Asian and Pacific Coasts 2017

The following sections are included:

• Preface
• APAC 2017 Paper Review Committee Members
• Contents

A two-dimensional numerical wave tank based on the CIP (Constrained Interpolation Profile) method was developed to investigate the shoaling of solitary waves at different slopes of beaches, which were simulated by virtual particles. The generation of solitary waves was first verified by comparing with the analytical solution, and the numerical cases were validated by experimental results from published paper. Then, three amplitudes of incoming solitary waves were simulated on two kinds of slopes: one was a straight beach; another was a composite one which means its inclination varies. Furthermore, elevation of the water surface was measured by wave gauges to examine the distinguished features of solitary waves on diverse beaches.

A nonlinear Schrödinger equation for the propagation of two-dimensional surface gravity waves on linear shear currents in finite water depth is derived. In the derivation, linear shear currents are assumed to be a linear combination of depth-uniform currents and constant vorticity. Therefore, the equation includes the combined effects of depth-uniform currents and constant vorticity. Furthermore, the influence of linear shear currents on the Peregrine breather is also studied. It is demonstrated that depth-uniform opposing currents can reduce the breather extension in finite water depth, but following currents has the adverse impact, indicating that a wave packets with freak waves formed on following currents contains more hazardous waves in finite water depth. However, the corresponding and coexisting vorticity can counteract the influence of currents. If the water depth is deep enough, both depth-uniform currents and vorticity have negligible effect on the characteristics of Peregrine breather.

To investigate the interactions between the bidirectional regular wave trains, the numerical ‘X’ configurations with different approaching angles were designed based on a fully non-hydrostatic 3D free surface flow model. The interactions of two identical regular wave trains with a relatively approaching angle of 16° were firstly simulated to verify the present model. Then, to have a deeper understanding of the influence of propagation direction on the interactions between the bidirectional wave trains, more numerical simulations with larger approaching angles were conducted. The results show that the approaching angle of wave trains is highly correlated with the interaction between bidirectional regular waves, large approaching angle can lead to intense interactions and strong three-dimensional characteristics of the wave trains after interaction. Furthermore, the maximum wave height produced by interaction was obviously observed to be reached before propagating to the center of the interaction region for large approaching angle.

Theoretical and laboratory studies are performed to analyze the wave attenuation phenomenon over fluid mud under current. In the theoretical part, a semi-empirical formula is derived to model the attenuation process under current. Based on the linear wave theory, the change of wave amplitude is related with the averaged damping effect of the muddy bed. By solving a differential equation, the exponential decay of the wave amplitude is confirmed. A function called damping function is used in the formula, and it is expanded into a series of wave parameters and some undetermined coefficients called auxiliary damping factors. Based on the assumption that the mud properties do not change under current, the formula is combined with the dispersion relation for linear wave under uniform current to describe the attenuation process under current. Laboratory experiments are conducted first without current. The data of wave attenuation are collected and inserted to the formula obtained in the theoretical analysis to figure out the values of the auxiliary damping factors. The second set of experiments is conducted under current and the collected data are compared with the calculated values obtained by using the newly proposed formula with the dispersion relation. The result of comparison shows good applicability of the new formula to the wave attenuation under current.

Due to refraction, the oceanic ridge acts as a waveguide forcing long-period waves to propagate along the topography. Based on the linear shallow water equations, analytical solutions of trapped waves over a hyperbolic-cosine squared ocean ridge are obtained, which are described by combining the associated Legendre functions of the first and second kinds. The spatial distribution pattern for each mode is discussed, and the wave amplitude gets the maximum at the ridge top and decays gradually towards both sides. The higher the mode number, the slower the rate of amplitude decreases, so that more energy is distributed over more of the ridge. The trapped wave number is not only related to the frequency, but also to the varying water depth parameters.

This paper presents results for studied on harbor resonance change according to harbor layout change in Sadong harbor where is located in Ullengdo island on the East of Korea. The dominant resonance modes simulated in 32 sec, 48 sec and 4.8 minute inside harbor. And the amplification factors obtained by 11.0, 11.1 and 10.4 when harbor layout is before construction, and 6.0, 6.1 and 7.3 in case after construction. The amplification factor after construction decreased in 30∼45% than results of before construction. This is due to incident wave energy trapped by expanded harbor basin after construction. On the other hand, the dominant resonance modes at expanded harbor basin after construction simulated in 34 sec, 48 sec and 70 sec, and amplification factor obtained by 11.6, 22.8 and 8.9 respectively. It is need to plan harbor resonance reduction measure about 48 second wave period in expanded harbor basin after construction.

Waves play a very important role in the mixing process of oil slick, and greatly affect the distribution of oil pollutants in the water column near sea surface. In this study, the mixing process of spilled oil under breaking waves is simulated by using a multiphase SPH-based model. The model is an extension of our previous model. Modifications for two-phase flow are introduced to solve the instability problems caused by the high density ratio at interfaces. The surface tension between two fluids is also included in the multiphase model. The model is tested by simulating the deformation of an initially square droplet in another fluid due to surface tension, which is a classic problem usually used to test the two-phase flow model. The density ratio between the two fluids has been set to be 1/1000. The results show that the new set of SPH formulations can well deal with the large density difference at the interface of two fluids. And then it is applied to simulate wave breaking where the water surface is covered by a layer of oil. The mixing process of surface oil slick in water column is demonstrated.

Big wave suddenly invaded to the beach, and three children were carried off to the sea by the wave though they played on the beach. The beach characteristic topography has the cusp topography and steep slope. This study tried to comprehend the reason why this accident occurred. Firstly, this study comprehended the wave condition when the accident occurred. Secondary, this study made the survey about the geographic feature of the beach. And this study obtained the geographic data for the numerical simulation from the aerial photograph which were taken by UAV. Finally, this study comprehended the wave dynamics on the beach by the numerical simulation. This study simulated the wave dynamics by the horizontal two dimensional numerical model and the vertical two dimensional numerical model.

The berm breakwater or reshaping breakwater is a special type of breakwater. The main advantage of this type of breakwater is the requirement of relatively smaller sized armour stones which accelerate the construction speed and reduce the cost of the construction. The stability of berm breakwater is strongly influenced by the weight of units used in primary layer, interlocking properties of the armour units, geometry (width and elevation) of the berm, down slope and the toe berm characteristics. In the present study, the experiments are carried out to study the structural and hydrodynamic response of trunk section in 13m water depth for the berm breakwater proposed at Gopalpur port, Orissa, India. The studies are pertaining that simulating the cyclonic wave condition of Phailin cyclone (October 12, 2013) which has crossed Gopalpur, partly damaging the berm breakwater under construction. The breakwater is designed as a non-overtopping structure with the crest level of (+) 11m CD. The berm width of 15m and the berm level of (+) 6.7m CD is adopted considering the constructional feasibility. The down slope of 1V:1.5H is considered. The armour stone gradation is 3T to 5T, 5T to 7T and 9T-12T has been adopted. For the present experiments, 1:35 scale model has been chosen and tested under long crested random waves. The stability of the structure is compared to the tests under design water level at Mean High Water Spring (MHWS) + storm surge and at MHWS. Swell and Sea wave parameters are considered for the MHWS + storm surge and MHWS respectively. The recession of the primary armour layer has been measured and which is compared with the stability and failure criteria reported in the literature and the design guidelines for berm width. It is found that recession is 2 to 3 times of the diameter of stone. The wave run-up and overtopping discharge also presented in this paper.

In the nature, wind load on the ocean engineering structure is about 1/10 of the total loads under the coactions of wind, wave and current. However, for floating structures in water or ships, if the damping of the mooring system is small, and the period of the main energy of wind field is close to the oscillation period of the mooring system, the pulsating wind may generate relatively obvious oscillation on the mooring system, and the pulsating load at this situation cannot be ignored. Even though wind is one of the major loads on ships, oil platforms and offshore structures in the marine environment, uniform wind is often used to simulate in the physical model experiments of ocean engineering at present. However, wind is not uniform in nature with strong random pulsatility. It is more practical to master the simulation law of fluctuating wind field rather than to study the ship stress and motion response under random fluctuating wind field. To explore the effects of these parameters on the wind spectrum, a serial of control experiments are conducted, which provides a testing environment of the following research on dynamics of water transport engineering.

