Turbulence measurements in side-cavity open-channel flows with various open-mouth shapes were conducted., by making use of PIV and LDA. The water-surface fluctuations in the side cavity, at the junction and in the main channel were measured simultaneously by three sets of super-sonic wave gauges. In the case of no partition plate, a vortex which was generated by the shear instability moves in the downstream. The scale of its vortex increases in the downstream. In the case of narrow open mouth, a stable vortex is generated inside of the side cavity. In contrast, in the case of wide open mouth, when a high-momentum water bulge moves from the main channel into the side cavity, the water surface moves upward in the side cavity. This semi-periodical phenomena associate strongly with seiche motions.

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Turbulent structures in open-channel flows over a concave bed are analyzed by using a hybrid method that combines a proper orthogonal decomposition (POD) with a multiresolution approximation (MRA). The flows over a shallow concave and a deep one are measured by a particle image velocimetry. At first, the time-series of the velocities are clearly classified into three components by using the MRA, including the fluctuation component due to the organized turbulence in a mixing shear layer between the main-channel and the concave. Then, the POD of the organized turbulence component successfully extracts their characteristics, such as the predominant spatial structures and their temporal interactions, as well as the effect of the concave shape. These results strongly suggest that the present hybrid method is effectively available for detecting the spatiotemporal coherent structures in the flows.

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Numerical analysis has been performed for the developing turbulent flow in compound meandering open-channel flow by using algebraic Reynolds stress model. The turbulent flow in compound meandering channel is one of the complicated turbulent flows, because the flow behavior is influenced upon many kinds of forces that are centrifugal force, pressure driven force and shear stress generated between main channel and flood plain. In order to set precisely boundary condition along complicated configuration, the boundary fitted coordinate system has been introduced in this analysis so that transport equations are transformed from the physical plane to the calculation plane. As a result of this calculation, it has been found that the present method is able to predict well the mean velocity distribution and the developing pattern of secondary flow that is especially affected by the flow over the flood plain. As for the comparison with Reynolds stresses, although the agreement with the experimental data is not perfect quantitatively, the present method is able to reproduce the characteristic features.

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A mathematical model of the formation of submarine canyons due to turbidity currents is presented in this study. A linear stability analysis is performed with the use of the momentum equations of turbidity currents, the dispersion equation of suspended sediment, and the Exner equation extended for sea beds subject to erosion due to turbidity currents. The analysis shows that the dominant channel spacing is of the order of 1500-8000 times the Richardson-critical layer thickness of turbidity currents. Evaluating the Richardson-critical thickness is of the order of 0.1-1.0m, the spacing of young canyons is of the order of 150-8000m. The theoretical results are found to agree resonably well with the observation.

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Direct numerical simulation of a fully-developed open-channel flow has been carried out for a range of subcritical Froude numbers at a fixed friction-velocity Reynolds number of 180. The effects of the free-surface fluctuations on the quantities important in understanding and improving turbulence models have been studied. The amplitude of the free-surface fluctuation increases as the square of the Froude number. The free-surface fluctuation has no directionality and its scale is larger than the viscous scale. Statistical quantities involving the vertical velocity component are most influenced by the Froude number but only in the region close to the free surface. The pressure fluctuation is influenced over much wider region.

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The application of the existing weakly nonlinear theories of sand bars with the use of the growth rate expansion method, in which the growth rate of perturbations is taken as a small parameter for expansion, is limited to the vicinity of the minimum critical aspect ratio (width/depth); the theory is only applicable to the case of alternate bars. In this study, weakly nonlinear analysis with the use of the amplitude expansion method, in which the amplitude of perturbations is taken as a small parameter for expansion, is presented in order to extend theories to the case of multiple bars. It is shown that the reasonably good agreement between experimental and theoretical results of bar wavelength and height.

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This paper provides a theory that pressure rising due to water hammer can be damped if smaller elastic air tubes are put in a pressure pipeline where water-hammer-associated waves propagate. In theoretical development, taken as a variable with small fluctuations responding to pressure fluctuations, the behavior of the tube is included in a term “the velocity of pressure waves”. According to an air ratio in the sectional area of the pipeline, a maximum value of water-hammer pressure is obtained from this theory. The results are summarized in a general-purpose chart. And, in the analyses and experiments conducted on the condition that a term “the behavior of cushion in a closed air cushion surge chamber” is considered to have large amplitudes, it is found pressure can be damped enough even with a smaller amount of air. For future study on the damping of pressure associated with the tube, this paper proposes the necessity to determine the range in which a term “pressure wave velocity” and a term “cushion behavior” function synergistically.

