In the aspect of water-environments, the studies on wind waves are very important regarding transport phenomena in atmosphere, lakes and sea. Dispersion phenomena in water under wind waves have been studied by many researchers, but they have taken notice of only surface layer beneath the free surface. The purpose of this study is to elucidate the diffusion in the surface layer and the lower layer as well. Visualization of dye diffusion and velocity field measurements by means of PIV and 2D-electro magnetic velocity meters were performed. The mechanisms of dye diffusion between the surface and the lower layers are different. In the surface layer, the diffusion can be estimated well by using Taylor's turbulent diffusion theory. In the lower layer, however, we found that the diffusion is like the chaotic mixing. To investigate qualitative feature of the chaotic mixing under wind waves, a mathematical model represented by the superposition of a periodic array of vortices and stationary water waves was proposed. The coexistence of free surface waves and large-scale vortices causes chaotic advection of fluid particles. This phenomenon will induce strong mixing of water in the lower layer even if the turbulent intensity in this layer is small.

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Charophyte ecology in Lake Myall, an oligotrophic lake in Australia, was investigated particularly focusing on the interaction with Najas marina and Myriophyllum salsugineum. Chraophytes intensively produces Gyttja, accumulating on the bottom. The Gyttja layer with its soft characteristics and low Redox potential inhibits colonization of submerged species except for Charophytes and Najas, thereby extremely decreasing biodiversity of flora of the lake. In Lake Myall, under high current, where Gyttja is washed away, M. salsugineum can grow on rocky bottom worsens the light climates for Charophytes, while in stagnant water, N. marina, although low in biomass most of the year, vigorously grows in May, suppressing Charophyte communities, although they are tolerant in low light regime. These process was confirmed by measuring light intensity inside the plant canopy, compared with depthwise and biomass distribution in the lake.

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Zizania latifolia is one of the most common emergent species in east Asia, occurring along the littorals of freshwater marshes and streams. This study is aimed at more information on Z. latifolia for further mechanistic understanding the competition between Z. latifolia and others from the view of carbon and nutrient cycle with its mophorogical changing. Carbohydrates were, continuously translocated downwards from April to May, slightly later than the beginning of the growing season, then peaking in August at 10 to 17gC/m² day, and lasted until November. The downward translocation amounted at about 20 to 60% of the net production until August, while from August to September almost all net production was mobilized into the rhizome system. After the senescence of shoots until the emergence of new shoots in March, the rhizome TNC stock substantially decreased due to respiration loss, while there was only slight loss in TSC, attributed to the mortality. These corresponded to the peaks in the downward translocation respectively due to the intensive shoot mortality in spring and the starting of senescence.

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Aquatic macrophytes function in several ways in aquatic environment. We have analyzed the effects of aquatic macrophytes focusing on the reduction of resuspension of bottom sediments. Aquatic macrophytes are known to suppress the development of wind wave in shallow waters. Reduced wave height leads to the reduction of the resuspension of bottom sediments. This function that aquatic macrophytes may have seem important in deciding the water quality of shallow water bodies. A numerical simulation model was developed to estimate the quantitative effects of aquatic macrophytes on the water quality of a shallow marsh. Simulation results showed good agreement with observed water quality data. A simulation case that assumed dense vegetation of which area was maximum in recent years resulted in less turbid and lower organic matter concentration. The degree of reduction in suspended solids presumed by the simulation agreed well with the previous records in Inba marsh, Chiba prefecture that experienced the decay of aquatic macrophytes. Restoration of native aquatic macrophytes is important to restore the marsh to a previous clear state.

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To perform a computation of water environments in lake with accurately evaluating discharge and pollutant loads in influent rivers, we develop a coupled river-lake model in which a river-flow simulation is employed with a new simplified horizontal coordinate system, named horizontal sigma coordinates. In the numerical simulation for river flow and sediment transports with the coupled river-lake model, the computational results for SS fluctuations in the river and lake give acceptable agreements with those of the observed data, demonstrating the fundamental validity of the present model. It is also noteworthy that the treatment of the erosion rate of sediments has a key role on an accurate computation of sediment transports in an urban river estuary.

