In this paper, results obtained from our previous study (Study on the Lumping process of the kinematic wave model based on the equivalent frequency transfer function) were applied to a practical runoff analysis. Conclusions are summarized below.
(1) This paper showed the method to examine the compatibility between observed rainfall and discharge through characteristics of the equivalent frequency transfer function. Twenty flood of 60 flood events at the Rumoi River and Kusiro River basins show poor compatibility. (2) A new method (moment method) to identify parameters of delay systems is proposed. This paper points out these parameters are function of average rainfall. (3) The method to calculate the time of concentration for slopes and channels based on parameters of delay system is presented. (4) Two new indices which specify the characteristics for slopes and channels are presented.

View full abstract

Flood control systems for urban areas in which outflows of rivers and sewers are correlated require crisis-management measures to be taken in advance to minimize the entire damage of excess floods. However, flood control projects through coordination between rivers and sewers must be given highest priority and must be considered immediately to cope with urban flood disasters, which occur almost every year. This paper deals with catchment areas of small sized rivers and sewers in plateau urban areas where sewages are naturally drained to rivers. It will present problems of the flood control measures being developed for each flood control project that is based on a rational method commonly used for sewers and small to medium sized rivers, by examining the actual conditions of rainfalls and characteristics of outflows and implementing concrete and practical case studies. It will then present a method for implementing flood control projects through coordination between rivers and sewers based on a composite rational method and clarify problems to be addressed in the future.

View full abstract

Although a number of bridges have been constructed overseas with Japanese ODA, many rivers requiring bridges have unequilibrium with a lack of flood control facilities. These rivers also have unique characteristics such as peak discharge continuing for several months and riverbeds consisting of fine sand. Their channels are unstable and relevant data are scarce. Therefore, problems related to planning of bridging sites, total length of bridges, and countermeasures for local scour are difficult to be solved. By thoroughly studying the information so far surveyed through Japanese development cooperation, the authors have integrated these issues into two topics: bridges over large alluvial rivers and bridges on flood plain roads. The problems are analyzed and new ideas are proposed.

View full abstract

Applicability of numerical model using κ-ε turbulence model to snowdrifts are examined. Results of experiments in the low temperature wind tunnel at Shinjo and field observations at the Mizuho station in Antarctica are compared with the results of the numerical analysis. The partial differential equations are discretized based on the SIMPLE method. Transport of solid particles is often modeled by the turbulent diffusion equations. In order to integrate such differential equation, the boundary condition at the bed are important for the precise calculation. The idea of snow entrainment coefficient is useful to descibe the bed condition. The functional form of such coefficient, however, is not established until now. The values of the snow entrainment coefficient are presumed comparing with the profiles of snow particle flux observed to the numerical calculations. The functional form of the snow entrainment coefficient is discussed comparing with the empirical function proposed by Garcia in sand case.

View full abstract

Two-dimensional (2-D) turbulence measurements of air-water interface in wind-given open-channel flows were conducted in the center of channel by making use of a laser Doppler anemometer (LDA). As the results, it was found that an air-shear influences largely on interfacial turbulent structures in water flow region. The turbulence intensity is so high up to the water interfacial region. Of particular significance is the large negative value of the Reynolds stress, in the condition that the surface stress due to the air-shear is prior to the water-bed stress.

View full abstract

Two-component velocities in side-cavity open-channel flows, in which the Froude number was changed systematically from subcritical to supercritical flows, were measured with a PIV (Particle Image Velocimetry). Further, the water-surface fluctuations were measured by three sets of supersonic wave gauges. It was found that the time-averaged velocity fields are similar to each other, irrespective of the Froude number. However, the spanwise length of the mean shear layer decreases with an increase of the Froude number. The length scale of the instantaneous horizontal vortex decreases with Froude number. However, the strength of the rotation speed of the instantaneous vortices increases with the Froude number. In contrast, the Strouhal number of the coherent horizontal vortices is not affected significantly by the Froude number in both the vertical-cavity and side-cavity open-channel flows.

View full abstract

Laboratory experiments and numerical simulations were conducted to investigate the characteristics of bores generated by gate-operation. The laboratory tests showed that the gate operation method affected the generation of undular bore, then the condition of immediate formation of undular bore was formulated by a parameter of gate-operation. The numerical simulation with the non-linear dispersive wave theory accurately reproduced the waveform and celerity observed in the laboratory experiments. Furthermore, an influence of gate operation method on the deformation process and the amplitude of undular bore was considered by the numerical experiments.

View full abstract

The seasonal change of sea level is strongly related to the sea level oscillation along the northwestern part of the North Pacific (NWPO). The relationship between the ocean currents around the Japanese coast and this oscillation was studied. It can be seen that a high correlation between the Oyashio's southward intrusion and NWPO is indicated. When the Oyashio intrudes southward, sea level height (SLH) in the North Pacific descends. In addition, it is recognized that SLH variation around Japan is not only caused by these pressure systems but also by the ocean currents, and the SLH at the Japanese coast is mainly the sum of sea level pressure (SLP) and volume expansion due to water exchange. Finally, the validity of the seawater density off the Sanriku coast represented by the changes in SLH and SLP was studied. It may be possible to use meteorological and water level data as historical long-term indicators of water density at the entrance of estuaries.

View full abstract

The directional spectra have been statistically analyzed for the waves observed off Gobo. The statistical analysis shows that the multi-peaked directional spectra occupy the relatively large percentage, especially in winter. The waves inside a harbor near from the observation station were also measured simultaneously. The reproduction procedures of the waves inside the harbor were proposed in order to evaluate the effects of multi-peaked directional spectra. The comparison of statistical properties between observed and predicted waves has concluded that the reproducibility of the procedures is fairly well and correct shapes of directional spectra outside should be employed for the estimation of harbor waves.

View full abstract

The study is motivated by new findings on oceanography of the Japan Sea and by research on climate change in the adjacent area. The primitive equation quasi-isopycnal model (MHI model) is applied to simulate principal circulation patterns in the Japan Sea for two different climatic conditions observed in the mid and late 20^th century. It is shown that redistribution of the Tsushima Current transport between western and eastern branches and development of the subarctic gyre in the northwestern Japan Sea are controlled by variation of vertical density stratification and baroclinicity in the sea, in accordance with climate change in the East Asia-Northwest Pacific marginal area.

View full abstract