Language：English   Publishing type：Research paper (scientific journal)  

Multirotor drones can be efficiently used to monitor macro-litter in coastal and riverine environments. Litter on beaches, dunes and riverbanks, along with floating litter on coastal and river waters, can be spotted and mapped from aerial drone images. Items detection and classification are prone to image resolution, which is expressed in terms of Ground Sampling Distance (GSD). The GSD is determined by drone flight altitude and camera properties. This paper investigates what is a suitable GSD value for litter survey. Drone flight altitude and camera setup should be chosen to obtain a GSD between 0.5 cm/px and 1.25 cm/px. Within this range, the lowest GSD allows litter categorization and classification, whereas the highest value should be adopted for a coarser litter census. In the vision of drawing up a global protocol for drone-based litter surveys, this work sets the ground for homogenizing data collection and litter assessments.

DOI： 10.1016/j.marpolbul.2023.115521

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)  

Meso- and microplastics have been collected via net sampling in marine and freshwater environments, but the effect of net clogging on evaluations of their concentrations (mPC) remains uncertain. We experimentally investigated the mPC uncertainties resulting from net clogging in the Ohori and Tone-unga Rivers, typical urban rivers in Japan, throughout 16 samplings with five filtration durations in one day. The weighted mean concentration in the Ohori River was significantly lower than that in the Tone-unga River, allowing us to examine the effect of clogging in rivers with different contamination levels. The variances in both rivers consistently tended to increase with increasing filtration duration, which can be expressed by applying the integral form of the Weibull reliability function (WRF). Furthermore, application of the WRF successfully revealed the optimal filtration durations in the Ohori and Tone-unga Rivers, which depended on the plastic abundance and sample volume. Since it could be difficult to obtain the plastic contamination level in advance, our suggestion is to predict the time sustained above 85 % filtration efficiency by applying a WRF-based model. In actuality, the sustained time in the Ohori (Tone-unga) River varied between 2.6 and 6.2 min (3.2 and 7.1 min) throughout the experiment, which permitted low mPC uncertainties of 12 % and 9.5 %, respectively. If notable uncertainty exists due to a low contamination level, a net with a high open area ratio should be used to increase the filtration duration. Hence, our results emphasize the importance of considering the open area ratio of nets used for sampling in studies. Our study provides insights into the occurrence of uncertainty due to net clogging to establish a standardized methodology for meso- and microplastic monitoring in aquatic environments via net sampling and consequently contributes to improving the sampling accuracy.

DOI： 10.1016/j.scitotenv.2023.161942

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Monitoring marine contamination by floating litter can be particularly challenging since debris are continuously moving over a large spatial extent pushed by currents, waves, and winds. Floating litter contamination have mostly relied on opportunistic surveys from vessels, modeling and, more recently, remote sensing with spectral analysis. This study explores how a low-cost commercial unmanned aircraft system equipped with a high-resolution RGB camera can be used as an alternative to conduct floating litter surveys in coastal waters or from vessels. The study compares different processing and analytical strategies and discusses operational constraints. Collected UAS images were analyzed using three different approaches: (i) manual counting (MC), using visual inspection and image annotation with object counts as a baseline; (ii) pixel-based detection, an automated color analysis process to assess overall contamination; and (iii) machine learning (ML), automated object detection and identification using state-of-the-art convolutional neural network (CNNs). Our findings illustrate that MC still remains the most precise method for classifying different floating objects. ML still has a heterogeneous performance in correctly identifying different classes of floating litter; however, it demonstrates promising results in detecting floating items, which can be leveraged to scale up monitoring efforts and be used in automated analysis of large sets of imagery to assess relative floating litter contamination.

DOI： 10.3390/rs15010084

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Japan Society of Civil Engineers  

DOI： 10.2208/journalofjsce.b1-e0088

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Microplastics (MPs), plastic particles <5 mm in diameter, have become an emerging ubiquitous concern for the environment. Rivers are the primary pathways that transport MPs from the land to the ocean; however, standardized methodologies for in-situ sampling in freshwater environments remain undefined. Notably, uncertainties in MP sampling methods lead to errors in estimating MP discharge through rivers. In the present study, the inter-sample variance of plankton net-obtained MP concentrations for two urban rivers in Japan was investigated. Numerical concentrations, expressed in particles·m−3, revealed that variance s2 was proportional to the mean m of replicated estimates of numerical concentrations. A derived statistical model suggested that river MPs disperse according to purely random processes; that is, Poisson point processes. Accordingly, a method was established to project the “precision,” the ratio of the standard error to m, of numerical concentrations based on the number of net sampling repetitions. It was found that the mean of two replicates maintained sufficient precision of <30% for conditions with high concentrations of ≥3 particles·m−3. Projected precisions under different levels of MP concentrations are also presented to help design future field campaigns.

DOI： 10.1016/j.envpol.2022.119811

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Japan Society on Water Environment  

Research on plastic debris in the ocean and rivers is being vigorously conducted, but there is little research on the dynamics of plastic from the basin, which is one of the sources of plastic waste, to rivers and coasts. In this study, we conducted a field survey of basins (roads) , rivers, and coasts in the Hikichi River basin, Kanagawa Prefecture, with the aim of clarifying the dynamics of plastic pieces in the basin, river, and coast. From the results of the sample particle recovery test, the target size of the plastic piece in this study was set to be > 1 mm. The results indicated that the numerical and mass concentration of plastic pieces in the road dust between districts considered were significantly higher in the commercial and residential areas, respectively, mainly because of the difference in plastic piece size distribution. A comparison of plastic materials on roads, rivers, and coasts showed that polyethylene (PE) , polypropylene (PP) , and polystyrene (PS) , which have low specific gravity, were predominant in the river and materials washed up on the coast, but not significant in the road dust.

DOI： 10.2965/jswe.45.11

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Language：Japanese   Publisher：The Oceanographic Society of Japan  

Although several new technologies have promoted the development of modern oceanography, human activities have caused many environmental problems, such as ocean pollution. In this paper, we focus on three topics of environmental DNA, BGC Argo, and bio-logging as the new methods contributing to the future development in oceanography. Accidentally released radionuclides have been a severe concern since the accident of the Fukushima Dai-ichi nuclear power plant in 2011. In addition, plastic debris has recently attracted considerable attention as an international issue. We thus focus on these two topics as a problem in the current ocean environments.

