of the breakwater of Shibushi Port has been conducted at the Oshikiri coast in Shibushi Bay, Kagoshima, Japan since 1968 and its outer breakwater has been extended nearly 4.0km. This offshore breakwater created large wave shadow sheltered area behind it and non-sheltered area on the adjacent sandy beach. The typhoon damages had been caused on the non-sheltered sandy beach, thus three groins were built to reduce a deposition by an excess longshore sediment transport into a sheltered area from the non-sheltered adjacent beach. In spite of these shore protection works, one segment of the Oshikiri coast (roughly middle of Fig. 1) was especially overwashed. by the Typhoon Olll(llth Typhoon in 2001). This coastal damage seems not to be caused only by wave sheltering effect of Shibushi Port (wave diffraction effect), but formations of three dimensional sub-aerial bathymetry such as crescentic longshore bar and trough features probably enhanced the overwash damage at a certain location of the beach where a national hospital and local residential area exist. Therefore, this erosional hot-spot-hke feature had to be studied in order to plan the emergency shore protection works at the site. The study shows that the erosion in the non-sheltered up drift coast was commenced mainly due to the wave sheltering effect (dWdx; wave height gradient by wave diffraction) and the generation of 3-D geomorphological features including the crescentic longshore bars and troughs. These nearshore topographies were generated while incident significant wave heights of Typhoons exceeds nearly 6m high on this coast. In addition, it is shown that the average spacing of the troughs is around 600-700m. Finally, submerged breakwaters so called artificial reefs in Japan are recommended to reduce the further coastal damage at the site…

Often coastal protection works are carried out to mitigate the effects of erosion, but do not attempt to address the cause. For example, rock/concrete walls, breakwaters or groynes along the beach act to mitigate the effects or to realign the beach. However, end effects on the shoreline downstream and the environmental imperatives to retain natural character often preclude hard structures. Also, coastal re-alignment may not be possible in built-up areas where natural alignments would sweep though modern shoreline developments…

Development of sand spit at a river mouth is affected by river discharge, sea waves, and tidal current. During a flood, remarkable change in river mouth morphology can be observed, followed by gradual recovery of sand spit topography. It is of practical importance to understand the behavior of sand spit at a river entrance during and after a flood, in connection with water level rise due to backwater effect caused by sand spit. In the present study, detailed surveying of sand spit recovery process has been carried out at the Natori River mouth, Japan after the flood induced by typhoon 0206…

Tidal flats play an important roll as a habitat for the rich ecosystems. Global warming would raise the sea levels about 1 m in the next 100 years. The Intertidal areas decrease or deform with raising the sea levels. Therefore, future variation of inner bay environment has received considerable attention, because the purification abilities of tidelands depend on the ecosystems…

On the average, there are 4-5 storms affecting the Yangtze Estuary every year. The storm-induced extreme waves and set up often make suspended sediment concentration rise. A lot of sediment is carried by currents into navigation channel and deposition occurs in the channel within and after storm, which sometimes affects ship navigating. It is very important for navigation safety to predicate accurately the storm-induced sedimentation in the channel…

The current emphasis on triple bottom line has sparked the growth of offshore wind farms as an alternative source of electricity. Caisson foundations have been typically adopted to support these offshore structures. This new foundation scheme has proved to be extremely effective in terms of cost and method of installation. However, the integrity of the foundation is found to be severely affected by the process of local scour around the structure. The current practice of designing the protection around such structures is likely conservative due to the limited researches done in this area…

The rapid development of the offshore oil and gas industry in past decades has required the extensive use of offshore pipelines to transport these petroleum resources. Erosion of seabed materials beneath a pipeline due to the scouring phenomenon will eventually result in the growth of free spans, leaving sections of a pipeline unsupported. Three-dimensional scouring has been identified as one of the major causes of pipeline failure…

A foreshore erosion due to a return flow caused by significantly overtopping waves, such as tsunami flood, is difficult to be numerically simulated, because of its complicated characteristics. There are two key factors of this phenomena: (i) the description of water surface behavior including dropping jet from the top of a seawall and (ii) the description of local scouring driven by dropping jet. For the description of water surface behavior, the MPS (Moving-Particle-Semi-Implicit) method, which can track the fluid motion with very high resolution without using computational grids even under the existence of the fragmentation of fluid, is appropriate choice. To describe the local scouring, new model of scouring on the concept of particle tracking is introduced, to extend standard MPS method, which only can treat fixed wall boundaries, to fit the description of movable bed, or deformable wall…

This paper presents the results of a series of experimental study on the local scour around a large circular cylinder under wave action. The characteristics of scour geometry in different conditions are described. Like the scour in front of a breakwater, there are two basic types of scouring pattern in front of a large circular cylinder. The experimental data together with the mechanism analysis indicate that the scouring patterns are dependent on the sand grain sizes as well as the wave conditions. The scour depth is found to depend mainly on the wave number, the relative cylinder diameter (the cylinder diameter to the wave length ratio), sediment diameter and the maximum velocity of the wave relations are proposed to expect the ultimate maximum scour depth and the developments of scour in front of the large circular cylinder. The applicability of the proposed formula is confirmed by experimental data obtained in a laboratory basin with a wave generator…

In assessing the impact of large structures in offshore regions, the first problem is to predict the threshold of sediment. By reanalyzing some of the previously published results and making use of Jonsson’s(1966)^[1] wave friction factor concept which enabled one to determine the magnitude of the maximum bottom shear stress associated with an oscillatory fluid motion, Madsen and Grant(1976)^[2] suggested that the shields criterion obtained from unidirectional steady flow was applicable as a general criterion for the onset of sediment movement also in oscillatory unsteady flow. In their Fig, however, the general trend of the data obtained from oscillatory flow conditions indicates that the critical value of the shields parameter is all above the shields curve determined from unidirectional steady flow experiments in the boundary layer of smooth turbulent-rough turbulent transition regime. It is obvious that this difference is systematic and can not be attributed to individual differences in determining just when initial sediment movement occurs. The purpose of the present paper is to contribute to the improved sediment criterion under wave action by analyzing the different boundary layer conditions between steady and unsteady flow. In this paper, by analyzing the mechanism of initiation of sediment in oscillatory flow and blending criteria in different boundary layers, a new and seasonal critical curve which can predict the sediment threshold under wave action is given, A vast amount of experimental data is found to show good agreement with the curve suggested by the author. From the criterion curve, a straightforward formula, which has better physical explanation, can be obtained. This analysis method will provide a new way for the study of inception of sediment transport in offshore region…

