In this paper, we try to simulate a bed-deformation using numerical computation. For calculation of sand particles, we employed Distinct Element Method called DEM. This scheme calculates the sand particle collisions by mechanical elements, such as springs, dashpots, and sliders. DEM enable us to calculate multi-particle collision. For flow calculation, the Unsteady Reynolds Averaged Navier Stokes model called URANS model was employed. In this model, we selected 2nd ordered non-liner k-e model for turbulence scheme. To coupling between the particle calculation and flow calculation, we apply the relationship between the saltation layer and the Shields stress which proposed by M. Colombini and A. Stocchino. In our previous results, we cannot simulate dune characteristic, such as sand wave movement, wave length, and wave height which correspond particular fluid condition. From this point, this paper proposes a new scheme which evaluate saltation layer with Shields layer. We conduct a numerical computation follow a well-studied fluid condition, and evaluate its effect on the bed-formations.

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We have made topographical map and analyzed distribution pattern of tidal flats in riverine estuaries of 16 rivers. Making use of the topographic map and other information, we selected the part of straight channel of 16 rivers and classified those into three areas from a viewpoint of the morphology of sand bar, that is, alternating sand bar, double mode bar, or no sand bar. Furthermore, we have calculated various physical parameter values which can affect the topography of river channel assuming the event of mean annual maximum water discharge and analyzed relationship between morphology of sand bar and those values. In the result, we showed the morphology of sand bar has strong relationships with river channel width/depth ratio at mean annual maximum water discharge but the border line between alternating sand bar and double mode bar is more vague than that in upper alluvium river channel.

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Elucidation of sloshing phenomenon is very important to reduce the damage of the tank in an engineering field. In this paper, a simulation of the tank sloshing using three-dimensional particle method is introduced. The accuracy validation of the sloshing of a rectangular tank is done through comparison with the results from the experiment and finite element method. In the simulation of a cylindrical tank, the water surface deformed corresponding to the natural period. In addition, swirl phenomenon was confirmed under the condition of vibrating the tank for a long time. These results show that the MPS method can apply to the three dimensional tank sloshing.

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This paper deals with a computational method with multiphase-modeling to predict the 3D free- surface flows through porous media consisting of multiple solid particles like the ground water flows in coarse gravel. In contrast to most of the previous methods, in the present method, the fluid-cells, which are sufficiently finer than the solid particles, are set up in the computational domain and the fluid-solid interactions are accurately calculated by a multiphase-modeling method that needs no empirical parameters such as the drag coefficient Cd. In addition, a parallel computational method is implemented on the basis of the 3D domain decomposition method using MPI. The predicted results are compared with experimental values and further applicability of our method is examined through the numerical experiments for the porous media consisting of randomly-arranged spheroids.

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Local scours around river structures during flood are affected not only by local 3D flow around structures but also by the larger scale phenomena of flood flow and bed variations. To compute local scouring around structure with computing large scale phenomena, we have developed the bottom velocity computation method, in which depth-averaged horizontal vorticity and water surface velocity equations are computed with shallow water equations to evaluate vertical velocity distribution. However, the assumption of shallow water conditions confines the applicability to relatively large scale phenomena. This paper presents applicable range and limit of 2D, 3D and quasi-3D numerical model by shallowness, which is defined as the ratio of representative water depth to representative horizontal scale. Then, we develop the general bottom velocity computation method without the shallow water assumption and apply to flow field around a cylinder on flat rough bed.

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Stream flows with steep gradient bed form complicating flow configurations, where super-critical and sub-critical flows co-exist. Computing numerically such flows are the key to successful river management. Contour-integral-based residual distribution, CRD, schemes are one of the numerical computation to simulate the flow with shock waves. In the last fiscal year, the Authors applied the CRD schemes to one dimension and two dimensions of the open channel flow, and showed validity as compared with the experiment-with-a-model result or the theoretical value. However, in the paper, application has not carried out the CRD schemes to a natural river. In this paper, the CRD schemes are applied for the Toyohira River of a steep slope municipal river, and the applicability in a natural river is shown.