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The previous researches about the Lake Kasumigaura have neglected the effect of groundwater on the water and nutrient budgets in the lake because they have believed that the effect of surface water is predominant. In this study, the National Institute for Environmental Studies (NIES) Integrated Catchment-based Eco-hydrology (NICE) model was expanded to include the interaction between the lake water and groundwater in this catchment. Although inflowing and outflowing streams are dominant in the annual hydrologic budget of the lake, the model shows that groundwater seepage plays a great role in the net water budget. Groundwater entering the lake from the north side is contaminated with high concentrations of nitrate and ammonia from intensive pig and cattle raising. This groundwater inflow plays an important role in the nutrient loading into the lake and consequently in the water quality and eutrophication.

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To clarify the pollutant loads in Lake Teganuma, which is one of well-known eutrophied lakes in Japan, we performed field measurements on external inflow and internal production loadings from June to October in 2003. The external loadings of T-N, T-P and COD through main inflow rivers and the North-Chiba water conveyance channel were discussed quantitatively. The percentage of the internal production loading for COD in total loadings was from 45 to 65% under normal atmospheric conditions. The measured results suggested an adequate correlation between the internal production loading for COD and the solar radiation although the discharges from the channel and the inflow rivers were not correlative to the internal production loading for COD.

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In a blackish lake, rich organic matters and nutrients are supplied from ariver, and salinity is provided from a sea. There exists a balanced ecosystem, and its stability greatly depends on the nutrient cycle. On the other hands, the matter cycle depends on the ecosystem. Therefore, it is important to understand the characteristics of the water qualities considering the ecosystem to manage and preserve the water environment in a blackish lake.
In this study, we evaluate the habitat environment for Corbicula japonica using its growth model. And, we analyze the seasonal and annual variations of water qualities, using a hydrodynamic model coupled with an ecological model to clarify the relation between thewater qualities and the amount of Corbicula Japonica.

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Lake Shinji has a distinctive environment based on the inflow, which the astronomical and meteorological tide causes, of the salt water from Lake Shinji, and the inflow from the Hii River. Recently, the extension construction is planned to defend from overflowing in the Ohashi River that connects Lake Nakaumi and Lake Shinji. It is the important problem that we study about the present mechanism of water environment in Lake Shinji. So, we calculate the estimation of water quantity and salinity fluxes, based on the data observed from summer to autumn in 2003, and examine them in various weather conditions. Furthermore this study focuses on the cause of the variation of the salinity concentration in Lake Shinji. Also, after the inflow of much salt water, it makes the halocline, DO under the halocline often disease in the lake, we state the phenomenon of the variation of DO and the salinity concentration.

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A simple one-dimensional model which can evaluate the fate and transport of nitrogen in wetland soil-vegetation systems was developed to calculate the nitrogen removal efficiencies of reed bed wetlands. Seasonal variations of temperature, seasonal variations of nitrogen uptake by vegetation, vertical biomass distribution in root, and oxygen transport by vegetation were considered in the model. Field observations were conducted to determine some model parameters, although almost of all parameters were adopted from published literature data in Europe and North America. The model calculation results for the concentrations of NH₄^-N and NO₃^-N in the soils were about ten and two times larger than that of observations results. However, the calculation results for nitrogen removal efficiencies indicated the same trends compared with previous studies.

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In semi-enclosed water areas, aquaculture has been performed actively in many places in Japan by utilizing their calm environment. In case of overproduction of culturing, however, aggravation of water quality environment, such as eutrophication and appearance of anoxic water, is inherent problem in semi-enclosed areas. Nagatura-ura Lagoon, the study area of the present study, is also one of the typical semi-enclosed brackish-water areas. Nagatsura-ura Lagoon has been used mostly for cultivating oyster for these several decades. In the recent years, however, the appearance of anoxic water causes severe damage to the fishery industry. In this study, filed observation has been carried out during summer of 2003. The salinity, water temperature, dissoloved oxygen and water level were measured in the study area. Through these measurements, the characteristics of water quality change in response to tidal variation were investigated to clarify the mechanism of sea water exchange in the lagoon area.

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A field observation was carried out to examine the effects of a floating-leaved plant (Nymphoides indica) community on the ecosystem and water quality in an irrigation pond. The appearance of the plant community and the values of various water quality items were monitored through a year (2003). The plant community suppressed multiplication of phytoplankton in the upper layer and generation of oxygen-deficient water masses in the lower layer and absorb a lot of nutrients from the water body and bottom mud in summer. In contrast, withering of the plant community leads temporary multiplication of phytoplankton and slightly gives negative influence on the ecosystem and water quality in fall and winter.