When we construct coastal structures such as the breakwaters, jetties and harbours, the prediction of medium or long term beach evolution around the coastal structures is required. Some mophodynamic models for predicting the mediumterm beach evolution(coasta1 area models) have been proposed such as, Watanabe et al(l986),de Vriend et al(1993). A coastal area model coupled with the shoreline model have been proposed by Shimizu et aL(1996). In the coastal area model, the nearshore current field has been determined using a depth-averaged (2DH) model. Recently, some coastal area models using a quasi-3D nearshore current model have been also proposed (e.g. Kuroiwa et al. 2000). Although these coastal area models have been applied to some practical problems, these models are still uncompleted because shoreline changes have not been sufficiently incorporated. Therefore, in order to predict 3D beach evolution with better accuracy, a 3D morphodaynamic model, that considers the effect of nearshore current profile and estimates the shoreline changes, is needed…

Erosion of the shore and deposition usually occur in the beach area. These two phenomena, in turn, arise in various forms such as the closure of river mouth, development of estuary and coastal sandbanks, and shoreline changes. Especially, withdrawing of the shoreline caused by the erosion now threatens to destruct the environment around the shore, and establishments and residences bordering the coast. Aware of these problems, a considerable number of researches have been conducted to quantitatively predict the future of the shoreline change, which is affected by natural surroundings and construction of establishments. These efforts have been made in order to preserve the environment of the shore, and to enhance its function as a tourism attraction and shore protection…

In Japan there are many pocket beaches of a variety of scales, and many fishing villages with a small port locate there. Historically these fishing ports have been located on the lee side of the headland, because of the wave-sheltering effect of the headland itself. In recent years, in order to modernize the fishing port, the facilities of the fishing port have been expanded, with the frequent construction of the new port in the outer region of the old fishing port. Although the enlargement of the fishing port was attained as a plan by this activity, many cases have been reported, in which the wave-sheltering effect affected the overall wave field on the pocket beach by protrusion of the breakwater from the lee side of the headland and induced severe beach erosion in the surrounding area. This study aims at investigating this problem, taking the Shiratsuru beach in Kumamoto Prefecture in Kushu in Japan as the example, and future measures are considered…

Laboratory experiments were performed on beach evolution and sediment sorting around coastal structures on a initially plane 1/20 sloping beach of uniformly graded sand. One experiment was for a detached breakwater, and the other for groins. Spatial and temporal variations of beach topographies and grain size distribution of surface sediments were described. A numerical model was developed on the basis of the enhanced Boussinesq equation and a sand transport model for mixed-grain size sands under atilt waves. The validity of the model was verified with experimental data…

Bed material in the field often has widely spreading grain size distribution. In general, topography change is predicted by evaluating sediment transport rates using representative grain size, for example, the mean grain size. In a beach where grain size distribution is narrow, such a procedure can apply for evaluateing sediment transport rates because almost all of the particles are transported with the same mode (bed load, suspended load or sheet flow). On the other hand, in a beach where grain size distribution is wide, direction of bed material transport depends on its grain size because the mode of transport of fine bed material is not always the same as that of coarse bed material. In addition, the interaction in sediment transport between fine and coarse bed materials have to be taken into account…

Various criteria of onset of sheetflow were developed but for uniform sediments under sinusoidal oscillatoly flows. A criterion of onset of sheetflow for nonuniform sands under nonlinear oscillatory flows is not yet comprehensively investigated, despite the criterion proposed by Dibajnia and Watanabe (1996) that required finther verifications. On the other hand, movement mechanism of individual sediment particles in sediment mixture is worthwhile to be investigated…

The importance of sediment transport in the swash zone has been widely recognized, however, the present understanding is not satisfactory. The main reason for this comes from the complexity of the sediment transport mechanism. One of the important and unsolved factors is the in-/ex-filtration effect on the hydrodynamics and the sediment transport…

The first phase construction of the Yangshan Deep-water Port (Shanghai International Shipping Center) is composed of three parts as harbor district, the Donghai bridge and land supporting base of the New Harbor City. The project of harbor district concludes 1600-meters quay, five berths of deep-water container ships, whose annual design handling capacity is 2.2 million TEUs and where the 5^th and 6^th generation container ships as well as the 8000 TEU container ship can berth. Till 2020 about 30 post-Panamax container ship berths should be finished, whose annual handling capacity is 15 million TEUs at least. The Donghai bridge, which is 31 kilometers long, connects the Luchaogang town in the north and the Xiaoyangshan Harbor District in the south. The part of the bridge over the sea is 25 kilometers in length and 31.5 meters in width, which is designed according to standard of the two-direction six-driveway highway. The New Harbor City, whose planning construction area is 95 square kilometers and residential population is 300000, is the land supporting base of the Yangshan Deep-water Port. At last there’ll be an ecotype, intellectualized and modern new harbor city with developed port industry, international transit system and unique style and features…

Beaches in Japan have chronically suffered from erosion problems for more than forty years owing to the decrease of sediment supply from rivers and interference with longshore sediment transport by coastal structures. As a result, for beach protection, many coastal structures such as groins, detached breakwaters and seawalls have been constructed, and these work effectively from the viewpoint of disaster prevention. However, the structures keep people from accessing beaches even under mild wave conditions, and deteriorate valuable landscape. Therefore we developed a new beach protection system with gravity drainage, which has no structures on a beach…

Toward clarifying the sediment budget of a river estuary, it is important to understand the process of deposition and movement of sediment of various grain sizes that is discharged fi-om a river in the coastal area. Because such discharged fine-grained components include high content of nubients such as nitrogen and phosphorus, and form water masses of high turbid they exert a considerable influence on water quality and biological activities of the sea. Reflection strength, measured along with flow velocity by ADCP, correlates with the concentration of suswnded solids in seawater. there is Dossibilitv 100 of estimating multi-layered turbidity. Moreover, if the relationship between turbidity and concentration of suspended solids is determind it is possible to estimate the volume of movement of suspended solids…

By analyzing surveyed data and result of numerical model, some special kinetic characteristic of flow and sediment found at north-branch in Yangtze River…

Based on eight groups of data of the Lingdingyang channel depth before and after dredging in each season, its characteristics of silting distribution in space and time are investigated. The causes of silting in the channel are analyzed considering the following aspect: topography of Lingdingyang, and change of discharge ratio of runoff and tidal flow, and the conditions of the sediment movement. By the fuzzy mathematical method, a formula is presented, which can determine silting by the different sediment sources…

Vortex ripple is widely formed in the coastal region. The vortex ripple enhance the separation of flow and turbulence, it plays a vital role in various coastal process, such as sediment transport, the wave attenuation and the mass transport due to wave. Nevertheless, the flow structure and sediment movement above vortex ripple has not been investigated owing to the complexity of the phenomena…

In the past, wave runups on a small-diameter pile are not considered as one of important design factors, since it is assumed that waves are not disturbed by the pile so that the runup heights are equal to the incident wave crest amplitudes. Main concerns have been focused on wave forces…