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The immersed boundary method (IBM) that has been populously used to represent non-slip conditions of velocity on complex and moving boundaries using rectangular coordinates has been extended to flow quantities other than the velocity with hon-homogeneous boundary conditions including Neumman-type conditions. The method is applied to compute velocity, thermal and scalar fields in non-isothermal flows. The method has been tested in the calculation of buoyant wall jets impinging on isothermal or adiabatic bodies. The calculation is first conducted in the case where the boundary position coincides with the computational grid points. The results are good and the method is found to be applicable to various practical problems.

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A numerical simulation method that can calculate open-channel flows in which the free surface partially or temporary overtops large obstacles on the bed has been constructed. The method can either be used as a direct numerical simulation or large eddy simulation (LES) with appropriate sub-grid models. The LES version has been verified in calculation of flow in collapsing water column and applied to an open-channel flow with an array of hemispherical objects on the otherwise smooth and flat bed. The details of the flow and the forces on the obstacles have been analyzed by the proposed method. The results show good results revealing the effects of the flow depth and the Froude number on the complex turbulent flow. It can be applied to simulating flows in real rivers with large rocks and boulders.

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The study proposes a simple wetting and drying scheme for analyzing environmental fluid flows using a fixed grid on z-coordinate. The wetting and drying process is especially important in the low-lying coastal areas with large amplitude tides and reservoirs with severe flooding and discharging because it drastically changes the horizontal extent of the water body. The basic idea of the present scheme is a partial-cell (cut-cell) representation of the structured grid based on a finite-volume method to reconstruct the computational domain in response to a surface evolution. The scheme was implemented to an object-oriented numerical model, Fantom3D, and tested against analytical solutions and applied to field scale phenomena. The computed results agree reasonably well with the analytical solutions. We showed that the proposed scheme is a useful technique to compute the flow in partially dry domain for the hydrodynamic models using z-coordinate.

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This paper describes the topographical changes of sand-bar and the destruction of herbaceous vegetation on the sand-bar in the Kita River. The sand-bar in the Kawasaka district was excavated with vegetation in 2001 through the special emergency project after the sever disaster due to flooding by Typhoon No.19 in 1997. A flood on Oct. 2004 destroyed again almost all vegetation in a recovery process on the sand-bar. Nowadays, herbaceous vegetation is restored over all the sand-bar because of no flooding since 2008.In the paper, the destruction of herbaceous vegetation by the topographical changes of sand-bar was simulated through the 2-D analysis of the riverbed evolution. It was considered from the simulation that almost all vegetation will be destroyed by the flood over the maximum discharge of 4,000m3/s. Moreover, it was found that vegetation will not be destroyed but grow thick by the flood under the maximum discharge of 2,000m3/s.

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This study proposes the methodology on an inverse estimation of a flood discharge hydrograph in open-channels with flood plains. The hydrograph is iteratively identified by an adjoint shallow-water model with the hydraulic observation data. The proposed method was applied to the flood flow in a 20km-long lower reach of the Tone River, which occurred in mid-September, 1998. The verification data is the flow field which is obtained by analyzing the aerial photos taken during the flood. The assimilated data consists of the time-series of the water level gained at observation stations within the domain. The results showed that the observed hydrograph is improved reasonably by the proposed method.

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It is important to reinforce the toe of levee back slope against failure by overtopping flow due to a flood exceeding the designed level. In order to control the running water from the back slope and to remove the inflowing water without delay, we proposed the toe protection works consisting of two units of drain ditch. In this study, the flow velocity, the pressure on ditches and the characteristics of flood flow have been investigated on the proposed toe protection works by using two model levees. As a result, it was proved that the high speed flow dives into the first unit of ditch downward in the case of the ditch with a projection. It was also recognized that the pressure on the top of ditches bocame more lower in its case. It was understood that the maximum water stage is restrained more lower in the case of the ditch with holes. Such the effect was attributed to the dispersion of the flow.