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Recently, reduction of fish catch and poor harvest of cultured laver have been serious social problems in the Ariake sea, which is a typical macrotidal semi-enclosed bay in Japan. Therefore, countermeasures of these problems have been needed. We have proposed a new water-purification method to control a pattern of tidal residual current by using “Bottom Roughness” which has an asymmetric 3-dimensional shape with directional resistance property.
In this study we examined the effect of Bottom Roughness on activation of tidal exchange between the northern part and the southern part of Ariake sea by both model and numerical experiments. As a result of the present study, it becomes clear that i) Bottom Roughness can activate the tidal exchange sufficiently and ii) tidal exchange at the cross-section connecting Ariake with Nagasu plays a very important role for mass transport in the northern Ariake Sea.

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The environmental impact assessment is becoming very important with increased public awareness to the environmental issues. In many cases, future conditions of water environment are evaluated referring to the results obtained from numerical simulations that are carried out based on the possible scenario. However, it is quite difficult to set some computational conditions in detail. In this study, to predict the tidal currents at coastal area, firstly, the numerical simulation model has been developed. This model was calibrated using global optimization technique named ACCO. Its accuracy of predicted result related to the tidal motion in Shimabara Bay was shown. Following, the tidal current simulation was curried out using weather data forecasted by mesoscale model, MSM. The calculated results show that the tidal motion of this bay is changed strongly affected by the wind blowing on the water surface, and temporal and spatial variation of meteorological condition should be adequately taken into account for the precise prediction of material transportation. Furthermore, from the results obtained by simulations regarding the uncertainty of forecasted weather data, it seems that uncertainty analysis will be required to evaluate the accuracy of predicted results.

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In the Minamata Bay, the remediation project on water and bottom sediment environment was completed in 1990. About 0.8 million m3 of bottom sediment contaminated by mercury was dredged. However, a recent measurement of mercury in the sediments [Tomiyasu et al., 2000] has shown that mercury is spreading around the center and southern parts of the Yatsushiro Sea from the Minamata Bay. Although the concentration of mercury in bottom sediment is lower nowadays (<10ppm), modelling for accurate prediction of mercury dynamics is necessary. In order to predict the mercury dynamics accurately in a coastal area, it is necessary to measure mercury transport in an actual sea.
Thus, the current observation by using ADCP (RD Instruments Workhorse 1, 200k Hz), which was mounted on the side of a fishing boat, was performed on the 2nd of December, 2002 and the 29th of July, 2003 to realize a three-dimensional structure of tidal current in the Minamata Bay. As a result, it was found that a horizontal circulation flow occurred during ebb tide in summer.

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This paper describes the occurrence of the front around the head of Tokyo Bay. Salinity, temperature and ADCP measurements were performed in Tokyo Bay during a spring tide on 21st November 2002. It was revealed the estuary circulation was suppressed and the down-welling appeared as a result of the front during the spring tide. Numerical computations were used to clarify the mechanism responsible for the front. A non-hydrostatic three-dimensional model (MEL3D) demonstrated the front at the bay mouth for a case when large tidal amplitude coincided with weak stratification. A two-dimensional two-layer model was used to confirm whether the stability of interface due to flow is significant for the occurrence of the front. As a result, the change in water depth and width are significant for the occurrence of the front in terms of the two-layer model.

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Clockwise circulation in the upper layer and the decrease in the level of interface were found from field experiments to occur around the head of Tokyo Bay on 10th August 2001. It was revealed that the clockwise circulation in the upper layer resulted from wind with clockwise vorticity around the bay head, which appears when the dominant north or north-easterly wind changed to south-westerly. To clarify the mechanism responsible for the decrease in the level of interface, numerical experiment was carried out by using non-hydrostatic three-dimensional model (MEL3D). The importance of the sea-bottom slope around the bay head and clockwise circulation in the upper-layer was demonstrated.

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Water near sea bottom in the head of a bay into which a lot of nutrients flow becomes deficient in oxygen during summer. The characteristics of the anoxic water are different between in the whole bay and at the enclosed area in the head of the bay. The vertical difference of temperature and DO (dissolved oxygen) in a bottom layer are correlative in the whole bay, and not so at the enclosed area. It is because there is excess consumption of oxygen at the enclosed area, which is influenced well on by the water temperature under a thermocline. In the present paper the factors which have influence on the development and decline of the anoxic water are discussed. When the anoxic water mass develops early in summer, the development of that depends on the temperature of the middle layer close under the thermocline. The higher temperature leads more consumption of oxygen in the process of the degradation of detritus. This consumption of oxygen is more important factor of the dynamics of anoxic water at the enclosed area than in the whole bay.