DOI： 10.5928/kaiyou.30.5_227

DOI： 10.5928/kaiyou.30.5_87_references_DOI_G5savtaxUtb9YPIqtJ56uYFW7aA

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Other Link： http://id.ndl.go.jp/bib/031832263

Publishing type：Research paper (scientific journal)  

Studies have recently focused on microplastics (MPs) in tap and drinking water. Directly comparing the results of different studies is difficult owing to the use of various methodologies. In particular, a study of particles on a part of the filter to reduce the analysis time can lead to uncertainty regarding the number of MPs in tap water. In this study, the analysis of particles on the whole filtration area using a Fourier-transform infrared (FTIR) microscope was achieved in approximately 1 h using a filtration unit with a smaller filtration area (0.13 cm2) and a large-opening (26 μm) filter. Forty-two samples collected from five countries were analyzed using this method. The concentrations of the MPs at each site ranged from 1.9 to 225 particles L−1, with a mean concentration of all samples of 39 ± 44 particles L−1. The size ranged from 19.2 μm to 4.2 mm. Fragments were the predominant shape while fibers and spheres were also observed. Based on a combination of the shape, size, and chemical composition of the MPs, we discussed their sources. The MPs could have caused contamination after processing by a water treatment plant because we detected a significant number of polyester fibers > 100 μm, which were previously detected in the air, and PVC fragments > 50 μm, which are often used in water pipes. This study proposed technical improvements to the whole filtration area technique to detect MPs in tap water.

DOI： 10.1016/j.scitotenv.2021.148231

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Unmanned aerial systems (UAS, aka drones) are being used to map macro-litter on the environment. Sixteen qualified researchers (operators), with different expertise and nationalities, were invited to identify, mark and categorize the litter items (manual image screening, MS) on three UAS images collected at two beaches. The coefficient of concordance (W) among operators varied between 0.5 and 0.7, depending on the litter parameter (type, material and colour) considered. Highest agreement was obtained for the type of items marked on the highest resolution image, among experts in litter surveys (W = 0.86), and within territorial subgroups (W = 0.85). Therefore, for a detailed categorization of litter on the environment, the MS should be performed by experienced and local operators, familiar with the most common type of litter present in the target area. This work provides insights for future operational improvements and optimizations of UAS-based images analysis to survey environmental pollution.

DOI： 10.1016/j.marpolbul.2021.112542

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Language：Japanese   Publisher：Japan Society of Civil Engineers  

Plastic pollution is a global environmental problem, and it is necessary to understand the fluxes of macroplastics (> 5 mm) from rivers to the sea. We developed a monitoring system for quantifying anthropogenic debris flux by applying an image analysis into video images captured by a IP camera system. The image analysis made the color differences among water surface, natural debris and anthropogenic debris clear. We have conducted continuous measurements of anthropogenic debris flux in the Tenpaku River and its drainage channel during 34 flood events. Anthropogenic debris flux in rising stages significantly increased comparing with those in falling stages. The mean concentration of anthropogenic debris in the rising stages was significantly related to antecedent precipitation index (API).

DOI： 10.2208/jscejhe.77.2_i_1003

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Language：Japanese   Publisher：Japan Society of Civil Engineers  

Marine plastic wastes have been mostly originated from inland, and it is important to monitor macroplastics inflow into oceans via rivers. This study aims to develop a new image processing to capture the area and types of macroplastics with deep learning. The learning data for floating debris were collected with the field test under normal and flooding conditions. CNN and YOLO were applied to find the area and types of macroplastics. The results indicated that the CNN and YOLO can capture acceptably the area and types of macroplastics in normal flow condition. It is noted that add of the learning data under flooding conditions can greatly improve the accuracy of distinguishing the types of macroplastics by YOLO.

DOI： 10.2208/jscejhe.77.2_i_901

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Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

A model is proposed for the beach process of buoyant marine plastics, specifically its beaching and backwashing, by introducing beaching and backwashing diffusion coefficients and the onshore-offshore advection-diffusion equations of plastics for the upper layers in the beach and adjacent coastal sea. The backwashing diffusion coefficient was estimated from the average residence time of the beached plastics and the beach width, and then the beaching diffusion coefficient was estimated from the flux-balance assumption between the beaching and backwashing fluxes. Finite difference calculations in the staggered-grid system demonstrated that the amount of beached plastics responds as predicted by the linear system analysis when the beach had an exponential decay type of unit impulse response regardless of the ratio between the residence time and the period of beaching flux fluctuation from the nearshore. The condition in which the flux balance assumption holds was also discussed.

DOI： 10.1016/j.marpolbul.2020.111548

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：MDPI  

Plastic debris presents a serious hazard to marine ecosystems worldwide. In this study, we developed a method to evaluate high-resolution maps of plastic emissions from the land into the sea offshore of Japan without using mismanaged plastic waste. Plastics were divided into microplastics (MicPs) and macroplastics (MacPs), and correlations between the observed MicP concentrations in rivers and basin characteristics, such as the urban area ratio and population density, were used to evaluate nationwide MicP concentration maps. A simple water balance analysis was used to calculate the annual outflow for each 1 km mesh to obtain the final MicP emissions, and the MacP input was evaluated based on the MicP emissions and the ratio of MacP/MicP obtained according to previous studies. Concentration data revealed that the MicP concentrations and basin characteristics were significantly and positively correlated. Water balance analyses demonstrated that our methods performed well for evaluating the annual flow rate, while reducing the computational load. The total plastic input (MicP + MacP) was widely distributed from 210-4776 t/yr and a map showed that plastic emissions were high for densely populated and highly urbanized areas in the Tokyo metropolitan area, as well as other large urban areas, especially Nagoya and Osaka. These results provide important insights that may be used to develop countermeasures against plastic pollution and the methods employed herein can also be used to evaluate plastic emissions in other regions.

DOI： 10.3390/w12040951

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

A model of the beach process of marine plastics was proposed based on the assumption of the beaching and backwashing flux balance, and its applicability was examined by means of time-invariant linear system analysis and particle tracking experiments with respect to the ratio between the residence time of plastics on a beach (tau(r)) and the period of nearshore current variability (T-0). Based on the theory, the balance was expected to hold when tau(r)/T-0 was much smaller than 1; however, good agreement was obtained between the theory and the particle tracking method for much larger values of tau(r)/T-0. The parameters, which are diagnostically given in the model, will be prognostically decided by the coastal dynamics in the future to develop robust beach process models. Nevertheless, we believe that a diagnostic approach would be another pillar in the strategy for estimating the amounts and distributions of marine plastics in the coming years.

DOI： 10.1016/j.marpolbul.2020.110910

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：NATURE PUBLISHING GROUP  

A new algorithm has been developed to quantify floating macro-debris transport on river surfaces that consists of three fundamental techniques: (1) generating a difference image of the colour difference between the debris and surrounding water in the CIELuv colour space, (2) detecting the debris pixels from the difference image, and (3) calculating the debris area flux via the template matching method. Debris pixels were accurately detected from the images taken of the laboratory channel and river water surfaces and were consistent with those detected by visual observation. The area fluxes were statistically significantly correlated with the mass fluxes measured through debris collection. The mass fluxes calculated by multiplying the area fluxes with the debris mass per unit area (M/A) were significantly related to the flood rising stage flow rates and agreed with the mass fluxes measured through debris collection. In our algorithm, plastic mass fluxes can be estimated via calibration using the mass percentage of plastics to the total debris in target rivers. Quantifying riverine macro-plastic transport is essential to formulating countermeasures, mitigating adverse plastic pollution impacts and understanding global-scale riverine macro-plastic transport.