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Experimental results of characteristics of flow resistance and boundary shear stress distribution along the wetted perimeter of rectangular cross-sectional channels are reported in order to discuss sidewall roughness effects on them. In the experiments, square cross-sectional acrylic bars are employed as artificial strip roughness elements. Three types of arrangement of roughness elements are examined, that is, on the channel bed, the side wall and both of them. Varying vertical slope and discharge, flow resistances are measured. In some selected runs, cross-sectional velocity distributions are measured and shear stresses on the boundary are determined by methods based on the logarithmic velocity law because the velocity profiles fit the law near the boundary. It has been found that effects of roughness elements on the sidewalls are restricted near them affecting slightly total flow resistance even in case with steep slopes and that shear distributions have very high non-uniformity suggesting influences of secondary flows.

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In open-channel turbulent flows with a rough wall, water surface profiles can be affected by the relative size of roughness element to a water depth and arrangement of roughness elements. In order to find characteristics of water surface profiles under various hydraulic conditions, an experimental study by using a simple surface flow visualization technique and a numerical study based on a large eddy simulation model that can take into account of water surface deformation were conducted for a rough wall boundary. Hemisphere particles were used as candidate of roughness elements for simplicity of establishing several particle distribution densities. It was made clear that water surface pattern can be classified by five types: flat, ripples, advection, parallel and cross. For sparse roughness elements, LES was conducted successfully to reproduce the above surface patterns.

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Phase lag of stream meandering to channel curvature is the point of studies on river channel meandering. The stream meandering is generated by centrifugal force basically, but the effect of the force is usually considered by separating into two components; depth averaged component and component of deviation from the average. Existing 1-D theory of channel meandering only takes account of the former. This paper presents a new 1-D formulation of stream meandering in which the both components of the effect of centrifugal force is taken into account by extending a theory that was originally developed for secondary flow calculation. Results of numerical simulation by using the model agree fairly well with experimental data obtained in a meandering channel as well as in a single bending channel. This paper also discusses weight of two kind mechanism of stream meandering through numerical experiments under various hydraulic conditions of meandering channel flow.

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Steep slope types of revetment are commonly used in Japan as a countermeasure intending to reduce flood damage in small-and-medium-sized rivers to expedite their improvement works and to save land cost. In result, cross-sectional shapes become narrow and deep, frequently causing severe destruction of channels in spite of the improvement. It follows local bed scours around change points in channel forms caused mainly by accelerated flow due to reduced channel roughness by the improvement. This paper presents a consideration on the reasons why cross-sections of small-and-medium-sized rivers in Japan had been changed into narrow trapezoidal shapes with steep side slopes according to historical changes of technical criteria in river improvement schemes, along with that on the difference of channel roughness determination among several technical criteria.

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A free-surface velocity divergence is highlighted as a key parameter of the gas transfer, because the accurate divergence value can be obtained with the advances of the PIV technique. However there still remain uncertainties about the relation between the free-surface divergence and the gas transfer velocity in open-channel flows such as natural rivers. In this study, we conducted a horizontal free-surface PIV in laboratory flume together with DO measurements. A new physical model of gas transfer parameterized by the free-surface velocity divergence is presented and this validity is examined intensively by comparison with present measured data.

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This paper discusses the SS transport by horizontal large eddies (HLE) from a narrow channel to surrounding vegetation areas in a constructed wetland. A series of flume experiments were carried out for several conditions of width/depth ratio and Reynolds number, referring to the ranges of the parameters reported in an actual constructed wetland. The unsteady velocity field was measured in detail by PIV technique. Numerical simulations were conducted under the same conditions as the experiments, and computation results agreed with observation results very well. The study clarified the dependency of HLE scale and intensity on the above mentioned two parameters. Numerical tracer experiments were conducted to investigate the basic characteristics of SS transport by HLE. The results show that the range of SS intrusion to vegetation areas is comparable with channel width. This fact suggests that a system of channels should be designed to distribute SS in a wide area of vegetation in a constructed wetland.