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Field tests of BaNK system were performed in Jigyo Beach. We have proposed ‘Beach and Navigation Keeper: BaNK system’ in order to cope with beach erosion and shoaling of fairway. The system is a method to control sediment transport due to wave-induced residual currents produced by submerged asymmetrical roughness. In Jigyo Beach, seashore transformation owing to waves has occurred and been restored every year as a coastal protection work. Transformation of the beach has been investigated on the basis of field survey from December 2000. Afterwards, plural submerged asymmetrical roughness were set in the beach as a field test. That was performed in 2002 and 2003 again with different setting pattern of the roughness. As a result of this research, it becomes clear that the BaNK system is able to control sediment transport in a sea.

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The relation between seawater exchange and sea current pattern was investigated. For this purpose, ocean currents conditions were observed in Sanriku Sea off using NOAA/AVHRR data. It was confirmed that density variation is not so much affected by salinity. Therefore, the regression function is derived from observed density and the density which was calculated using constant value of salinity and observed temperature. Using the regression function, σ_t distribution in Sanriku sea off is evaluated from sea surface temperature data. As the result, the behavior of Oyashio water mass was observed from the σ_t distribution. Analyzing time series temperature and salinity data in Ohfunato bay, it was confirmed seawater exchange occurred under the influence of Oyashio water mass. It was also observed distributions of chlorophyll-a and nutrient change at this seawater exchange and small density variation affects chlorophyll-a distribution at the depth of middle layer.

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Wave hindcasting with use of a shallow water model is conducted in order to estimate wave conditions on the Western Seto Inland Sea during Typhoons 9119 and 9918, which gave rise to severe damages to the coastal areas. Space-time variation of winds over the area calculated by either a space interpolation of wind data measured at coastal stations surrounding the sea area or a parametric typhoon model is given as input condition. Comparison between hindcast and measurement for time variation of wave height and period at coastal stations around the area reveals that hindcast waves under interpolated wind fields yield closer agreement with measured waves over those under typhoon model winds. Also, a detailed discussion is made for spatial distribution of the maximum wave height.

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Tsunami waves in river channel typically form undular bore to ascend the channel. The undular bore can not neglect the acceleration of vertical direction, so that the nonlinear dispersive wave theory can be applied to the governing equation. In this paper, the equation was used to conduct numerical experiments in order to investigate the propagation characteristics of tsunami in the river channel. The experiments were conducted by varying parameters which were Froude number of steady flow in river, bottom friction, the slope of the river bed and incident waveform of tsunami. As a result of the experiments, the following useful knowledge was obtained. The river channel topography is likely to induce the wave dispersion, and this tendency increases with decrease in the bed slope. The high hazardous reach by the infiltration of tsunami is almost same from river mouth despite the bed slope.

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Directional wave spectra and spreading parameter are measured to investigate properties of wind waves observed in the Sea of Japan. Goda and Suzuki have shown that the peak value of spreading parameter s decreases as the deepwater wave steepness increases based on the observation by Mitsuyasu et al. and Wilson's formula. The values of directional spreading parameter s observed at Oyashirazu Coast faced the Sea of Japan do not decrease in accordance with the relationship proposed by them. It is found that the value of s decrease as the wave height larger than 4m increases.
Transfer function from water surface displacemento wave pressure fluctuation are also evaluated with the field observation data to study the effect of nonlinearity of waves on them and estimate water surface elevation from the wave pressure fluctuation. The values of transfer function in the range of frequency larger then twice the peak frequency decrease rapidly compared to the linear theory. The transfer function measured are formulated and used for estimation of representative wave heights from the wave pressure fluctuation.

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The Naruse River mouth showed stable topography at least for these 46 years. However, sand bar on the lefthand side of the river mouth has been declining in recent years. The behavior of the morphology of the river mouth after the flushing of the sand bar has never been observed. In this paper, characteristic morphological change at the Naruse River mouth is shown with the use of aerial photographs and morphological maps. In order to determine the main factor of morphological change, empirical orthogonal functions are applied. It is concluded that the decline of the sand bar has occurred by the construction of the headlands. Furthermore, the mechanism of the sand bar intrusion into the river is explained by wave overtopping over the left-hand side sand bar at the river mouth.