Historically, the main purpose of coastal defence was seen as preventing or reducing coastal disasters through the construction of seawalls and other 'hard' structures. More recently, 'soft' countermeasures involving beach management, together with effective systems of population evacuation have become increasingly important. Where structures are regarded as necessary, an integrated system of shore protection may be employed linking a combination of features such as seawalls, submerged breakwaters, artificial reefs, beach nourishment and so on…

Recently, the problem of wave overtopping has been studied experimentally in horizontally two-dimensional wave field. The properties of wave-overtopping rate for the multi-directional random waves were shown by Sakakiyama and Kajima(1996) and Tomita et al.(2000). On the other hand, in the numerical approach, Moriya and Mizuguchi(1996) calculated wave-overtopping rate for the obliquely incident regular waves along a semi-infinite seawall by utilizing the Boussinesq equations and the wave-overtopping formula of Kikkawa et al.( 1967). However, the validity of that model is not confirmed for random waves. In designing drainage facilities behind the seawall, we are required to estimate maximum wave-overtopping rate as well as time-averaged one, considering multi-directional random wave field…

Recently in Japan, coastal structures are constructed with consideration in various aspects such as environment and utilization in ordinary conditions as well as disaster prevention. In that context, stepped gentle slope seawalls that give good accessibility to waterfront are now often used as the near-end protective facility in Japan's Complex Coastal Protection Concept. It is, however, important to estimate accurate wave overtopping rate in the storm conditions, because disaster prevention is the fundamental function of them…

Some neural network stability models for rubble mound breakwaters are proposed and analyzed. The proposed models give the more reliable results than the well known van der Meer’s formula. Among them, the neural network model having the slope angle and the wave steepness as independent inputs shows the best performance. But the neural network model having independent input parameter for significant wave height, significant period is found not to be useful for the design of rubble mound breakwater because the design parameters exceed the training data ranges. In addition, a reliability analysis technique using the trained neural network model is proposed. Based on two analysis examples, it was found that van der Meer’s formula gives the larger or smaller failure probabilities than the neural network models. Therefore, one should be very careful in making a decision whether the designed armor units are safe or not if he/she uses only empirical formula. To avoid this situation, it is heavily recommended that more advanced models such as the neural network model proposed here should be simultaneously considered.

A new diffusion coefficient model, which considers the effect of chloride binding and evaporable water in concrete, is proposed. FEM program developed on the basis of the new diffusion coefficient model provides an estimation of chloride concentration with concrete depth and aging, and predicted chloride concentrations are compared with experimental values.

The apparent diffusion coefficient, which is a function of chloride binding, evaporable water, and diffusion coefficient, varied according to water-cement ratio. But, curing temperature did not affect the ratio of apparent diffusion coefficient to ordinary diffusion coefficient. The FEM program using the apparent diffusion coefficient estimated the experimental chloride concentration in a little error range. On the contrary, the chloride penetration analysis using ordinary diffusion coefficient overestimated the diffusion rate. Therefore, it is recommended to use the apparent diffusion coefficient proposed in this paper for predicting the initiation age of chloride-induced steel corrosion instead of the ordinary diffusion coefficient.

Recently Shimosako and Takahashi (1999) developed a Level 3 reliability design method to calculate the expected sliding distance of the concrete caisson of a vertical breakwater. This method includes stochastic variability in deepwater wave height, tide level, and shallow water wave transformation, and calculates the expected value of the accumulated sliding distance during the lifetime of the breakwater. Monte Carlo simulations were used to take into account the uncertainties of the above-mentioned design factors…

Many studies on the application of the reliability design method, as an alternative of the conventional one, to caisson-type breakwater have been carried out (e.g. Shimosako and Takahashi, 1998, 1999; Takayama et al., 2000; Goda and Takagi, 2000; Goda, 2001). Especially, the computation of the expected sliding distance proposed by Shimosako and Takahashi quantitatively clarifies the risk of sliding failure, and the expected sliding distance is a useful stability index against sliding of a caisson in the reliability design. However, detail studies for accurate estimation of the expected sliding distance are not sufficient until now. Therefore, this fact motivated this paper…

In the recent years, breakwaters with perforated front walls have been widely used. it can reduce the wave reflection and wave run-up in front of the structures. Then, the construction cost may decrease…

Although the breakwater covered with wave-dissipating blocks is one of the most popular coastal structures, collapse of the wave-dissipating block mound due to the direct wave attack have been reported. The required condition of the breakwater covered with wave-dissipating blocks is to keep the arrangement of the blocks with the suitable gap between blocks for absorbing wave enegy. And also the engagement between blocks is required to keep sufficient resistance to the wave attack. Flexibility in deformation fitting itself to the change of ground level, such as land subsidence due to the seabed liquefaction or scouring, is an advantage of the wave-dissipating block mound. Therefore, the change of engagement between blocks after the land subsidence is important in the design of wave-dissipating block mound. However, a large deformation of mound brings extremely high stress over the yeild condition of the concrete blocks, under which the part of the block-leg is destroyed. That failure of the block-leg leads to the lose of the engagement between blocks, and resultant lift off the single block unit. Consequently lose of the engagement between blocks could lead to the catastrophic destruction of the wave-dissipating block mound. In this paper, to understand the disaster mechanism of the wave-dissipating block mound under the sudden land subsidence, the numerical simulator based on the Distinct Element Method was proposed…

Ocean surface water waves traveling in water of varying depths may experience a lot of physical phenomena such as reflection, diffraction, shoaling and refraction due to variation of bottom topography, nonlinear interaction among different harmonics and interferences with man-made structures. The present study mainly concerns with reflection of water waves propagating over submerged breakwaters…

The mass transport flow and the radiation stress flow induced by water wave play an important role on the dynamic research of coastal engineering. On scouring around a large-scale circular cylinder, Kaitsui^[1] considered not only sediment transportation of the radiation stress flow but also Eularian flow and the mass transport flow. Saito^[2] even thought that the mass transport flow near the bottom boundary layers plays a key role. But till now, few studies have been made on currents in front of a vertical breakwater caused by different incident waves, especially on those along breakwaters…

Under the existence of momentum liquefaction of seabed due to the action of high waves, a subsidence of armor blocks and rubble stones, which weaken the protection against scouring, occurs. In the maintenance planning of the coastal structures, the prediction of the subsidence of armor blocks and rubble stones is one of important items. The key factor of the subsidence of armor blocks and rubble stones is the block-block or stone-stone interaction, while most of the previous studies have treated the subsidence of single block or stone. A behavior of rubble stones at the foot of seawall under the momentum seabed liquefaction is experimentally and numerically investigated. Especially in the numerical model, the stone-stone interactive structure of rubble stone mound is explicitly taken into account…

Large-diameter cylinder inserted in soils is a new structure style in nearshore and port engineering. It has been used as retaining quay walls and other kinds of port project structures such as dikes. It has wide potential application for its efficiency. The bearing and failure mechanism of big diameter cylinder in soft clay under wave action is very complicated. The design theory and calculating method is still under development. It is very important to do some research on the calculating method of the bearing capacity…