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A lot of aquatic plants are observed in actual rivers and they have a potential to improve water quality. A large-scale coherent vortex is generated near the vegetation edge, which dominate the momentum and scalar transport. Thus, estimating the flow resistance of vegetated flows is of great importance in river management. In such vegetated open-channel flows, both the geometry of the vegetation elements (shape, size, flexibility and vegetation density) and turbulence characteristics affect the hydrodynamic resistance significantly. However, any important relation between the vegetation motion and the flow resistance property have not been yet established. Therefore, in the present study, we highlighted these important topics and measured the instantaneous velocity structure and coherent motion in open-channel flows with flexible vegetation by using PIV-PTV technique. As the results, the hydro-mechanic interaction between the flow and flexible plant motion was revealed.

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The roles of vegetation for environments are well known; a) absorption of CO2 and supply of O2 during the process of photosynthesis, b) production of carbohydrate, as producer in the pyramid of eco-system, c) climate mitigation by the latent heat release and reflection of solar energy radiation (umbrella effect) and d) psychological effects of green for the human. The interaction between air- or water-flow and vegetation promotes the exchanges of momentum, gases and heat between them. In order to understand these processes, the investigation of the turbulence characteristics, large-scale coherent structures are indispensable. The interaction of air- or water-flow and plant canopies resembles partly to the mixing shear layer and partly to the wall boundary layer flows.By the LES numerical simulation, the followings are confirmed : the reliability of the scheme and program by comparing the results for near-wall flow with the standard data, the formation of spanwise oriented long eddies by the inflectional-point instability mechanism in the initial stage of flow, evolving, in the low LAD (Leaf-Area Density) case, into the "roller and ribs" system proposed by Hussain or the double/multiple structure by Hino, and for the case of high LAD into the undulating streamwise streaks which resembles the near wall turbulent structure

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This study aimed to clarify the fundamental phenomenon of salinity intrusion in ice covered river. We carried out salinity intrusion experiment to which model ice-sheet floats on the water surface and one-dimensional two-layered unsteady flow calculation. In this experiment, the vertical flow velocity was measured using particle image velosimetry technique. In the experiment in which ice-sheet exists, the model ice-sheet indirectly attenuated the salinity intrusion because Reynolds number does not become large. Shear stress was computed by having assigned the experiment data to one-dimensional two-layered unsteady flow equation. In both ice and no-ice condition, Interface shear stress has large influence on salinity intrusion. It was shown that the calculation model built by this study can reproduce salinity intrusion experiment.

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To grasp the temporal change of hydraulic phenomena in tidal area of the Uchikawa River during saltwater intrusion into the river, a long-term observation was carried out using the ADCP. As a result, detailed vertical velocity distributions of two-layer flows with salt-wedge type in tidal area of the Uchikawa River were observed. It was found that saline water with weakly-mixed type made intrusions into the Uchikawa River regardless of seasonal and/or tidal effects. Especially, time series of flow velocity had periodicities during salinity intrusion. Furthermore, flows in both upper and lower layers were laminar flow and showed F_d1≈0.4 in the front part of saline wedge, and then turbulent flow zone within F_d1≤0.4, 10⁴≤Re_1,2≤10⁵ was observed when fresh and saline two layers had been stable. It can be inferred from previous studies that it is possible to estimate the interfacial resistance coefficient fi using the proposed Iwasaki number φ function for the tidal area of the Uchikawa River.

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Continuous measurement of flow rate has been carried out in an especially shallow and wide gravel-bed river (water depth 0.6 m at low-flow conditions and width 115 m) using FluvialAcoustic Tomography System (FATS) with a couple of 25 kHz broadband omni-directional transducers (0.05 m diameter). The reciprocal sound transmissions were performed between the two acoustic stations located diagonally on both sides of the river. In addition to the flow rate, cross-sectional average temperature were deduced from the sound speed data collected by the FATS. A maximum relative difference between FATS and rating curve estimates was approximately 30%. The rating curve method underestimated short-term variations of the flow rate. FATS successfully measured the cross-sectional average temperature. Spectra of velocity and flow rate were estimated in wide frequency range.

