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The annual intensive field observations have been conducted using Tanabe-Nakashima observation tower by research group of Shirahama oceanographic observatory in Tanabe bay, Wakayama prefecture. In this study, we have conducted CTD (Conductivity (salinity)-Temperature-Depth) measurements supplementarily in the same bay area during the same period as the annual intensive observations. Those CTD results showed seasonal variations of water temperature and salinity, such as thermocline and density stratification which were observed at many points in Tanabe bay and freshwater entering from neighboring rivers. This paper reports our observation activities in 2016 and shows CTD results and three-dimensional structures of water temperature and salinity based on observed data.

This paper shows some results of intensive field observation carried out in the summer of 2016. The vertical profiles of currents and water temperature measured as well as wave and wind conditions, and salinity observations carried out at the observation tower of Shirahama Oceanographic Observatory. In the summer in 2016, one typhoon (TC16, MALAKAS) approached close to the observation site, and the high wave and strong wind conditions more than 40m/s captured during the observation. Under the high wave and strong wind condition, ADCP (Acoustic Doppler Current Profiler) measured high echo intensities for several hours, and this result indicates that strong mixing occurs. Water temperature variation at 30m deep has opposite phase to the fluctuation of salinity. This result means that low temperature and high salinity water approaches to the observation site. It is also found in water temperature distributions in November that some influences of the warm and cool water mass exist.

The purpose of this study is to clarify the influence of entering fresh water from rivers into Tanabe bay area. The water temperature of fresh water is one of an important factor for ocean flow structure and three-dimensional structure of water temperature and salinity in coastal area. Fluctuation of river water temperature is repeated every day and seasonally, and it is influenced by elevation, atmospheric condition, confluence of river branch, groundwater, and water utilization of upstream area. In this study, we have conducted field measurement of river water temperature in neighboring rivers of Tanabe bay and will continue it for the next few years, in order to create estimated equations for river water temperature based on our measurement results. In this paper, we reported measurement method and initial progress of measurement results.

This paper shows some results of a field observation carried out in the summer of 2015. The vertical profiles of currents and water temperature have been measured as well as wave and wind conditions, and salinity observations have been carried out at the observation tower of Shirahama Oceanographic Observatory. In the summer in 2015, no typhoon approached around the observation site, and the high wave and strong wind conditions have not been captured during the observation. Several short-term rainfalls due to front and low pressure occurred, and it is reported that local areas in Shirahama town and neighboring towns suffered some damages with windblasts from late August to early September. It is found in the observation results of water temperature that the temporal variations of water temperature have a period of 3 to 6 days in the deeper layers like 20m deep and 30m deep. The cyclical fluctuation of water temperature at 30m deep has opposite phase to the fluctuation of salinity. This result means that low temperature and high salinity water approaches to the observation site periodically and that some influences of the water mass of the open sea exist.

This paper presents numerical simulation of riverbed variation using two-dimensional depth-averaged flow model with a simplified Lagrangian bedload model and its application to actual river. The scheme of Lagrangian-type bedload model resembles the actual phenomenon of sediment movement in comparison with the model of Euler type and it is useful when the change of sediment movement direction is extreme on a small scale. The Lagrangian-type model can simulate a change in the direction of moving sediment considering the local flow and bed slope along the moving paths regardless the computational grid structure. However, the heavy computation load is a significant bottleneck for a simulation in many cases. In this study, we introduced the simplified Lagrangian bedload model to a two-dimensional depth-averaged flow model and applied the model to an actual river.

The purpose of this study is to clarify the relation between sediment transport from river and topographical changes of mouth-bar by field measurements in Tonda river, which is second grade river flowing in south of Wakayama prefecture. Upstream areas of Tonda river were damaged by slope failures due to heavy rainfall which was caused by Typhoon No. 12 in 2011, and a large amount of sediment was supplied into the river. In this study, we will conduct field observations using RTK-GNSS during the next few years in order to capture the transporting phenomena of the overabundant supplied sediment from upstream area to estuary and sea. In this paper, we reported our recent results of field measurements.