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It is well known that colloidal particles, such as clay minerals, which enter into the sea from river inflow, change their sedimentation velocity due to the interaction with other particles as aggregation and disaggregating. These mechanisms are comparable to that of the scavenging effect used for the sedimentation/diffusion analysis of radioactive materials. So, in this research, concentration analysis was conducted on the basis of a soil discharge scenario with considerations given to flow, mixing, scavenging. Using this sedimentation-diffusion model it is possible to predict the amount of clay particles, which reach the seabed near shore or river mouth based on aggregation/disaggregating interactions.

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Field observations were carried to investigate effects of suspended sediment on the behavior of dissolved phosphate in estuary of the Ishikari river during the snowmelt season in 2004. Suspended sediment was sampled during the snowmelt flood at Sapporo Oh-hashi, at the same time water quality was observed in the coastal area near the river mouth. The phosphorus chemical combined forms of the samples were analyzed, and experiments were conducted to study variation of the release of phosphate to salinity and pH change. Behavior of the phosphate adsorption from the suspended sediment was followed the Langmuir relation in each salinity and pH condition. At the flood dissolved phosphate concentration changed at the estuary, and was highest at lkm from the river mouth. And the behavior of the dissolved phosphate in estuary was explained by the Langmuir relation.

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In Banjo estuary, clam resources declined once, but recovery of the population is observed. To reveal potential of the fishery ground and major factors on clam life history, patterns of waves and currents around the river mouth sand bar and water temperature changes were analyzed. Patterns of wave directions and nearshore currents show the function of the sand bar as the bather of waves to protect habitats of estuary organisms. Long-term measurements of the water temperature indicated its severe changes might effect the survival of clam pelagic larvae and larval clams. Conservation and management of the river mouth sand bars dedicate estuary ecosystems and fishery.

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The seabed environments were investigated at 20 stations located in the northern area of Ariake Sea in July 2004. The spatial distributions of sediment characteristics and nutrients in porewater were obtained. It is found that the area where the acid volatile sulfides (AVS) content exceeds 0.2mg/gdry spreads along the west coast, and the seabed conditions in the area are bad. The concentrations of dissolved inorganic nitrogen (DIN) in porewater increase from the southwest to the northeast, and the concentration of phosphate (PO₄-P) takes the reverse distribution. The spatial distributions of nutrients seem to depend strongly on the process of adsorption and desorption of PO₄-P and the process of nitrification and denitrification of DIN.

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Sediment transport in semi-closed sea is very important, because this is closely linked to not only maintenance of port facilities but also coastal environmental issues. We analyzed sediment transport in the Hiroshima Bay using a 3-D baroclinic numerical model with a sediment transport model that realistically simulates cohesive and noncohesive sediments. There is a characteristic horizontal distribution of bottom layer turbidity in the Hiroshima Bay, i.e., the turbidity is higher in the southwestern part than in the northeastern part. The result of the model showed that sediments resuspended by strong tidal current in Seto parts make the north-south gradient of turbidity. In addition, discharge from the Ohta River brings about the east-west gradient of turbidity. The strong tidal current at Seto part tends to erosion. On the contrary, northern part of the Itsukushima tends to deposition.

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In this paper, study on a new concept concerning on the classification of the local mixing types of the salinity intrusion in the tidal estuary was conducted using monitoring data of the Nagara river estuary. Flow diagram on the mixing types (highly stratified type, partially mixed type, well mixed type) was proposed using newly introduced non-dimensional flow parameters which estimate the strength of tidal effects and buoyant force. Comparison between proposed concept of flow diagram on the mixing type and field data was conducted and it presents good agreements. Proposed flow diagram and flow parameters are useful not only for the classification of local mixing but also to understand the physical characteristics in the tidal estuary.

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The strong stratification on the downstream region after the Nagara river mouth Barrage construction has been reported. The purpose of this paper is to extract the features of saline intrusion and analyze the flow mechanism of this stratification triggered by the Nagara Barrage using monitoring data. Several special features of salinity intrusion were reported and revealed salinity intrusion was effected not only the reduction of tidal prism by barrage construction but also topographical and hydraulic features of Nagara river estuary. This paper also treated the relationship between DO concentration and saline intrusion and revealed strong correlation.

