Salt in a salt lake accumulated as a result of perfect evaporation of inflow water during the dry season. Water in a salt lake had a high salinity and its isotope indicated a little evaporation in the wet season because precipitation replenished the salt lake and there was no residual water during evaporation process in salt lake. In a marsh, both perfect and partial disappearance of water by repeated evaporation and water supply from upstream contributed to high salinity and high isotopic ratios because residual water had high isotopic ratios and dried areas accumulated salt. On the other hand, salinity and isotopic ratios depended on ratio of evaporation and water supply during evaporation excluding perfect disappearance of water.

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Multiple computational schemes associated with the spatial interpolation in a collocated grid system are investigated in a MAC method. The simultaneous linear equations of the scalar potential φ=pⁿ⁺¹-pⁿ include the second derivatives of the pressure pⁿ discretized by the central difference with the interval of Δx_i in the the CBP (Cell-Boundary Pressure) scheme, which utilizes p_n on cell boundaries in the prediction stage. However, the same derivatives are evaluated with the interval of 2Δx_i in the CCP (Cell-Center Pressure) scheme that estimates the pressure gradient at the cell center points. It has been shown that the CCP scheme is likely to cause the free-surface or pressure instabilities, although the CBP scheme deals with them. Conclusively, the combination of the CBP scheme and PG scheme, which calculates uⁿ⁺¹_i with the pressure gradient at the cell center points in the correction stage of the MAC method, is particularly effective together with the HSMAC method for the velocity-pressure relaxation.

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An implicit numerical algorithm (C-ISMAC method) has been proposed for incompressible flows with a collocated grid system. The C-ISMAC method, which is based on an implicit SMAC method proposed for staggered grid system, enables us to utilize higher-order schemes for discretization as well as to largely decrease the necessary computational time. This method was applied to cavity flows, incompressible flows in an enclosed area and free-surface flows with a fifth-order QSI scheme for convection terms. As a result, it was shown that the computational speed becomes two to five times faster than a usual explicit method and that the computational accuracy of the QSI scheme is still preserved in the C-ISMAC method.

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The inflow-sediment-induced water-wave generation is investigated by the solid-liquid two-phase flow model which is discretized by the Lagrangian particle method. The physical process of the wave generation can be clarified in detail by tracking the sediment-water-mixing process and the resultant momentum transfer from sediment to water. The MPS method, which is free from a numerical diffusion, is applied to track the water-sediment interface and the water surface wave with high resolution. The time series of the water-surface elevation are compared with some alternative wave-generating methods, to estimate the wave-making efficiency of inflow sediment.

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In order to clarify the effects of seawater density stratification, topography-dependent winds within an embayment, and wave set-up, on the storm surge level, we carried out a storm surge computation for the Ise-Wan Typhoon which struck the Ise Bay area in 1959. We employed a multi-level model that takes into account the density stratification and the wave set-up for the storm surge. A spectral shallow water model was employed for the wave hindcasting.
Obtained results are as follows: seawater density stratification increases the tide level deviation by approximately 20-30cm near the coast. Topography-dependent winds within an embayment causes variations of the tide level deviation by approximately 30cm. In addition, the wave set-up increases the tide level deviation by approximately 50cm on open coasts that face the ocean. By introducing these factors into storm surge computation, more accurate prediction of tide level deviations can be obtained.

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The global warming, due to increasing emission of carbon dioxide into the atmosphere by human activities, is one of the most serious problems of our planet. A greater attention has recently been given to the technique of ocean sequestration of CO₂, in which CO₂ is directly introduced into the middle or deeper layers of the ocean and dissolved in seawater. And we developed a flow model of the Pacific Ocean using the data assimilation system, and confirmed a good reproducibility of surface and deeper layer flow fields. Behaviors of CO₂ in the Pacific Ocean were examined by means of a numerical simulation, utilizing the calculated results of the flow fields, it was suggested that CO₂ must be introduced into the layers deeper than 1000m of the Ocean.

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To clarify the effects of Kuroshio-related offshore ocean current fluctuations on the coastal current system, we performed field measurements of the velocity and water qualities in the Kashima coastal region extending to the shelf edge. The results show that the deflection of Kuroshio current towards the Kashima coast induces a strong south ward current in the wide extent of the coastal region and there by the Oyashio influenced water intrudes with a sharp temperature and salinity front to the coastal area from the northern offshore area. The frontal eddies of Kuroshio current may have an another appreciable influence to the coastal current field, i. e., the warm water from a frontal eddy intrudes to the surface layer of the shelf sea with about 20m thickness.

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Relations between nutrients in the sediment and the growth of Typha angustifolia and Typha latifolia are represented by Michaelis-Menten equation with half saturation constant of nitrogen and phosphorus. Interactions of nitrogen and phosphorus concentration are expressed by their multiplication or the Libieg minimum low. Competitive growth model was developed for evaluating the influence of eutrophication on their competition. The analysis including the competition of radiation shows that the biomass and TLAI are more affected than the shoot height. On saturated nutrient conditions, Typha angustifolia has more superiority than Typha latifolia irrespective of latitude, however, the superiority of Typha angustifolia decreases on unsaturated nutrient conditions. Nutrient conditions greatly affects their competitive superiority or inferiority.

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