Theoretical one-dimensional method, estimating distribution discharge ratio is limited to apply to natural rivers because it is derived from condition with uniform flow in branch channels. Simple numerical model to understand flow characteristics and distribution discharge ratio of dividing flows has not been established even though it is important to understand the characteristics and distribution discharge ratio for flood control. In this paper, the explicit 2D-computed numerical model with square grid apply to compute flow pattern in experiment flume with bifurcation, the computed results agree with measured result of the flume. 2D shallow water model is applicable to dividing flows for obtaining flow characteristics and distribution discharge ratio.The results of numerical experiment with non-uniform flow condition indicates that downstream water level in the branch channels are related to the discharge ratio.

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The applicability of MPS method as an assessment tool for flow regimes in installing a current water wheel in an open channel as one of the development of micro-scale hydropower generation in irrigation systems, was examined. As a result, the simulated flow regimes agreed qualitatively with the experimental results at given rotational speeds of the water wheel. However, the simulated energy difference between upstream and downstream of the water wheel was about 20% larger than the experimental results at given rotational speeds in the case the length of water turbine runner was 0.1m. The main reasons were considered to be numerical pressure fluctuation known as a problem of original MPS method, and lack of phenomenal representation based on employing the 2D single-phase model.

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In this paper, a computational method has been developed with multiphase-modeling to predict the 3D natural convection in porous media consisting of multiple solid particles. In the present method, the fluid-cells, which are sufficiently finer than the solid particles, are set up in the computational domain. Furthermore, in addition to the mechanical interactions between the different phases, their thermal interactions are taken into account in the present multiphase modeling. The phase-averaged governing equations, including the energy equation to predict temperature distributions, are discretized with a finite volume method and the numerical solutions are based on an SMAC method. The basic heat conduction and convection problems were solved with the present method to confirm its validity. In addition, it was applied to the natural convection arising in porous media. Through the numerical experiments, its applicability was discussed.

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In consequence of the huge spatial scale, the computation load of Tsunami simulation tends to be too large to afford. In order to overcome this difficulty, a rapid numerical simulator was constructed by applying the GPGPU technology to solve the 2-dimensional shallow water equations. This simulator is based on an explicit finite volume scheme combined with unstructured triangular meshes. With the power of GPGPU, this simulator can be used to simulate large scale Tsunami movement. Furthermore, by using unstructured meshes, complex boundary could also be represented well. And, the Recursive Spectral Bisection (RSB) method was used to enable GPU computations. The simulation results for the run-up Tsunami in Tone River caused by Tohoku earthquake (2011) are verified and validated, and show that it is sufficiently accurate for real-world simulations.

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The Tsunami caused by the 2011 Tohoku-Pacific Ocean Earthquake wreaked enormous damage on coastal area. Numerical computation model which can simulate Tsunami propagation, run-up and inundation with high accuracy is required. In this paper, the two dimensional CRD (Contour-integration-based Residual Distribution) scheme which is numerical computation to simulate the flow with shock waves is applied for run up and inundation of the 2011 Tohoku-Pacific Ocean Earthquake Tsunami in the Ishinomaki city and the Kitakami River. This paper shows that CRD scheme can evaluate the propagation velocity and wave height of Tsunami in the sea, the river and the inundation area.

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In this paper, a 2-D numerical model for shallow-water flows using the Weighted Essentially Non-Oscillatory (WENO) scheme and the Finite Difference Method is developed. In the model, the Cartesian coordinate system is adopted, and the FAVOR method is introduced into the governing equations. The regular grid system is adopted as the computational grid. The model was applied to dam-break flows and to complex flows with hydraulic jump in order to verify the validity of the model. For the dam-break flows, the model was able to reproduce the theoretical solutions with high accuracy. Moreover, for the complex flows, the model was able to calculate the hydraulic jump without numerical oscillation and also the calculated water surface was in good agreement with the experimental results. Thus, it is shown that the presented model using the WENO scheme is very useful for the simulations of shallow-water flows.