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Some hydraulic structures collapse due to flow out of the back-filling sand behind a sea wall, under flood and stormy waves. This type of destruction caused by the cavity behind the sea wall is closely related to cyclic loading of water pressure acting on the sand surface around the structure. In order to get basic information to establish a prediction technique of flow out of the back-filling sand under cyclic water pressure variation, small-scale tests were carried out considering the characteristics of the cyclic loading and the sand bed. Furthermore, the stress state in the sand bed was analyzed by the numerical analysis using poro-elastic theory. Effect of various characteristic variables on fluidization was clarified experimentally and theoretically.

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Field observations of sea salt quantity transported by winter monsoon have been performed on a reclaimed land facing Japan Sea The landward transported sea-salt quantity and the deposit rate have been estimated quantitatively and their leeward profiles have been normalized by introducing the representative scales. Especially, the normalization gives us an empirical expression for the deposit rates by winter monsoon and Typhoon 9117. The transported sea-salt quantity decreases rapidly in the dimensionless distance less than 25 because of the settling of sea-salt particles. The representative scales induced for the normalization depend strongly on the mean wind velocity at the height of 10m. The empirical expression for the deposit rates and the quantification of the representative scale enable us to predict the settling flux of sea-salt at an arbitrary place in the coastal area.

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I proposed a new tsunami inversion method with a priori information that the distribution of solution is smooth. An unknown parameter of this inversion method is the water surface displacement on the sea, and the 2-D distribution of water surface displacement can be directly estimated by this method. To clear the error of estimation, the numerical experiments were executed, changing the conditions such as location and number of observation points, and observed time. As a result, it became clear that the error of estimation was strongly concerned with the resolution index of unknown parameters, which was introduced in this study.

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The seawater level change, wind and rainfall by the low atmospheric pressure or typhoon are the important extemal forces acting in a brackish lake. In order that they may take various transfer types, the influence on a brackish lake is not uniform Then, we classified the low atmospheric pressure and the typhoon according to the transfer course. And we clarified the relation between their transfer types and the flow in Lake Nakaumi. The following results were obtained; (1) On the transfer course, a low atmospheric pressure can classify into two types and a typhoon can classify into four types. The water level change by Type 2 typhoons is characteristic. (2) Since the water exchange accompanied by typhoon passage is greatly influenced by inflow of river water, the water environment changes suddenly by the Type2 typhoon with much precipitation. (3) The change in the density distribution is recovered in about one week On the other hand, since the turbidity distribution is biochemistry-influenced, its influence remains several weeks. (4) It is necessary to accurately evaluate water exchange ability that the low atmospheric pressure and typhoon have in order to grasp flow and water quality change of Lake Nakaumi.

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Phragmites australis stands along the down Stream of Ara River was investigated as NPO activities.
Although salinity level was from 0.0 to 6.8psu, there was no difference in physiology of P. australis between spots. The nitrogen content of P. australis in Ara River was relatively high compared with that of overseas stands. Characteristics of secondary shoots were different from that of primary shoots in the emergence period, diameters of stems and elongation patterns. In addition to studying the up to date information on P. australis, citizens successfully present the results in the academic conferences, and then new direction was shown.

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Seasonal and spatial changes in water quality in Lake Teganuma were investigated by using the field data and were simulated by a flow, water quality and sediment model. Chlorophyll-a and COD increased, and inorganic nitrogen, phosphate, total nitrogen and total phosphorus decreased toward downstream direction. Chlorophyll-a increased in summer and decreased in winter, and inorganic nitrogen and phosphate decreased in summer and increased in winter at the observation point of Nedo-shita. These observed variations of nutrients were practically reproduced in the simulation of the flow, water quality and sediment. Furthermore, according to the mass balance, 50 percent of total phosphorus in the inflow load was transported to downstream and the rest of 50 percent was accumulated to the bottom of the lake. Moreover, the results of the simulation suggested that 20 percent of total phosphorus in the inflow load is release from sediment.

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Field observation was performed at a neap tide to know characteristics of flow and transport of nutrients in a mangrove area which locates in Ishigaki Island, in which geographical features, vegetation, water qualities, characteristics of soils and flow were measured by using various devices. It was found that the concentrations of nutrients (PO4-P, DOC) in the groundwater of the swamps were 3-8 times larger than those in the main channel. The nutrient flux caused by groundwater flow was estimated by field measurements and numerical simulations. As a result, the amount of nutrients transported from the swamps to the main channel by the groundwater flow was the same order as the nutrient increases along the river flow, indicating that the flux of nutrient due to the groundwater flow played an important role in supplying nutrients at neap tide.

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