To compare the future changes and their uncertainties of typhoon intensity and storm surge between Super Typhoons Haiyan (2013) and Melor (2009) due to the differences of global warming scenarios (SRESs) and general circulation models (GCMs), two kinds of ensemble pseudo-global warming experiments are conducted using a high-resolution typhoon model and a storm surge model. In the case of Typhoon Haiyan (2013), the future changes of the ensemble-averaged minimum central pressures are relatively small in both SRESs and GCMs. The uncertainty (standard deviation) of peak intensities in GCMs is greater than that in SRESs. In the case of Typhoon Melor (2009), the peak and landfalling intensities averaged tend to be intensified in both SRESs and GCMs. Because of its future intensification, the future storm surge at Mikawa Bay, Japan, is also likely to be enhanced. It is concluded that the uncertainty of typhoon intensity change of the well-mature typhoon is greater than that of the landfalling typhoon, owing to stronger vertical wind shear of a mid-latitude westerly jet.

In order to examine the detailed mechanism of typhoon intensity changes under the future climate, a number of sensitivity experiments on typhoon intensity are made using a high-resolution typhoon model. The uncertainties of the future intensity changes are also quantified by the comparison of the sensitivity experiments among global warming differences (GWDs: sea surface temperature, air temperature, wind speed, and relative humidity) derived from general circulation models (GCMs). The comparisons of ensemble averages of simulated typhoon intensity between sensitivity experiments and a present-climate experiment indicate that sea surface temperature in GWDs is responsible for intensifying the future typhoon by about -19.6 hPa. On the other hand, air temperature in GWDs is accountable for weakening the future typhoon by about +45.5 hPa. The comparisons of standard deviations of typhoon intensity between sensitivity experiments and pseudo-global warming experiments suggest that the uncertainties of air temperature and wind speed in GWDs significantly reduce the reliability of the future projections on typhoon intensity.

One-month wave simulations were performed from Oct. 1st to Nov. 1st in 2014. The one-way numerical models composed of WRF (Weather Research and Forecasting) and SWAN (Simulating WAve Nearshore) were used. This research focused on evaluations of both a resolution of wind data and a difference between structured SWAN (STSWAN) and unstructured SWAN (UNSWAN). The results show some differences among case studies. High resolution wind data affect peak values of significant waves at typhoon periods. In addition, the overestimation of swell caused by typhoons decreased at the nearshore points, in particular at Shimoda by using UNSWAN. As a conclusion, there is little difference between STSWAN and UNSWAN on the overall simulation of wave climate. However, UNSWAN is useful for simulating nearshore waves and has possibility to predict wave climate with higher precision than STSWAN.

Increasing the tsunami disaster resilience of the Southwestern coastline of Sri Lanka is a pressing problem, due to the continuous presence of unprotected human settlements in tsunami-prone areas. Even though a variety of different tsunami countermeasures can be attempted, due to budgetary limitations early warning systems are typically used. Some types of coastal structures (such as coastal railway embankments, revetments etc.) have the potential to mitigate the impact of tsunami, which is often overlooked in research. The engineering resilience of these structures needs to be improved if they are to withstand a tsunami, though upgraded structures can offer a multitude of co-benefits to residents. This research assesses resident’s willingness to pay (WTP) for hard defensive measures, as well as the socioeconomic factors that influence residents’ WTP. WTP of residents to upgrade a coastal railway embankment and a revetment in Dimbuldooa and Wenamulla villages was measured by conducting a structured questionnaire survey of 200 residents. The results of the survey were triangulated through five expert interviews with representatives of government agencies, construction companies and academia, and two focus group discussions with residents. The findings suggest that it is necessary for disaster risk managers to pay special attention to socioeconomic factors to successfully enhance the resilience of community.

Typhoon Meranti (locally named Ferdie) traversed the Northern Pacific Basin, affecting the Batanes Islands on September 10 to 15 of 2016. It was estimated that PhP 244.6 million in damages to houses and communities was left in the typhoon’s wake. Numerically modeling the storm surges during Typhoon Meranti, and incorporating the sea level rise simulations is vital in assessing the long-term vulnerability of Batanes’ coastal communities. This study aimed to simulate storm surges during Typhoon Meranti using the Advanced Multi-Dimensional Circulation (ADCIRC) model and to apply a sea-level rise scenario to the validated and calibrated model. The model was calibrated and validated versus tide station observations at Basco Port, Batan Island. The model yielded an RMSE of 14.45% versus the observations. The maximum surges simulated along Batan islands were below 0.50 meters, while it was observed that simulated storm surges in Sabtang island reached 1.50 meters. The sea-level rise scenario simulations were observed to output storm surges 93.65% higher in 2030 than those observed during Typhoon Meranti. It was also observed that the relative difference of the storm surge heights decreased from 2030 to 2100.

The present study carries out the comparison of the water level associated with the numerical methods: Finite Difference Method (FDM) and Finite Volume Method (FVM) and the simulation considered on the present climate condition along the coast of Bangladesh. The governing equations of the first model are discretized through FDM and solved by a conditionally stable semi implicit manner on an Arakawa C-grid system. For the second model, α-coordinate is used for the irrational bottom slope representation and the mesh grid of the study domain is generated by the unstructured triangular cells. The feasible study domain with coast and island boundaries are approximated through proper stair steps for the FDM and the unstructured mesh representation for FVM. A one-way nested scheme technique is applied to the first model to include coastal intricacies as well as to preserve computational cost. Both the models are applied to extrapolate sea-surface elevation associated with the catastrophic cyclone 1991(BOB 01) along the seashore of Bangladesh. The simulation results from both the models are statistically copacetic and make a good acquiescent with some observed and reported data. In the statistical viewpoint, both the method has a good acceptance in storm surge simulation, but this study ensures the strong positive reconciliation with observed data and FVM simulation data. In Bangladesh region, it will be wise decision to use Finite Volume Methods for simulating the storm surge.

India being an agricultural based country depends mainly on rain water and river for the purpose of irrigation and other domestic uses. Due to deforestation and urbanization, large area of unpaved surface is converted into paved surface, which prevents percolation of rainwater into ground. As a result, surface runoff and intern the chances of flood increases. Flood causes damage to hydraulic structures, agricultural land, properties and lives. On the other hand many states of India are facing water scarcity. So it is important to carry out flood forecasting to reduce uncertainties in hydrological predictions, which balances these two problems. Some of the catchments in India are ungauged as a result, surface runoff estimation will be inaccurate and also it is very difficult to understand catchment properties and hydrological response to rainfall. Suitable methods are desirable for hydrological evaluation of watershed in the absence of runoff-rainfall data. Remote Sensing and Geographic Information System with appropriate rainfall runoff models, provides ideal tool for estimation of direct runoff, peak discharge and hydrographs. This study focuses on estimation of peak flood discharge at coastal inlets, from river outlets along the southern coast of India in Kerala. Flood estimation methods recommended by Central Water Commission (CWC) India, in report 5a and 5b is considered as reference and Soil Conservation Service Method (SCS ) used for peak flood estimation.

In response to the potential floods caused by typhoons to Shanghai city, China, several proposals emerged to protect the region. This paper, based on the ‘System Engineering Approach’, presents the design process and a feasible design for the storm surge barrier system in the Yangtze Estuary. A challenge for this 15 km long barrier system is to cross Yangtze Estuary, including two islands and three channels at the Yangtze River mouth. A storm surge barrier is required to close the coastal spine and prevent storm surges in the Yangtze Estuary, but not to obstruct shipping under normal conditions.

Super Typhoon Meranti was one of the strongest typhoon that made landfall in the Philippines in 2016. Following the typhoon event, a post-disaster survey was conducted by Tajima et al. (2017), wherein inundation levels and wave runup heights were measured at 37 locations along the islands of Batan and Sabtang, Batanes. This paper discusses the results of the numerical modeling efforts performed to simulate the storm tide levels in Batanes Islands, and the comparisons of the simulations with the observed water levels. The numerical storm tide model for the study area was developed using the two-way coupled Delft3D-SWAN hydrodynamic and wave models. The observed water levels from the tide monitoring station in Basco Port in Batan Island indicated that the peak water level during the passage of Typhoon Meranti is only 0.87 m above MSL, while the simulated peak water level is 0.72 m above MSL. Comparing the results of the simulations to the findings of the post-disaster survey conducted by Tajima et al. (2017) showed that the simulated peak water levels at the survey locations were consistently and drastically lower than the measured water levels. The observed error in the simulated peak storm tide in Basco Port is less than 20 cm, and therefore does not account for the large differences between the measured inundation levels and simulated and measured inundation levels. The large differences are attributed to other nearshore processes (e.g. surge height amplification due to the fringing reefs) that are not considered in the current storm tide numerical model setup, and shall be investigated in a future study.