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A numerical model for 2D free-surface flows over a drying and wetting topography is developed. The model is based on finite volume method using HLL (Harten, Lax and van Leer(1983)) and HLLC (Harten, Lax and van Leer and Contact (2004)) numerical flux, which were based on approximate Riemann solver, and the treatment of source term such as bed slope term were also incorporated. The model is verified against two experimental data of unsteady flow over wetting /drying topography. It shows that the model can reproduce the complex behavior of the flows with reasonable accuracy.

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A multi-level grid type turbulent shallow flow model combined with an equilibrium sediment transport model (KMR-MB: Kinematic Mesh Reconstruction for Movable Bed) is proposed. KMR method is a kind of multi-level grid model with dynamic refinement and combining grid cells to capture efficiently unsteady flow phenomena. Saito et al. (2012)1) have applied the KMR approach to open channel flows around a bridge pier and shown the advantage of the model. They used the maximum value of the strain and rotation parameters for the threshold for quad-tree and 3 x 3 type grid divisions. We have extended the model for computations of morphological phenomena in rivers by incorporating an equilibrium sediment transport model as well as a bed continuity equation, and employing new criteria for grid cell refinement. We employed an average curvature of the bed surface as the criteria for refinement and combining quad-tree type grid cells. The present model has been applied to simulate the alternative bar formations. The experimental result by Akahori et al (2011)2) was used for validation of the model. The comparison between numerical and experimental results showed that the present KMR-MB can simulate excellently the phenomena with less CPU time than the fixed grid computations.

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Contour-integration-based residual distribution, CRD scheme is one of numerical computational methods to simulate flows with shock waves. Authors have applied the CRD scheme to the open channel flow, and shown validity as compared with the experiment-with-a-model result or the theoretical value. However, for applying to various flows, the boundary condition of dry-wet is required. In the paper, when the CRD scheme is applied to a steep gradient river, the boundary condition of dry-wet is shown paying attention to a discharge error. And the shock capturing method of two dimensional calculation for raising applicability the CRD scheme is shown.

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In this paper a smoothed particle hydrodynamics (SPH) numerical model for 1-D shallow water equations is presented for evaluating effectiveness of various SPH modification techniques and their combinations: artificial viscosity, symmetrization and correction methods of consistency condition error. Though it is known that the original SPH method has serious instability problem and poor accuracy without those techniques, there are quite few studies about quantitative error and effectiveness analysis of those techniques. We evaluate them through numerical examples of wave propagation. The result shows that at least the combination of artificial viscosity and a consistency correction method is required for the accuracy equivalent to the finite difference method.

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Energy loss at manholes under surcharged conditions is as important as the friction loss in pipes in the design of storm sewer networks and in flood-analysis. Some researchers have already proposed the formula to calculate the energy loss at three-way manhole under surcharged conditions. However, in most of these proposed formulas all variables of structural elements for the pipes and the manhole have not been considered enough yet. Therefore, development of the formula to exactly calculate the energy loss at three-way manhole is needed. In this study, the effect of diameter ratios between inflow pipes and an outflow pipe, the ratios of flow rates between inflow pipes and connected angles among those pipes on the energy loss at three-way manholes were investigated and a new formula was proposed for the energy loss coefficients at three-way manholes that considers all structural elements and hydraulic parameters except drop gap between inflow pipes and an outflow pipe.

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To analyze urban stormwater runoff in storm sewer systems, three runoff models, which are InfoWorks model, MOUSE model and XP-SWMM model, have been widely used. In the three models, SLOT model that has a fictious slot in the pipe crown and analyze a pressurized flow as an open-channel flow, are employed to analyze surcharged flow with flooding from manholes. In the analysis, the slot width and the pressure wave celerity are needed and the large differences in simulated results (stage hydrographs and inundated volume hydrographs) have been introduced by the difference of the values of pressure wave celerity and slot width. Nevertheless, the evaluation equation has not been suggested. In this paper, basic flow equations of the pressurized flow are derived considering the storage of runoff water in lateral pipes, and through the derivation the evaluation equation of pressure wave celerity and slot width is suggested.

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Generally, pumped-storage hydropower plants with constant speed type can change generating power in order to maintain the frequency of electricity grid, provided that turbine mode is selected. However, the existing pumped storage plant with this type can control the power evacuated to the grid even in the pumping mode just by adopting simultaneous operation. In the operation, some units are in turbine mode and others in pumping mode. In this paper, hydraulic problems, which were not considered in the design stage, in the simultaneous operation of the existing pumped storage hydropower plant, such as surging,water hammer pressure and head loss at the branch are examined. It is confirmed that these problems wouldn't affect the possibility of the simultaneous operation.

