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This study investigates an oil spill which involved an ironworks factory in Saga prefecture, during the severe flooding that hit southwestern Japan in late August 2019. The aim of the study is to provide an overview of the accident, highlighting the causes and the consequences of this compound disaster. Furthermore, the study analyses the emergency response and clean-up activities in order to identify lessons learned, and propose recommendations for future flood triggered oil spills. The work presented is based on the integration of information available in newspaper articles, government documents and reports, and data and interviews collected during two field trips in the affected area. The permanence of oil and the strong oil odour in adjacent crops as well as on irrigation canals and citizens’ houses was revealed during the first field trip, about one month after the accident. The analysis of the documentation on metal working oil revealed that it might have long-lasting impact in terms of environmental pollution. The presence of oil impacted also the implemented emergency response actions, since vertical evacuation, practiced by many residents during the disaster, actually put many of them in more danger as they ended up trapped in oil-covered floodwaters with strong vapours that were reported to cause nausea and skin irritation. Remarkably, it was also found that a previous oil spill had already occurred at the same site following a severe flooding event, highlighting the need to improve preparedness and develop more effective strategies for accident prevention. Disaster preparedness that specifically considers both the natural hazard and the potential for related technological scenarios should be enhanced, in particular regarding chemical accidents triggered by floods. Japan, as well as other parts of the World, is experiencing stronger rainfall events due to a changing climate leading to unprecedented flooding. Therefore, industry, government and citizens should consider the possibility of an increase of weather-related compound disasters in planning and implementation of climate change adaptation strategies.

This paper is concerned with the deposition of sediment due to dune forests (Nakatajima dune, Japan) and CC block system on a riverbank (Padma, Bangladesh). Measurements of sediment deposition were carried out at Nakatajima dune, Japan and at Padma riverbank, Rajshahi, Bangladesh using Global Positioning System (GPS). 2442 m3 sediment migrates each year to the East side of Nakatajima dune by wind and the edge of the dune develops about 6-7 m/year due to the existence of forests. Sedimentation rate is also greater in shallower mangrove areas. The trapped sediment height varies from 8.0 to 10.0 cm in the mangrove-lined bank. Mangrove forests help to trap 25% more sedimentation at low tide than at high tide. On the other hand, only for setting up the CC block and groynes along the bank, the sedimentation rate is observed almost twice than that of the previous year. An analysis shows that there is a similarity of sedimentation among dune, beach forests, mangrove forests and CC blocks. Journal of Bangladesh Academy of Sciences, Vol. 43, No. 1, 67-78, 2019

When erosion occurs, sand beaches cannot maintain sufficient sand width, foreshore slopes become steeper due to frequent erosion effects, and beaches are trapped in a vicious cycle of vulnerability due to incident waves. Accordingly, beach nourishment can be used as a countermeasure to simultaneously minimize environmental impacts. However, beach nourishment is not a permanent solution and requires periodic renourishment after several years. To address this problem, minimizing the period of renourishment is an economical alternative. In the present study, using the Tuvaluan coast with its cross-sectional gravel nourishment site, four different test cases were selected for the hydraulic model experiment aimed at discovering an effective nourishment strategy to determine effective alternative methods. Numerical simulations were performed to reproduce gravel nourishment, however, none of these models simultaneously simulated the sediment transport of gravel and sand. Thus, an artificial neural network, a deep learning model, was developed using hydraulic model experiments as training datasets to analyze the possibility of simultaneously accomplishing the sediment transport of sand and gravel and supplement the shortcomings of the numerical models.

Eutrophication in an estuary occurs as an effect of the enrichment of nutrient inputs from rivers. This condition has become one of the most common environmental issues experienced around the globe and especially in Japan. Atsumi Bay is a eutrophic coastal area in Japan. The objective of this research was to analyze the influences of nutrient inputs from the Umeda River into Atsumi Bay on pre- and post-rainfall water quality conditions. This study was conducted from July to October 2010. The results showed a decrease of surface salinity after rainfall indicating that huge freshwater inputs had overlaid the surface layer of Atsumi Bay rather than the bottom layer. Moreover, post-rainfall conditions showed an increase of chlorophyll a as an effect of phytoplankton growth, followed by an increase of particulate nutrients. On the other hand, dissolved nutrients decreased due to uptake by phytoplankton and dilution by freshwater.