The tidal record on the East Coast of the United States reveals the frequent semidiurnal perturbation of the storm surge on the South Atlantic Bight. Tropical cyclones were examined to be one of the main triggers for these perturbation events. The peak of the storm surge is centered in the mid of the South Atlantic Bight, and radiating along the coast southward and northward. The process-oriented experiments were designed with parametric determination based on the historic events. The experiments were carried out in order to further discuss the various factors of tropical cyclones for their effect on the storm surge and tide interaction. The experimental analysis shows the storm surge and tide interaction is the most severe when a cyclone is moving orthogonal to the coastline, although the parallel-to-shore tropical cyclones are the most observed in history. The intensity of the semidiurnal perturbation to storm surge is positively correlated to the wind strength and the radial of the maximum wind speed of a cyclone, but negatively correlated to the translation velocity of a cyclone. For a cyclone moving parallel-to-shore, the corresponding storm surge perturbation lasts the longest and is the strongest, when the “fetch” of the alongshore wind with speed >17m/s (the criticality of the wind speed of the Tropical Storm based on the Saffir-Simpson category) reaches the maximum on the continental shelf of the mid of the South Atlantic Bight. High correlation is found between the tropical cyclone induced alongshore oceanic current and the semidiurnal perturbation to storm surge.

Super Typhoon Meranti brought extreme waves which resulted in severe inundation in the coast of Batan on 13 September 2016. A post-disaster survey revealed the maximum wave runup height of 6.3m and the maximum inundation depth of 6.1m. This study focuses on the small coastal community called Ivana where wave amplification and wave concentration were observed. A 1D Boussinesq model is constructed to simulate the wave transformation over the fringing reefs fronting Ivana. The results show that the 1D model can capture the basic wave characteristics and how they evolve over the reef. However, the 1D model cannot account for the two-dimensional variation of the wave properties. In the case of Ivana, further investigation by a 2D model is recommended to simulate the possible occurrence of either standing or progressive edge waves.

Numerical analysis of the inundation of the land behind the Roxas Boulevard Seawall is carried out to study the impacts of critical historical typhoons on coastal flooding. The numerical implementation based on ADCIRC with a coupled surge-inundation capability is discussed relative to existing conditions of the seawall. The simulative analyses are undertaken to study the implications of a “do nothing” scenario wherein the critical typhoons cause overtopping and inundate the land behind it. The results indicate the inland extent of potential inundation, reduced depth of the peak storm tide in front of the seawall, a rapid gradient of inundation depth behind the seawall, and the prominent role of Pasig River in inundation propagation inland, among other things.

This study aims to determine the behavior of storm surge in San Pedro Bay generated by historical storms to understand the storm surge characteristics produced by different storm parameters. For this purpose, the Advanced Circulation Model (ADCIRC) is the hydrodynamic model used to simulate the storm surge in San Pedro Bay and the Holland 1980 Typhoon Model is used to model the pressure and wind distribution over the model domain. A total of 12 historical typhoons, including Typhoon Haiyan, are selected based on wind intensity and proximity to the study site as well as typhoons that have generated storm surges in the past. Results show that storm surge is concentrated at Basey, Samar for typhoons with tracks above or crossing the bay while typhoons with tracks south of the mouth of the bay have simulated storm surges that have almost equal rate of decrease from the inner part to the mouth of the bay. The windspeed may be an indicator of the severity of the storm surge. Typhoon Haiyan 2013 with 110 kts (204 kph) maximum sustained) wind speed has simulated storm surge peak of 4-6 meters, Typhoon Agnes 1984 with 105 kts (195 kph) wind speed has simulated storm surge peak of 2-3 meters, and Typhoon Axel 1994 and Typhoon Cecil 1979 with 75 kts (139 kph) wind speed both have simulated peak surge of 1-2 meters, inside San Pedro Bay. Moreover, the results show that Tacloban in Leyte and Basey in Samar are the most storm surge-prone areas, which may experience 1-6 meters of storm surge depending on the typhoon characteristics. Furthermore, a slow-moving typhoon has longer time to peak than fast-moving typhoons.

Tsunami caused by Tohoku earthquake in 2011 had flooded many oil storage tanks, and these tanks brought many secondary damages on coastal area by fires. In order to reduce those secondary damages, an idea of using a mooring line to check the drift of the oil storage tank was proposed. This research examines an effective mooring system that restrains the motion of a floating tank in tsunami flow. A series of hydraulic experiments were carried out under some different mooring conditions in order to discuss the characteristics of tank motion. Furthermore, this study discusses the characteristics of a drag coefficient to obtain an equation to estimate the fluid force on a semi-immersed cylindrical tank.

When a tsunami comes to seaside industrial areas, seawater would enter landside areas through underground pipelines and induce inundation disasters. In the present study, the authors aim to investigate the risks of this tsunami inundation via the pipelines using the numerical simulation model. The results indicated that the influence of the tsunami inundation via the pipelines on seaside areas is not small and especially it will likely to influence the initial phase of evacuation. It is therefore important for port authorities and city planners to consider such risks when developing tsunami mitigation plans.

Tsunami run-up through the river is one of important features for better predictions and estimations of inundation characteristics. This study carried out numerical investigations of observed tsunami inundation around the Kido river especially focusing on the prediction of run-up speed of tsunami along the river. Based on non-linear long wave model, a sensitivity analysis was first carried out by changing several computational conditions such as tsunami profile, bottom frictions and the river discharge. It was found through this analysis that these conditions, within the range of expected uncertain variations, have certain influence on predicted run-up speed of tsunami. Second, this study also investigated the influence of the different discretization schemes of the model on predictive skills of the speed of tsunami run-up. Difference of conservative and non-conservative forms of non-linear term was investigated through numerical experiments of non-viscosity Burgers equations and it was found that the difference of these forms has significant influence on the predicted propagation speed of the bore. The same analysis was applied in the case of the Kido river and it was found that the tsunami run-up speed was increased up to 40% by selecting appropriate discretization schemes of conservative form.

The real-time prediction of the meteotsunami is very difficult because the micro-pressure wave is too small and quick to identify from numerical weather forecasting results. In this study, we analyzed the meteotsunami from high time resolution measurement data and examined predictability of it by an artificial neural network model (ANN model). The appropriate combination of input data is very important factor in order to make a highreproducible model. In addition, the number of units of intermediate layer, training epochs and a lead-time are also notable model parameters. We discussed about these effects based on sensitivity analysis of an ANN model.

A tsunami force has unknown features due to its complexity, and makes it difficult to be predicted accurately. As a typical example, in the 2011 off the Pacific coast of Tohoku earthquake with huge tsunami, many breakwaters slid or fell down by the unexpectedly terrible damages caused by the tsunami. For effective design of coastal structures, achieving a correct prediction of the tsunami pressure should be an urgent subject. In the existing studies, the tsunami force F with an overflow is estimated by using a compensation coefficient α based on the hydrostatic pressure as: F = αρgh. The compensation coefficient α is usually set as α = 1.1 for the front of the caisson and 0.9 for the rear of that constantly. However, in recent studies, it was found that Parameter α can be easily and randomly changed depending on the boundary condition, and unfortunately, estimation method of its effective has not been developed yet. To resolve this problem, in this study, hydraulic experiments targeting on tsunamis with their overflows on a breakwater are implemented to examine the variability of the compensation coefficient α. And from the experimental results, a simple and effective estimation method for the compensation coefficient α is newly proposed.

After field surveys on the Tohoku earthquake tsunami in 2011, coastal engineers recognized the importance of persistent coastal structure to reduce the tsunami damages. It is important to understand the characteristics of tsunami flow formed around the breakwater and rubble mound with three-dimensional configuration. The applicability of CADMAS-SURF has been investigated mainly in two-dimensional wave deformation problems and few investigation has been done in the case of three-dimensional tsunami flow problems. CADMAS-SURF/3D was employed to simulate tsunami flow over the breakwater. In this study, a numerical half-basin domain was considered in 3D simulations. Hososhima Yojima breakwater was selected as the prototype structure. This is one of the breakwaters that are needed to be reinforced to realize a persistent breakwater against a supposed L2 tsunami attack on the eastern side of Kyushu Island. This study firstly discusses the applicability of CADMAS-SURF to the three-dimensional tsunami flow problem. Some hydraulic experiments were conducted to verify the validity of numerical results. This study also discussed some characteristics of tsunami flow over the breakwater such as tsunami flow passes through the gap between caissons, the effect of the partial subsidence of caissons on tsunami flow above the rubble mound, and the characteristics of tsunami flow in around a breakwater.

Hydrodynamic properties of the breaking bore run-up process were investigated under a sloping dry bed condition. A series of laboratory experiments were performed using a 1:7.5 stainless steel slope and a dam-break type PVC-made flume. Under the dry bed condition, different flow velocities were generated by adjusting initial water levels from 8cm to 24cm in the upstream reservoir. The bore propagation velocity and the maximum run-up height were obtained from images recorded using a high speed video camera. Existing models underestimate the present measured maximum run-up height, which is ascribed to the phenomenon that multiple ensuing bores generated by the water mass compression overpass the preceding bore front during the run-up process. Nevertheless, water depth of run-up front under the dry bed condition is much smaller than that of the wet bed condition which contributes to the generation of multiple ensuing bores.