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After the high-growth era started from the 1960`s, most of the small and medium-sized urban rivers in Japan were reconstructed with concrete walls on all sides. Despite the significant improvement for flood protection purposes, such river reconstruction resulted in incuriosity or indifference among people because the flow feature lost its variety due to simple and monochrome river works. In light of the present poor urban river status, this study aims at improving the stream landscape by installing small-sized structures into originally monotonous flow. We propose two types of stream landscape structures, i.e. a double arch type structure and submerged island type structures. The first type generates an oscillating hydraulic jump artificially between two low weirs. The second type produces large scale Karman vortices in shallow water depth conditions. The hydraulic features of each type are examined in detail experimentally by using a flume specifically designed for the present purposes

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Many houses were broken and washed out by the supercritical tsunami flow overflowed from river embankment. Under the supercritical flow, drag force characteristics of dense obstacles and bed shear stress around them have not been clarified. Therefore, the objective of this study is to find out the effect of spacing of neighboring obstacles on the drag characteristics of quadratic prisms (house model) and bed shear stress distribution around them. Drag force acting on the house model and bed shear stress were measured by force gauge and shearing strain sensor, respectively. Four cases for different overflow depth and three cases for different G/bh (where, G and bh is horizontal spacing of each house model and width of a house model, respectively) were conducted. Drag force acting on the house model and bed shear stress between two house models (tm) increased with narrowing G. When G/bh=0.4, drag force and tm became 1.6 and 1.4 times comparing with single house model, respectively. However, when G/bh=1.2, drag force and shear stress became almost the same with single house case.

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A drag coefficient, lift coefficient and equivalent roughness are crucial factors for designing revetment and bed protection blocks of rivers. The drag coefficient and lift coefficient to specify the hydrodynamic forces acting on the blocks have been investigated for various types of concrete blocks mainly in sub-critical flow conditions. Although super-critical flow can be seen in steep slope rivers and downstream of weirs, authorized values for those coefficients have not been established in such flow condition. The coefficients measured in sub-critical flow are therefore applied in designing structures at present condition. In this study, the hydrodynamic force acting on concrete blocks and connected stones in super-critical flow conditions was experimentally investigated. Experimental results showed that the drag and lift coefficients for single setting in super-critical condition were a little bit larger than those for sub-critical condition and those coefficients for group setting were identical to the sub-critical condition.

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Frazil particle distribution in ice-covered rivers is not well understood. In this paper, we carried out field observation in northern Hokkaido. In this result, shape of frazil particle distribution is sharper than normal distribution. and it is inclined to left side than normal distribution. Frazil particle size has two peaks, namely, high frequency size (0.46mm) and average size (2.45mm). Relationship between frazil transport capacity and dimensionless flow strength was investigated in an ice-covered river in Japan. Much frazil capacity has transported, because frazil particle size is small compared with previous research. Relationship between frazil particle size and 2nd power of shear velocity was examined. As the result, we considered transportation of frazil particle is smaller than transportation of soil particle.

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Data acquisition of river flow information especially at a peak flow condition is indispensable for a proper management of a river basin. However, due to the difficulty to conduct a float method appropriately in an extremely fast flow, non-contact methods such as imaging techniques or radio wave velocity meters have become good candidates as alternative methods. Among them, imaging techniques used to have a weak point difficult to apply during the night, but we could overcome this problem by using a far infrared camera in the present research. The field measurements conducted at the Uono River yielded consistent results with radio wave velocity meters even in a dark condition. In addition, traceability of surface features composed of small wavy patterns to the surface flow was verified in a straightforward manner by comparing a space time image (STI) generated while applying the STI velocimetry (STIV) to the surface flow images.