Damage to storage tanks in coastal area due to tsunamis can cause extensive fires. In order to prevent damage to storage tanks, tsunami wave loads acting on a storage tank have to be investigated. This study aims at investigating the features of the tsunami wave loads and the method for estimating them. In a wave basin, the tsunami wave load acting on a storage tank is measured under both conditions of the presence of the surrounding tanks and of no surrounding tanks. Inundation depth and horizontal velocity on the storage site are also measured under the condition of no surrounding tanks, which are used for estimating the tsunami wave load. The vertical component of the tsunami wave load is estimated by buoyancy based on the static pressure calculated from the inundation depth. The horizontal component of the tsunami wave load is estimated by Morison equation. The analysis shows that Morison equation estimates the measured impulsive force at the beginning of the inundation.

Two series of experiments were conducted to investigate the performance of gravel nourishment for the beach encountering erosion problem. The effect of gravel nourishment was obtained by comparing the results of beach profile variation in the series of hydraulic experiments. The key findings in this research are the influence of armoring-effect and mixture-effect in sediment transport. The results of this study could be the insight and recommendation in solving the beach erosion problem.

Yuk, J.-H.; Aoki, S., and Joh, M., 2016. Wind-induced water exchange between stratified basins. In: Vila-Concejo, A.; Bruce, E.; Kennedy, D.M., and McCarroll, R.J. (eds.), Proceedings of the 14th International Coastal Symposium (Sydney, Australia). Journal of Coastal Research, Special Issue, No. 75, pp. 188–192. Coconut Creek (Florida), ISSN 0749-0208. Water exchange between Inohanako Estuary and Hamanako Bay, Japan with density stratification is investigated using the field data. The basins are connected by a narrow channel with length 200 m through which waters and nutrients are exchanged between them. The principal axis of channel between two basins is located nearly in the north-south direction, thus it is natural that the water flow between the estuary and bay is influenced more by the north-south component of wind than the east-west component of that. Although the relationship between water exchange and the east-west component of wind is relatively low compared with the north-south componen...

Kim, H.D.; Aoki,S.; Kim, K.H.; Kim, J.; Shin, B., and Lee, K., 2020. Bathymetric survey for seabed topography using multibeam echo counder in Wando, Korea. In: Malvarez, G. and Navas, F. (eds.), Global Coastal Issues of 2020. Journal of Coastal Research, Special Issue No. 95, pp. 527–531. Coconut Creek (Florida), ISSN 0749-0208.Bathymetric survey measures the water depth of the ocean floors accurately. This survey helps produce a nautical chart which is used in numerical simulations, constructions, and more, as well as this project itself. This particular study was conducted to measure the water depth and map the ocean floor of Wando, Korea. With the help of various types of equipment, including multibeam echo sounder, differential GPS (DGPS), motion sensor, gyro compass, and sound velocimeter, bathymetric survey was made possible. Multibeam echo sounder was attached to the boat, emitting a total of 256 beams from a point centered directly below the boat. Water depth data was acquired from the underwater sound velocity using the return time of the beam. DGPS calculated the error value by comparing the position data of the control point at the base station where the position is already known via the Korea Hydrographic and Oceanographic Agency and where the position value is measured by using the receiver of the GPS. Throughout the survey, abnormal bodies were found even after the quality control filtering. These objects were as such classified through further detailed investigation.

A series of field observation of turbidity and current velocity etc. were carried out at the sea bottom off a river mouth during flood periods. The measurement location was 1.2 km off the mouth of Tenryu River, Japan, where water depth was about 18m. Four flood events of which the maximum mean hourly discharge ranged from 1,570m3/s to 4,620 m3/s were selected and the time series of river discharge, turbidity, water temperature, salinity and current velocity were compared with each other and the relationships between them were discussed. Furthermore, vertical profiles of turbidity and salinity observed after a flood were used in the discussion. Bathymetric changes surveyed off the river mouth were also taken into account.

The sand dredging activities may cause various physical and environmental changes such as beach erosion, evolution of beach profile, change in current and wave field. To evaluate the relationship among the volume of sand dredging, method of sand dredging, time of sand dredging, shoreline retreat and evolution of beach profile, some experiments were conducted and a two-dimensional numerical model was used. The effect of sand dredging volume on shoreline retreat was investigated by dredging various amounts of sand at one time under the same regular wave condition. The results showed that the relationship between shoreline retreat and dredging volume is nonlinear. In the other considerations, sand bar was dredged as different methods i.e. periodic sand dredging method under the same regular wave condition as well as one time dredging under different regular wave conditions. The final shoreline retreat in the last two methods was nearly equal to the first method, however, the progress of shoreline retreat was slower. After sand dredging in all cases, the beach profiles were not translated to the same original form. Infill rate of the bar after sand dredging is also discussed in term of average absolute sediment transport rate.