The authors have concerned in the assessment about Cambodian shoreline since 2008, and made many observations and made the geographical map, water flow mechanism, weather and etc. This study reports the observation result and feature of geography, tidal change and weather. And furthermore, this study simulate the tidal flow and wind-driven flow. Ultimately, this study try to know the flow mechanism of this region. Firstly, this study performed the field survey and got the information about the feature of the current, topography, the tidal level and the wind. Secondary, this study made the geographic data by the sonar data. Finally, this study did the numerical simulation about the tidal current and the wind-driven current, and tried to comprehend about the current mechanism in this region.

Tidal energy is one of the clean and non-depleting renewable energy sources. In contrast to other clean sources, such as wind, solar, geothermal etc., tidal energy can be predicted for years ahead. Also, the medium, seawater, is more than 800 times denser than air and the astronomic nature of the underlying driving mechanism results in an essentially predictable resource, although subject to weather-related fluctuations. These features make it an important energy source for global power production in the near future. There are various types of tidal power plants across the world with varying tidal elevation. Also the method of conversion of the tidal energy into electrical energy is site specific. For example, we can adopt conventional method to extract energy in high tidal regions. But when it comes to low tidal regions like the southern India where tidal elevation measurements does not exceed 2.5m, there is a need of low flow turbines which can extract higher energy from lower head. An important factor that is responsible for the velocity of tidal stream is the tidal inlet dimensions. In this paper, an attempt has been made to identify the feasible locations for extraction of potential tidal energy along the Indian Coast.

Rip current observation has been conducted with a X-band radar at a swimming beach in Japan for 40 days in a summer. The radar set is on the beach, approximately 300 m backwards from the water line, to observe the sea surface states over 1500 m in the longshore. Instantaneous radar images are processed every 2 minutes to yield time averaged images. From the time averaged images, features like distribution of waterlines, breaker zone, locations of rip channels, rip heads and currents can be interpreted. Rip channels and occurrence of rip currents are manually digitized from the time averaged images. In the first half of the observation period, rip currents seemed to occur randomly, and were not connected with rip channels. On the contrary, after an attack of high waves in the middle of the observation period, most of the rip currents were detected in the vicinities of rip channels. During this period, rip channel migrations were observed. Occurrences of rip currents have been detected in the whole period when the incident wave height exceeded 0.3 m.

Simulative analyses were carried out to study the effects of sea level rise (SLR) and global climate change scenarios on storm tide levels fronting the Roxas Boulevard seawall. Storm tides under historical typhoons and various periods of SLR were computed using ADCIRC storm surge model. The contribution of storm waves to the non-overtopping crest elevation was also studied using a nearshore wave model. Return periods of various design water levels were also associated with the various SLR and GCC scenarios to establish bases for the rehabilitation design of the RB seawall.

Sediment transport is the mechanism by which coastal erosion and accretion proceeds. Siltation in harbours and their approach channels is one of the major concern connected with the expansion of existing and development of new harbours in the coastal ecosystem. The economic of harbours is directly related to their annual maintenance dredging, and as such a proper assessment of the quantity of siltation and provision of adequate measures for the maintenance of approach channel depths would form an important integral part of planning and maintenance of the port. Model studies on littoral drift and sediment transport along coastline south of Chennai port is carried out using LITPACK and integrated Coupled Model MIKE21 FM with Hydrodynamics (HD) model, Spectral Wave (SW) model and Sediment Transport (ST) model. Two alternative locations for the sand trap were considered and these sand traps were examined in detail for the trapping efficiency and safe dredging operations. The annual sediment deposition in the proposed Sand Trap near the approach channel is of the order of 0.58 Million m³. The model simulations indicated accumulation of sediments immediately on the up drift side of the sand trap with some siltation near the junction of trap and the approach channel. A minimum gap of 75 m to 150 m has to be provided between the breakwater toe and the top edge of the side slope of sand trap

A two-dimensional porous-elastoplastic model, in which the influence of the reduction of the effective stress on the soil strength has been considered, is proposed to investigate the accumulation of pore water pressure under standing wave. The simulation results show that the liquefaction is likely to occur around the node due to the accumulation of pore water pressure. The liquefaction leads to the decrease of soil resistance, which has great effect on the development of the residual pore pressure. The simulation demonstrates that if the decrease of soil resistance is not considered, the soil liquefaction depth will be overestimated.

Transport of sediment discuss with physical phenomena including bottom shear stress. However, soil particle surface has negatively charge and adsorb cations. Understanding of transport and deposition of sediment, we need to consider not only physical phenomena but also chemical phenomena including adsorbed ion and ion concentration. In this paper, we focused on variation on property of sediment by ratio of adsorbed cation, pore water ion concentration. To consider the resuspension of sediment, it is important to clarify the factor of critical shear strength change. In this study, we focused on liquid limit related with shear strength. Considering cohesion and repulsion force of sediment based on DLVO theory, ionic strength of pore water and adsorbed ion are important parameters determining electric double layer thickness and surface potential. It is expected that when the ionic strength becomes higher, the electric double layer becomes thinner and sediment tends to aggregate easily. In this study, to understand the factor of shear strength change, we discussed relationship among liquid limit, adsorbed cation of sediment, ion concentration of pore water. The results revealed that amount of adsorbed ion have a little effect for liquid limit. However, strong correlation exists between the ionic strength of pore water and the liquid limit.

This study investigates characteristics of wave deformation on a coral beach and behavior of coral gravels under such forward-leaning waves through two different laboratory experiments. All these experiments were captured by multiple video cameras mounted beside the glass wall of the flume and water surface fluctuations, topography change, nearbottom current velocities and gravel velocities were quantitatively extracted through the analysis of recorded images. Primary findings of the experiments are as follows: (i) deformation of nearshore waves and bed profiles dynamically interacted with each other and developed steeply sloping coral bed around the swash zone enhanced the formation of partial standing waves; (ii) initiation of motion of the gravels depends not only on the local bottom shear stress but also on the positions of each gravel relative to the others; (iii) after the initiation of motion, behavior of gravels were dominantly determined by the surrounding flow velocity but not by the bed conditions.

It is important to estimate the scouring depth for the design of coastal facilities against tsunamis. The past researches indicated that the maximum scouring depth was proportional to the overflow time. In this study, in order to clarify the relation between overflow time and scour depth behind the structure, experiments and numerical calculations were carried out and analysis of the past experiments was conducted and discussed. The results showed that the scour depth could be evaluated approximately using the total flow rate and the verification of the numerical simulations were confirmed

Yangtze Estuary deepwater channel improvement project started in 1998. The channel depth have been dredged from 7.0m (under Theoretical Lowest Water Level) to 8.5m, 10m and 12.5m. After the project, which formed the regulating line along the groins heads and adjusted the flow fields, deepened the mouth bar area and merged the ebb with flood channel, a faintly-curved channel was obtained in the North Passage. At the same time, in other passages such as in South Passage and North Channel, the mouth bar is still persisting after the project as long as mouth bar terrain has disappearing in north passage. In this study we will focus on the Yangtze Estuary, with major aims: (a) to reveal the evolution process through field data analysis before and after the project reveal, and compare the different evolution model of three main passages in Yangtze Estuary, (b) to understand and quantify the effect of measures like the navigation works on the natural morphological system, (c) to obtain more insight in the large-scale morphological development in estuaries and the underlying processes and mechanisms, with specific interest in the bifurcating channels and the development of the inter-tidal flats, (d) to predict the long-term impact of the human interventions to the large scale morphological development of the estuary, to understand and quantify the large-scale response of the morphological system to human interventions with emphasis to those related to navigation channels. It is aimed to improve our fundamental knowledge on small-scale processes around navigation channels and increase the understanding of the large-scale response of estuaries, to explain the complex phenomenon of the high siltation in the North Passage of Yangtze estuary. The results will be useful for a proper management of the estuary.

Beyond the boundary and design criteria of Low Crested Breakwater (LCB), the success of LCB applications largely depends on the layout of the installation. The layout includes vertical and horizontal properties. Vertical layout related to the peak elevation position of the structure to the sea level, both to Mean Sea Level (MSL) and High Water level (HWL). Horizontal layout regarding LCB placements related to the optimal distance from the shoreline, the length of the structure, and the width of the gap between LCBs. These three parameters determine sediment volume accumulated behind LCB. This paper presents a summary of field experiences that is useful for the development of LCB as one of the methods of coastal protection. The objective of developing LCB structure is to make LCB concept as preferred coastal structure that is applicable to all types of materials commonly used for coastal protection structures.