The new type of breakwater with box foundations consists of box foundation penetrated into soft seabed soil and upper structures in various forms. The structure as a whole can be installed on the site conveniently, be transported over water by means of pneumatic floating and can also be reused if necessary…

In constructing breakwaters located on a soft ground, considerable expenditure and time consumption are required for a ground improvement. The conventional breakwaters such as a rubble mound breakwater and a caisson breakwater constructed on the soft ground reveal several problems, i.e., an economical low-efficiency, a difficulty in construction, a guarantee of safety, and a seawater pollution due to heavy dredging and dumping materials. Therefore, many attempts have been made to develop new type of breakwaters that can be applicable for soft ground efficiently, for example, a floating type breakwater, membrane type breakwater, pile type breakwater, curtain type breakwater, and so on. Those breakwaters may be applicable for soft ground, however, as not a main breakwater but a secondary assistant breakwater…

The safety of coastal and offshore structures such as piled wharves, shore trestles, oil drilling platforms, etc, has great relation to the wave impact. Under confused sea condition, the wave impact load on the structure is destructive when waves propagate underneath the structure and surge up to its subface. And the structure’s service life may also be threatened by the negative pressure occurred when waves separate from the subface of the structures…

With the development of artificial neural network (ANN) ^[1], it had been widely used in engineering fields. Mase, et al.^[2] established a model utilizing ANN to judge impact of waves on the superstructures of composite breakwaters. In this paper, on this basis, the BP (back-propagation) network with one hidden layer is modified and a neural network is established to calculate wave forces on a vertical wall by use of the additional momentum method and auto-adjustive learning rate. The comparison between the experimental values and the calculated results by Goda's formula ^[3], the Chinese standard formula ^[4] and the present method shows that the neural network is suitable to predict wave forces on a vertical wall. Figure 1 shows the establishment process of neural network…

For the direct measurement of the wave forces acting on a rubble mound breakwater, a breakwater frame model was devised. The core part in the model was filled with approximately 40 thousands of specially shaped empty polyhedrons instead of natural stone to reduce total weight. The specific gravity and pore ratio of this alternative core material are 0.55 and 0.43, respectively. Natural armor stones were adopted for the cover layer and filter layer on the front slope of this model…

A rubble mound breakwater is the most fundamental structure to protect coastal area from wave actions. Although numerous studies on the stability of armor blocks have been conducted, very little knowledge is available on the wave pressure exerted on the rubble mound breakwater (for example, Troch and De Rouck, 2002). Where the bearing capacity of the subsoil is large enough to support the breakwater, precise evaluation of total wave pressure may not be necessary. However, if the geotechnical property of subsoil is not appropriate, careful examination on the total wave pressure must be conducted to assure the stability of the breakwater against a slip failure of the subsoil caused by the weight of breakwater and the wave pressure acting on the breakwater…

Submarine pipelines are usually employed for the conveyance of oil and gas, seawater for cooling systems & watersupply projects, disposal of drainage water etc. In the case of pipelines close to the seabed, the proximity of the seabed influences the forces on the pipeline in the coastal zone. The flow behavior and the forces on the pipeline are affected due to the presence of another pipeline adjacent to it. In addition, the beach slope also alters the flow field around the pipelines and the distance between the pipelines as well as the clearance between the pipe and the sea bed governs the wave induced forces on them. For an efficient design of parallel submarine pipelines near a sloping bed, a proper understanding of the effect of vertical clear spacing between the seabed and the bottom of the pipe and the effect of the horizontal clear spacing between the adjacent pipes is essential. This prompted the investigators to take up a detailed experimental program on the present topic…

In the model test of Yanshan Deepwater Harbor of Shanghai International Shipping Center, 30 kilometers away from shoreline outside the mouth of the Hangzhou Bay, a “composite simulation type” research method of compound models is used to simulate and study the tidal flow variation characteristics and sediment movement variation process in the project sea area before and after the construction schemes are put into effect…

Many researches have been carried out on wave diffraction from structures in an open water area. For a uniform cylinder MacCamy and Fuchs (1954) developed an analytic solution. For arbitrary 3D bodies, many numerical methods are available. However, for wave diffraction from bodies in front of vertical walls, less research has been seen…

At Qiantang estuary, when the tidal range is large while the water in the river is relatively shallow with a decreasing depth toward upstream, the back slope of the tidal wave catches up with the front gradually due to increasing nonlinearity and riverbed resistance. The front slope of the tidal wave becomes more and more steep and finally a violent bore is formed…

Many coastal structures constructed for the purpose of harbor securing and shore protection are porous. It is well known that wave properties such as height, energy and force are changed considerably inside the porous structure. However, all these changes depend on the several structural parameters including width, material size and porosity of the structure. Therefore, it is essential to investigate the influence of all these parameters. Wave motion in permeable structures is often studied experimentally. However, in the recent years several numerical modeling are also done. Losada et al. (1995), Hsu et al. (2002) and Liu et al. (1999) are the few examples of previous studies on wave structure interaction in porous media. However, all of these studies are related with breakwaters where part of the wave energy is transmitted by overtopping or passes through the structure. In case of seawall there is no transmission of wave energy. Hence, different characteristics of reflection, energy dissipation and wave damping are expected…

For the formation of artificial harbours and boat marinas, breakwaters are constructed aiming to maintain required tranquility. Among various types of breakwaters, vertical breakwaters require less space, less construction material and time saving. However, the vertical impermeable front face on its seaward side experiences excessive dynamic loading due to reflections of the incident waves. There are several methods adopted, such as dissipating chamber systems to reduce the loads as well as the reflection from the structures. The vertical wave screen are mainly used as breakwaters in small boat harbours and marinas, where less space for breakwater construction, less reflection requirement, and wave transmission is permitted to a limited level. They are also used as wave dampers, in order to reduce the reflection of wave from existing vertical breakwaters. The permeable screen may be made of rectangular, triangular or circular elements, the configuration of which depends on the degree of allowable transmission of waves on its leeward side. The present study is to investigate the hydrodynamic characteristics of twin vertical wave screen breakwaters through an experimental investigation…

The main purpose of the breakwater, which is the most typical element in harbor plan, is to maintain the calm area in a harbor by preventing waves propagated from offshore. But, because of blocking nature of the impermeable breakwater, which causes fundamental environmental changes in coastal water circulation system, has brought about serious environmental problems. In recent years, the construction of the permeable breakwater, which allows the seawater exchange to improve the water quality in a harbor, is being carried out. Although the permeable breakwater is able to improve the water quality by expediting the seawater exchange, it can create transmitted waves, which could disturb the calmness in a harbor. In this study, the numerical models was established to analyze the wave field in a harbor which is constructed in the permeable breakwater. The time-dependent mild-slope equation was used as the governing equation for the model, and the arbitrary transmitted coefficient condition was used as the boundary condition on the permeable breakwater. For the verification of the model, the two dimensional hydraulic model test was used to analyze the transmitted wave of a permeable breakwater. Also, the applicability of the model was examined for the real harbor with permeable breakwater by comparing the analysis of the wave field, which was obtained by applying the model to the Jeju New Harbor, with the results of the three dimensional hydraulic model test.