Djumanto, Rasul E, InoueT, Aoki S. 2017. Phytoplankton distribution in Mikawa Bay of Japan in relation to temperature and salinity variables.Bonorowo Wetlands 1: 16-25. Species composition and horizontal distribution of phytoplankton in relation to temperature and salinity variables were investigated in Mikawa Bay of Japan. Surface seawater was filtered with a 30 cm diameter conical plankton net with a mesh size of 53 µm weekly from mid-August to late September 2011. Surface layer temperature and salinity were measured with a CTD sensor. Phytoplankton samples were observed with an inverted microscope with phase contrast at 100-400 magnification. The salinity and surface temperature data, as well as the density of the phytoplankton horizontally, were made contour maps by connecting the location of each sampling station having the same value. Contour maps were created using surfer software. The result showed that the average of temperature at the 1 m surface layer was ranged from 22.7 to 28.7 oC. Meanwhile, salinity was ranged from 11.8 psu to 30.0 psu. Phytoplankton was abundant in the area with the high temperature and low salinity. The most abundant species among station of sampling in Bacillariophyceae was Chaetoceros sp(p). (52.2%) followed by Pseudo-Nitzschia sp(p) (27,7%), and then Coscinodiscus sp(p). (6.3%). On the other hand, the most abundant in Dinophyceae was Dinophysis sp(p). (1.1%) followed by Ceratium fusus (0.9%), and then Ceratium furca (0.8%) which was mostly dominant in off river mouth area. The density center and contour lines of phytoplankton population were changed and moved depending on salinity or temperature profiles.

Ishikawa, T.; Komine, T.; Aoki, S.I., and Okabe, T., 2014. Characteristics of rip current drowning on the shores of Japan. The characteristics of rip current drowning on the shores of Japan was investigated using the analysis of the lifesaver's rescue reports of 2013 and field observations of some beaches. Although the necessary rescue equipment and the water safety information such as signboards were mostly prepared, a large amount of rip current drowning occurred. On most re-occurring rip current drowning beaches, there are permanent rips and fixed rips associated with the characteristic of topography and the coastal structures at most beaches under the relatively high wave condition. Especially, in the case lifesavers cannot determine the swimming areas, swimming areas are generally determined by the local regulations from local governments and shop owners on most beaches. The most important outbreak factor regarding the rip current drowning is the human factor such as the management problems ...

When erosion occurs, sandy beach cannot maintain the sufficient sand width and the foreshore slope becomes steeper by the frequent erosion effect. As a result, the beach is trapped in a vicious circle of becoming vulnerable by the incident waves. In order to repair or protect the erosive beach, beach nourishment can be used as a countermeasure while minimizing the environmental impacts. However, beach nourishment is not a permanent solution and requires periodic renourishment after several years. To alleviate such problem, minimizing the period of renourishment must be an economical alternative. In that respect, selecting the optimum grain size of the sand for the beach nourishment is very important. Generally, larger grain sized sand is more resistant to the erosion, thus extending the period of renourishment. In addition to selecting the optimum grain size of the sand nourishment, determining the durability as well as maintaining the familiarity of the users of the native sand should be considered.

Storage tanks located in coastal areas can be damaged by tsunami. The damage can lead a spill of gas or oil, which cause an extensive fire. Another huge tsunami triggered by earthquake is predicted to strike Japan in the near future. Therefore, tsunami wave load acting on storage tanks has to be investigated. The authors have investigated the characteristics of tsunami wave load acting on a storage tank (Araki et al., 2017a; 2017b). In this study, bore wave pressure acting on a cylindrical storage tank was measured. The characteristic of the pressure was discussed.

The study examined the summertime behavior of phosphorus (P) and estimated P fluxes in the Inohana Lake Estuary, Shizuoka, Japan through a field observation conducted in the summer of 2007 and a bo...

Sandy beach shows gradual topographic change with long-term and short-term variations corresponding to the conditions of waves and tides. Because of the irregularity in the profile change, it is difficult to investigate the characteristics of shoreline change in detail. In this research, long-term survey of the beach profiles has been carried out on three different coasts almost every week for more than ten years. The topographic data were analyzed and the characteristics of the long-term and seasonal beach profile change were discussed using the statistical methods and the empirical orthogonal eigenfunction method (EOF).