The morphological features of the cuspate foreland extending at the east end of Mikawa-oshima Island in Mikawa Bay were investigated by field observation together with the examination of aerial photographs taken between 1977 and 2014. The change in the shoreline configuration of the Konose-bana cuspate foreland on the south shore of Sado Island was also studied while referring to the results of the previous study. On the basis of these field data, the BG model was used to predict the cyclic change in shoreline around the tip of the cuspate foreland in response to the change in wave direction.

On Embudu Village Island in the Maldives, the seasonal movement of a pair of sand spits can be observed, which are generated by the seasonal changes in wave direction associated with the tropical monsoon. Field observation of the beach changes on this coral cay was carried out in May 1992. Satellite images of the cay taken between February 2005 and November 2013 were compared to investigate the planar changes of the cay. The BG model (a model for predicting three-dimensional beach changes based on Bagnold’s concept) was used to predict beach changes of the coral cay. The calculated beach changes were in good agreement with those measured. It was confirmed that the wave-sheltering effect of the island itself played a decisive role in the beach changes.

Several years ago, the river mouth bar disappeared at the Shimanto River mouth in Kochi Prefecture, Japan. After the disappearance of the river mouth bar, wave invasion into the river was enhanced and a sand bar in front of the left bank of the river, which had been stable for a long time, was rapidly eroded and sand was transported upstream, resulting in the formation of a sand spit. The formation of the sand spit was investigated by shoreline analysis using satellite images together with a field observation. Then, the topographic changes of the sand spit were numerically reproduced using the BG model.

This study was carried out for a proposed fishery harbour in Wennappuwa, in Northwestern coastal stretch of Sri Lanka. Simulation of nearshore coastal processes such as hydrodynamic and sediment transport processes to ensure safe navigation and continues harbour operations are the main objective of this study. MIKE 21 modelling system was used to simulate hydrodynamics and sediment transport processes. With the hindcast nearshore wave climate, coastal processes were simulated for representative nearshore wave climate conditions. According to the MIKE 21 HD (Hydrodynamics) model results, it was identified that proposed port configuration is favored for its hydrodynamic performance. MIKE 21 ST (Sediment Transport) model was used to understand sediment transport patterns, especially at harbour entrance and approach channel to investigate the siltation possibilities. According to the simulated results which are based on average wave conditions, it was found that net sediment transport is directed from south to north direction. However, sediment transport movement has not supported to move sediment significantly in to the harbour through its entrance. Hence, sediment bypass can be expected through the harbour entrance with the proposed configuration. Thus, suitability of the harbour location and layout were justified with the numerically simulated results.

A coastal land area of approximately five km2 around the Pondok Bali beach in Subang, Indonesia, has been lost to the sea for the past decade. Before this land loss, there were several fish ponds with mangrove trees. The local people have suffered from the relative sea level rise, as they have had to abandon their houses because of the frequent inundations. To understand the status and causes of this coastal problem, the perception and adaptation strategies of the people, and potential countermeasures, we performed interview surveys in the associated villages and local governments. By using a sea chart of 1965 and satellite images, we calculated the cumulative volume change of deposition and erosion around the Cipunagara River mouth areas, where Pondok Bali is situated. Further, we conducted field measurements of turbidity and velocity, as well as bathymetry in the Cipunagara River to estimate the sediment supply. From the interviews, we found that a decrease in sediment discharge is a major cause of the erosion around Pondok Bali, which is due to the change of the river channel in 1965, when a floodway was constructed. At the present river mouth, a huge river delta has been formed owing to the sediment supply from the river. We also found that the local villages and governments have been considering countermeasures for reducing land erosion and promoting sustainable land use in the Pondok Bali areas, such as a plan for creating a new branch off from the main channel of the river to the Pondok Bali areas. However, further discussion on the new branch route is required among the associated villages because the effect of the new branch on Pondok Bali is unknown. From the field survey in the river, we calculated the sediment flux and estimated the total sediment supply to the river mouth, and this information is used for assessing the feasibility of the plan.

As a study on beach erosion in a developing country, beach erosion in Kalibo City, located in the northern part of Panay Island in the Philippines, was investigated together with the deformation of a sand spit using satellite images. The study area is the shoreline of 7.7 km length between New Washington, south of Kalibo City, and the sand spit located southwest of the city. Field observation was carried out on January 16, 2014, two months after Typhoon Haiyan hit the area. In this area, the shoreline has severely receded owing to the decrease in sand supply from the Aklan River. Local optimization of shoreline protection using seawalls has been employed, resulting in no fundamental solution to the erosion.

A two-dimensional numerical model using the fifth-order weighted essentially nonoscillatory (WENO) scheme is presented in order to estimate topography change due to tsunami with high accuracy. In the model, the Cartesian coordinate system is adopted, and the fractional area/volume obstacle representation (FAVOR) method is introduced into the governing equations in consideration of applying the estimation to such as harbor shape with complex topography. In order to verify the validity and applicability of the model, it is applied to small-scale laboratory experiments and to large-scale actual topography change. Consequently, although the model cannot reproduce local scouring around breakwater where three-dimensional flow is developed, it is clarified that the model can reproduce the topography change well by contracted flow around a harbor.

A field investigation for deformation of a river-mouth sand bar in the Tenjin River, which is located at Tottori prefecture in Japan, was carried out. The topographic surveys using RTK-GPS, UAV and RC boat were conducted from July, 2015 to March, 2017. Moreover, 4 cameras were set at the both sides of the Tenjin River embankment in order to monitor the deformation of the river-mouth bar. From these measurements, the characteristics of the deformation of the sand bar tip in the opening of the river mouth were analyzed and the validity of an alternative survey technique using RTK-GPS, UAV and RC boat was confirmed.

The beaches at the mouth of the Cai River, which flows into Nha Trang Bay, Vietnam, have been eroded, resulting in the disappearance of sandy beaches on both sides of the river mouth. Satellite images taken between 2002 and 2015, and the effect of a storm that occurred in 2008 were analyzed. The most important cause of the beach erosion was sand excavation from the sand bar on the right bank to obtain materials for land reclamation on the left bank. Another cause was sand movement due to waves in the upstream direction along the left bank of the river. To recover the sandy beach, the construction of training jetties is expected to be effective, similarly to the case of the bay mouth jetty of Dam Nai Bay in Phan Rang, Vietnam.

Topographic changes around the Co May River mouth located 9 km east of Vung Tau, Vietnam were investigated. An asymmetric shoal develops in the east–west direction around the river mouth, suggesting the predominance of westward longshore sand transport in this area. A large amount of sand was transported into the mangrove forest in the hinterland by storm waves, resulting in the widening of the sand bar, and then this sand bar was eroded by longshore sand transport along the river bank, resulting in the development of a sand spit at the upstream end. Moreover, the exposure of a mud layer composed of cohesive material showed that the right river bank was subjected to sand deposition under storm wave conditions and wave abrasion owing to longshore sand transport.

On a sand dune, a blowout is often formed owing to wind effect. The formation of a blowout was observed on November 25, 2016 at the Node coast facing the Pacific Ocean, where a blowout has been formed to leave a concave topography. Then, a model for predicting the formation of a blowout was developed using a cellular automaton method, in which two important factors of saltation and avalanche were taken into account. The results of the numerical simulation were compared with the measured results on the Node coast, and the predicted and measured shapes of the blowout were in good agreement.

Aiming at the siltation problem at the waterway in the east branch of the Daliao River Estuary, the two-dimensional tidal current sediment numerical model has been established based on the analysis of hydrodynamic and sediment characteristics. In combination with the experience of channel governing of the Daliao River Estuary, three regulation schemes have been compared by using numerical model. The results show that there is a small influence on hydrodynamic force in the Daliao River after training works and dredging is not sufficient to maintain the channel flow. After building eastern and western jetties, the maximum thickness of sediment siltation in channels is only 0.62 m/a and the regulation effects are relatively good.

Water level determines flooding and considerably effects wave climate. Hence, it is important to consider it in both disaster mitigation and coastal structure design. Unlike other water level components such as storm surge and waves, astronomic tide is periodic and predictable. The oceans and bays are forced-oscillating system, allowing astronomic tide to oscillate with the same frequencies as the tide-producing forces. While astronomy determines the tide constituents’ frequencies, it is the basin hydrodynamics that controls their amplitudes and phase lags. Tide time series record is needed in harmonic analysis to predict astronomic tides. The predictability of tide allows the analysis of storm tide level through the extraction of storm surge component in the water level time series. This method to synthesize the storm surge was validated in this study as an application to disaster mitigation. To de-trend the 1969-2015 hourly water level from National Mapping and Resource Information Authority (NAMRIA), sea level rise was examined. Least-square linear solution to the monthly mean values (1901-2015) was utilized. Results showed that the slopes of the trends of sea level are rapidly increasing over time because a varying trends for 1901-1968 (1.76 mm/year) and 1969-2015 (13.6 mm/year) was obtained. The de-trended 1969-2015 hourly water level (through 13.6 mm/year trend) was used to hindcast the astronomic tide. The results are the storm surge values of 47 historical typhoons that tracked within Manila Bay (study area). Finally, to apply the NAMRIA tide data in coastal structure design, tidal datum values were compared to the computed values (through zero-crossing method). Results showed that the selection of wave period on which an individual wave will be defined causes large variation on the compared tidal datum values (NAMRIA-specified versus computed). NAMRIA uses the tidal day (24.84 hours) as the wave period while results in zero crossing method showed that the length of periods of individual waves being analyzed is ranging from 12 to 275 hours.