DOI： 10.1038/s41598-020-59201-1

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Publishing type：Research paper (international conference proceedings)  

In recent years, climate change has been responsible for many flood disasters. It is essential that protective measures should be developed against these. One of these measures is a flood forecasting system in which rising water-levels in rivers are predicted ahead of time. Although several researchers have applied artificial intelligence, and especially deep learning technology, to flood prediction, there is a lack of clarity regarding which deep learning approach is most effective in flood prediction. This study aimed to investigate the prediction of floods from water-level data by using a deep learning approach with data collected from the Kinu River. We adopted the LSTM (long short-term memory) algorithm, which is a type of recurrent neural network that readily reflects time-series data. In this study, we collected water-level data from five stations on the Kinu River, a branch of the Tone River, Japan. The results indicate that it is possible to utilize water-levels to predict flood events with a high level of accuracy.

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Language：Japanese   Publishing type：Research paper (scientific journal)  

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Language：Japanese   Publishing type：Research paper (scientific journal)  

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Language：Japanese   Publishing type：Research paper (scientific journal)  

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Language：English   Publishing type：Research paper (international conference proceedings)  

Microplastics (MPs), which are plastic pieces smaller than 5 mm, are causing widespread pollution in the aquatic environments of rivers, oceans, and lakes. Many researchers have measured MP concentrations mainly near water surfaces because the specific gravity of major plastics is lower than 1.0. In order to accurately estimate microplastic flux into oceans via rivers, it is necessary to evaluate the vertical profiles of MP concentrations in rivers. To address this, we conducted field surveys for grasping the vertical distributions of MP concentrations in a river. Two peaks in the vertical profiles of MP concentrations appeared in the surface and bottom layers of the river water. It was also noted that the specific gravity of MPs found in the bottom layer were slightly greater than those of the surface layer, showing that the vertical profiles of MP concentrations were influenced by the specific gravity of MPs. These facts indicate that the microplastics with large specific gravity (>1.0) can concentrate near the riverbed regardless of vertical mixing.

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Publishing type：Research paper (international conference proceedings)  

In recent years, environmental pollution caused by microplastics (MP) has become a global issue, yet only a few studies have considered MP pollution of freshwater fish, in contrast to the substantial research done on seawater fish. Thus, the purpose of this study is to examine MP pollution of river fish. To this end, we obtained Ayu (Plecoglossus altivelis) from Tama River Tokyo and Ugui (Tribolodon Hakonensis) from Komaoi River, Hokkaido. We also collected MP samples from the river water in both locations in order to examine the relationships of MP pollution between fishes and river water. Our findings were as follows. In the Komaoi River, MPs were detected in 2 out of 8 Ugui with 0.25 particles on average and up to 1 particle per individual. In the Tama River, MPs were detected in 2 out of 2 Ayu with 4 particles on average and up to 4 particles per individual. Thus, the MP pollution in the Ayu was higher than in the Ugui. In addition, the MP numerical concentrations in the Tama and Komaoi Rivers were 3.75 and 0.50 particles/m3, respectively. Together, these facts show that the MP pollution in the Tama River was greater than that in the Komaoi River and consequently had a greater tendency within its fish.

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Authorship：Lead author   Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：The International Association for Hydro-Environment Engineering and Research (IAHR)  

DOI： 10.3850/38wc092019-1811

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：FUJI TECHNOLOGY PRESS LTD  

The heavy rain that hit Western Japan in July 2018 triggered the worst rain-related disaster in the Heisei era, with the total of dead and missing persons exceeding 230, mainly in the Hiroshima and Okayama Prefectures. At several locations along Oda River (of the Takahashi river system) and its tributaries, dikes were breached due to large-scale flood, leaving 51 persons dead. This paper aims to shed light on the scale of inundation along Oda River and its tributaries and identify the characteristics of and critical factors for human damage. Field surveys were conducted to measure flood marks in flooded areas and river channels, and gauge the extent of damage to people and property. The surveys found that a large area was inundated on the north side of Oda River, with an inundation depth exceeding 5 m for 1 km in the south-north direction and 3.5 km in the east-west direction, which made vertical evacuation of residents difficult. The findings that about 80% of the dead were found on the first floor of their houses, with those who had lived in a one-story house and those who had lived in a two-story house accounting for 50% each of the deceased, indicate how difficult even vertical evacuation was. The findings appear to be related to the considerable inundation depth and high rate of water level increase, along with the fact that the majority of the deceased were elderly people.

DOI： 10.20965/jdr.2019.p0874

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：TAYLOR & FRANCIS LTD  

Typhoon Jebi in 2018 caused severe damage along areas of Osaka Bay, Japan. After the storm, a Japan Society of Civil Engineers (JSCE) coastal survey group surveyed the coastal impacts and recorded watermarks inside Osaka Bay and along the Pacific. The maximum storm tide recorded by a tide gauge was 3.29 m at the Osaka Tide Station, which is a historical high for Osaka Bay. Coastal flooding consisted of both storm surge and wave run-up in almost all locations, with flooding exceeding 5 m and 12 m in elevation from mean sea level in the inner parts of Osaka Bay and along the Pacific coast, respectively. Coastal damage was severe in areas located outside of coastal barriers, such as ports and harbors, while residential areas were mainly well protected and spared due to coastal protection systems. In addition, some inland flooding occurred in the Kobe-Ashiya regions due to the storm surge propagating up several small rivers. This survey report summarizes the findings of the post-event survey by JSCE and analyzes the relation between maximum water level and resulting damage.

DOI： 10.1080/21664250.2019.1619253

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCI LTD  

The numerical and mass concentrations of microplastics collected at 36 sites on the surfaces of 29 Japanese rivers were mapped and compared with four basin characteristics (basin area, population density, and urban and agricultural ratios) and six water quality parameters (pH, biochemical oxygen demand (BOD), suspended solids (SS), dissolved oxygen (DO), total nitrogen (T-N), and total phosphorus (T-P)) in each river basin. Microplastics were found in 31 of the 36 sites, indicating that some plastics fragment into small pieces before reaching the ocean. The microplastic concentrations are significantly correlated with urbanisation and population density, indicating that the microplastic concentrations in the river depend on human activities in the river basin. Furthermore, we found a significant relationship between the numerical and mass concentrations and BOD, which is an environmental indicator of river pollution. This result demonstrates that microplastic pollution in river environments has progressed more in polluted rivers with poor water quality than in rivers with good water quality, leading to the conclusion that the sources and inflow processes of microplastics in river environments are similar to those of other pollutants. Our findings can help identify potential sources (i.e., point and non-point sources) of fragmented microplastics to improve waste management in Japan and model the transport fluxes of fragmented microplastics in Japanese rivers using water quality parameters and basin characteristics. (C) 2018 The Authors. Published by Elsevier Ltd.

