A new technique for quantifying SPM concentration by using a scanning ridar was developed and applied to the observation of SPM above the Meiji-shrine forest and the Sinjuku-city in summer 1997. The following results were obtained; 1) coupling of calibration by using outputs of ground based SPM sampler and theoretical correction for so called Raoult's effect of aerosol particles made it possible to estimate SPM concentration from rider signals, 2) temporal and spatial distribution of SPM concentration were observed by the rider, and they were used to discuss corresponding meso-scale climate meteorological fields such as diurnal change of atmospheric boundary and sea breeze penetration.

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A mathematical model was developed in order to analyze heat, liquid water and water vapor movement in a soil column associated with evaporation from soil pores at the interface between the dry and capillary layers. In the proposed model, the evaporation is taken as the vapor pressure difference between the soil pore space and that at the surface of the water films surrounding to soil particles. As a consequence, the energy equation and mass balance equations for liquid and for water vapor can be solved simultaneously. The proposed model was able to reproduce well diurnally varying temperature, volumetric water content and vapor pressure profile, obtained in a laboratory.

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A damping characteristics of turbulence intensity were compared between the theoretical model and the experimental data with a laser Doppler anemometer (LDA). The effect of the surface-wave fluctuations was then considered, and the damping effect near the free surface was expressed as a function of the Froude number. Furthermore, Reynolds Stress Model (RSM) was used to calculate the turbulent statistics of open-channel flows in comparison with the experimental data. PIV (Particle-Image Velocimetry) was then used to measure evolutionary patterns of coherent vortices in the center of the channel. Finally, the mean bursting period was evaluated with LDA measurement. By using these methods, a relationship between the “bursting phenomena” and the “boils (surface renewal eddies)” was investigated intensively as a function of the Froude number.

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A method of numerical analysis of the flow in an underground diversion channel with enclosed pressurized air is proposed. The calculated values of water levels in vertical shafts and pressure heads in a tunnel agree well with experimental values.

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Field observations and measurements of debris flows were carried out at three locations on Mt Unzen-Hugendake in 1992 and 1993. Two of the instrumented study sites were a downstream reach of the Mizunashi River, which are 12m and 25.1m wide and have an average slope of about 0.05 and 0.025, respectively. The other was a downstream reach of the Nakao River, which is 7.2m wide and have an average slope of about 0.025. Radio current-meter and ultrasonic water level gauge were used to obtain surface velocity, depth and discharge for the several flows.
The value of nondimensional surface velocity was found u_s/u*=5-10. Peak discharge was found Q=347m³/sec at the Mizunashi River and Q=57m³/sec at the Nakao River.

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A numerical simulation model is presented to describe the cycling of substances in gravel rivers. The chemical formulas describing the physiological action of attached algae and other microbes are employed in the model in order to correctly estimate the distributions of the substances. The hydraulic characteristics of gravel rivers are specifically taken into account in this model.
The results of the numerical simulation reveal that the deposition of the suspended organic matter and the erosion of organic sediment play important roles in determining the cycling of carbon in gravel rivers.

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It has been pointed out that the turbulent structures near a free surface have a close relationship with coherent vortices, and that those characteristics are greatly affected by the presence of the free surface. Furthermore, mass transfer across an air-water interface is a fundamental and very important process in environmental and geophysical problems. Therefore, three different turbulent conditions were considered; namely, bottom shear driven turbulence, wind shear driven turbulence, and combined wind/stream driven turbulences. The aim of this study is to evaluate the relationship between the turbulence structure near the interface and the gas transfer process across the air-water interface. As a results, the mechanism of gas transfer across the air-water interface is well explained by a small-eddy model.

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Amodel for undertow and longshore current was developed and calibrated with field data obtained over a longshore bar. The model well predicted undertow velocities in the field and in a large-scale experiment, while a model calibrated with small-scale experiment data underestimated the velocities. Although cross-shore distributions of the longshore current over longshore bars predicted with the model calibrated with experimental data had peaks seaward of the bar crests and did not fit with the distributions measured in the field, the distributions predicted with the present model had peak velocities shoreward of the bar crests and fitted with those in the field.

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When a large amount of sea water spray is transported landward by a strong wind, severe salt damages will be caused in the wide coastal region. In this study, the quantity of spray generated from white caps under strong winds has been investigated experimentally by using a wind-wave tank. Spray quantity depends strongly on the friction velocity on the water surface and the settling velocity of spray. The drag coefficient on white caps is given by an increasing function of the wind-wave factor. It is shown from image data processing that the settling velocity of spray decreases in inverse proportion to the height from water surface. The vertical profiles of spray concentration can be expressed universally by using these results.

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Submarine groundwater discharge (SGWD) and associated nutrient fluxes at Hasaki sandy beach along Kashima coast in Japan are investigated through field measurements and numerical simulations. The field data indicate that (1) groundwater has higher concentrations of land-derived nutrients than seawater; (2) microbial activity near the shoreline induces mineralization, reduction and oxidation of nitrogen and phosphorus; and (3) in the portion of the aquifer underlying coastal forest, nitrate is appreciably utilized and removed. A numerical model incorporating effects of water-table and tidal fluctuations is developed to evaluate SGWD with high accuracy. Assuming that the aquifer consists of homogeneous sandy soil, the simulation results show that the impact of SGWD on the marine and estuarine ecosystems is less than that of Tone River runoff. Nutrient flux via groundwater seepage is a minor component of primary productivity in the surf zone.

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The motion of a 2-D heavy turbulent thermal as well as a horizontally propagating density flow subsequently formed after impinging on the bottom is studied by large eddy simulations (LES). The governing equations, which consist of the filtered 2-D Navier-Stokes equations and mass conservation equation, are solved using the combined cubic spline (CCS) scheme. The eddy viscosity is evaluated by the Smagorinsky model.
The comparisons of computational results with experimental results show that the motion of both falling and horizontal propagating stage is well simulated by the present numerical model. The added mass coefficient A_m for the thermal is estimated as 0.6, based on numerical simulation. The good agreements between experimental, computed and theoretical results of half width, average buoyancy and mass center velocity of the thermal are achieved. The numerical experiment reveals that motion of the thermal is dependent on the initial volume of dense fluid, even if initial buoyancy remains constant.

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