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Takase River in the southeast of Aomori Prefecture is a tidal river with the compound channel. Filed measurement and laboratory experiments were carried out in order to understand mixing characteristics of river estuary in this paper. Salinities of Lake Ogawara were able to estimate from field data. Furthermore, experiments were performed in compound channel with the effects of narrow section. The transverse mixing coefficients were obtained from these results using diffusion equation, and compared with those in compound channel. It was showed that the mixing coefficients were related to the product density current parameter and cross-section of channel parameter. Therefore, it was found that Takase River estuary was influenced by compound channel from these results.

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Field observations on characteristics of salinity intrusion and vertical mixing were conducted in an urban tidal river, the Horikawa River in Nagoya City, in order to understand the effects of stratified flow and reciprocating flow on water quality. We measured time series of vertical distribution of water depth, velocity, salinity, temperature, DO etc. during one tide by using an electromagnetic velocimeter and a multiple water quality meter. The vertical mixing type in the measured region was basically classified as a mild mixing type, but a considerable change of mixing type was observed with time and location. An increase of installed water slightly affects a stratified flow structure at the measuring site. Salt water has lower DO value than that in fresh water and it is moving up and down through a bottom layer during tidal motion.

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A three-dimensional numerical model has been developed using large eddy simulation, to simulate the motion of axisymmetric gravity currents, which are generated by direct dumping of sediments into quiescent water. The model governing equations are three-dimensional, incompressible Navier-Stokes equations and mass transport equation. The solution technique employs operator-splitting algorithm to split governing equations into three parts, namely, advection part, diffusion part, and pressure part. The advection part is solved by the Quadratic Upstream Interpolation for Convective Kinematics with Estimated Streaming Terms using Universal Limiter (ULTIMATE QUICKEST) scheme. The Compact Finite Difference (CFD) scheme is used to solve diffusion part and the Successive Over-Relation (SOR) method is employed for pressure part. The modified Smagorinsky model, which includes a buoyancy term, is used for turbulence closure. The flow characteristics of the experimental axisymmetric gravity current, including intrusion distance, front height, front velocity, and the amount of deposited particles obtained from experiment are found to be in agreement with the simulations.

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In the Banjo River (Saiki, Oita), the population of clam drastically decreased after 1994 and has not been recovered yet. In order to make the reason clear some field surveys on water quality (: DO, salinity, water temperature, etc.), sediment quality and flow patterns were carried out from 2003 to 2004 in the Banjo estuary and Saiki Bay. Measurement results by ADCP showed the dominant flood current through the shorter navigation channel and the dominant ebb current through the longer one. In addition, water body tended to be stagnant in a neap tide and oxygen deficiency was measured in the longer channel. It was confirmed that temporal variation of DO concentration in the Banjo estuary depended on both flow patterns of tidal current and a redox conditions in the sediment.

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This paper deals with a transportation of the organic matter in Ohtagawa estuary connecting to Hiroshima bay. The samples of the organic mud were obtained from the sediment trap net installed in this area. The movement of the organic mud is estimated by the variations of the trapped organic mud among the observation points in quality and quantity. The most essential ingredients were particles of 75 micrometers or less. The C/N ratio in the sea area is different from thar in the river. It tends to rise with the soil grain fraction increasing. There was a sharp contrast between Ohtagawa River and Tenmagawa River in terms of the different source of the organic mud from September to October because of the different transportation systems between two rivers.

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Nutrients concentrations in the sediment in the estuary of the Chikugo River were surveyed around the flood period. After the flood period, Fe-P, Al-P and Ads-P concentration increased in the sediment of the tidal flat at the front of rivers. On the other hand, concentration of these components in the sediment of the tidal flat, which is far from river mouths, did not increase. Moreover, concentrations of nitrogen and organic carbon in the sediment decreased in the tidal flat. It was clarified that the discharged sediment from the river basin affected the nutrient concentration and environment of the surface sediment in the estuary

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In estuaries, mixture of seawater creates unique water environment. After a flood, observations of water quality in the river mouth were conducted in order to understand the vertical distribution of suspended solid in the seawater mixing layer. At the upper part of mixing layer, suspended solid concentration is higher than at the lower part of mixing layer. There is a correlation suspended solid diameter and salinity. Suspended solid concentration increases from upstream to lower stream during low tide.
The concentration distribution model including diameter distribution model could reproduce the concentration distribution of suspended solid in salt water mixing layer.