It is important to understand the hydrodynamics of a group of plants for the application of it as a good alternative material for protecting the banks of inland waterways against waves and current compare to the classical materials as concrete block or stones. This paper describes an investigation into the wave damping capacity of plants. The damping of waves transmitting a group of model plants installed in the wave flume are measured. The wave forces acting on an array of circular cylinders, which is a simple model of a group of reeds, and wave damping by it are also measured and evaluated theoretically…

For determination of absorbing coefficient, one-dimensional wave is studied to give the analytical expression of absorbing term, and the analytical predictions are compared to available physical laboratory data in flume for wave propagation through bottom-mounted breakwaters. We consider the problem of wave partial/full reflection and transmission by a wave-absorbing layer with the focus on the understanding of wave reduction by wave-permeable structures. We obtain accurate predictions of reflected and transmitted results around the wave-permeable breakwater for various incident-wave conditions. The results show that wave permeable breakwaters with proper absorbing coefficient can be used as an effective alternative to massive gravity breakwaters in reduction of wave transmission in shallow water.

A sloshing phenomenon in a liquid storage tank is numerically simulated. In nature a sloshing problem in a tank, i.e., a liquid storage tank or a cooling water tank in a nuclear power plant can cause a severe disaster during an earthquake, or an excessive motion of a oil tanker at sea. During excessive sloshing, the sloshing-induced impact load can cause a critical damage on the tank structure. Recently, this problem becomes an important issue in FPSO design. A three-dimensional free surface flow in a tank is formulated in the scope of potential flow formulation with the nonlinear free surface conditions. A finite-element method based on the Hamilton’s principle is employed as a numerical scheme. The problem is treated as an initial value problem. The nonlinear computations are made through an iterative method at each time step. In the computations the hydrodynamic loading on the pillar in the tank is obtained. The computed results are compared with previous results obtained by others.

The present investigation was carried out for one year from March 1988 to February 1989 and focuses on hydro-plankton aspects in parts of Bay of Bengal. The hydrological factors were mainly governed by the monsoon and river systems flowing into the Bay. A marked seasonal fluctuation in salinity, dissolved oxygen, water temperature and suspended particles were observed, generally which is a unique feature of northeastern coastal part of the Bay of Bengal…

Many short-period climatic variations over the circum-pacific area can be associated with the abnormal behavior of the Aleutian Low. The Aleutian Low plays an important role in generating weather patterns over the contiguous United States (Garriot, 1904; Kelein, 1965). The synoptic aspects of the teleconnection involve the position and strength of the westerlies as well as the longitude and amplitude of the quasi-stationary, a long-wave train generated downstream from the variable Aleutian Low. The dependence of the Aleutian Low in fall on the sea-water temperatures in the Northern Pacific developed during the antecedent summer is considered (Namias, 1976). Namias suggested that the few cases where the indicated relationship apparently failed could be explained in terms of external influences like the blocking of the Bering Sea, or the occasional existence of unusually strong SST gradients which change atmospheric baroclinicity and sometimes influence the Aleutian Low. It transpires that a 500hPa height fluctuation corresponding to the PNA pattern presented by Wallace and Gutzler (1981) causes the SST anomalies represented by the first EOF. Yamada and Sekine (1997) indicated that a southward shift along the Japanese coast of the subarctic gyre in response to the southward shift of the Aleutian Low results in the negative SST anomalies, which can not be attributed to either the sensible / latent heat fluxes or Ekman transport…

In order to understand an ecosystem of nearshore region facing to an open coast, it is important to know a primary productivity and a nutrient budget of it. However, a nutrient cycle in an open coast has not been understood enough yet, because it might be strongly affected from an offshore region but the mechanism and quantity of nutrient supplies from offshore region has not been revealed yet. The objective of the present study is to show the basic seasonal variation of nutrients in an open coast and to reveal the influence from offshore region to near regions, especially an effect of oceanic currents fluctuations through a long term field measurements…

In recent years, Ariake and Yatsushiro sea has encountered serious environmental problems, such as seaweed damage by anomalously multiplied planktons. A lot of aggravating factors can be included on this issue: for example, the decrease of tideland area, large amounts of polluted water into sea by the development in the coastal and land area surrounding these seas, amounts of other polluted solid materials and into sea caused by severe flood or variation of the river shape, variation of tidal stream or influx of warm seawater by typhoon or long term variation of ocean current. However, it is still not clear in detail because of its complexity. In order to make causal analysis and construct guideline for recovery, it is indispensable to make comprehensive attempt including chemical-physical environment and biochemical processes…

Near-surface current measurements by two High-Frequency oceanic surface radars (HF radars) of the Frequency Modulated Interrupted Continuous Wave (FMICW) type were carried out during the period from December 7, 2000 to March 6, 2001 in order to investigate the characteristics of short-period fluctuations of surface circulations in Sagami Bay, Japan induced by the Kuroshio warm water (KWW) intrusion (Fig. 1). When the KWW intrudes into the bay through Ooshima west channel (OWC), cyclonic and anti-cyclonic circulations are generated in the central part of the bay and in the lee of Oshima Island (Fig.2), respectively as suggested by previous studies based on mooring and drifting buoy observations (e.g. Taira and Teramoto, 1986; Kawabe and Yoneno, 1987; Iwata and Matsuyama, 1989). Radar-derived velocity field clearly shows that these two circulations fluctuate with periods of about 8-11 days. When the KWW strongly intrudes into the bay from OWC, cyclonic and anti-cyclonic circulations become large and the centers of the circulations move southwestward and northeastward, respectively. In addition, warm water intrudes into the mouth of Tokyo Bay and coastal front appears at the bay mouth. On the other hand, KWW intrusion weakens, the circulations become very small (Fig.3)…

The Hugli estuary is situated in the western part of Sunderban gangetic delta and is a classical example of a tidedominated sink for contaminants coming from industrial, aquaculture wastes, domestic sewage, agricultural pesticides, soil erosion, marine traffic and runoff from upstream mining sites. The metropolitan city Kolkata itself discharges about 398 million tons per year of municipal sewage and domestic effluents to this river. The living resources have been degraded recently due to increase in population pressure, pollution and natural resource consumption to the extent of overexploitation. This paper summarizes some of baseline studies on heavy metals, organochlorine pesticides in sediments and water in the estuary and their impact on the biota and outlines some of the future plans required to undertake for better management of the river system. Physicochemical variables of water (temperature, salinity, dissolved oxygen, pH, turbidity, alkalinity, hardness, ammonia nitrogen, nitrate nitrogen, conductivity, total dissolved solids, biological oxygen demand and chemical oxygen demand) as well as sediments (organic carbon, pH and grain size) are also considered and correlated with the level of contaminants…