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This paper deals with the results of field observation on the body change of Tri-Pyra groynes after floods and its consideration. Nine groynes which were made only by stone and gravel were constructed at the gravel and stone bed channel of the Kinu River. The length and the height of the groyne are about 10m and 2m respectively. Soon after the construction, floods occurred 4 times in 2 years. Field investigation and 2D flow calculation lead to the conclusions that the local erosion around the groyne during the floods was negligible and that the deformation occurs according to the coming off phenomena of surface stones of 20cm in diameter at high flow velocity larger than 3m/s. This information is considered to contribute to practical application.

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This paper describes the flow resistance (or bed roughness) due to lush vegetation in the Asahi River during the flood event which occurred in September 2011. First, we investigated the vegetation condition based on the field observations in the floodplain of the river, and simply classified a variety of flourishing vegetation into three categories by using previous reports and handbooks. Secondly, the distributed Manning’s roughness coefficients in the floodplain were inversely estimated by using a data assimilation approach with the water level data gained longitudinally during the flood. The results showed that the roughness is closely related with the category or type of dominant vegetation in the floodplain, and is likely to decrease slightly during the flood because the vegetation is bent, broken and washed-out.

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After the Dainichigawa dam construction gravel supply to downstream from the dam site decreased in the Tedori River. As a result, river bed degradation progressed and gravel bed area gradually decreased. Furthermore, exposure of soft rock remarkably progressed around 14km to 15km from the river mouth. The exposure of soft rock not only endangers hydraulic structures but also deteriorates river environment. Therefore, gravel bed restoration works using groin group composed of connected stones were carried out. After the groins installation, parts of the groin were deformed during the flood in 2011. This paper aims to clarify the deformation mechanism of them using two-dimensional flow analysis. Numerical results showed that the hydrodynamic force acting on the groin caused by high velocity surpassing its design transformed the parts of the groin.

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The forestation in rivers causes several problems, because it reduces river flow capacity, and the forestation by invasive spices sometimes affects endemic species and the biodiversity in a river habitat. The wash-out of vegetation during a flood is known to be a reasonable measure for preventing the forestation. However, the relationship among the wash-out condition, a river discharge and a bed deformation has not been clarified yet. This paper investigates the vegetation growth rate and the wash-out condition of vegetation during the flood at Ohara area in the Asahi River, based on the field observations and the numerical simulations. The observation results showed that the large discharge during the flood induced the bed deformation and the wash-out of vegetation, and the simulated results indicated that the non-dimensional bed shear stress of can evaluate the washed-out condition more suitably.

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Although water elevation is generally assumed to be uniform in the lateral direction, there has been little information on measured results for lateral variations of water elevation in rivers under floods. In the present study, we performed water elevation measurements at several cross-sections of the Edogawa River. Results showed that the differences of water elevation between the main channel and the floodplain that occurred during flooding were mainly due to a small mound that was formed between the main channel and the floodplain that prevented any water exchange between the two. The influence of lateral variations of water elevation on the evaluation of roughness parameters and river discharge was examined.

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Various velocimetric tools like ADCP, image-processing technique, radio current meter and electro-magnetic sensor were used to conduct simultaneous measurement of river discharge in Uono River. The comparison of measurement accuracy of the above tools was conducted by using two unified interpolation and extrapolation techniques of point-velocities like DIEX (Dynamic Interpolation and EXtrapolation) method and a previous method. The results indicated that 1) the surface velocity measured by the above velocimetric tools gave good agreements with the ADCP data, 2) the relative errors of discharge in the previous method was large due to the treatment of lateral velocity profile near banks and float coefficients, and 3) the relative errors of discharge in the DIEX method may remain low even with a few measured velocities.

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The authors of this paper have established an automatic water-discharge measurement system with a fixed type Non-Contact Current Meter (NCCM), especially Radio wave type. In the system, following three points must be discussed; 1) measurement of a representative flow velocity with the NCCM, 2) estimation of a velocity index, as well as 3) measurement of a river-bed fluctuation. In this paper, the authors mainly focused on the first point including the characteristics of water surface velocity, which were affected by wind and river-bed vibration. The water surface velocity obtained by NCCM indicates appropriate fluctuation cooperated with river-bed fluctuation. Comparing with ADCP measurement, the water surface exposed by the strong wind under-measured by NCCM which is needs to be corrected. The authors show the characteristics of those phenomena and introduce the wind-correction equation.