This paper shows some results of a field observation carried out in the summer of 2014. The vertical profiles of currents and water temperature have been measured as well as wave and wind conditions, and salinity and dissolved oxygen level observations have been carried out at the observation tower of Shirahama Oceanographic Observatory. In the summer in 2014, a total of 4 typhoons (No.11, No.12, No.18 and No.19) approached to the Kii peninsula, and the high wave and strong wind conditons due to 2 typhoons (No.18 and No.19) have been captured during the observation. When the typhoons passed around the observation site, the high wave and strong wind occurred. However, the observation data of 2014 doesn't have clear shift of water temperature and salinity like the one by the typhoon No.18 in 2013. On the other hand, it is repeatedly found in the observed data that the reduction of water temperature and the increase of salinity happened simultaneously. This result indicates that the water temperature and the salinity around the observation site have some influence of the water mass of the open sea.

This paper shows some results of a field observation carried out in the summer of 2013. The vertical profiles of currents and water temperature have been measured as well as wave and wind conditions, and salinity and dissolved oxygen level observations have been carried out at the observation tower of Shirahama Oceanographic Observatory. During the observation, one typhoon (No.18, MAN-YI) approached to the Kii peninsula. When the typhoon passed around the observation site, the vertical mixing develops well, and water temperature at all measurement points show almost uniform distributions. It is also found during the typhoon passing that coastal upwelling through the Ekman transport happened clearly due to continuous southward wind. An EOF analysis decomposes the water temperature variation during the typhoon passing into 1) the increase and decease of water temperature and 2) the magnitude of the temperature difference in the vertical direction.

This paper presents an experimental study on the impacts of series of spur-dikes on bed topography and sediment sorting process of bed surface around impermeable spur-dikes. It was found that the vortex systems around spur-dikes were different in comparison with different number of spur-dikes and different submerged conditions on equilibrium stage. Compared with the results of single spur-dike cases and series of spur-dikes cases, the vortex systems are quite different between the spur-dikes. These differences cause different sediment transport and sorting process between the spur-dikes. The coarsened longitudinal region and fine sediment regions were observed, and it was indicated that series of spur-dikes also create not only bed morphology, but the diversity of surface bed composition. Furthermore, the scouring, deposition and sorting processes around spur-dikes were simulated by 3-D RANS with non-equilibrium bed load model using unstructured mesh system. The simulated results show generally good agreement with the experimental results of bed morphology and sediment sorting.

This paper presents an experimental study on the impacts of orientation of a spur-dike on the bed topography and sediment sorting process of bed surface around a single impermeable spur-dike. The importance of one governing parameters, the orientation of the spur-dike, was emphasized through quantitative and qualitative evidences. It was found that each case of the spatial progress patterns of scour-deposition and sediment sorting were different in comparison with different types of orientations. Compared with the deflecting and attracting types of spur-dike, the repelling type has the property of promoting deposition in the wake region of the spur-dike. This property is caused by the difference of flow structure in the vicinity of spur-dike. The coarsened longitudinal region and fine sediment regions were observed, and it was indicated that the repelling type of spur-dike has the strongest intensity of sediment sorting of the three orientations of spur-dikes.

本研究では，均一型砂質堤防の越水模型実験を実施し，砂質堤防の越流侵食現象が再現可能な数値解析モデルの構築を図った。実験では，堤防の越流破壊現象について粒径および浸透流の進行が越流侵食に与える影響について考察を行った。数値解析では，粒径および浸透の進行によって変化するせん断抵抗の影響を考慮した堤防の越流侵食モデルの構築を図った。流れの水深積分モデル，堤体内の浸透流解析，非平衡流砂モデルの枠組みによる土砂輸送，斜面安定解析の4つを結合し同時に解析することにより越流侵食破壊現象の再現を試み，一部の検証ケースにおいて計算モデルの結果は概ね良好な結果が得られ，堤防越水時の不飽和堤土の侵食評価において，浸透水によるせん断抵抗の変化を考慮することの重要性が示された。, In this study, experiments were conducted to clarify the mechanism of embankment erosion due to overtopping flow under saturated and unsaturated sediment, and a numerical model was developed to compute the erosion of river embankment by flow overtopping. An influence of saturation and sediment size in the erosion process was discussed using the results of experiments. In the computation of erosion process of embankment, the infiltration process and shear strength due to suction on the unsaturated sediment bed were considered as a new equation. In order to simulate a phenomenon of embankment erosion, the numerical model consists of four modules, two-dimensional shallow water flow, seepage flow, sediment transport using framework of non-equilibrium model and two-dimensional slope stability. The developed model was tested for erosion of embankment. The numerical results of embankment surface erosion and moisture movement in the embankment were agreeable with the results of experiments.