The coastal area, which becomes the object of this investigation, is enclosed by many artificially-built islands and breakwaters in the head of Osaka Bay as shown in Figs.1 and 2. Every summer algal blooms have been often observed at the sea surface, besides anoxic water has been formed near sea bottom and upwelled dependently of wind's direction and strength. Complains are voiced by the residents who live in high multi-floored apartments built in the reclaimed islands. Under such circumstance, there remains only one small area still in almost natural condition with a sand beach. The final target of this research is to propose the policies from the standpoints of restoring the lost sand environments and actively creating new environments. As the first step, the authors carried out field surveys for better understanding seasonal variation of water qualities. Some researchers have been reported the existence of the anoxic water at the head of Osaka Bay, but it is not well known that the mechanism of the anoxic water in the enclosed coastal areas such as a port and a water area behind the reclaimed island. In the present study, we discuss the spatial and temporal distributions of anoxic water and the physical and biochemical dynamics controlling the water based on long-term field surveys…

Hiroshima Bay, surrounded by Kurahashi Island, Yashiro Island and other islands, is the bay connected to Seto Inland Sea. Recently there have been environmental problems of various degrees of severity, namely sea-level rise, eutrophication and 'red tide' occurrences, etc. The incidence of eutrophication due to the overload of nutrients has caused poor health of the ecosystem and economic loss in fishery. Therefore, the study of processes and mechanisms related to eutrophication such as aerobic and anaerobic decomposition of organic matter, and nutrient cycles including phosphorus and nitrogen cycles is important…

Youngil Bay has a rectangular shape on the east coast of Korea, see Figure 1. Hyungsan River supplies pollutants and water to the center of the bay. The tidal range around the bay is as small as 4 cm, and the circulation of the seawater in the bay is not sufficient to keep the seawater clean since 1975. Waves are relatively strong at the entrance of the bay but weak along the coastline inside the bay. The area is relatively shallow ; water depth is under 80 m throughout the bay. The extent of contamination is especially higher at some areas in the bay than at other area because of supply of organic materials from the industrial area nearby. The COD at some areas in the bay reaches over 5 mg/L, which is considered to be a very serious situation. The river discharge from Hyungsan River is about 20 t/s on average, and reaches up to about 3600 t/s at extreme flood cases. Possible treatments of the contamination in the bay are under study. Flushing out the bay with the river flood discharge by adding groins around the river mouth is a countermeasure. Artificial circulation with pumping will be another countermeasure. An existing depth-average 2-dimensional horizontal, finite-difference numerical model system, KU-2DHFC was used for the simulation of flow and dispersion of the two cases. Exchange rate with the outer sea was improved for each development scheme.

In 1980's, red tide began to occur in Ariake Bay. In recent years, occurrence frequency and scale of the red tide is increasing (Takagi et al., 2002). Once red tide occurs, oxygen depleted water is produced near the seabed through aerobic decomposition of excess organic matters settled from the upper layer. Anoxic environment causes mortality of benthic organisms which have the function of purifying the water, resulting in the negative spiral of the water environment…

Development and use of new energy sources such as renewable energy and recycled energy have become much more common in recent years due to concerns about the global environment and depletion of traditional energy sources Hydrogen is a clean energy source that can replace fossil fuels, which are some of the causes of global warming Metal hydride (MH) has been studied as a method for storage of hydrogen Application of the energy storage capabilities of MH in various fields is eagerly awaited. The MH actuator is being developed as a method for directly obtaining a mechanical force using hydrogen pressure generated by a temperature difference applied to a MH…

A hydraulic model test is one of the important tools for design of hydraulic facilities. However, floods are often assumed as the condition of hydraulic model tests, because a lot of hydraulic model tests aim at the verification of hydraulic feature of the facilities. Therefore, the example that evaluated the reproducibility of result of the hydraulic model test after construction is few…

In considering environmental management of the coastal sea, it is important to understand the influence of various materials discharged from a river. Although the sea and the river basin often are studied separately, it is necessary to regard both areas as a single unit and to clarify the cycle of water, sediment, nutrients, etc. over a wide area…

Nutrients have always existed in natural water, but not at the present excessive concentrations. Excess amounts of phosphorus and nitrogen cause rapid growth of phytoplankton, creating dense population, or blooms. These blooms can lead into many environmental problems such as sunlight penetration reducing, and oxygen depletion. Therefore, for water quality management, including in the area of coastal waters, quantitative evaluation of nutrient condition is required…

Over the past decade dredging has been increased to deepen navigation channel in port and harbor of Korea. Fine sediment resuspended by the dredging activity is transported into coastal waters in the form of plume. The transport results in increases in SS (suspended sediment concentration) above background levels and sedimentation on the seabed. To assess the environmental impact we have to know the behavior of the plume exactly. Numerical models have been developed to understand and predict the behavior of suspended materials in coastal waters…

When an artificial beach is designed, its safety and landscape are recognized as the important factors from the viewpoint of citizen use. Then, the beach becomes semi-enclosed in some cases, and the seawater exchange rate is low. The micro-topography such as tide-pool, crack and notch in natural beach dose not appear. It is expected that the water quality is bad and the appearing lives are poor. The purpose of this study is to discussed substance cycle especially of nutrients in an artificial beach by using observed data and a numerical model…

AS the utilization of deep-sea water is extended, the volume of discharged wastewater may become greater than before. Under such circumstance, it is more important to precisely evaluate the environmental impact by the discharged wastewater. In the case of submerged outfall diffusers, complicated interactions between the discharged water jet and ambient tidal flow takes place, which may influence not only the near-field mixing processes but also the diffusion away from the outfall. In addition, the diffusion pattern may significantly vary with the seasonal fluctuations of temperature and salinity in coastal area. Using a three-dimensional hydrodynamic model, the present paper discusses the effects of ambient flow and seasonal variation of coastal environment on the mixing and diffusion processes of discharged deep-sea water…

Tidal flat is dynamic systems, responding to periodic tidal inundation and climate change. Thermal and hydraulic structures in a tidal flat are controlled by alternating inundation and evaporation. Tidal flat provides an essential refuge and habitat for a great diversity of plants and animal species, and it is essential to manage the tidal flats to ensure the survival of this critical link in the ecosystem. It is, therefore, necessary to understand thoroughly the physical and biological processes in the ecosystem. In particular, temperature, subsurface flow and salinity processes influence plants and animal life, and they are an important factor determining the background state of health and sustainability of the ecosystem…