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In recent years, vegetation grows thickly in river channels even on originally gravel river beds. Riverine vegetation is one of the most important parameter for flood control, biodiversity conservation and so on. Consequently, it is quite important to develop efficient methods for monitoring these vegetation.
This research evaluated high resolution satellite remote sensing and classification trees methods for classification of riverine vegetation in the midstream of Tama river. The estimated vegetation classes were compared with the vegetation classes in the existing actual vegetation map and the accuracy were evaluated. These results suggest that the method having a combination of high resolution satellite IKONOS data and classification trees is useful for monitoring riverine vegetationin riparian ecosystem.

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Field surveys have been conducted on the floodplain at the Honmura district in the Kita River after the severe flood damage by Typhoon No.19 in 1997. The process of changes in topographical feature and vegetation luxuriance corresponding to the flow scale has been quantitatively explained through the analysis of the aerial photographs by authors.
In the paper, a vegetation factor VF, which expresses the degree of luxuriance of vegetation, is introduced to quantitatively analyze the relation between vegetation luxuriance situations and flow scale. The factor is assumed to be a linear function of the maximum discharge in the year, and function parameters are determined from the trial and error method. From the simulated results, it is shown that the history of destruction and restoration of vegetation on the floodplain at the Honmura district in the last 36 years can be quantitatively inferred from the scale of flood by using the introduced vegetation factor. Moreover, it is found that the destruction and restoration of vegetation has been repeated roughly every six years under the critical discharge of 2, 300 m³/s.

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For elucidating the fundamental characteristics of Phragmites japonica that grow on a gravel-bed river bar in middle stream of Ara river, artificial sedimentation experiment on the plants' colony was conducted and the strength of runner was measured by push-pull gauge. Quadrates were set and runner expansion was measured seasonally. Sedimentation experiment with 0.1m thickness on May had no effect on the growth of P. japonica. The length of runner is closely related to the cumulative shoot height of parent colony of the runner. Even the newly formed colony has enough strength to stand against the high velocity. The velocity is higher than that for the initiation of the gravel movement. Then the lateral distribution and their seasonal development of the colony is very important to evaluate their effect on the flow resistance. Dynamic growth model of P. japonica formulated by using the lateral enlargement characteristics of the runner has a potential to express the seasonal variation of shoot biomass and lateral biomass distribution.

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A numerical simulation model is presented to describe primary production and species transition of stream periphyton communities, in which the net growth rate of periphyton biomass is estimated by the balance of primary production, immigration, respiration and detachment of the periphyton biofilm. The interspecific competition of filamentous periphyton and non-filamentous periphyton is included in the model via the differences of the algal densities and the immigration patterns to the substrate. The solar radiation inside the periphyton biofilm is estimated by the Lambert-Beer's equation, and the nutrient distribution inside the biofilm is calculated from the diffusion equations of nutrients. The physiological parameters used in the present computations are evaluated from the laboratory data on periphyton growth. The results of the computation show that the model can predict the temporal variation of periphyton biomass and the species transition from the non-filamentous periphyton to filamentous periphyton well.

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Net-spinning caddis larvae set up nests on the substratum in a cobble river. Their abundance is clearly existed on the substratum with fewer disturbances, and moreover causes “substratum adhesion” which suppresses the flux of bed-load transport because they bind a large amount of bed-materials. In this paper, we modeled the population dynamics of the net-spinning caddis larvae (Stenopsyche sp. and Macrostemum radiatum) by taking into account of the different dynamics between the number of their individuals and their individual growths and the conventional knowledge about their responses of emigration, immigration and environmental capacity to various flow conditions. Combining the numerical simulations of the caddis population dynamics and the flow computation in a study reach with our experimental results about the substratum adhesion due to the caddis inhabitations enabled to explain the actual substratum adhesion with temporal changes in the cobble river with fewer disturbances.

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River improvement and maintenance works can play an important role in conserving rivers and restoring them to a more natural state. This paper focuses on aquatic organisms (specifically, benthic animals) as indicators of river conditions, toward clarifying the relationship between inhabitation by these animals and the physical conditions of a river channel (flow velocity, water depth, bottom materials) and the food environment (i. e., periphyton and particulate organic matter). The relationship was examined by comparing pools and riffles in various types of river channels, such as those with and without river improvement works.
The examination found that improved sections have less storage of organic matter than unimproved sections have. We also confirmed our findings on restoring a river to its natural state by varying the physical conditions and food environment in the improved section.