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In this paper, the authors conducted the simultaneous observation of flood flow and moving bed velocity by using tethered boat equipped with ADCP and the Real Time Kinematic Global Positioning System (RTK-GPS) in Shimanto River during medium flooding. With this measurement system, moving bed velocity at each position was estimated with subtracting moving velocity vector of the boat estimated by RTK-GPS from velocities obtained by ADCP bottom trucking function. As the results of transverse observation with discharge of 3000m3/s, cross-sectional profiles of flow and moving bed velocity were obtained. Moreover, we examined measurement technique of the Acoustic Backscatter Turbidity (ABT) with ADCP.

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A method of aerial photo analysis of flood flow presented by Minoura et al. was improved and applied to a flow through the confluence of the Tone River and the Watarase River where the angle between the low water channel is 40 degrees. The proposed method is composed by two parts; image correlation analysis by a computer and manual correction by stereo visualization. In the first part, result from conventional correlation analysis was rearranged by inspection through a stereoscope. In the second part, a routine for stereo image rotation was introduced to increase accuracy of analysis for streamlines having a large angle to the flight direction. The flow characteristics at the confluence were discussed based on the results obtained from the analysis.

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To evaluate the detachment process of attached algae in rivers, a series of flume experiments were carried out. Time-series analysis of NDVI (Normalized Difference Vegetation Index) image of cobbles covered by attached algae was conducted to estimate the change in Chl-a or the decrease in attached algae density. A new method to convert NDVI to Chl-a was developed to measure the attached algae density on cobbles in a nondestructive and continuous way. Quantitative analysis of the detached rate of attached algae has shown that the detachment ratio can be closely correlated with the work done by sediment impinging on the cobbles.

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For comprehensive managements for marine debris including inland area which is known to be a source of marine debris, it is necessary to monitor the behavior of floating-litter in rivers and coasts. In the present study, we presented an automatic and continuous monitoring technique for floating-litter transport L in rivers by using a video image monitoring and a new image processing technique. In this technique, image pixels of floating-litter are detected using spatial gradient of image colors P’ larger than a threshold value P’ th which is related to image colors in pixels of no floating-litter. The results indicated that L evaluated by the technique gave good agreement with the observed data in several floods in the Edogawa River, demonstrating the fundamental performance of the present technique.

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A new 3D numerical flow model named as TITech-WARM is developed. The model is specialized to calculate the water flow in water reservoirs. To restore spatial structure of water temperature precisely, the model is developed based on the CIP-Soroban method. While the CIP scheme is employed as an advection solver to avoid numerical diffusion error, a new adoptive mesh system 'Soroban mesh' is adopted. To estimate a time development of water temperature, heat exchanges between water surface and atmosphere are modeled with the Swinbank and Rohwer equations. Furthermore, to take account of aeration processes utilized in many reservoirs, the model is combined with a vertical 1D double plume model. The developed model is applied to the Kamafusa water reservoir. Through comparisons with field observational data of water temperature and flow, it has been found that the model has the capability to restore the flow structure well.

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Wind wave energy balance equation has a capability to predict time development of a spatial distribution of wind wave induced by strong wind fields. While it has been expected that the equation is suitable for the wind wave estimations in the lakes because the equation can take account of topographic effects caused by spatial changes of the lake's depth and shoreline, huge computational cost is obstructing the utilization of numerical simulations of the equation in daily wind wave predictions. In this work, to overcome the difficulty, GPGPU technology was applied and its efficiency of acceleration of numerical solutions was investigated. By using decoupled model as a source term of wind wave generation, efficient acceleration was realized. The developed GPGPU solver was applied to Kasumigaura Lake. The simulation results for the Typhoon show that the solver can provide highly rapid solutions.

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Lower Shinano River is known as a typical low-lying river in Japan. This area was suffered from serious damages by inundation by the 2011 flood. Therefore it is important to clarify the hydraulic phenomena and the characteristics in the flood in order to establish the flood control plan.This study aims to analysis the flood flow in the river branches in lower Shinano River by the quasi-three dimensional numerical method using observed water surface profiles during 2011 flood. We could evaluate the flood discharge hydrograph and floodwater storage and elucidate the complicated mechanism of flood flow in the river branch in lower Shinano River.