DOI： 10.1016/j.envpol.2018.10.111

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Language：Japanese   Publishing type：Research paper (scientific journal)  

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Authorship：Lead author,　Corresponding author   Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Japan Society of Civil Engineers  

<p> The storm surge induced by Typhoon Jebi caused flooding in the city areas around the Takahashi River in Hyogo Prefecture. To investigate the river-related flood disaster, we have conducted in-situ survey for measure the height of high-water marks and a two-dimensional plane flow simulation. The river-related flood occurred due to the increase of river water level induced by the storm surge, and mainly caused by the overflow from bridges whose elevation is lower than that of levees. After that, the flooding water spreaded for thirty minutes. The inundation area is approximately 0.11 km², and the maximum inundation depth was 0.62 m. On the other hand, the rainfall hardly contributed to this disaster because the peak time of water level induced by the rainfall was before 31 minutes.</p>

DOI： 10.2208/kaigan.75.I_265

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Japan Society of Civil Engineers  

&nbsp;Numerical and mass concentrations of microplastics in sizes < 5mm were investigated based on <i>in-situ</i> surveys on the surface of two rivers (Edo River and Ohori River), and annual flux of floating microplastics of Edo River were estimated by using a statistically significant relationship of the concentrations with river discharge. Good correlation between MP flux and discharge (i.e., L-Q relation) was also found in Edo River. Annual flux of numerical (mass) MP concentrations on the Edo River was 1.5&times;10¹⁰ pieces (2.42 ton). The ratio of numerical (mass) MP flux under high flow conditions was 73.5% (84.1%) in the total flux. These results indicate that the high ratio of MP flux in flooding conditions was similar to that of macro debris flux in rivers.

DOI： 10.2208/jscejhe.74.I_529

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Japan Society of Civil Engineers  

&nbsp;The overgrowth of cyanobacteria, which causes Algal bloom will continue to be a major concern regarding the eutrophication problem in dam reservoirs and lakes. The current main-stream monitoring method of Algal bloom is visual examination, in which administrators of dam reservoir and lake keep records using &ldquo;Apprearance Algal bloom Index&rdquo; in daily patrolling. However, with this method, there is a limitation to the detailed analysis and grasp of Algal bloom because of the limit of Algal bloom's confirmation place or the possibility of human errors, etc.. In this study, in order to make an automatic judgment of the &ldquo;Algal bloom level&rdquo; described in "Appearance Algal bloom Index" from digital images, the images of Algal bloom were taken and the water quality in Kasumigaura were analyzed. As a result, the relationship was found between &ldquo;G-B level&rdquo; and Chl.a or &ldquo;Algal bloom level&rdquo;. In addition, the usefulness of the automatic judgment of Algal bloom level using digital images in which Algal bloom is actually occurring was demonstrated through this study.

DOI： 10.2208/jscejhe.74.I_823

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Japan Society of Civil Engineers  

<p> In order to clarify the transport process of plastic debris from land, the accumulation of macro-, meso- and micro-plastic debris on river banks were investigated in the Arakawa River. The plastic debris were accumulated at the downstream site comparing with the upstream sites. The amounts of meso- and micro-plastics on the higher river bank was more than that near the river edge, indicating that the degradation of plastic debris could progress on the river bank. In addition, the degradation level of plastic debris collected from the river banks was understood by measuring a ratio of absorbance at carbonyl and methylene groups. The degradation level was high in order of micro-, meso- and macro-plastics, indicating that the degradation level of smaller plastic debris was high.</p>

DOI： 10.2208/jscejhe.75.2_I_433

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Japan Society of Civil Engineers  

<p> The occurrence of earthquake and flood compound disaster in Japan was investigated by collecting the data of earthquake intensity and levee breach due to flood. The frequency of earthquake occurrence in 2000s was almost consistent with that in 2010s, while the frequency of levee breach due to flood in 2010s was greater than that in 2000s. In addition, the frequency which the yearly-maximum water level exceeded the design high-watar level has been increased since 2000s. Consequently, the time-interval between earthquake occurrence and levee breach in 2010s was shorter than that in 2000s, indicating that the possibility of occurrence of earthquake-flood compound disaster may increase.</p>

DOI： 10.2208/jscejhe.75.2_I_103

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Japan Society of Civil Engineers  

<p> To reduce the computational load and improve the robustness of a flood prediction system (DIEX-Flood), which can estimate the water level longitudinal distribution in the current and future, we corrected the equation of DIEX-Flood and improved the data assimikation algorism. As a result of applying this method to Kinu river flood, it can calculate multiple cases of floods. Furthermore, we proposed a new flood forecasting method combining DIEX-Flood and deep learning. This prediction method can forecast water level longitudinal distribution in the future, so it makes possible to know spatial and temporal distribution of flood risk. This method can be expected accuracy improvement by assimilating water level data such as crisis management type water level gauges.</p>

DOI： 10.2208/jscejhe.75.2_I_217

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Japan Society of Civil Engineers  

<p> An inland flooding could be occerred frequently due to localized torrential rainfall enhanced by climate change. However, quantitative monitoring measurement has not yet been well-established for evaluating the damages and drainage management of inland flooding, as well as its threshold for evacuation from such complicated and qualitative information. In this study, for the purpose of grasping the risk of inland flooding, the reformed DIEX-Flood model, which interpolate and extrapolate water-level data into a streamwise direction with satisfying hydraulic principles, can calculate accurately with high-speed calibration performence. The improved model was verified by using the water level observation data of sewer pipe. The results indicate the proposed method can forcast streamwise distribution of water-level with high accuracy by using data assimilation. In data assimilation, the correction of forcasting is made with less influence from the rainfall prediction errors and other potential errors.</p>

DOI： 10.2208/jscejhe.75.2_I_211

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Japan Society of Civil Engineers  

<p> We found double peaks in a vertical profile of microplastic concentration in rivers by conducting the field surveys for observing the vertical distribution of microplastic concentration in the Edo River. The first and second peaks appeared in the surface and bottom layer, respectively. The vertical profile was dependent on the specific gravity of microplastics, and the specific gravity found in bottom layer was significantly greater than that found in the surface layer. Furthermore, the settling velocity of microplastics was larger than their rising velocity according to their specific gravity. These indicate that the microplastics having greater specific gravity can concentrate regardless of vertical mixing in a river.</p>

DOI： 10.2208/jscejhe.75.2_I_439

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Japan Society of Civil Engineers  

&nbsp;In this study, we investigated flood disaster and evacuation behavior in Asakura city, Fukuoka prefecture due to 2017 northern Kyushu flood. We conducted field surveys for house damage and flood process in Akatani, Kita, Naragaya and Myoken River-basin which huge disaster was found in this flood.We also examined human damage in this site through literature search and interview with residents. The results showed that most of dead stayed in the homes and most of their home were damaged due to this disaster, showing the importance of horizontal evacuation. It is noted that predicted hourly precipitation by weather forecast system of JMA was lower than the measured precipitation in this flood. We also summarized the relation between weather warn-ing and flood conditions in several flood disasters.

