Regional sediment transport processes were investigated on the Tenryu River and the Enshu-nada coast. A numerical river sediment model was developed, which involved sediment dynamics in reservoirs and riverbed vegetation. The model was verified by the mineral properties of surface sand particles sampled in a wide area, which were identified by image processing technique based on a digital microscope. It was found that the spatial and temporal variation in sand properties reflected the local geology and the interruption of sediment movement by dam construction. Shoreline model was combined with the river sediment model and improved to account for individual movement of sediments from different sources. The model indicated that the interruption of sediments in reservoirs would eventually change sediment properties around the river mouth and degrade the beach durability against erosion unless effective countermeasures are introduced.

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  A block mound is a most popular construction in coastal facilities. In a construction block mound, a numerical tool, which solves settlement/sedimentation process of blocks under high accuracy, is required. In this study, the solid-liquid turbulence flow model of high resolution is developed by introducing the Smagorinsky model as sub-grid scale turbulence model. The fundamental performance of the developed simulation model is confirmed from the relation between the drag coefficient and the Reynolds number, and the settling mode of settling two particles. In addition, the sedimentation process of multiple blocks is performed, and the effect of the introducing the Smagorinsky model is shown computationally.

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  Runoff analysis using radar-Automated Meteorological Data Acquisition System (AMeDAS) composite precipitation (RAP) data for an distributed hydrological model were conducted in a middle-scale river basin Ayagawa (137.5 km²), Kagawa, Japan. The RAP data were observed spatially, 2.5 km×2.5 km resolution. The result shows that the accuracy of river water discarge was improved by 30-60% compared with the ground-based precipitation data, those were observed at around 17 km interval. Based on a classification of the rainfall characteristics, we clarify that not only a decrease of total amount of precipitation but a weak and specially dispersed precipitation (1∼4 mm/h) in the long events improved the accuracy.

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  In the Ota River, we had investigated kind, positions and properties of vegetations and prepared to measure temporal changes in water surface profiles of a flood. In 2005, the largest flood in the past 50 years occurred in the river. Vegetations on sandbar formed inner bank side were destructed by the flood flow. Unsteady 2D analysis of flood flow and bed variation using observed temporal changes in water surface profiles demonstrate the flood flow characteristics, bed variations and mechanism of vegetation destruction. Vegetation destruction was caused by the bed scouring of sandbar. The concept and means for the vegetation management are derived from the present investigation.

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  The author investigated an issue of the standard least-square criterion (SLSC) which has been used in Japan. It is most important that SLSC is in itself a random variable and it has a probability distribution, and the distribution depends on the number of sample. We have to notice it in flood-control planning and use different thresholds of SLSC (namely, e.g. SLSC=0.04), depending sample sizes. Thus, the author proposes that we indicate the threthold's cumulative probability like “the threshold correspons to 16%-percentile in the probability distribution”. Moreover, the author investigated the way which has been used for estimating the expected value of damaged amount by floods, which is used in Japan.

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  The purpose of this study is to make clear a second closure turbulence model which can correctly and economically reproduce turbulence in stratified open channel flows. This study focuses on 2 representative second closure models, and assesses those performance. Firstly, the changes in the Prandtl-Kolmogorov constant and turbulent Schmidt number of those models are compared using analytical approach. Then, the accuracy is assessed using the experimental results in tidal estuarine flume. Finally, the model-constants which can reproduce the experimental results are made clear with reference to the findings obtained by DNS and LES analyses.

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  We conducted field measurement on floating-litter transport in an urban river under flooding conditions to determine the amount of organic materials and nutrients contained in the floating litter which comprises a major portion of marine litter. The observed result indicates that the maximum values of the transported litter volume were 10⁴-10⁵ times greater than the minimum values. The volume of floating litter transported during the rising stage was about 10 times that transported during the falling stage for the same discharge, showing appreciable hysteresis between the floating-litter transport and discharge. The floating-litter transport under flooding conditions was also found to contribute significantly to the pollutant load from watersheds.

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  A new type current meter using a pendulum supported in wires was developed in HORS (Hazaki Oceanographical Research Station, a 427-m-long pier in Ibaraki prefecture). A spherical float was connected to the thin steep pipe and the float was kept about 1.2 m below the averaged sea surface. Three thin wires were attached to the pipe and tensions of the wires were observed using load cells. The longshore current velocity was estimated analyzing the tension data. The observation was done during 28 days without any data lack. Comparing with the velocity data observed with an electric magnitude current meter, the longshore current velocity was well estimated even in the surf zone.

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  In this note, we propose a new method for rever water lever prediction form past rainfall. The proposed method is carried out by caluculating a stream flow form amount of rainfall and caluculating future water level from the stream flow and measured water level at water gauge station. We prove through experiments which is used of real data that the proposed method is effective. Finally, we comment on the respects in which the proposed method is improved and on the future prospects.

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  In this note, we propose a improvement for river water level prediction form amount of rainfall and actual survey river water level. First, we show a background and a purpose of this note. Next, we explain the conventional Nearest-Neighbor method and the proposed method. Next, we prove that the proposed method is effective in comparison with the conventional Nearest-Neighbor method through experiments which is used of real data. Finally, we comment on a respects in which the proposed method is improved and on a future prospects.

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