本稿は, 木津川(淀川流域)及び中国府河(岷江流域)にある水制群を対象に, 水制周辺の地形及び河床材料の現地調査結果の基にした, 河床表層材料の粒度分布特性とそれらの環境関連性に関する研究報告である。今回の調査により, 水制周辺における流砂の縦断及び横断方向における分級現象の重要性を指摘した。水制により河床材料の連続性は失われ, 河川主流部の河床では粗粒化現象が見られ, 水制と水制の間ではシルトや粘土などの細かい砂が堆積しやすい区間になる。さらに, 透過型水制の背後では不透過型のそれよりも河床材料の粒度分布の粒径範囲が広く, 環境にも優しいと考えられる。水制直下流では二次流などの影響で顕在化する粗粒化領域, そしてその周囲に細粒化する領域(サンドリボン)の存在も確認した。また水制周りの地形及び流れに関する情報に配慮したところ, 粒度分布は河床形態と局所的流れ構造と密接な関連性があることも判明された。, This paper presents the characteristics and environmental implications of the grain size distribution around two typical groin sites in the Kizu River (the Yodo River basin, Japan) and the Fuhe River (the Min River basin, China). The results show that groins enhance sediment sorting processes longitudinally and laterally. Longitudinal sediment coarsening is observed in the mainstream narrowed by groins. The relatively closed bay area between two consecutive groins is capable of trapping fine sediment materials such as silt and clay. Moreover, the area behind a permeable groin exhibits more diversity in terms of grain sizes compared with that behind an impermeable one. Due to lateral sediment sorting, sand ribbons form at the downstream of groins. The results also indicate that the sediment size distributions are closely related to the local channel morphology and the complex flow structure around the groins.

水制周辺の洗掘現象において, 水制高と河床の粒度分布が局所洗掘に与える影響, そして, 水制がもたらす河床表層の粒度分布変化と水制高の関係性について明らかにするために, 越流型および非越流型水制に対していくつかの混合砂河床の移動床実験を実施し, 考察を行った。実験結果より, 越流型水制の場合も非越流型と同様に, 河床粒度の幾何標準偏差が最大洗掘深評価に重要なパラメータと成り得ることが示され, そして非越流型水制は越流型に比べて水制頭部の下流域で顕著な洗掘傾向が見られることが明らかとなった。また, 越流状態の異なる流れ場の計測により, 水制が高いほど水制先端近傍の下降流が大きくなり, その影響で水制が高いほど水制頭部から下流に伸びる河床表層の粗粒化域の横断幅が広くなることが明らかとなった。, This paper presented an experimental study on the impact of both spur dyke height and grain size distribution on the bed topography and bed surface composition around an impermeable spur dyke. The importance of governing parameter, i.e. the relative spur dyke height, which is inverse number of overtopping ratio, was emphasized through quantitative evidences. It was found in the current experiments that the spatial progress pattern of scour-deposition in the non-submerged and nearly non-submerged condition was different compared with full-submerged condition. Furthermore, in the submerged experiments using non-uniform sediment bed, it was found that the maximum scour depth decreased with the increased of the standard deviation as well as in non-submerged spur dyke experiments. The flow measurement around the spur dyke revealed the difference of three-dimensional flow structure under the different spur dyke submergences, and the relationship to the variation of the surface bed composition. It was also found that with the increase of the spur dyke height, the longitudinal coarse sediment region was expanded to transverse direction in the downstream region of spur dyke head.