DOI： 10.2208/jscejhe.74.I_1171

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Language：Japanese   Publishing type：Research paper (bulletin of university, research institution)   Publisher：Japan Association for Wind Engineering  

DOI： 10.5359/jawe.44.288

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER  

Composite analysis was conducted using high-frequency radar data obtained during 2006-2015 in order to gain a better understanding of the current field in the Ariake Sea. The seasonally averaged surface current in the Ariake Sea was directed southward in all seasons, except around river mouths during summer. Heavy rainfall enhanced the outflow along the eastern coast of the Shimabara Peninsula from Isahaya Bay to the southern area 2-5 days after heavy rainfall. Spring-neap differences were clearly seen in the southward current along the Shimabara Peninsula. Interannual variation in the M (2) tidal current amplitude was synchronized with the lunar nodal cycle.

DOI： 10.1007/s10872-018-0464-2

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

The amount of marine debris washed ashore on a beach in Newport, Oregon, USA was observed automatically and sequentially using a webcam system. To investigate potential causes of the temporal variability of marine debris abundance, its time series was compared with those of satellite-derived wind speeds and sea surface height off the Oregon coast. Shoreward flow induced by downwelling-favorable southerly winds increases marine debris washed ashore on the beach in winter. We also found that local sea-level rise caused by westerly winds, especially at spring tide, moved the high-tide line toward the land, so that marine debris littered on the beach was likely to re-drift into the ocean. Seasonal and sub-monthly fluctuations of debris abundance were well reproduced using a simple numerical model driven by satellite-derived wind data, with significant correlation at 95% confidence level.

DOI： 10.1016/j.marpolbul.2018.04.075

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The abundance of marine macro-debris was quantified with high spatial resolution by applying an image processing technique to archived shoreline aerial photographs taken over Vancouver Island, Canada. The photographs taken from an airplane at oblique angles were processed by projective transformation for georeferencing, where five reference points were defined by comparing aerial photographs with satellite images of Google Earth. Thereafter, pixels of marine debris were extracted based on their color differences from the background beaches. The debris abundance can be evaluated by the ratio of an area covered by marine debris to that of the beach (percent cover). The horizontal distribution of percent cover of marine debris was successfully computed from 167 aerial photographs and was significantly related to offshore Ekman flows and winds (leeway drift and Stokes drift). Therefore, the estimated percent cover is useful information to determine priority sites for mitigating adverse impacts across broad areas.

DOI： 10.1016/j.marpolbul.2017.08.060

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Authorship：Lead author,　Corresponding author   Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Japan Society of Civil Engineers  

&nbsp;The significant wave height in Ise Bay was measured by applying the Bayesian inversion method (BIM) proposed by Kataoka and Nagamatsu (2016), which is a modification of the method by Hashimoto and Tokuda (2003), to the Doppler spectrum measured by high-frequency (HF) radar. The significant wave height can be accurately measured by removing a random noise included into the Doppler spectrum using low-pass filter. In order to verify the spatial distribution of ocean waves measured by HF radar, the ocean waves are simulated using the third-generation wave model Simulating Waves Nearshore (SWAN), and then compared with those measured by HF radar. The abnormally high wave height was locally measured by HF radar because of unknown noise found by applying wavelet analysis. Therefore, we will develop a technique for effectively removing the noise in the future to monitor ocean waves using HF radar in shallow waters.

DOI： 10.2208/kaigan.74.I_1459

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Language：Japanese   Publisher：Japan Society of Civil Engineers  

<p> It is necessary to monitor and forecast an inland flood to prevent a city from it. A primary issue of the monitoring for the inland flood is how to calculate discharge and water-level distribution. The authors have developed the dynamic interpolation and extrapolation (DIEX) method which interpolate and extrapolate velocity in a cross-section, and DIEX method for flood prediction (DIEX-Flood) which interpolate and extrapolate water-level data into a streamwise direction with satisfying hydraulic principles. In this study, DIEX and DIEX-Flood models were improved to be applicable to a pipe flow. In order to verify the fundamental performance of the present method, laboratory experiments and numerical simulations were conducted. The results indicate that DIEX method can evaluate smooth cross-sectional velocity and discharge with high accuracy. DIEX-Flood evaluates streamwise distribution of water-level with high accuracy throughout the calculation area.</p>

DOI： 10.2208/jscejhe.74.5_I_1495

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<p> This study aimis to investigate the influence of difference of radar rain gauge on the runoff and flood analysis. The target of this study is huge rainfall event due to 2017 Northern Kyushu flood. As radar rain data, we used the rader/rainguage – analyzed precipitation data by JMA and C-X composit data by MLIT. We conducted runoff analysis by using RRI model. Flood analysis was conducted using iRIC Nays 2 DH with the upstream boundary condition obtained by the runoff analysis. The results indicated that the difference of the radar rain gauge gives significantly those of outflow discharge, flood volume and maximum inundation depth.</p>

DOI： 10.2208/jscejhe.74.5_I_1501

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Residence times of microplastics were estimated based on the dependence of meso- and macrolitter residence times on their upward terminal velocities (UTVs) in the ocean obtained by one- and two-year mark-recapture experiments conducted on Wadahama Beach, Nii-jima Island, Japan. A significant linear relationship between the residence time and UTV was found in the velocity range of about 0.3-0.9 ms(-1), while there was no significant difference between the residence times obtained in the velocity range of about 0.9-1.4 ms(-1). This dependence on the UTV would reflect the uprush-backwash response of the target items to swash waves on the beach. By extrapolating the linear relationship down to the velocity range of microplastics, the residence times of microplastics and the 1D onshore-offshore diffusion coefficients were inferred, and are one to two orders of magnitude greater than the coefficients of the macroplastics.