An extraordinary high tide was induced by the storm surge in Mikawa Bay, caused by Typhoon 0918 in October, 2009. One of the unique and important characteristics of the storm surge is a sudden sea level rise of 2m in one hour, which occurred after the Typhoon passed by. In this paper, generation mechanism of such a sea level rise and dynamics of the surge is discussed using the ADCP current data obtained during the storm as well as the tide and wind records at the observation stations around the bay. The wave-like behavior of the surge indicates that the main cause of the sudden sea level rise may be attributed to the propagation of water mass form Ise Bay triggered by the sudden change in wind direction. Furthermore, tide records in Mikawa Port for 30 years were analyzed and the risk of the disaster by the storm surge was discussed.

The estuarine circulation and the material transport associated with that in shallow waters around the mouth of Toyogawa River was studied through the field measurement of currents and chemical analysis of waters, carried out in summer, 2008 and 2009. The estuarine circulation was observed throughout the measurement period. The circulation was driven mainly by the wind and was not strongly correlated with the river discharge. Nutrients released from the bottom sediment under the hypoxic condition of bottom waters are transported by the estuarine circulation into the shallow waters, which may contribute to the primary production around the river mouth.

The study was carried out to investigate the seasonal variations of water quality and nutrient flux in Inohana Lake by using the intensive field measurements and modeling approach. A significant amount of phosphorus is regenerated from the bottom sediment in conjunction with the lower bottom DO concentration and phosphorus is supplied from the lower layer into the upper layer during the stratified seasons. For the phosphorus exchange with Hamana Lake, the inflow from Hamana Lake is dominant during the stratified seasons, while the outflow to Hamana Lake is dominant during the transition and mixed seasons. The change of material transport accompanying with the seasonal change of water mass causes the change in water quality in Inohana Lake.

Water exchange between Inohana and Hamana Lakes with density stratification is investigated based on the field data obtained in 2009. The basins are connected by a narrow channel with length of 200m through which waters, nutrients and other materials are exchanged between them. According to the authors' previous study, the water exchange was mainly caused by the wind, where even eastward wind induces significant exchange of waters. In this study, using the field data measured by ADCP and CTD, a mechanism of wind-induced water exchange is discussed. A simple theoretical approach suggests that the dynamic response of density surface in Hamana Lake to the wind force causes the circulating flow in the channel.

This study conducted field observations in terms of the number of blown sand impacts and wind velocity for two hours on 21 February 2009 at an open ocean beach in Japan in order to investigate characteristics of the aeolian sand transport flux over a sand dune slope. The Charnock constant related to wind shear on the sand bed surface calculated from the wind velocity data on the slope had a larger value over a flat. Furthermore the aeolian flux on the slope tended to be larger than that on the flat. Knowledge of the Charnock constant and the aeolian flux on the flat and slope was obtained from the field measurements which will become a great help for further investigation of the aeolian sand transport mechanisms.

The area around tidal inlet is potentially dangerous for marine activities because of strong tidal currents and waves together with the complexity of topography. This study intends to collect useful information about the flow field around tidal inlet for prevention of marine accidents. Field observations of waves and currents have been conducted on two sites of Imakirekuchi Inlet at Lake Hamana in Shizuoka Prefecture and Daiichikoguchi Inlet at Saroma Lake in Hokkaido. The continuous 30 days observation of currents at both sites were successfully conducted. By analyzing the observation data, characteristics of temporal- and spatial-variation of currents in and around the inlet have been examined to clarify the relation among tide, current, and topography.

Bathymetric data in a wide coastal area were derived from frequent monitoring using fishfinder and GPS data logged during fishing operation in Enshu-nada Sea. The offshore bathymetric changes in near critical depth were evaluated by the annual changes of contour line positions along the cross-shore direction and these standard deviations. The analysis revealed long-term trend with short-term fluctuation in the sea bottom changes associate with the frequent monitoring data. We found that slow erosion appeared in the offshore area except around river mouth and inlet was indicated.

Reproductive activity of loggerhead sea turtles can be classified into 3 stages: landing, oviposition, and hatching. The purpose of this study is to investigate the influence of environmental factors such as beach elevation and sand temperature on the reproductive activity of loggerhead turtles nesting on the beach. It was found that the number of landings in the period 2005-2008 was smaller on the beach in front of detached breakwaters than the other areas of beach without breakwaters. The length of tracks with successful nests (oviposition) was significantly larger than the length of tracks with abandoned nesting attempts (oviposition failure). In the hatching stage, sand depth was found to affect incubation temperature.

