[in Japanese]

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A method of estimating evapotranspiration during plant growth is proposed based on field observations. Water balance measurements were carried out for a crop of corn using a weighing lysimeter, and sap flow was measured using the stem heat balance method. It was clarified that evapotranspiration in planted plots is 2.1 to 2.2 times that for a bare plot, and that the water consumed by the corns is 192 to 295 times the weight of the dry matter. A model of evapotranspiration was constracted using the characteristics of plant growth, the meteorological conditions and soil moisture content. The validity of the proposed model was confirmed by comparing the calculated and observed results for evapotranspiration during plant growth.

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This study proposes a numerical scheme for modeling dispersive flow in the presence of discrete heterogeneities such as fractures and flow barriers. The singular solution for flow around the heterogeneities is analytically coupled with the CVBEM through the principle of superposition. In order to utilize the analytical solution of dispersive flow for one-dimensional (1D) problems, two-dimensional (2D) flow is decomposed into flow along multiple 1D streamlines, which can be tracked by using the stream function in the CVBEM. The complete 2D solution is recovered by combining the individual 1D solutions. The utility of the model is verified through tracer-test problems and will be found in stochastic-simulation studies.

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The authors conducted a set of survey on suspended sediment transportation in the Kataniwa River, during the flood on September 22nd '96, and June 19th '97, and found out that the peak of wash load concentration appeared earlier than the peak of discharge, and fluctuation of wash load concentration followed the fluctuation of the rainfall intensity. To investigate these phenomena, a numerical simulation model, which describes the run-off of water and sediment transportation on the Kataniwa river basin, was developed. The model was given two processes of sediment transportation; wash load yields by the impact of raindrops and surface flow on the surface of basin, and suspended load yields in the channel. The result of simulation showed fairly good agreement with the observed data.

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The local scour just downstream form a groundsill undermines the foundation of the structure and expose the structure to danger from failure. To prevent it, bed protection works are installed in the downstream of the structure. Bed scour also take place just downstream from the bed protection works. Because complete protection against the local scour is almost impossible, the design method that makes allowance for a certain degree of the local scour should be considered. The vertical two-dimensional numerical model describing the flow and local scour just downstream of a groundsill is developed. The model showed that allowance of the local scour could improve the flow field and shear velocity distribution.

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To clarify the fluid forces on a swimming fish in water, we present a computational method for a flow around several fish with the experimental data of actual fish behavior. Laboratory experiments and image processing techniques are employed to obtain the swimming fish behavior in still water. With these data, numerical simulations for a flow around the swimming fish are performed with Cartesian coordinate system. The results indicate that the separation of the boundary layers around the fish occur due to the wavy motion of a tail fin and the large deformation of fish body, resulting in the appreciable vortex streets in the wake. It is noted from the computational results that these fish behavior cause the propulsion and drag of the swimming fish through the spatial variation of the pressure distribution around fish. We also examine the hydrodynamic influences between two fish on fluid forces with the computational results.

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In this study, PIV measurements in and around side-cavities of open-channel flow, i. e. groyne flow were conducted. The experimental condition is that two side-cavities were set continuously in the downstream direction with various aspect ratios. The aspect ratio of the downstream side-cavity was fixed to 2.0, whereas that of the upstream side-cavity was changed to 2.0, 5.0 and 10.0. The distance between these two side-cavities was changed to four kinds of patterns. Measurements were carried out in the downstream side-cavity. The flow direction of the time-averaged velocity was changed to the main channel direction by the effects of upstream side-cavity. The position of the shear layer changed toward the main-channel direction and the Reynolds stress and momentum distribution were increased. Furthermore, the wavelet transform was conducted about the instantaneous velocity fluctuations. As the results, at the low and peak-frequencies the convection direction of coherent vortex changed and the intensity of vortex was increased.

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Numerical calculations and laboratory experiments were conducted in order to understand the run-up and mixing of internal waves over a sloping boundary. The numerical model employs the CIP method to reduce the numerical diffusion. The κ-ε model was also used to explain the turbulent viscosity effect. Experiments were carried out in a two-dimensional wave tank with a horizontal-flap type wavemaker. A fluid consisting of fresh water and salt water was prepared to imitate the density stratified coastal ocean. An image processing technique was used to reveal the propagation and mixing of internal waves. The displacement and the mixing of internal waves were well predicted by the present numerical model.

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Large-scale vortex structures beneath a free-surface in breaking waves are visualised by a characteristic distribution of a surface temperature estimated by infra-red radiation in this paper. Counter-rotating streamwise vortices occurring at wave plunging disrupt a so-called skin layer on the surface to entrain into bulk water underneath the layer. Because of a distinctive difference in temperature between the skin layer and bulk water, the spatial distribution of the surface temperature reflects the intensity of local water mixing on the surface due to the sub-surface stream-wise vortices. Typical length- and time- scales of the stream-wise vortices are determined throughout a surf-zone by utilizing a temperature spectrum and its temporal variation on the basis of the infrared measurements.