DOI： 10.1016/j.marpolbul.2017.05.012

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In the present study, we determined the common morphological characteristics of the feces of Mytilus galloprovincialis to develop a method for visually discriminating the feces of this mussel in deposited materials. This method can be used to assess the effect of mussel feces on benthic environments. The accuracy of visual morphology-based discrimination of mussel feces in deposited materials was confirmed by DNA analysis. Eighty-nine percent of mussel feces shared five common morphological characteristics. Of the 372 animal species investigated, only four species shared all five of these characteristics. More than 96% of the samples were visually identified as M. galloprovincialis feces on the basis of morphology of the particles containing the appropriate mitochondrial DNA. These results suggest that mussel feces can be discriminated with high accuracy on the basis of their morphological characteristics. Thus, our method can be used to quantitatively assess the effect of mussel feces on local benthic environments. (C) 2016 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.marpolbul.2016.11.040

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&nbsp;Microplastics is the major concerns in the ocean's environment. There are many researches and surveys in the oceans, and while there are a few researches in the rivers around the world. As the first step of the microplastics researches, we considered the basic methodology of the microplastics survey. And then we investigated the distribution of microplastics in the multiple Japanese rivers. We found that the order of magnitude of number density of microplastics in the rivers was an one-order lower than that in the sea near Japan.

DOI： 10.2208/jscejhe.73.I_1225

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Authorship：Lead author,　Corresponding author   Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Japan Society of Civil Engineers  

&nbsp;To study the trapping of floating macro debris in rivers, we have investigated the budget of debris by measuring the amount of inflow, outflow and accumulation of debris by conducting an in-situ survey in the tidal flat of the Arakawa River, which is surrounded by wave dissipating blocks. The inflow of debris was predominant in the budget of debris in the tidal flat and one to two orders greater in magnitude than the outflow of debris. In addition, the inflow of debris was related to the water level in the Arakawa river and had a local maximum at the water level between high and low tides. Hence, we established a Gaussian model for estimating the inflow of debris using water level. The Gaussian model enabled us to estimate the accumulation of debris in the tidal flat.

DOI： 10.2208/kaigan.73.I_1435

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Authorship：Lead author,　Corresponding author   Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Japan Society of Civil Engineers  

&nbsp;The dependence of the accuracy of ocean waves measured from the Doppler spectrum by high-frequency (HF) radar on the azimuthal difference (&Delta;&phi;) in the HF radar beams is investigated using numerical simulation. The directional spectrum is most accurately estimated at &Delta;&phi; = 90&deg;, while its measurement accuracy is least accurate at &Delta;&phi; = 180&deg;. Nevertheless, it is worth noting that the measurement accuracy is constant in 30&deg; < &Delta;&phi; < 150&deg;. The dependence of measurement accuracy of the directional spectrum results in lowererd measurement accuracy of wave direction. On the other hand, the measurement accuracy of frequency spectrum weakly depends on &Delta;&phi;. As a result, the significant wave height and period can be accurately measured regardless of &Delta;&phi; except in the case of &Delta;&phi; = 180&deg;

DOI： 10.2208/kaigan.73.I_1657

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Japan Society of Civil Engineers  

&nbsp;Typhoon No 10 brought a heavy rain to northern Japan specially to Tohoku and Hokkaido areas and caused heavy flood disasters. The heavy rain recorded was 66mm per hour in Iwaizumi city, Iwate prefecture. In this study we conducted a field survey and a numerical analysis to understand the flood inundation mechanism in Otomo district, Iwate prefecture. The results show that, there are two stages of flooding in the city which are flood from streams and flood from the Omoto River. The initial flow velocity was 0.5m/s~1.0m/s. Therefore, evacuation was a difficult situation. From the above results, it is confirmed that the early evacuation is necessary in this kind of situation.

DOI： 10.2208/jscejhe.73.I_1411

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&nbsp;The mechanisms of the short-period variability of the bifurcation current &ldquo;Friwakecho&rdquo; were investigaeted using high-frequency ocean surface radar observation data, water temperature records, wind data, and sea level records. Statistical analysis of the data indicated that the variability of the bifurcation was highly coherent with wind veloticy field fluctuations, lagging about 90 degrees. In the west-northwestward winds dominated regiem, the Kuroshio front approached the southwestern coast of the Kii Peninsula, and then the bifurcation current strengthend. When east-southeasteward winds dominated in and around the Kii Channel, the Kuroshio front or the bifurcation current moved offshore about 15 km, weakening/ ending the bifurcation current.

DOI： 10.2208/kaigan.72.I_463

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We propose a belt transect setting strategy for mark-recapture experiments (MREs) to evaluate the time-independent 1D diffusion coefficient (< D-p0 >) of marine litter in the cross-shore direction that determines the backwashing flux of the litter, based on two-year MREs for plastic floats (PFs) on Wadahama Beach, Nii-jima Island, Japan. When the alongshore width of the belt transect (L-t) was of the order of, or longer than, the length scale of wave-induced nearshore current circulation (L-c), the PFs were rarely transported alongshore across the selected transects prior to being backwashed offshore. Thus, the transect residence time became longer and showed a much weaker dependence on the transect position, in contrast to when L-t was even shorter than L-c. We therefore obtained the diffusion coefficients close to the value of (< D-p0 >) when we set L-t to the order of, or longer than, L-c. (C) 2016 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.marpolbul.2016.05.016

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Authorship：Lead author,　Corresponding author   Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Japan Society of Civil Engineers  

&nbsp;A Bayesian inversion method for estimating the directional spectrum in deep water (BIM_deep) has been modified to accurately estimate the directional spectrum of ocean waves in shallow water from the Doppler spectrum measured by high frequency (HF) radar. The applicability of the modified Bayesian inversion method (BIM_shallow) and BIM_deep in shallow water has been verified by numerical experiments. We found that BIM_shallow can accurately estimate the directional spectrum even if the Doppler spectrum depends on water depth due to the linear dispersion relation in shallow water. In contrast, BIM_deep cannot accurately estimate the directional spectrum in the range of relative depth less than or equal to 1 (<i>h</i>/&lambda; ≤ 1). Consequently, BIM_deep is applicable when <i>h</i>/&lambda; > 1.

DOI： 10.2208/kaigan.72.I_1711

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A key factor for determining the residence time of macroplastics on a beach is the process by which the plastics are backwashed offshore (backwash process). Here, we deduced the backwash process of plastic fishing floats on Wadahama Beach based on the analysis of two-year mark-recapture experiments as well as nearshore current structures revealed by sequential images taken by za webcam installed at the edge of a cliff behind the beach. The analysis results revealed the occurrence of a combination of offshore currents and convergence of alongshore currents in the surf zone in storm events around a submerged breakwater off the northern part of the beach, where 48% of the backwashed floats were last found. We conclude that the majority of the floats on the beach were transported alongshore and tended to concentrate in the convergence zone, from where they were backwashed offshore by the nearshore currents generated in the events. (C) 2015 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.marpolbul.2015.10.060

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

We established a method for evaluating beach cleanup effects (BCEs) based on a linear system analysis, and investigated factors determining BCEs. Here we focus on two BCEs: decreasing the total mass of toxic metals that could leach into a beach from marine plastics and preventing the fragmentation of marine plastics on the beach. Both BCEs depend strongly on the average residence time of marine plastics on the beach (tau(r)) and the period of temporal variability of the input flux of marine plastics (1). Cleanups on the beach where tau(r) is longer than Tare more effective than those where tau(r) is shorter than T. In addition, both BCEs are the highest near the time when the remnants of plastics reach the local maximum (peak time). Therefore, it is crucial to understand the following three factors for effective cleanups: the average residence time, the plastic input period and the peak time. (C) 2014 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.marpolbul.2014.12.026