Short-term topographic changes of the Nakatajima dune, which is located on an eroded beach on the Enshu-Nada coast, have been investigated with continuous field surveys over two years period (2007-2009). Measurements of wind and wind-blown sand transport rate were also carried out several times in winter. Based on the field data, overall properties of the sediment transport on the dune are first described in the paper. Eastward migration of the dune is then indicated with relation to the topographic changes and the distribution of the sediment transport rate. Quantitative estimate of the average volume of transported sand are well predicted by some existing formulae

The purpose of this study is to develop a measurement method for suspended sediment using ultrasonic wave. Some experiments were carried out to measure suspended sediment concentration and echo intensity reflected by suspended sediment in a tank, and the relationship between measured concentration and echo intensity was investigated. The experimental results show that the relationship is consistent in the experimental condition with the wide range of sand grain size and mass concentration without information of sand grain size in suspended sediment, while the measurement by an optical turbidity sensor needs this information to estimate mass concentration from turbidity. Furthermoreit is indicated that the measurement method using ultrasonic wave may be possible to measure suspended sediment spatially.

During the summer of 2005, we carried out an intensive field survey of current velocity, salinity, temperature, and water density in Inohana Lake, Japan, which is a semi-enclosed and highly stratif...

A theoretical formulation that describes energy transformation and dissipation caused by air bubble entrainment in water is proposed, in which the potential energy increase, induced by air bubble displacement and thermodynamical work done on air bubbles, are considered. Laboratory experiments were carried out with measurements of void fraction distributions under vertical steady plunging jets and plunging breakers of water waves. The energy dissipation rate has been estimated from measured data of void fractions and compared with the total energy dissipation rate. The ratios of energy dissipation rate caused by bubble entrainment to total dissipation rate have been found to be 4%–8% for vertical circular plunging jets and 36%–40% for plunging breakers.

Mechanism of sand movement was investigated around of the Magome River mouth located on the Enshu-nada by the comparison of old geographical maps in about 200 years and by a color sand tracer experiment. The long term advancement of the shoreline as well as the rapid retreat in the last 20 years were identified. The movement of four color sands placed on the updrift and the downdrift sides of the river mouth jetty and in the jetty channel was monitored for three months. Entrapment of westward longshore transport by the jetty was found to be significant. A sand bypassing system was found to be feasible by utilizing an existing sewage discharge channel connecting the Tenryu River mouth to the Magome River.

An intensive field measurement was carried out in Inohana and Hamana Lakes including a narrow channel to investigate the phosphorus transport process in Inohana Lake during summer. Inohana Lake has a two-layer structure of the phosphorus distribution: the particulate phosphors (PP) in the surface layer, while the phosphate phosphorus (PO4-P) in the bottom layer. The phosphorus inflow from Hamana Lake through the bottom layer is dominant over the riverine loading and Inohana Lake becomes a sink of phosphorus from Hamana Lake. The settling and release fluxes of phosphorus are larger than the input and output of the phosphorus in Inohana Lake. The phosphorus budget suggests that the phosphorus accumulates in the sediment during summer.

Questionnaire surveys were conducted to investigate discrepancies between consciousness of citizens for tsunami disaster prevention assumed by administrations and actual consciousness of residents and visitors in tsunami vulnerable areas. It was found that the residents expect hardware measures (structures) against tsunami attacks, whereas visitors prefer software measures for evacuation. It is important to guide citizens toward software measures and give appropriatei nstructionsf or effectivee vacuation. Citizenws ho have experienceo ft sunamia ttack orlivingn ear the coastlineh ave clear images for threat of tsunamis.Goodc ommunicationb etween administrationsa nd citizensc an restrain the reduction of efficiencyf or tsunamip rotectionm easures.

In order to estimate sediment transport near a river mouth and a narrow inlet, it may be important to investigate the behavior of the long-period waves with periods of several minutes generated by wave groups in the sea. In this study, characteristics of the long-period waves and associated flows near Tenryu river mouth and the inlet of Hamana Lake are discussed based on the field data. Long-period waves are developed almost linearly to both significant wave heights and periods outside the inlet, but they are reduced about half in the inlet. The long-period fluctuation in the flow seems to consist of two components; one is associated with the long-period waves and the other is generated by tidal currents.

Beach changes around the mouth of the Magome River on the Enshu-nada coast and the long-term deformation of Nakatajima sand dune were investigated. The dune material originates from the Tenryu River. The supply of fine sand from this river has decreased owing to the construction of the dams in the upstream basin of the river, and the coastal forest was excessively planted close to the shoreline, resulting in decreasing sand supply from the shoreline to the sand dune. Thus, this sand dune has significantly been starving. To conserve this sand dune, supply of new sand or reuse of sand is required.