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Transition of infrared radiation on a sea surface is strongly influenced by reflection of sunlight and sea surface disturbances. The field measurements of breaking waves in surf zone were conducted by the highly sensitive infrared camera. The characteristic changes of infrared images due to bubble formation at the sea surface are discussed. The distinctive patterns of infrared images are associated with the incident wave phase and the wave breaking. The velocity fields on the sea surface are estimated by the PIV method and the correlation between the sea surface velocity and infrared image changes is discussed. The quantitative method to measure sea surface disturbance by the breaking wave is proposed using the infrared radiation image and image processing technique.

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The montecalro simulation method which uses experimental equations or Distinct Element Method (DEM) is powerful method to estimate the probability of failure for rubble structures. But, the method has problems such as long CPU time, limitation of experimental equations and so on. This study developed Stochastic Distinct Element Method (SDEM) that makes possible to evaluate the probability of failure without long CPU time. SDEM is a method that applied the first order approximation method in the probability theory to DEM. Applicability of SDEM was verified by comparing to experimental results. It was found clearly that SDEM was a suitable method for the performance based design.

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Comprehensive observations of tidal currents and water properties (temperature, salinity and density) have been conducted in Zanpa Sea of Okinawa. This sea area has very complicated bottom sea topography, coastal configuration and shelf. Getting the eight significant components of the harmonic tide-current from the raw current data, the characteristics of barotropic tide current and internal waves are clarified. The characteristiccurve analysis of internal wave groups reveals the generating and transmitting mechanisms of the internal waves that mainly control the East-westward current in the sea are identified. These results may contribute to the understanding of the currents around islands of Okinawa.

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Ishigaki Island is located at the southern-most end of the Ryukyu Islands of Japan, and is encompassed by well-developed fringing reefs. In this study, we conducted field survey in east coast of Ishigaki Island to investigate the characteristics of currents in the reef area. At the same time we conducted numerical computation of currents by an improved shallow water turbulence model (SDS-Q3D) with high accuracy bathymetry of the reef area estimated from remote sensing data analysis. Numerical computation shows good agreement with field survey results and demonstrates importance of morphology effects on the characteristics of the currents in the reef area.

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The accuracy and economic value of the ensemble wave prediction (EWPS) using Japan Meteorological Agency operational ensemble weather prediction system (EPS) are assessed relative to the value of wave hindcast and deterministic wave forecast. Reliability of probability forecasts by EWPS were tested by analyzing Brier Score and Ranked Probability Score for different threshold levels for wave height. The probability forecasts derived from EWPS give 20-25% better performance for 1 day and 30-35% better performance for 4 days forecasts than the deterministic forecast. Using a cost-loss model for the decision making, relative economic value for EWPS was investigated. EWPS performs better than the deterministic forecast in terms of relative economic value for the wave event that exceeds 1m height. The relative economic value of EWPS shows significantly improvement from the deterministic wave forecast when the cost-loss ratio is apart from 0.5 and the forecast time length becomes longer.

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A field observation was performed to know the transports of particulate materials in a mangrove area. In the observation, the concentrations of dissolved and particulate materials and the temporal and spatial variations of soil environment in the mangrove forest were measured. A numerical computation for the transport of suspended sediments and the associated transport of nutrients during flood was performed for two different types of flood. The results of the observation and the computation have revealed that the movement of particulate materials in the mangrove area is much influenced by the phase-lag between the peak of flood and the tide. It was also found that phosphorous is provided to the mangrove forest by floods.

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A numerical simulatiuon model is presented to describe the material cycling in a mangrove area, to which the ecosystem model is applied in order to take into account of the chemical and biological reaction. In this model, the nutrient transport from the groundwater to the river is estimated by tandem use of field measurement and numerical simulation for groundwater flow. The water movement and the temporal variations of nutrient concentrations obtained from the numerical simulation show a good agreement with the observed results, indicating that this model is valid for simulating the material cycling in a mangrove area. The result of the numerical simulation has revealed that the amount of the supply of dissolved nutrient from the mangrove area to the coastal area at spring tide is 2 to 5 times larger than that at neap tide.

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Two strong earthquakes occurred off the southeastern coast of Hokkaido in northern Japan on 26 September 2003. The earthquakes gave various damage in the southeastern part of Hokkaido. A number of tsunamis associated with the earthquakes have been observed on the southern coast of Hokkaido as well as the northern part of Japanese mainland. The characteristics of the tsunami are that the wave propagation exceptionally continued longer than a day because of the generation of edge wave, and the tsunami ascended many rivers as much as approximately 10km away from the river mouth. In this paper, the properties of the river-runup of the tsunami were discussed on the basis of the hydrographs of the water level and results of the field surveys on Tokachi river, Kusiro river, Saru river and Mu river. We pointed out that understanding the risk of the river-ascending tsunami is particularly important for hazard mitigation.

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