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Japan Society of Civil Engineers  

This study examines the possibility of detecting the first wave of a tsunami by oceanographic radar based on a virtual tsunami observation experiment. Radial velocities obtained by tsunami simulation are converted into modulating signals and superimposed on signals measured by oceanographic radar installed on the Mihama coast. Then the radial velocities are calculated from the combined signals which are to be measured by oceanographic radar. We call this procedure 'virtual tsunami experiment', and use it to investigate the possibility of tsunami detection using cross-correlation between two observation points in a radial direction. When the cross-correlation increases significantly and in a correlated manner with the passage of the first tsunami wave, we judge that the oceanographic radar has detected the tsunami at the points where the correlation is calculated. We found that the location of the furthest-offshore points where the first wave was detected by the radar depends on the distance between the two observation points. The dependence of the distance of tsunami detection on the distance between the two points is also discussed.

DOI： 10.2208/kaigan.71.I_337

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：IAHR-INT ASSOC HYDRO-ENVIRONMENT ENGINEERING RESEARCH  

Most marine debris are primarily supplied from inland areas; however, few monitoring data exist for floating-litter transport from rivers to the ocean due to the absence of appropriate monitoring methods. In this study, we developed an automatic and continuous monitoring technique for floating-litter transport L in rivers by using an image monitoring and processing technique in which different types of litter (scatter-type and mass-type) are separately analyzed. The results indicated that L evaluated by the present methods was in good agreement with the observed data in the Mogami River, Yamagata, Japan, demonstrating the fundamental performance of the present monitoring method.

DOI： 10.2208/jscejhe.71.I_1225

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Large quantities of plastic litter are expected to wash ashore along the beaches of the East Asian marginal seas in the coming decade. Litter quantities were predicted using three techniques: a particle tracking model (PTM) used in conjunction with two-way PTM experiments designed to reveal litter sources, an inverse method used to compute litter outflows at each source, and a sequential monitoring system designed to monitor existing beach litter using webcams. Modeled year-to-year variation in litter quantities indicated that the amount of litter would continue to increase in the East Asian marginal seas if the level of outflow remains constant in the coming decade. The study confirms that about 3% of all East Asian beaches may potentially experience a 250-fold increase in the amount of plastic beach litter washed ashore in the next 10 years. (C) 2014 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.marpolbul.2014.01.057

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The exponential decay of the amount of new litter on Wadahama Beach, Nii-jima Island, Japan revealed by 20-month mark-recapture experiments demonstrates a linear response of the beach to the input of target items. Here we show the amplitude and phase characteristics of the beach as a time-invariant linear input/output system and discuss the hydrodynamic and geomorphological factors that would determine the characteristics with the aid of a diffusion equation. The characteristics are fully determined by the residence time of the items (tau(r) = 209 days) and can be described as functions of the ratio of tau(r) to the period of input variability. The decay is reproduced well by the analytical solution of the equation with a constant diffusion coefficient (D), whose order was estimated by tau(r) and the backshore width. Generally, D would depend on hydrodynamical statistics and beach geomorphology as well as the dimensions and density of the items. (C) 2013 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.marpolbul.2013.09.049

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：ACADEMIC PRESS LTD- ELSEVIER SCIENCE LTD  

We numerically estimated the inflow flux of terrestrial grass, which is the main floating macro-debris, into Tokyo Bay from April 2008 to March 2009 based on a two-way particle-tracking model and an inverse method applying a Lagrange multiplier. In the estimation, we used surface current velocities derived by high-frequency ocean radar and the quantity of grass collected by clean-up vessels which are operated daily in the bay. At least 2115 m(3) yr(-1) of the grass flowed into the bay annually, and the contribution of a flood event to the inflow flux of grass was larger than that of the inflow flux of freshwater. We show that 39% of the annual inflow flux of grass into the bay was collected, and 61% flowed out of the bay or sank to the seabed. The numerical estimation in this study will be useful to establish a system for predicting patches of floating macro-debris in the bay, and to evaluate the effects of river development or clean-up along river banks and flood plains in the upper reaches. (C) 2013 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.ecss.2013.09.005

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Japan Society of Civil Engineers  

For comprehensive managements for marine debris including inland area which is known to be a source of marine debris, it is necessary to monitor the behavior of floating-litter in rivers and coasts. In the present study, we presented an automatic and continuous monitoring technique for floating-litter transport L in rivers by using a video image monitoring and a new image processing technique. In this technique, image pixels of floating-litter are detected using spatial gradient of image colors P&#039; larger than a threshold value P&#039; th which is related to image colors in pixels of no floating-litter. The results indicated that L evaluated by the technique gave good agreement with the observed data in several floods in the Edogawa River, demonstrating the fundamental performance of the present technique.

DOI： 10.2208/jscejhe.69.I_769

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A series of drained triaxial compression tests (TC) were performed on specimens prepared in the laboratory and rotary core samples retrieved from the field of well-compacted cement-mixed gravelly soils (CMG). The effects of the following factors on the compressive strength qmax were evaluated: the degree of compaction Dc and cement content (when compacted at the optimum water content); the curing time; the grading characteristics of gravelly soil; and the specimen volume. The followings were found from the data for a wide variety of CMG having c/g= 2.0 ∼ 6.0 % compacted by using two energy levels (1.0Ec & 4.5Ec). The effects of Dc are equally important as the cement content. An empirical equation is proposed using two independent variables, the soil skeleton porosity ns, which controls the initial compressive strength, and the cement void ratio Cr, which controls the increasing manner of qmax with curing time. The effects of sieving method to obtain smaller particle materials for small TC specimens from an original gravelly soil having larger particles are not significant. However, significant effects of specimen volume (i.e., 72 mm × 72 mm in cross-section times 150 mm high versus 300 mm in diameter times 580 mm high) is highlighted.