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The Tanaka, Sugo, Inadoi retarding basins which are located along the Tone River have an important role on flood control in the lower Tone river. The lower Tone River has some flood control problems such as flood discharge capacity of the river. In this paper, we developed the unsteady two-dimensional analysis of flood flows using the time series data of observed water surface profiles in the Tone River including the three retarding basins. The calculation model provides a good explanation for flood storage volume in the three retarding basins of 2001 and 2007 floods. Some remarks are given to calculate correct hydrographs of flood storage volume in retarding basins.

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The Kanda River flows through densely urbanized area. Therefore, the Kanda River basin has large-scale sewerage systems and many flood-control reservoirs along the river. The inflow discharge hydrograph from sewerage into river influences flood hydrograph of the Kanda River, but its volume is unknown. So, estimating the inflow discharge hydrograph from sewerage into the Kanda River is important for river managements. We applied the two-dimensional analysis of flood flow using time series of observed surface profiles in Kanda River. As a result, the calculation method provides good results for evaluation of inflow discharge hydrograph from sewerage. It is found that the discharge ratio of main stream to sewerage discharge is 5:2 at the confluence of Jyuniso trunk line and 3:2 at the confluence of Momozonogawa trunk line.

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In this study, the quasi-3D model composed of depth-integral vortex equation and shallow water equations was extended on the basis of finite volume method employing non-orthogonal grids for properly evaluating complex boundary of the confluences. And, we developed the flux integral method considering non-orthogonal direction of grid line based on the CIP-CSL scheme for evaluating the convection terms more accurately also in the complex flow field of the confluence. The extended quasi-3D model was applied to recent large floods at the Go River confluences to investigate the flood flow and bed variation during the flood events. From the calculation results, we clarified that separation zones formed at the confluences have pronounced effects on the three dimensional flow structure and bed variations for the downstream channel.

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Nitrogen purification function of paddy is attracting much attention against eutrophication of rivers and lakes. This study investigated the nutrient purification function of paddy by field tests and analysis of 1D, 2D.1D nitrogen removal equation was derived from the law of conservation and compared to field tests. The results obtained are very much in agreement with the field tests. Then, Nitrogen purification function and flow in the paddy was examined by plane two-dimensional analysis. As a result, nitrogen purification function was improved on condition which prepared waterway in the paddy. However, the nitrogen purification function was decreased on condition that flow becomes fast near the outlet.

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Turbulence plays an important role for feeding process of planktonic organisms in aquatic environments. Small scale turbulence benefits the predator by increasing its encounter rate with prey, but makes the predator more difficult to capture the prey by reducing the time available for it. In the present study, planktonic predator-prey interactions in homogeneous isotropic turbulence are studied by a series of numerical experiments, and the effects on the capture rate of turbulence, range of predator's detection of prey, minimum pursuit time (in which the predator identify, approach, and attack the prey), and predator's motility are closely investigated. The results clearly show that there exists indeed an optimum level of relative motion between predator and prey maximizing the capture rate and that the level depends on the turbulence level and the behavioral characteristics of the predator. We also discuss the characteristics of the capture probability (the ratio of capture to encounter rates) and the contact time (the time over which a predator and its prey stay in contact), which are fundamental parameters required in understanding and modeling the planktonic feeding process.

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Behavior of multi-port submerged buoyant jet is very complicated especially in ascending region to surface. Mixing and dilution process is 3-dimensional, which makes us to use hydraulic model experiment and accompanying 2-dimensional simulation with virtual outlet to predict the dispersion area of warm water discharged from power plant. According to the development of super computer, a 3-dimentional turbulent closure model has been applied to simulate the initial mixing of discharged buoyant jet and following dispersion at surface in a coastal ocean, simultaneously. However, it still needs long computational time and a large computer resource. A simple 2-dimensional model using virtual outlet is proposed to approximately simulate the dispersion of submerged buoyant jet in surface layer, where virtual outlet can be easily decided without hydraulic experiment or 3-dimentional simulation.