Recent floodings in urban areas have made local government unit to discharge excess runoff in the open sea. Discharge pipelines are then installed normal to the shoreline to help mitigate inundation in lowland areas. However, severe erosion in the downdrift side and significant change in nearshore topography are observed in the vicinity of the discharge pipeline. Field survey, with the use of UAV, is conducted in Fuji Coast to investigate nearshore topography around the structure. Field data analysis reveals that updrift side of the structure exhibits a convex cross-shore profile whereas downdrift side exhibits a concave cross-shore profile. A photogrammetric technique known as Structure from Motion (SfM) is then used to develop the three-dimensional model of the topography around the structure. It can be shown that estimation of nearshore topography is possible through UAV-based measurements. Finally, preliminary experiments are carried out with the aim of reproducing the erosion-accretion process observed in the field. It is shown in this paper that the process can be reproduced in a laboratory scale model. Further experiments are conducted to reproduce the process in a larger scale and quantitative measurements will follow so that more pertinent information can be obtain to elucidate the erosion-accretion mechanism occurring around these discharge pipelines protruding across a shoreline.

A high resolution beach sediment mapping technique was developed on the basis of serial pictures taken from a UAV (Unmanned Aerial Vehicle) mobilized alongshore with a walking speed at an altitude of 10 m above ground. Two dimensional wavelet transform was introduced to determine the size of sediments in the range from 10⁰ cm to 10² cm. The system was applied to the 16 km long Fuji Coast, composed of sand and gravel originated from the Fuji River. Distributions of sediment size in the foreshore zone were successfully estimated both in the cross-shore and the alongshore directions.

Monitoring shoreline change is one of essential tasks for appropriate design of coastal management and protection strategies. As one of remote sensing technologies, synthetic aperture radar, SAR can be a promising option because SAR is affected neither by cloud coverage nor by sun illumination. In this study, various kind of parameters, such as the grain size of bed materials, incident angles and wave height, were analyzed and it was found that the grain size is one of the most important factors for the shoreline monitoring skills using SAR.

In this paper, a new method of beach nourishment, in which sediment dredged from an offshore bar is deposited at the shoreface, is proposed as one of the measures for beaches that suffer from irreversible beach erosion due to a single storm event. A series of laboratory experiments were carried out to investigate the effectiveness of the method. Some parameters that may influence the effectiveness were discussed based on the experimental results by regular waves. Effect of irregularity of the waves is also shown.

The South Pacific Island nation of Tuvalu, which is composed of coral gravel and sand, is vulnerable to storm waves and sea level rise, resulting in beach erosion. Beach nourishment with self-produced coral gravel and sand was implemented in Tuvalu as the first trial of a user- and eco-friendly type of coastal conservation measure in Pacific Island countries. In order to examine the applicability of this type of coastal conservation measure, continuous monitoring has been carried out for one year to check the change in shoreline and beach profile. Beach monitoring for large-scale reclamation project, which was executed at the neighboring coast in almost the same period, was also conducted to compare the change of beach in the two different projects. The results show that the executed gravel beach nourishment can maintain stability under seasonal and extreme condition of wave actions.

As a part of the Pilot Gravel Beach Nourishment Project in Tuvalu by Japan International Cooperation Agency (JICA), approaches to establish a community-based beach management had been implemented as the first trial among the Pacific Island countries. A community-based beach management requires an active public participation; however, public awareness on beach seemed to be quite low in the beginning of the Project because of the terrible beach condition with dumped rubbish scattered on the beach. Therefore, raising public awareness on beach and making people understand and experience the benefits from the beach were considered necessary to establish the community-based beach management. In the Project, several public relations and educational activities were implemented for these purposes and one notable effective activity was the beach sports festival that was firstly held in Tuvalu. Public awareness on beach, especially on beach use and environment, was much improved through these activities so that community and residents voluntarily started beach management activities such as periodic beach cleaning and public notification of illegal activities on the beach. These changes contributed to maintain the good condition of the Project beach for almost one and half year after the construction.

On the Ichinomiya coast located on south Kujukuri Beach, a world famous surfing ground was threatened. A conflict regarding the construction of artificial headlands as a measure against beach erosion took place among the administration of coast, surfers, fishermen and users of the coast in 2010. Roundtable discussions to reach a consensus regarding conservation and use of the coast were held to solve the conflict since June 27, 2010. Meetings were held five times between June 27, 2010 and September 3, 2011, and shore protection measures of the coast and the impact of the construction of the artificial headlands on the beach and surfing grounds were discussed. Finally, a consensus was reached among the administration of coast, surfers and users of the beach. This beach will be the place of surfing Olympic games to be held in 2020.

To date there were few studies of wave energy converter that utilize the gravity force of sea water as a prime mover of wave energy converter to generate electricity. In this work, physical model of wave energy converter based on water mass gravity force to generate electricity were investigated. Experiment was conducted at Hydraulic Laboratory, Hasanuddin University, Makassar Indonesia. The physical model of wave energy converter be made up of connecting chain, gravity weight container (Mg), counter weight (mc), rotating shaft, gear box and flywheels. The amount of extracted power was calculated based on converter shaft radial speed (RPM) and torque. Experiment result showed that gravity weight volume is strongly determined the amount of power generated by the converter. The maximum harvested power was 1.66 Watt at wave height of 7 cm, wave period 1.2 second and water container volume is 4.5 liters. In this experiment five gravity weight pairs were employed that successfully extracted 85 % of theoretical available wave power. This experiment result showed that the proposed wave energy converter that utilizes the gravity force of water trapped in a container, gives significant contribution to the existing wave energy converter technology in harvesting the ocean wave power as a promising source of renewable energy.

In order to design a reliable breakwater that will withstand severe environmental conditions, accurate prediction of hydrodynamic interactions with multi-bodied structures must be considered. However, the interaction processes among dual cylindrical caisson breakwaters, which consist of a partial porous outer cylinder and an impermeable inner cylinder, are very complex and numerous. In the present study, the 3D numerical analysis method is developed with eigenfunction expansion method to evaluate the water wave interaction. The wave forces on the array of dual cylindrical caisson breakwaters with partial porous area are presented for various conditions.

Breakwaters have been severely damaged quite often since they are directly exposed to large waves. And damage level of breakwaters has been scaled up because of abnormal global climate changes. So, recently, an interlocking concept has been much attention to enhance the structural stability of conventional caisson structures designed individually to resist waves. However, interlocking methods proposed so far have not been actively applied to the design of actual breakwaters because of structural stability, construction and economic issues. In the present study, a modular caisson was proposed that can maximize the existing caissons and improve structural stability and workability by using the modular interlocking system like LEGO ; and behavior and interlocking effect of the modular caisson breakwater are evaluated by numerical analysis method. From the results of the study, because of clearance between caisson units, the modular caisson units are interlocked by two interlocking behaviors : (a) indirect interlocking behavior by frictional force at contact surfaces between interlocking parts, (b) direct interlocking behavior by shear resistance between interlocking parts ; the direct interlocking effect by shear resistance is larger than the indirect interlocking effect by frictional force ; interlocking effect of the modular caisson breakwater is similar to the all-bonded long caisson breakwater.

Based on the experimental results for profile change of wave dissipating blocks covering a caisson breakwater, the model profiles for the damaged block layer are made and the relation between the damage progression and change of performance is investigated. The results of the numerical experiment using the model profiles show that the overtopping rate increases by a factor of 1.5 compared to that of the initial profile with damage progression. Furthermore a statistical model based on the Markov chain is applied to the damage progression process and the total cost for the maintenance of wave dissipating blocks is estimated by using an assumed repair cost and loss. This method can be applied to find a policy of repair that minimizes the total (life cycle) cost, however, it is necessary to evaluate the practical amount of repair and loss reasonably.

