We had 17 significant rainfalls during 1979-1995 in Ube city. 8 rainfalls of them caused the inundation in the lowland region of city. Tank model is used in this paper to set the criterion water level whether the inundation will occur or will not Try and error analysis presents the parameter set of Tank Model as shown in Fig3. The criterion Tank water level (D line) is obtained D=35mm. If we have the forecast rain curve, we can predict the occurrence of inundation in the city by inputting the rain into the Tank. Several prediction experiments were made by use of the short time point rainforecasting method (PRFM). The results show the present inundation prediction scheme is useful for the urban water disaster prevention action.

View full abstract

The way of estimating effective rainfall is an important unsolved problems in flood runoff analysis. This paper consists of three parts. The first explains how to introduce the new boundary conditions into unsaturated flow equations under which infiltration into the deep soil layer occurs. In the second part, the authors estimate the effective rainfall based on other runoff models such as the tank model and the entropy method, and compare results from the first and second parts. Finally, the authors derive a lumped model based on unsaturated flow theory. The proposed lumped model can yield the infiltration loss into the deep soil layer, and all parameters of the model are identified based on soil characteristics and basin topology.

View full abstract

In order to constnict the countermeasures against flooding, a floodwater simulation model with a high degree of accuracy is required. We constnicted a new numerical simulation model in an urban residential area to apply a two dimensional shallow water model. This model employs the general curvilinear coordinate system to reproduce the road network and houses and considers the hydrodynamic force acting on the houses. We estimated the force by the experiments. The applicability of the model was verified by reproducing the results obtained from large scale hydraulic model experiments. Finally, the model was used to carry out case studies of actual urban districts and the countenmeasures were investigated.

View full abstract

The study focused on the type of river composed of a steep slope gravel-bed reach connecting with a mild slope sand-bed reach. Sediment supply for each grain size range to the targeted rivers during Holocene was estimated from the volume and grain size of their alluvium. The supply was compared with dam deposit data and the present sediment load in the corresponding river reach. To reproduce the alluvial processes accompanied by alluvial river formation for the past 10000 years, conceptual model experiments and 1-D calculation of bed profile variation were carried out. Through these results, clear physical explanation was obtained on the bed profile evolution with sharp longitudinal sorting. An idea of ‘effective grain size range’ was proposed as an engineering framework for the prediction of bed profile variation due to sediment supply change.

View full abstract

Strong rising current produced from V-shaped structure in the stratified fluid was studied experimentally and numerically. Flow visualization were conducted to reveal the mechanism of creation of rising current in homogeneous flow field. Experimental studies were also conducted in the linearly stratified flow field. Large eddy simulation (LES model) was selected for numerical studies. The results of simulation by LES model were verified by comparison with experimental results.
From both of experimental results and numerical simulation, it was found dihedral angle of about 90° was most effective angle for the rising effects. Rising height may reach 6.5 times of the plate height in homogenous flow and has reduced in stratified flow to 2.8 times of the plate height with Ri=0.8.

View full abstract

Internal hydraulic jump occured at back of submerged hump disturb stability of two layer stratifiedflow and may influence condition of water enviroiunent substantially. In this paper we oberveprofliles of interfaces in laboratory, and show that compound Froude number, which consist of hyraulic feasures in each layer, and the lower layer thickness at control section appeared atthe downstream of hump are important parameters to control the interface stability and diseussthe relation between these parametes.

View full abstract

When a bypass tunnel is practically applied to a reservoir for the purpose of transporting bed load past the reservoir, the verification of its hydraulic stability must be considered. In this paper, by an experimental investigation a phenomenon is observed in a tunnel that great pressure variations with suction are periodically occur in the case of highly unsteady situation such as an abrupt change of sediment discharge. Moreover, by the use of a numerical simulation method, it is found that the phenomenon is due not to the variation of flow discharge nor local flow velocity but to the occurence of deposited layers and the phase change from open channel flow to pipe flow, as well as to the progress of deposited layers with the spatial re-distribution of the total energy head between the inlet and outlet of the system.

View full abstract

In recent years, Lake Abashiri which is connected to abashiri river has confronted with serious problems concerning about water quality and environment caused by salifications of the lake. Present authors carried out field observations in brackish lake and the tidal river of abashiri, in order to make clear the actual conditions and the mechanism of the salification of the lake. We found that the lake has been salified since 1925, and the interface between the salt and fresh water has been gradually rising for these 60 years because of the decreasing inclination of annual precipitation.

View full abstract

An effcient numerical model is developed for the analysis of wave-induced floating-body motion in nonlinear and random waves. A multi-term coupling technique, which favorably represents the fluid motion in vertically integrated forms, is used to derive the basic wave equations. This acheives more general applicability and higher computational efficiency of the corresponding FEM-based model, as compared to conventional numerical models. The result of fundamental examinations, conducted via comparisons with other analytical and numerical models, show sufficient reliability of the present model.

View full abstract

The most suitable dispersion terms for tsunami simulation were investigated through the analysis of the dispersion relation and the comparison with hydraulic experiments. A new computation algorithm, two-step mixed finite difference scheme, is also developed for the computation of run-up on land composite regions, and the model of tsunami simulation including correction terms to improve numerical results are introduced by analysis for errors of difference equations, and the calculation of accuracy confirmed by one-dimensional propagation.

View full abstract