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This paper discusses practical techniques to measure fluctuation of velocity as well as of water surface level in a large scale hydraulic model test which is often carried out in open air. 1/70 scale model of a cut-off channel of actual river was used for the purpose. PIV measurement by using a fine resolution digital camera with short interval shooting was adopted for continuous velocity measurement in a wide area. A set of six servo level gauges was used for time series measurement of water level on each transect line. The data sets obtained separately by the methods mentioned above were synchronized by referring to a time series of water level measured at a fixed station. Correlation analysis of the synchronized data clarified the coherency of periodic fluctuation in time and space, and practical efficiency of the method was verified.

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A discharge monitoring system with velocity measurement by two H-ADCPs and numerical simulations using DIEX method was applied to flood-discharge monitoring in a compound channnel in Edogawa River under flooding due to typhoon no.1112. In the present system, we used two H-ADCPs in which one was installed in the main channel and the other in the floodplain. The results indicate that the calculated velocity and discharge using the present method with two H-ADCPs give good agreements with the field data measured by ADCP. The relative errors of calculated discharge by the present method using two H-ADCPs are appreciably lower than that using a H-ADCP. This fact demonstrates that the present method using two H-ADCPs are useful to monitor flood discharge in a compound channel.

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An automatic continuous monitoring system for bed-load transport is newly presented using H-ADCP measurements and numerical simulation by a DIEX method. Using line velocity measured with the H-ADCP, the DIEX method may calculate cross-sectional velocity and lateral profile of bottom friction which is applied to evaluate bed-load transport with a conventional bed-load formula. The present system has been applied to monitor discharge and bed-load transport in Edogawa River. The results indicate that the discharge and bed-load transport obtained by the present system are in good agreement with observed data. The RMS values of relative errors for the calculated discharge and bed-load transport are respectively 3.3 and 5.8%, demonstrating high performance of the present monitoring system for bed-load transport.

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In the conventional discharge rating method using HQ-curve, one approximate line is drawn using least squares method to express the relation between measured water-level H and discharge Q even though this relation does not show one-to-one correspondence at flood time, and there is a possibility that the Q rated by the HQ-curve would have an error against the true Q. In this study, the discharge rating method using HK-curve is suggested instead of conventional HQ-curve method. K means Conveyance. As a result of 2-dimensional numerical calculation, it is shown that the relation between H and K can be expressed by one approximate line because the relation shows one-to-one correspondence, and the Q rated by this method can express the true Q accurately.

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Marine litter is mainly supplied from inland area through rivers under hydrologic events. However there have been little information for quantity and quality of floating litter through rivers into coastal region and further behavior of floating litters in river and coastal area. In the present study, GPS floats with mobile phone were used to track a Lagrangian behavior of floating litters in rivers under floodings. In this study, we conducted field measurements of 10 GPS floats in two flooding events in Egogawa River. The results indicate that most of GPS floats were drifted in banks of river mainly due to wind stress. It is found that the moving distance of GPS float for simulated vegetation was larger than that for simulated artificial debris.

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This study investigates the potential predictability of regional precipitation over Indochina during the Asian winter monsoon by downscaling outputs of seasonal prediction by a general circulation model (GCM) statistically. Singular decomposition analysis reveals two distinct temporal-spatial patterns between regional rainfall and sea surface temperature (SST) in the tropical Pacific. One is anomalous dry condition over central and south Vietnam associated with a conventional El Nino pattern with the peak variability in the eastern tropical Pacific. The other is anomalous dry condition over north Vietnam associated with a new-type El Nino which has peak variability in the central Pacific. Our hindcast results show that the prediction skill associated with the conventional El Niño mode is relatively high although the new-type mode is difficult to predict. These conclusions tell us the importance of individual physicalmechanism-based validation in the application of statistical downscaling for regional climate.

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Return period is one of the most essential concepts in flood frequency analysis, but it has been applied without respecting its two aspects: local and global ones. The return values are generally calculated by considering the reciprocal number of return period as an occurence rate (or exceedance probability) per one year, which is an instantaneous quantity defined in the local aspect. On the other hand, the return period should be literally confirmed as the averaged time interval for the successive occurences, which is the global sense. In the latter viewpoint, we discuss the estimation error accompanied with the passage of time even for the stationary timeseries of extremes.