In response to a recent increase in plane's passengers in Tokyo metropolitan district, extension of Haneda Airport and furthermore construction of a new offshore airport in Tokyo Bay, the third airport in the capital sphere, is planned to solve future shortage of slots for planes. On the other hand, there is growing concern in conservation of environment in the bay. Recent increase in the knowledge of the importance of shallows and tidal flats for the conservation of water quality and marine ecosystems, reclamation of these areas has started to be avoided considering its impacts on the bay environments. Development in the offshore areas in the bay, however, has not necessarily become a social environmental issue because its environmental impacts are still unclear…

This paper presents the results of a coastal engineering, and environmental evaluation, of design parameters, for a fishing boat harbour facility at Anibare Bay, Republic of Nauru. The Government of the Republic of Nauru (RON) requested the South Pacific Applied Geoscience Commission (SOPAC) Secretariat, Fiji Islands, to evaluated the development, and comment on the impacts on the harbour facility on sedimentation and erosion of the adjacent coastline, and also, advise on maintenance of the constructed facility at the development site. An in-country site visit was made and a follow-up visit was done, so as to gain further information and insight on response of the beach-coastal system to the engineered facility. It also provides additional and new time-series observation data.

Chilka lake (19°28′-19°54′N; 85°05′-85°38′ E) along the eastern seaboard of India is one of the largest brackish water bodies in tropical Asia supports more than 150,000 people’s livelihood. Its geomorphic, physiographic, hydrographic and faunistic features conform to the characteristics attributed to a ‘typical’ lagoon. Since 1981, the Government of India has declared it as a Ramsar site and this year the lake received the “Ramsar Award” for successful restoration program monitored by different federal agencies…

In the analysis of the shoreline changes on a coast, where continuous longshore sand transport is interrupted by structures and the downcoast is eroded, comparison of the shoreline changes based on the aerial photographs is often used and useful results have been obtained on several coasts. However, the analysis of the shoreline change does not necessarily lead to sufficient understanding of the events occurring on the coasts and rather direct comparison of aerial photographs is useful. The disappearance of the natural coastal sand dune and sandy beach in Japan has been caused not only by the recession of the shoreline due to decrease of longshore sand supply, but also by the excess advance of the coastal forest as a part of the land use change behind the coastline. This study aims at investigating this issue by using the method of direct comparison of aerial photographs taking the Node coast as the example. Finally it is concluded that in order to prevent further devastation of the coastal environment, overall comprehensive management in the widespread coastal zone including the coastal forest is needed…

With the development of industries in the Yangtze estuary, more and more projects, such as port and waterway construction, land reclamation in deeper waters as well as coastal protection works, have been conducting in the estuary. More detailed knowledge of the tide hydrodynamics and sediment transport mechanism in the water is needed for construction and management of the projects because of difficulties in modeling the characteristics of fine cohesive sediment movement and the complicated flows driven by river discharge, tide, storm surge and wind induced wave…

Yatsu tidal flat is located in the inner zone of Tokyo Bay, Japan, and is extremely unique because of its environmental condition that is enclosed with concrete revetment with the reclaim of its circumference…

Seagrasses are unique marine flowering plants, which grow in shallow, subtidal or intertidal unconsolidated sediments. Seagrass beds have been recognized as a valuable resource critical to the health and function of coastal waters. They have a function of purification of polluted waters through nutrient uptake, supplying foods for aquatic animals and providing shelters to fries, which provide the basis for a highly productive ecosystem (Fonseca et al., 1998). During the past a few decades, however, tremendous losses of this habitat have occurred as a result of development withim the coastal zone. The Environmental Agency (2000) reported that about 4% of seagrass and seaweed beds in Japan disappeared between 1978 and 1991. Those losses have been recognized as one of the causes of the degradation of coastal marine ecosystems, such as decrease in coastal habitats and biodiversity, and increase in nuisance algal blooms due to the lack of water purification function…

The horseshoe crab Tachypleus tridentatus is one of the endangered species and the ecological key species representing the coastal environment. In the past its habitats spread on many coasts of the Seto Inland Sea and the coasts in Kushu. In recent years, however, the number of this animal has been decreasing rapidly in spite of various measures to protect the environment. There are several causes, but one of them is due that many measures had been taken locally in a superficial manner because of the difficulty of selection of the fundamental measures. In this study the history of conservation of horseshoe crab and its spawning ground assigned to a natural monument in Kasaoka Bay in Okayama Prefecture and measures for protection are investigated. Kasaoka Bay was one of the very famous habitats of horseshoe crab in the western Japan. In this bay large-scale land reclamation had begun since 1968, resulting in the disappearance of the ebb tidal flat, being a habitat of larval horseshoe crab. As a measure, a new habitat area of this animal was assigned to a national monument as well as many other activities. However population of the horseshoe crab came to be endangered. Lack of thinking of environmental capacities and physical factors is a critical point. This history tells us the useful information to reconsider the present and future environmental conservation activities, especially in the eco-coast works, in which many kinds of protective measures are to be taken on the Japanese coasts…

Mangrove forests are among the most productive wetlands on earth, representing specialized communities of organisms adapted to the saline environment of the tropics. However, they are also rapidly disappearing throughout the world…

Coastal structures were designed for protection of infrastructure or protection of human life. However due to recent modification of coastal zone law in Japan in 1999, the basic concept of coastal engineering work has been changed. In designing structures, we, Japanese coastal engineers should consider harmonization of structure with surrounding environment. In the present paper, we will consider landscape in coastal environment and the role of dynamic waves in the landscape design. In order to design better landscape, it is necessary to analyze the classic spectacles, which are maintained over the generations in these 1500 years in Japan. Also it is necessary to clarify existing common recognition by applying the concept of collective unconscious.

Typhoons have caused catastrophic damage in Japan by flooding due to storm surges. In spite of implementation of shore protection works and warning notice systems, storm surge disasters have occurred still in recent years…

As an Island Sri Lanka has always been closely related with coastal environment and maritime related activities. Its 1770-km long coastline is a critical lifeline that supports the country’s socio economic and environmental development. Sri Lanka’s coastal region contains 24 percent of the country’s land area and 32 percent of the population within 67 coastal bounded administration units. Also it contains 65 percent of the urbanized land area and nearly 80 percent of the tourism related activities, and produces 70 percent of total industrial output. The coastal region produces 80 percent of the country’s annual fish production from both coastal and brakish water areas. The main infrastructures high ways, rail link and Airports are located within the coastal zone and therefore the coastal areas are extremely important for the national economy…

