This paper aims to assess the protection effect of riverbank covered with reeds from a physical viewpoint through field tests and laboratory experiments. A field observation is made on the erosion rate of reed covered levee of a channel for agricultural water use, and the fall of soil mass from the bank. A laboratory experiment was carried out to assess the erosion of soil masses including reed roots. The mechanism and volume of the fall of soil mass covered with reeds is investigated. From these investigations, it became possible to correlate the relationship among the erosion rate of soil masses, the density of reed and the kind of soils.

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A refinement on a depth averaged model of open channel flows with the effects of vertical acceleration is investigated in this paper. We first derived a refined momentum equation of the depth averaged model formulated by the depth-averaged velocity, applying the iteration procedures to modify a vertical velocity distribution under irrotational condition and modifying the dispersion terms to avoid the singularity in linear dispersion relation. To evaluate the model performance, the equation was applied to the free surface oscillation in a water tank. The solution of linearized equation and the non-linear approximate solution were derived and were compared with the Airy waves and the numerical results by vertical 2-D CFD model, respectively.

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For evaluating the hydrograph of flood flow, the water storage in rivers and the peak discharge attenuation, the flood observation was performed at the Edo river reach In this observation, the temporal change in water surface profile and flood discharge hydrograph were measured in detail. By using an unsteady two-dimensional analysis based on the temporal change in observed water surface profiles and flood discharge hydrograph, the discharge hydrograph and the water storage of flood flow are estimated accurately. Through this analysis, the accuracy of flood flow observation is made clear and the highly accurate method to estimate the water storage and the peak discharge attenuation for river planning is proposed. The effects of unsteadiness of flood flow on the deformation of discharge hydrograph and the peak discharge attenuation are shown from the flood flow analysis at the Maruyama river reach where the unsteadiness of the flood flow is large.

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Recently in Japan, there are a lot of flood disasters in urban area due to heavy rainfall almost every year, so many simulation models have been developed to predict the flood damage. In this study, an inundation flow model is developed which consists of four sub-models (mountainous area, river network, sewerage network and drainage basin) and applied to the Neya River basin. The validity of this model is confirmed by comparing the numerical results with the actual inundated area or the water level of the river network. Then, the computation is executed for the rainfall condition observed in this area in 1957, and it has been found out that this model can express the inundation process in this river basin.

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This paper deals with the seawater exchange caused by density gradient between the outer bay and inner bay using density profile around the bay mouth and velocity profile above the mound. It is revealed that the mechanism of seawater exchange is greatly influenced with the density intrusion depending on the horizontal density gradient. When the density of the outer bay is smaller than the inner bay, the seawater exchange occurs in the upper layer, and cannot be expected in the lower water. But, when the density of the outer bay becomes bigger than the inner bay, for example, after coming typhoon, seawater exchange is accelerated by two types of seawater exchange mechanism. One is intrusion of the outer bay water, the other is out flow due to internal wave (entrainment).

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A model describing one-dimensional ionic transport in saturated soils and its solution procedure are presented. The developed model is solved by coupling of transport and chemical equilibrium calculations, in which CIP scheme is used for the transport calculation. Numerical results of this model agreed well with the results of cation exchange column experiments. The proposed model was also applied to the numerical simulation of acid-flushing of a lead-contaminated soil. A series of simulations demonstrated that the model is useful to examine the effects of discharge rate and injected acid concentration on the decontamination rate. The advantages of the proposed model and the solution procedure are low computational cost and simplicity allowing for inclusion and extending the model to different chemical reactions or other reaction-based transport systems.

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Flow-duration curves are often used as the basis for grasping the hydrological regime. The flow duration curves by ordinary procedure are usually quite hard to distinguish the difference of one curve from others especially at their high and low flow days. In this study, the new graphical procedure for the flow-duration curves is proposed, in which high and low flow days are both enlarged in a logarithmic way to easily differentiate several flow-duration curves. This is termed “ascending and descending order logarithmic flow-duration curve” from its simple procedure. The process of reaching this idea is described and the characteristics and usefulness of these flow-duration curves are investigated by comparing with the ordinary ones using the Chikugo river discharge data as an example.

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The change of competitive superiority between Miscanthus sacchariflorus affected by July cutting in last year and invading Solidago altissima had been analyzed. Belowground initial biomass in next spring was decreased about 30% by the cutting. The shoot height and aboveground biomass were also quite decreased. Energy flux from belowground to aboveground organ in heterotrophic season was about 0.5 times compared with uncut site. Dynamic growth model of S. altissima was constructed for evaluating their competition. S. altissima was inferior to M. sacchariflorus due to light limitation by the stands in usual, however M. sacchariflorus received damage by July cutting was inferior next year. The shoot height of M. sacchariflorus affected by the cutting was 1.5m smaller than usual and also smaller than that of S. altissima. It greatly affects their competition for light.

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