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We have developed a technique for detecting the pixels of colored macro plastic debris (plastic pixels) using photographs taken by a webcam installed on Sodenohama beach, Tobishima Island, japan. The technique involves generating color references using a uniform color space (CIELUV) to detect plastic pixels and removing misdetected pixels by applying a composite image method. This technique demonstrated superior performance in terms of detecting plastic pixels of various colors compared to the previous method which used the lightness values in the CIELUV color space. We also obtained a 10-month time series of the quantity of plastic debris by combining a projective transformation with this technique. By sequential monitoring of plastic debris quantity using webcams, it is possible to clean up beaches systematically, to clarify the transportation processes of plastic debris in oceans and coastal seas and to estimate accumulation rates on beaches. (C) 2012 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.marpolbul.2012.06.006

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Authorship：Lead author,　Corresponding author   Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：日本海洋学会  

As a first step toward understanding the marine litter balance in Tokyo Bay, we confirmed the applicability and accuracy of the two-way particle-tracking model (PTM) and the inverse method using a Lagrange multiplier developed by Isobe et al. (2009) and Kako et al. (2010) for the East China Sea using high-frequency ocean surface radar-derived surface current velocities and a drifting litter collection database managed by the Ministry of Land, Infrastructure, Transport and Tourism. We focused on how the accuracy of these methods depends on horizontal diffusivity (HD). We found that the two-way PTM and the inverse method are applicable to Tokyo Bay: the errors of identifying marine litter sources by the two-way PTM are within 10 km, and the estimating marine litter inflows are 0.9 to 1.6 times the true inflows. The errors of identifying the sources depend on the HD: the possibility of incorrect identification by the two-way PTM increases with larger HD. In addition, the errors depend on the strengths of the horizontal dispersion field produced by horizontal velocity shear. The possibility is also high for current fields with strong horizontal velocity shear. Also, when the HDs are larger than the corresponding true HDs, the inflows are overestimated. However, the dependence of the estimation on HD is not linear: if the HDs are larger than twice the true diffusivities, estimated inflows are less than twice the true inflows. Even if the HDs are one order of magnitude greater than the true diffusivities, the estimated inflows are smaller than six to seven times the true inflows.

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Authorship：Lead author,　Corresponding author   Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Japan Society of Civil Engineers  

We computed the quantity of macro plastic litter by detecting the pixels of colored plastic litter using photographs taken by webcams installed at four coastal locations in Japan, and applying a projective transformation to the photographs. The technique involves generating color references using a uniform color space to detect plastic litter pixels and removing misdetected pixels by using a composite image method. We successfully obtained a time series of the quantity of plastic litter. The use of webcams to monitor the quantity of plastic litter enables beach cleanups to be performed effectively and to clarify the mechanism by which plastic litter is beached. Our final goal is to grasp the transportation of plastic litter in the East Asian seas by combining an ocean circulation model and the webcam monitoring of plastic litter quantity.

DOI： 10.2208/kaigan.68.I_1471

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Japan Society of Civil Engineers  

High frequency ocean surface radar observation reveals the velocity fields of propagating tsunami waves and subsequent 30-40 minute period natural oscillation in the Kii Channel, Japan induced by the March 11, 2011 moment magnitude 9.0 Tohoku-Oki earthquake. Technical issues of the ocean surface radar system concerning the detection of tsunami waves and natural oscillation velocities are also discussed.

DOI： 10.2208/kaigan.68.I_196

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ACADEMIC PRESS LTD- ELSEVIER SCIENCE LTD  

Signals from the tsunami waves induced by the March 11, 2011 moment magnitude (M-w) 9.0 Tohoku-Oki earthquake and from subsequent resonances were detected as radial velocity variability by a high-frequency ocean surface radar (HF radar) installed on the eastern coast of the Kii Channel, at a range of about 1000 km from the epicenter along the eastern to southern coasts of Honshu Island. A time-distance diagram of band-passed (9-200 min) radial velocity along the beam reveals that the tsunami waves propagated from the continental shelf slope to the inner channel as progressive waves for the first three waves, and then natural oscillations were excited by the waves; and that the direction of the tsunami wave propagation and the axis of the natural oscillations differed from that of the radar beam. In addition, spectral analyses of the radial velocities and sea surface heights obtained in the channel and on the continental shelf slope suggest complex natural oscillation modes excited by the tsunami waves.The major advantage of the HF radars as tsunami detection is early warning as the tsunami is still far offshore. There is no doubt on this importance beside still technical and operational studies are needed. Our results adds a new role of the HF radars to measure the detailed surface current fields with high spatiotemporal resolution toward understanding detailed processes of resonant response to tsunami waves in coastal regions. (C) 2011 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.ecss.2011.08.009

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Authorship：Lead author   Language：Japanese   Publishing type：Article, review, commentary, editorial, etc. (trade magazine, newspaper, online media)  

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J-GLOBAL

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Language：Japanese   Publishing type：Article, review, commentary, editorial, etc. (trade magazine, newspaper, online media)  

CiNii Books

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Language：Japanese  

J-GLOBAL

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Language：Japanese   Publishing type：Article, review, commentary, editorial, etc. (trade magazine, newspaper, online media)   Publisher：Japan Society of Material Cycles and Waste Management  

To show that the handling of debris from on the land and in and around rivers becomes a source of marine plastics debris and microplastics, this paper follows the transport of riverine debris, the composition of riverine debris, and microplastics pollution based on several field surveys. The results of surveys indicate that most riverine debris is being transported during flooding conditions and 6% of all this debris is artificial debris, i.e. plastics. This clearly demonstrates that debris from land and rivers is ultimately becoming a source for marine plastics. Microplastics pollution escalated along with this increase in the urban ratio of the river basin. Capture technology for flowing riverine debris to reduce the inflow of floating debris into oceans is discussed in the paper.

DOI： 10.3985/mcwmr.29.309

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Authorship：Lead author   Language：Japanese   Publishing type：Article, review, commentary, editorial, etc. (trade magazine, newspaper, online media)  

J-GLOBAL

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Authorship：Lead author   Language：Japanese  

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Language：Japanese   Publishing type：Research paper, summary (national, other academic conference)  

J-GLOBAL

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Authorship：Lead author   Language：Japanese  

J-GLOBAL

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Authorship：Lead author   Language：Japanese   Publishing type：Rapid communication, short report, research note, etc. (bulletin of university, research institution)  

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Language：Japanese   Publishing type：Research paper, summary (national, other academic conference)  

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Language：Japanese   Publishing type：Research paper, summary (national, other academic conference)  

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Language：Japanese   Publishing type：Research paper, summary (national, other academic conference)  

J-GLOBAL

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Language：Japanese   Publishing type：Research paper, summary (national, other academic conference)  

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Authorship：Lead author   Language：Japanese   Publishing type：Rapid communication, short report, research note, etc. (bulletin of university, research institution)   Publisher：国土技術政策総合研究所  

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Authorship：Lead author   Language：Japanese  

J-GLOBAL

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Authorship：Lead author   Language：Japanese   Publishing type：Research paper, summary (national, other academic conference)   Publisher：国土技術政策総合研究所  

J-GLOBAL

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Authorship：Lead author   Language：Japanese   Publishing type：Rapid communication, short report, research note, etc. (bulletin of university, research institution)  

J-GLOBAL

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Authorship：Lead author   Language：Japanese   Publishing type：Rapid communication, short report, research note, etc. (bulletin of university, research institution)   Publisher：国土技術政策総合研究所  

CiNii Books

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Authorship：Lead author   Language：Japanese  

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