In the previous studies on low reflective double curtain seawalls comprised of curtain walls and a rear-side vertical wall, it was presumed that an upper side of the water chamber of the seawall was open to the atmosphere. Therefore, there is no restriction on the behavior of piston mode wave motions in the water chambers and consequently significant wave energy dissipation due to such wave motions is active. However, in the real site of wharves and piers, the upper part of low reflective seawalls is generally capped by ceiling slabs to be able to use the space for loading and unloading cargos to boats and ships. Under such general situations, it may be necessary to keep air ventilations above the water chamber to be able to activate piston mode wave motions and consequently to dissipate reflected waves from the pier. In this study, we have proposed a method to set vertical slots on curtain walls for the ventilation. Effectiveness of such vertical slots on the curtain walls has been examined experimentally and theoretically. Additional examinations have also been carried out to study the size of vertical slot on the wave dissipation effect

Mangrove forests play an important role in coastal disaster mitigation as a natural measure by dissipating wave energy, which performance would change according to mangrove structures, including mangrove density, tree height, root height and tree diameter. This study was aimed at assessing the wave energy dissipating function in terms of mangrove structures and determining the necessary thickness of the mangrove forest to reduce the impacts of waves on the Bac Lieu coastal zone, Vietnam. Standard plots with the unit distance of 20 m mangrove were set for each transect, ranging from the seaside edge of mangrove to 100 m distance inland. Properties of mangrove structures were measured at three transects to ensure the representation of the study area. Waves were measured along the transects using wave gauges and characteristics of wave attenuation due to the drag force of one existing mangrove species, Avicennia sp., were analyzed. The density, height and diameter of mangrove trees were found to be distributed relatively evenly, with a slight increase of the number of trees per standard plot from 183 at the seaside edge to 218 at the 100 m distance inland. Regarding mangrove root, while its density was relatively uniform along transects, its height varied significantly. The amplitude of wave in the Bac Lieu coastal zone changed substantially with the tidal phase ranging from 0.09 to 0.22 m. The wave reduction between the seaside edge and 20 m and 100 m distances inland from the edge, respectively, increased from 32 % to 91 %. A number of mangroves characteristics influenced the rate of reduction of wave height per unit distance, most notably the physical structures of mangrove trees, especially their densities. The wave reduction coefficient was positively correlated with the thickness of mangroves (r = 0.96). When the distance of wave energy transmission through mangroves was greater or equal to approximately 76 m, the wave energy reduction reached 80 % or above, which assures the wave energy would not influence the coastal zone. Therefore, in Bac Lieu with dense mangrove trees, a thin band of mangroves could provide an adequate defense to protect the coastal area in this tidal range under normal wave conditions. However, for the case of storms with high waves and surges, more thickness of mangroves would be required to guarantee the protection function, which should be analyzed in future studies.

Based on the Yangtze Estuary and Oujiang Estuary in China, a bifurcation estuary is generalization and its physical model and numerical model are established to study the effect of building a pair of guiding jetty and four pair of spur dikes in one branch on tidal currents of bifurcation estuary. The calculating results show that there is a critical length of guiding jetty and the velocities at ebb strength is up to the maximum value. Through the regression analysis of the predominance of ebb current, Euler unit discharge and Stokes unit discharge, the reasonable relative length of spur dike (the ratio between a spur length and 1/2 channel width) in the bifurcation estuary is 0.4∼0.6.

With the rapid growth of offshore wind industry, the predition of the wave loads on different pile-supported structures is of great importance. To investigate the wave loads, a series of physical experiments and numerical simulations were conducted. As a new characteristic geometric scale, an equivalent diameter is proposed to analyze the dimensionless total wave loads. With the equivalent diameter, unified empirical formulas of wave loads versus Keulegan-Carpenter (KC) number is obtained for different complex pile-supported structures.

The strongly nonlinear interaction between a solitary wave and the submerged barrier is investigated numerically in the present paper. Based on the Cartesian grid method of constrained interpolation profile (CIP), a two-dimensional numerical wave flume specializing to Navies-Stokes equations was established to simulate the propagation of a solitary wave over the submerged structure. The free-surface motion and hydrodynamic forces acting on the submerged breakwater were presented in this work. The comparisons between the numerical results and experimental data for the free surface elevations show a good agreement in both upstream and downstream of barrier. Complicated hydrodynamic behaviors, including wave breaking and overtopping, were captured by the numerical model which demonstrates that the CIP-based model has the ability to provide the reliable predictions for the wave transmission over the submerged structure.

A tidal stream turbine is a device for harnessing energy from tidal stream, and the turbines layout has great influence on the economic benefits of tidal stream farm. In previous studies, the turbines layout is mainly determined by artificial optimization method, which is difficult to obtain the utmost utilization of tidal stream energy. Open source code OpenTidalFarm provides an automatic method to optimize the turbines layout and better utilize the tidal stream energy. In this study, the source code is applied to reproduce the tidal hydrodynamics and optimize the turbines in the Zhoushan Demonstration Project layout. Numerical results are in good agreement with the field measurements in terms of amplitude and velocity. With fixed total number of turbines, automatically optimized turbines layout can contribute to a higher electricity power compared to aligned layout.

The purpose of this study is to analyze the effect of vertical telescopic breakwater on water level reduction in the event of a storm surge. This is investigated by developing an evaluation method using CADMAS-SURF/3D and STOC-ML. The flow velocity between the breakwaters corresponds to the theoretical value evaluated based on the water level difference. The results indicate that the aperture can be reduced to 5.5% - 6.0% when analyzing the breakwater with 7.2% aperture using STOC-ML. As an extension of this study, it is possible to obtain approximate water level reduction using dimensionless quantities including the conditions of wave and breakwater.

A tsunami pressure acting on an onshore structure is generally evaluated by a formula with using an inundation depth η and a water-depth-coefficient α, which is based on the Froude number Fr in many cases. The definition of the water-depth-coefficient α is variously proposed by a semi-empirical way, and it is noteworthy that they are commonly based on only incident waves. Considering the real phenomenon and the practical procedure of design of the onshore structures, it is clear that synthetic waves including reflected waves should be considered. However, since the existing studies do not focus on the influence of the reflected waves, their applicability to the real phenomenon is not guaranteed yet. This paper performs hydraulic experiments with targeting tsunami running up the land to examine the influence of the reflected waves for more appropriate definition of the water-depth-coefficient α. Our experimental results in the cases with subcritical flow show unexpected increments of the inundation depth due to the refection of the forward tip of the run-up tsunami on the land, which implies a difficulty in obtaining the pure incident waves for the water-depth-coefficient α and would bring about overestimation of tsunami forces. Moreover, this study newly proposes a simple and effective method to evaluate the tsunami force with focusing on standing waves in front of the wall.

Many caissons of breakwaters were slid or overturned due to tsunami overflow pressure caused by 2011 Tohoku earthquake. To prevent this sliding failure, the pressure estimation method under tsunami overflow was introduced in the new design guideline of breakwater against tsunami in 2015. In this guideline, the uplift and the overburden pressure are not considered, instead only buoyancy force acting on the caisson is considered. However, under tsunami overflow, the pressure difference between the bottom and the top of breakwater caisson, especially the caisson having a large parapet, can be extremely larger than the buoyancy force. In order to examine this excess uplift force, a series of hydraulic experiments were conducted. The experiment was conducted in an experimental flume in which the large pump was installed to produce tsunami overflow. Pressure gauges, water level gauges and velocity meter were installed at the top and the bottom of the caisson model. Through the experiments, it was clarified that the large uplift pressure and the small overburden pressure cause the upward force larger than the buoyancy force. This upward force reduces the stability of caisson, especially the caisson having the large parapet.

For an open-deck pier of a coastal resort development, a comparison of 2 preliminary engineering designs involving the standard non-overtopping deck and the less conventional overtopping design is carried out. The common basis for horizontal siting and its results based on optimal prevailing waves are presented. The two design outputs are compared in terms of geometry and sizes of the pier’s structural elements. The option of overtopping pier is also discussed relative to its storm tide overtopping risk and the expected pier maintenance plan. For this study coast, a non-overtopping pier design yields leaner pier geometry and smaller structural sizes. It is recommended that a nonovertopping pier design be always considered for a storm-tracked coastline.

The dynamic response of different types of spar and semi-submersible type floating offshore wind turbines are investigated subjected to wave and wind loads in operational conditions. The study is performed for the NREL 5MW wind turbine supported on spar and semi-submersible platforms. The study includes the analysis on the wave interaction with supporting structure and determination of the time-domain dynamic response of offshore floating wind turbine. The hydrodynamic coefficients added mass, damping, excitation forces and Response Amplitude Operators (RAO’s) of the different motions of the floating platform are analyzed for different wave heading angles. The coupled dynamic analysis is performed for both regular and irregular waves and the coupled response of platform motions, tower base forces and moments for different wave and wind load conditions is analysed. The present study focuses on the overall performance of the different types of spar and semi-submersible type offshore floating wind turbines.