Small island countries in the South Pacific have been suffering from increased coastal inundation, flooding, and erosion. Fenney (1989) and Carter (1990) reported the occurrences of cyclones over the past century "to average about one cyclone per year with a severe cyclone once every four years" (SOPAC 1996). Loss of mangroves and increased bleaching of coral reefs (Wilkinson 1998) have been also reported. Moreover, IPCC (2001) predicted sea-level rises due to global warming by 2100 to be from 9cm to 88cm. These factors would induce increased threats on the coastal zone in these countries. Therefore, mitigation options to coastal disasters and sea-level rise are an issue of high priority for small island nations such as Fiji, Samoa, Kiribati, Cook Islands, Tuvalu, Solomon Islands, Federated States of Micronesia (FSM), Marshall Islands and Tonga, for almost 90% or more of the vital political, social, and economic zones are located in vulnerable coastal areas. These countries have paid many efforts by conventional or traditional means to protect their coastal areas against the natural disasters. However, it seems that these efforts are not effective and sufficient…

Aim of the study is to show a simple model for cost allocation between construction and maintenance of coastal facilities, which is basically depend on LCC. The authors already suggested financial limitation and LCC 1). Here, the authors mainly concern about the following two problems…

The coastal area contains diverse and productive habitats important to human settlements, development and local subsidence. Planning the coastal land use plays a vital role in coastal zone management. Human-based parameters such as social values, land prices, available natural resources, etc., must be given importance thru the design of pre-determined steps to bring a situation that is mutually beneficial to all concerned entities. Land use change analysis provides a picture on how people react or adapt to environment depending on their needs and values. If these things are fully captured as basis of the land use plans, the people will feel important, thus, will uplift their sense of commitment in the planning and management of coastal areas…

The western and southern coastal belts of Sri Lanka are both socially as well as economically important stretches due to high population density and high concentration of fisheries and tourism infrastructures. This coastline has become more vulnerable to sea erosion, partly due to seasonal variation in the wave climate and partly due to the human interference in the natural sediment movement process. Human interference is in the ways of sand mining in the rivers (thus reducing the sand supply to the coast), destruction of nearshore coral reefs for economic activities, utilizing coastal zone for unwarranted development activities and ad-hoc construction of hard structures to arrest the coastal erosion…

Being an island with a total of 1770 km long coastline, the aquatic environment which endowed with rich aquatic habitats plays an important role in Sri Lanka’s economy. The exploitable fishery resources of the country could be broadly categorized into fresh water, brackish water and marine water, of which marine waters provide more than 80% of the total fishery resources…

Coastal natural resources in the Cox’s Bazar coast of Bangladesh have been used for multi purposes and strongly influenced socio-economic development. Remote sensing imageries provide cost-effective support in compiling the latest information about the environment and natural resources, while GIS brings new functions for multidisciplinary technology and decision support. The integrated analysis can serve as vital inputs for better planning, policy formulation, and decision-making in national development. Landsat TM image and topographic maps of some coastal islands namely Kariadia, Matarbari, Moheshkhali and Sonadia in Cox’s Bazar coast were analyzed; and hill, plain land, tidal land, mangroves and waterways were identified and mapped. The opinions of the local community are considered based on the results of a participatory rapid appraisal carried out among the coastal stakeholders. The major sources of livelihood for coastal communities are agriculture, aquaculture, fishing, fish drying, sea salt production and trading. Proper resource utilization and integration among stakeholders activity can increase environment-friendly production efficiency, which have a positive role in successful poverty alleviation program and socio-economic development of coastal rural communities. Finally, this study demonstrates the utility of extracted coastal information to coastal zone managers.

A X-band nautical radar system has been employed to observe sea surface patterns during a storm event. Wave gauges and current meters are employed in a conventional field survey, however, the deployment of the instruments is limited, especially in the surf zone. In this context, a radar system is introduced here, which can remotely and broadly infer the sea surface state even during a severe sea conditions…

There have been several methods to measure sediment transport rate as suspended load, as well as bed load (e.g., Horikawa, 1988; Seymour, 1989). As for the former mode of sediment movement, the methods proposed up to now can be classified into two groups: (1) light transmission meters and (2) sand samplers. Both type of the measuring system has provided a number of observed data that has been utilized for understanding mechanism of sediment movement and resulting beach topography change. However, all of these existing systems are not suitable for simultaneous data acquisition in vertical direction with sufficiently high spatial resolution, because of the size of a sensor. In the present study, a profiler system is developed for measuring system, which enables us to determine spatial and temporal variation of sediment concentration under waves and/or unidirectional flow.

An accurate estimation of gas transfer velocity at the air-sea interface is very important to understand environmental mechanisms of the ocean and coastal area. A wind dependent gas transfer model proposed by Liss and Merlivat model has widely used the last decade. The gas transfer velocity of the Liss and Merlivat model increases rapidly when the wind speed exceeds 13m/s. This rapid increase of gas transfer velocity is explained by several reasons such as enhancements of wave breaking induced turbulence, breaking wave induced air bubbles, and sea spray. However, quantitative roles and detail mechanisms of the enhancement are not well known due to the lack of detail measurements. To understand the gas transfer enhancement in high wind speed region, the bubble mediate gas transfer is one of important phenomenon…

In a surf zone, numbers of bubbles are entrained through a splash-up cycle of plunging jets, possibly impacting on physical and biological nearshore environment – sediment transport, vegetation and water quality. Especially, size and number distributions of the bubbles are predominant factors to determine the drags for the surf zone flow and also gas transfer rate in this region. The distributions may depend on the local fluid motion under breaking waves and surfactant contained in seawater. In this paper, size spectra of the entrained bubbles in the surf zone and the effect of surfactant to the spectrum are investigated on the basis of an acoustic experiment. An interconnecting relation between the jet motion and the bubble size is also examined. The so-called micro-bubbles, suspended in water for long time, were trapped in situ experiments, and the void fractions under seawater breaking waves were also estimated…

Major inner bays in Japan are in chronic eutrophication and suffering from so-called red tide and blue tide or anoxia in summer, which often cause serious damages to coastal fisheries and environments. In order to improve the water quality and reduce the damage, various kinds of countermeasure have been carried out, which include reducing inflow load of nitrogen and phosphorus, removing organic bottom mud and covering the bottom mud with sand etc. Continuous monitoring of water quality is very important to grasp the effects of these countermeasures and to take proper procedures. Mikawa Bay (area = 604km², mean water depth = 9.2m) is a shallow and closed inner bay connected to Ise Bay, where the water quality problems have increasingly been serious due to eutrophication. The prefectural government has continued water quality measurement every month at about 20 locations in the bay. More frequent measurements at more locations are however necessary to understand the dynamic behavior of water quality in the bay…

Coral reefs frequently exist in complex and dynamic environments. Although anthropogenic effects such as introduction of terrigenous sediments are often assumed to be primary stressors of coral reef communities, a quantitative link between these potential stressors and the decline of reefs is seldom established. This study aims to derive meaningful relationships between data gathered from inland field surveys, hydrologic modeling and results of remote sensing data analysis in monitoring the sedimentation in a coral reef environment. In demonstrating a direct coupling between land and ocean processes, remote sensing acted as the integrating method of analysis…