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We numerically studied saline intrusion and the related river flows in the Abashiri River Estuary that connects the Ohotsuku Sea and the Lake Abashiri in northeast Hokkaido. A three-dimensional object-oriented hydrodynamic model, Fantom3D, was used to investigate the stratified flow dynamics in this estuary. In the computation, the estuary was decomposed into 15 domain objects having different sizes to properly express the narrow and highly bending river channel. The one-way nesting technique was also used to resolve depth-scale eddies in the channel. The computed results were compared to observed data obtained in Sept 2006. The water level, velocity and salinity measured at four locations along the estuary were in reasonable agreement with the computed results. The secondary flow at a bending section and the variation of mixing type along the river were also discussed using the computed results. We showed that these computed results are qualitatively agreed well with the previous investigations.

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Dynamic numerical simulation of water condition is useful for reservoir management. In developing countries, however, meteorological and hydrological time-series required for the numerical simulation are often unavailable. This paper presents a case study for generation of data absent at the Joumine Reservoir, Tunisia. Data of Wind Finder on web site and daily sunshine duration at the nearest weather stations were utilized for data generation of cloud cover and solar radiation being based on meteorological correlations found in Japan which is located in the same latitude as Tunisia. Time series of inflow water temperature was estimated from air temperature using a numerical filter expressed by a linear second-order differential equation. Numerical simulation by a vertical 2D turbulent flow model for stratified water body with the generated data successfully reproduced the seasonal thermal condition in the reservoir obtained with a thermistor chain for eight months in 2009.

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Field investigations were conducted on 22 November 2011during rainy season and 16 March 2012 during dry season to estimate the present state of density stratification of Koggala Lagoon, Sri Lanka. The variation of salinity, water temperature and dissolved oxygen were measured vertically at the neap tide condition. Koggala lagoon exhibits an entirely different mixing state depending on the season. In rainy season, lagoon water was brackish and in weak mixing state. On the other hand, in dry season, water in both the lagoon mouth and inside the lagoon exhibit the state of strong mixing and high salinity. In both seasons, high temperature, high salinity and, low dissolved oxygen at the deep layer of water were found in the central part of the lagoon. The salinity level at the bottom was higher than the estimated level based on water budget analysis.

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Momentum transfer of open channel flows in the lateral direction is important in sediment transport, environment in rivers, etc. Three-dimensional (3D) computations of shallow open channel flows on two parallel lanes of bed with different roughness parameters are presented in this paper. Lateral transfer of streamwise momentum is caused by three different effects, i.e., a cross-sectional secondary current due to turbulence anisotropy (secondary current of the second kind), a turbulence mixing with shear instability and a mass transfer from the rough-bottomed lane to the smooth-bottomed lane due to flow redistribution. Vermaas et al (2011)1) have shown experimentally that the rate of contribution of each mechanism to momentum transfer is closely affected by depth. We tried to simulate the momentum transfer on the roughness transition using three dimensional computational models with a URANS type k- turbulence model. The present numerical results showed that the computational model with a second order non-linear k- model could estimate excellently the each effect on the momentum transfer depending on a flow depth.

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Three dimensional open-channel turbulent flows with rough wall beds composed of randomly distributed gravel particles were simulated by using a large eddy simulation model for a relatively shallow water condition. The bathymetry of an actual rough bed was measured by a photogrammetric method and the digital data thus obtained was directly introduced into the LES. An immersed boundary method was incorporated to the model for reproducing such an arbitrary boundary condition. Experimental examinations were also conducted to evaluate the simulation. It was made clear that the correlation between water surface fluctuation and velocity fields become higher for larger Froude number. The effect of gravel size on the turbulent scale was revealed by comparing integral scale in different direction. In addition, a new method to visualize volume of fluids passing through a horizontal plane was devised to investigate large scale turbulence structures that interact with water surface.

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Quasi-3D model and SDS (sub-depth scale) turbulence model are combined to simulate the horizontal shear layer development along the interface of bank vegetation. Turbulence productions caused by bottom friction and vegetation drag are formulated based on previous experiments on turbulence intensity in flows in an open channel and through model vegetation (cylinder arrays). Computations are made for two flow conditions of flume experiment with vegetation model published in literatures. Good agreements are obtained for transverse and streamwise velocity profiles in the developing shear layer containing horizontal coherent vortices. The characteristics of turbulence components are also predicted well. Furthermore, simulation results suggest that strong SDS turbulence is generated near vegetation boundary and transported to vegetation zone and main channel by horizontal coherent vortices.