Wind is one of the important dynamic factors acting on coastal engineering structures. This paper discusses the appropriateness of the methods that adopt constant wind and wind speed using gravity similarity law, which is consistent with the hydrodynamic similarity, to study the interaction of wind and coastal engineering structures for most current laboratory simulations. The results show that it is feasible to simulate random wind in laboratory so that wind effects can be more truly reflected. For the stability analysis of fixed structures assembled with slender rods, the gravity similarity law ( Fr = 1 ) can be adopted and DAVENPORT or von Karman spectrum can be used as wind spectrum. For a floating structure, the wind effects include two parts. One part includes inertial forces FI and resistances FD that are generated when wind forces directly act on the structures, which can be simulated by gravity similarity law, and here API or NDP spectrum can be adopted to simulate random wind; the other is the drift velocity of flow, whose magnitude is proportional to the fetch length and wave age, caused by the wind–water surface interaction. It is pointed out that wind effects on coastal engineering structures, especially the dynamic response of floating structures, may be underestimated when constant wind and gravity similarity law are used in laboratory simulation, therefore the similarity method and its corresponding results should be properly modified.

Granulated coal ash (GCA), a by-product from coal fired power plants, has been proven to be effective in improving sediment and water qualities in the littoral regions severely deteriorated by wastewater discharge. Based on the achievements of GCA application in Japan, it is found out that GCA plays an important role in restoring the ecosystem of marine environment through various mechanisms, notably neutralizing acidified sediment due to the hydrolysis of CaO, adsorbing nutrient salts and hydrogen sulfide, and decreasing the oxygen consumption in bottom water. This paper describes the potential of using GCA in improving water quality in the Pasig River through various methods based on recent study results. The pilot study at the Estero de san Miguel is currently under preparation with the Pasig River Rehabilitation Commission.

Field observations were conducted to investigate the effects of physicochemical conditions on the distribution of the genus Halophila in subtropical Nakagusuku Bay (Okinawa, Japan). Four species belonging to the genus Halophila (H. ovalis, H. major, H. nipponica, and H. decipiens) were found growing in the study area. H. nipponica was most frequently shown in Nakagusuku Bay and H. decipiens was encountered less frequently, while H. major was mainly present at the same sites as H. ovalis. Statistical analysis using physicochemical data obtained at each observational site revealed that the distribution patterns of H. ovalis and H. major were independent of nutrient conditions, but were strongly affected by surface wave motion. The occurrence of H. ovalis was confirmed up to a depth of 8.3 m, and H. decipiens occurred below a depth of 9 m with H. nipponica where the organic content was high and wave motion was smallest among the observational sites. H. nipponica showed a preference for relatively high sedimentation and large amounts of organic materials and its distribution was independent of flow conditions. H. major grew together not only with H. ovalis but also with H. nipponica.

Tsunami protection breakwaters constructed at the mouth of Ofunato Bay were collapsed by the 2011 Tohoku Earthquake Tsunami. Before the 2011 Tsunami, anoxic/hypoxic water masses developed every summer in the bay. To understand anoxic/hypoxic environment after the Tsunami event and to inform appropriate reconstruction of the breakwaters, field measurements of water temperature, salinity, dissolved oxygen (DO) and currents were conducted in 2012 and 2013. DO concentrations in the Bay in 2012 and 2013 were not anoxic/hypoxic as they were before the 2011 Tsunami. We clarified that the primary factor supplying DO into the lower layer of the inner bay was intermittent intrusion of low temperature, high density, and high DO water masses from the outer bay.

Kenya is located in the eastern Africa. Currently, among 35 million people in Kenya, there are only about 5 million people can use electricity. The problem in power shortage is serious. Kenya Lamu Power Co., Ltd. plans to construct Kenya Lamu3×350MW (supercritical) Independent Power Station Project in LAMU Region. The power plant uses seawater as cooling medium. In order to demonstrate the feasibility of the power plant and the effect of drainage thermal discharge on surrounding water area, a 2D and 3D numerical models of tidal currents and thermal discharge are established and the thermal discharge of two drainage schemes are simulated. The research results show that the influencing area of temperature rise in open channel drainage scheme are larger than that in pipe drainage and the temperature rise in water intake in pipe drainage scheme is larger than that in open channel drainage.

Sediment quality strongly depends on organic matter conditions in the sediment, thus identifying organic matter conditions in sediment is very necessary. The thermal analysis (TG/DTA) is widely used to understand the ignition characteristic of sediment. It has been reported that different types of organic matter have different exoergic temperatures. Unfortunately, no any TG/DTA analysis standard has been proposed for sediment analysis. In other words, TG/DTA analysis of sediment is different from a study to another study. This study is aiming at proposal of TG/DTA analysis for identifying organic matter conditions in sediment. Different sediments collected from different littoral regions in Japan were used in the TG/DTA analysis. The sediments were first oven dried, and then were passed through 75-μm sieve. The sediments with and without passing through 75-μm sieve were used in the analysis. In the analysis, different weights (10 to 30 mg) of samples were ignited from 25 to 850°C with heating rates of 1, 5, 10, and 20°C /min. It was observed that a more accurate analysis could be obtained when the sediment less than 75-μm was used, specifically for the sediment collected from the littoral region exposed to wastewater discharge. The exothermic peak easily appeared with increasing weight of the sample, which easily identified organic matter conditions in the sediment. Moreover, mass loss on ignition of the sediment burned at ≤5°C /min was higher than that at ≥10°C /min. This ensured that organic matter was incompletely burned at≥10°C /min. It can be concluded from our results that 20-30 mg of sediment passed through 75-μm sieve should be burned at 5°C /min to obtain a more accurate analysis of organic matter conditions in sediment.

In the coastal region exposed to wastewater discharge, large amounts of sediment accumulates on the seafloor. The decomposition of large amounts of organic matter releases an excess amount of reduced substances (e.g., Fe²⁺, H₂S) in sediment. The diffusion of reduced substances into water body consumes oxidants, leading to the aggravation of water quality (the redox potential was around –200 mV vs Ag/AgCl) which influences on marine ecosystem. In the literature, the improvement of water quality by lowering the diffusion of substances from sediment under the uses of steel slag and granulated coal ash has been studied. This study is aiming at developing an electrochemical method from improving water quality. Laboratory experiments were conducted to examine the change of water quality after applying the developed method. In the experiment, the carbon electrodes were installed near sediment surface (anode electrode) and water surface (cathode electrode). The current (recovering electron from bottom water) was made by connecting the electrodes with an external resistance of 100 Ω and a potentiostat (for fixing current). To understand the improvement of water quality, the electrode potential of bottom water was measured continuously during the experiment. It was found that the electrode potential of bottom water increased according to the electron recovery, indicating the oxidation of reduced substances existing in bottom water at the anode electrode. Interestingly, a more improvement of water quality could be obtained with increasing the current of electron recovery. It can be concluded that an electrochemical method can be a mean for improving water quality, and a larger current of electron recovery leads to a more improvement of water quality.

Natural resource management and socio-economic planning in coastal zone to implement sustainable development have become a quite challenging topic. The State Oceanic Administration of China has published the management regulation of the feasibility assessment on the sea area usage since 2008. It clarifies that the feasibility assessment must be carried out for the exclusive usage of sea area in Chinese inland and territorial waters. After that, the technical guide of this assessment has been issued. By taken the usage purpose, scale and characteristics of the sea area into consideration, the feasibility assessment can be categorized into three grades. If a project has different usage purposes on sea areas, the assessment grade should be consistent with the highest one. In this paper, three real cases i.e., Hong Kong-Zhuhai-Macau Bridge (HZMB), Supporting Facility Project for International Cruise Port at Phoenix Island and Ningde Doumi central fishing port with the first, second and third assessment grade, respectively, are introduced. On the basis of detailed understanding and investigation of the marine resources and the present development situation of each case, this paper analyzes the necessity of the project construction and need of sea area usage, and evaluates the rationality of the site selection, area and period, and the project consistency with local marine functional zoning and relevant planning. After that, the negative influences of the projects are presented, and in terms of the relationship between the project owner and stakeholders, the solution and suggestion of the project sea area usage are proposed. By comparison of these cases, we can conclude that there exist obvious differences on the study scope, evaluating emphasis and data requirement for different assessment grades. It provides a clear view on the feasibility assessment on the sea area usage in China. The system of the graded feasibility assessment which is judged by how a specified project uses sea, the occupied area of the project in the sea (sea area usage) and the characteristics of the area (for example, sensitive or insensitive), balances the rights and interests of the project owner and other stakeholders, and promotes the reasonable usage and sustainable development of the ocean.