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We tracked fish behavior using radio telemetry in experimental streams, and analyzed it with a behavior prediction model to understand the relation between fish behavior and flood flow.
The results are summarized as follows. 1. Upward migration began w ith flood discharge, however, there was a threshold in flow rate for the start of the migration. 2. Experimental results were simulated successfully by a model that is driven by hydraulic characteristics such as velocity and acceleration. 3.Thus, hydraulic characteristics which can influence fish behavior seemed to be current velocity and acceleration.
Upward migration of fishes during flood seems able to be explained by combining our fish behavioral prediction model and hydraulic model.

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It is known that ayu spawn at the rapid in the lower reaches. However, suitable value of the flow depth and velocity were not known, as yet. It was pointed out that the velocity near the bed is more important than the bulk mean velocity, due to ayu spawn on the bed. At first, the suitable partial velocity for spawning of ayu is derived on the basis of the previous data and field measurements. It was found that the suitable partial velocity normalized by the burst speed of ayu is in the range of 0.04-0.25. In contrast, the bulk mean velocity and flow depth were used in environment assessment like a PHABSIM. The suitable curves of ayu were not known. The field measurements were conducted to obtain the suitable curves. As a result, it is pointed out that not only the bulk mean velocity and flow depth, but also the growth of the attached algae is necessary for PHABSIM. Further, ayu makes their territory not only in the rapid but also in the pool.

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Fishway is constructed to keep the migration of anadromous fishes, which are often prevented by the river structures, such as weir and dam. In the design of fishway, wide-range distribution of flow velocity is important, to help fishes, which choose their cruising speed and dashing speed with feeling strength of neighboring flow velocity. To simulate fish behavior in fishway, the individual based characteristics including the interaction with neighbors is the key factor. To describe this, the fish-school Boid, or individual based model, is developed herein. The numerical fishway is proposed by combing this fish-school Boid with the 2D-Raynolds-equation based flow simulation. Time dependent characteristics of the migration of fish school is virtually demonstrated by the CG-based animation.

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A numerical method was developed to predict the impact of short-term variations of river flow on the spawning environment of Ayu (Plecoglossus altivelis). In this method, flow field and bed deformation were calculated with a general coordinate system, which can be applied to a complicated shape of channel geometry like a natural river. The characteristics of the bed material are important factor for spawning bed of Ayu, and therefore the grain size distribution of the bed was also calculated with morphological model for non-uniform sediment. In addition, suitability of flow velocity, bed material, and depth for spawning environment of Ayu were modeled on the basis of experimental results and field investigations. The developed numerical method was applied to the analysis of the curved river where deposits of fine sediment exist on the bed. Four different regimes of high-rate flow were supposed to occur, and their impacts on spawning environment were predicted.

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AMPARU is a large tidal lagoon located on the west coast of Ishigaki Island, where a variety of small crabs range over. In these thirty years, however, accumulation of red clay from the watershed has been changing the topography and the hydraulic characteristics of the lagoon, and then changing the environments for the crabs to habitat there. This paper presents a result of a field survey that is the basic stage of a study to understand the special distribution of crabs in relation with the conditions of bed materials and hydraulic characteristics in the lagoon. First, spacial distribution of five kinds crabs and there burrows are clarified through photograph analysis and quadrat survey, and it is concluded that the burrow's distribution can be an effective information to estimate the distribution of three kinds of crabs who make burrows. And then, it is found that the habitat distribution of each kind of crab can be highly related to their living characteristics, such as territorial competition, burrow takeover, seasonal torpor and efficiency of nutrition as well as environmental conditions such as grain distribution of bed materials, organic matter content and submergence frequency.

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Nitrogenous fertilizer use of the world increased rapidly in the second half of 20th century. This change has been the main cause of human-induced disturbance of global nitrogen cycles. In this paper, we focus on river nitrate transport of the world. Much of river nitrate comes from soil layers of terrestrial areas. Thus, we first estimated nitrate leaching from soil layers using a terrestrial nitrogen cycle model using datasets of nitrogen fertilizer use, climate and soil conditions, and subsequently, simulated river nitrate transport. The terrestrial nitrogen cycle model consists of several flux calculations at daily time scale. A global river channel network data was used in the river nitrate transport simulation. These calculations were carried out using datasets of 1955, 1965, 1975, 1985 and 1995. The result of 1995 was compared with mean nitrate concentration data of several large rivers observed by GEMS/Water and agreed with it reasonably. The transported nitrate at river mouth was then aggregated to see its load to oceans. Finally, comparing each year result, significant impact of fertilizer increase was found.

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