This paper aimed to propose a calculation model for predicting concentration of airborne chloride ion at arbitrary time and location. In this model, actual meteorological data and costal conditions are used as input data. Generation, transportation, and adhesion processes of airborne seawater particles are modeled while distinguished generation condition at the particle origin. The model separates the particle generating into 2 zones, far-ranged sea surface and coastal wave breaking, which has significant influence on particles generation. Moreover, the model attempts to be applied to overall structures by simplifying the modeling processes. Model verification has been conducted with existing observation records.

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  In order to clarify oxygen consumption processes during the resuspension of muddy sediment, some experiments on the chemical and biological oxygen consumption were carried out using sediments sampled in the inner part of Ariake Bay. In the layer of 0-5mm, the average chemical oxygen consumption rate from the experiment start to 30 minutes decreased to 0mgO₂/l/min. On the other hand, the temporal change of the biological oxygen consumption rate was small. The contribution rate of the chemical oxygen consumption to the total oxygen consumption accounted for more than 80% in both the surface and lower layer from the experiment start to 60 minutes and until 360 minutes later accounted for more than 60%. The duration of the chemical oxygen consumption increases significantly with sediment depth (i.e., the decrease of the oxidation-reduction potential). In the oxygen consumption process at the time of the resuspension of the sediment, it is important to consider the unsteady characteristics of the chemical oxygen consumption, estimation of the resuspended sediment thickness, profile of the quantity of reduced materials and elapsed time after the resuspension.

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  Laboratory experiment on relation between bed load and algal detachment revealed that bed load with the diameter of around 5-10mm is most effective to remove the filamentous algae attached to gravel bed. A prediction model of detachment of filamentous algae, which consists of flow equation, sediment transport equation and the relation between bed load and algal detachment, was constructed and applied to a actual river. The rate of algal detachment due to the artificial flood in about 1 km downstream reach from Miyagase dam, Kanagawa, Japan was estimated by this model. The comparison between the observed survival rate (77%) and the calculated survival rate (73%) of attached algae shows a good agreement. The same calculation was performed for an assumed river in which the river bed contains a larger amount of fine gravel fraction than the present river bed in the observation area. In this case, almost all attached algae were removed by the bed load of fine gravel fraction. This result suggests that an artificial flood with fine gravel supply is indispensable to remove the filamentous algae in downstream reach of dam.

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  Fish can migrate through fishways, when the velocity in fishways is smaller than fish's burst speed. The burst speed depends on fish species, body length and flow velocity. Although, there is little information on burst speed, it is known that the burst speed is nearly estimated as ten times of body length. This study discusses the burst speed of several fish species, i.e., Plecoglossus altivelis altivelis, Zacco platypus, Zacco temminckii and Carassius gibelio langsdorfi, in flowing water. A new formula and its coefficients which can be evaluated the burst speed on the basis fish species, body length and flow velocity are suggested. Further, the approach time and its distance to the burst speed are also made clear.

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  This paper describes the swimming behavior of isolated ayu in statistic water as a first step toward understanding behaviour of fish. In this experiment, we used the circular pool with changing the radius to five cases between 0.75-1.15m. The swimming trajectory of ayu in the circular pool was recorded by the digital video camera. The result showed that the swimming trajectory can be described by nodes and branches. The frequencies of the swimming distance, angle between each branch and swimming speed are modeled by the gamma distribution and normal distribution. It is thought that these results contribute to swimming behavior analysis which can predict the swimming trajectory of fish.

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  The tsunami fragility functions are proposed as new measures for estimating structural damage and fatality due to tsunami inundation, by integration of satellite remote sensing, field survey, numerical modeling, and GIS analysis. The tsunami fragility functions are expressed as the damage probabilities of structures or fatality ratio with regard to the hydrodynamic features of tsunami inundation flow, such as inundation depth, current velocity and hydrodynamic force. It expands the capability for estimating potential tsunami damage in a quantitative manner.

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  To measure the diameter and the terminal velocity of natural rainfall drops, consecutive images of falling raindrops were taken by an ultra-high-speed video camera developed by the authors.
  The relationship between the terminal velocity and diameter was obtained from the images, and the behavior of raindrops that moved downward along with time passage was clearly observed from the consecutive images. The terminal velocity obtained from this measurement is smaller than that obtained from Gunn and Kinzer's indoor experiment, in case the equivalent drop diameter is larger than 1.5mm. Since the number of the samples is not sufficient, further experiments are planned to conform the result.

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  A strong low-pressure system traveled along Japanese Main Island in October 2006. High waves and storm surge attacked Kashima Coast resulting huge erosion over the area. This study analyzes sand loss in sub-aerial zone of northern part, a stretch of approximately 38 km from Ooarai Port to Kashima Port, and of southern part, a strech of approximately 15 km from Kashima Port to Tone River, using airborne laser data measured in October 2005 and November 2006. Longshore distribution of cross sectional change has been estimated from the laser data. Eroded volumes of sub-aerial zone were estimated as 620,000 m³ for the northern part, and as 600,000 m³ for the southern part. Patterns of erosion were controlled by headlands, and by drainages at beaches without headlands.

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