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A flood protection forest is highlighted as one of conventional river-management methods, which fits reasonably into natural environment. This study focuses on one-line tree models laterally placed in open-channel flows, and we conducted horizontal PIV and drag force measurements to examine a reduction efficiency of a mean kinetic energy due to the tree members. A flow structure is closely related to a wake phenomena for sparse alignment of the trees, and in contrast, it is similar to a jet for dense one. It was found that the drag force is formed being relevant to the separation zone behind the trees, and a semi-theoretical formula which can predict reasonably the energy reduction efficiency was developed in the present paper.

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In many natural rivers, aquatic vegetation occurs in patches of finite length. In such vegetated flows, the shear layer has not formed at the upstream edge of the vegetation patch and coherent motions develop downstream. The longitudinal advection of these coherent vortices contributes significantly to mass and momentum transport. However, there is almost no detailed information about the developing process of large-scale coherent structure within the vegetation patch. So, in this study, we consider the effect of the limited length vegetation patch. Flow images were taken by CCD and the instantaneous velocity vectors are analyzed by PIV techniques. The results showed that (i) the 3-D diverging flow occurs at the vegetation patch edge and (ii) as the coherent structures develop downstream in nonwake zone, the rate of the vertical momentum transport by Sweep motions becomes larger.

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The present paper is concerned with large scale vortices developing along the interface between main flow and vegetated zone in a prismatic open channel. Two types of flume experiment and LES are carried out to clarify the evolution of large vortices and to discuss the vegetation modeling. In one experiment a continuous vegetation belt stands along the centerline of the channel whereas in the other experiment patched vegetation zones are installed along the channel centerline. Flow visualization is followed by measurement of water levels and three velocity components. It is demonstrated that a row of large vortices is produced along the edge of the vegetation belt and that the large vortices survive over the gap region between the vegetation zones with active lateral mixing. LES employing the concept of vegetation density shows that it can reasonably reproduce the flow field in the vegetation zones and that further refinement is necessary for the better prediction of the flow downstream of the patched vegetation zones.

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This paper describes the derivation of a simple-depth averaged flow model including the deformation of velocity distribution to reproduce the water surface profile of a hydraulic jump. The obtained model results are also discussed in comparison with the previous experimental results. Initially, the fundamental form of the streamwise velocity in a power series of depth is used and the coefficients of each term are considered to be dependent on a spatial coordinate. The relations between the coefficients are later derived using 2-D continuity and momentum equations. These relations are successively utilized into the depth-averaged continuity and momentum equations to obtain the set of equations for water surface profile analysis. The comparisons of analytical results with the previous experimental results indicate reasonable agreement. However, further improvement in the model is required.

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In this study, gas transfer velocity through free surface is investigated in open channel flow with a series of spur dikes. Spur dikes formed closed dead-water zones between the neighboring members. The slow-speed circulation observed in such cavity zones is quite different from high-speed mainstream. Therefore, the cavity zones and the mainstream are assumed to have different reaeration coefficient. The reaeration coefficients are evaluated by means of laboratory measurements. The measurement theory is also specially developed together with consideration of gas transfer through the junction between main-channel / side-cavity. It is found out from present results that reaeration coefficient depends strongly on the aspect ratio (width/length) of dead water zones under same hydraulic condition.

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Since groynes are often used for various purposes recently, it is still important to repress local scour around groynes in river management. In this study, a training dike placed in front of groyne is employed as a scour-repression method and the effects of length and location interval were investigated experimentally. The maximum scour depth and scour volume are decreased by putting the training dike. The scour repression rate is increased as the location interval increases. The training dike weakens the deflecting flow at the edge of groyne, and generates the transverse vortex behind it. These two factors affect the scour mechanism around groyne including horse-shoe vortex. In the case of narrow interval, transverse vortex becomes strong, but the deflecting flow becomes weak. In the case of wide interval, the deflecting flow becomes larger again, but horse-shoe vortex in front of the groyne becomes weaker. As a result, local scour is repressed reasonably with an increase of location interval in the range of the present experimental condition.

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