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A goodness-of-fit evaluation for hydrologic frequency models using SLSC (Standard Least Squares Criterion) is widely used in Japan. As the critical value to the SLSC goodness-of-fit evaluation, 0.03 is usually used. However, the critical value is recognized as a variable depending on a sample size of hydrologic data and a hydrologic frequency model. In this study, statistical characteristics of SLSC is examined. Then, based on the analysis, a statistical hypothesis testing is introduced into the SLSC goodness-of-fit evaluation for hydrological frequency analysis models.

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The high- and low-water design of river basins in Japan is mostly based on probabilistic precipitation and river discharge data. In this study, a number of hydrological and statistical analyses were executed using annual maximum one- and two-day precipitation data and annual maximum daily river discharge statistics for the Hii River basin for reference in high-water planning work. The results showed increases or decreases in many probabilistic hydrologic indexes between past and present, meaning that differences in design precipitation or design flood discharge may arise in the future even for the same return period. It was also concluded that the operations of flood control facilities may need to be improved.

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Extreme precipitation, usually causes flood event, is often associated with a tropical cyclone in the Asia-Pacific region. Furthermore, especially in Japan, extreme precipitation is also influenced by Baiu. In this study, we analyze observed gridded dataset of daily precipitation from 1951 to the present in order to understand the trend of extreme daily precipitation. Firstly, we classify extreme daily precipitation into tropical cyclone-origin, Baiu-origin and the others, and investigated their frequency changes in the Asia-Pacific region. The trend in tropical cyclone-origin precipitation depends on each region; it significantly increases in Pacific Ocean coast in Japan and decreases in Philippines. These trends may be influenced by the change in intensity of precipitation associated with tropical cyclones. On the other hand, the change in extreme daily precipitation in Japan is not significantly governed by Baiu.

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The purpose of this paper is to suggest possibility of the application of the middle and small river channel planning by photogrammetry with digital aerial cameras. We have obtained the spots of surface elevation both topographical survey in river with VRS-GPS or Total Station and photogrammetry with digital aerial camera (UltraCamX), and evaluated numerical differences of longitudinal water level by 1D-flow analysis using those spots.As a result, the difference of cross section area(per survey line) between topographical survey and photogrammetry(high-resolution 5cm/pixel)is 0.8m2 (0.03 m2/m) and the water level caluculation results were at almost same between using topographical survey dates and using photogrammetry(low-resolution 10cm/pixel) edited by human. However, the edited photogrammetry required much processing time although it was accurate. Then, in order to have applied to the river channel planning, a near-infrared photograph can identify as the vegetation area and would performe processing automatically as much as possible.

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In this study, the effects of the fluvial wood zone in landside upon overflow characteristics of flood flows are investigated experimentally, theoretically and numerically. The wood zone arranged on gently sloped back face of levee is considered. It is found that river water level is heading-upped by the woods zone, so that overflow characteristics in the vicinity of the crown of the levee may be changed from complete to locally submerged outflows, depending on characteristics of the wood zone, levees and flood flows. It may cause such a problem that river water level and overflow discharge are unable to be related. A discharge formula, that includes both effects of characteristics of the wood zone and levees, is developed for this purpose, and is validated through experimental and numerical investigations.

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The ability of flood control in retarding basin depends on side weir, we must take care of river line and the flow of side weir. In other words, when there is curve near the side weir, flood control is depends on submerged overflow, we must decide the size of side weir using for hydraulic model test.In this paper, it is most suitable size of the side weir by hydraulic model test in Okura retarding basin which is planned on river Kurokawa in Kumamoto pref. We decide the best size of the side weir for flood control and decrease flood control capacity 64,000 m3 from the beginning design, in this way reduce the amount of digging and led to a reduction in construction costs.

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The Kurobe river which is very steep river on alluvial fan yields a mass of sediments from drainage basin. Depositing sediments in dam reservoirs deteriorate a function of water storage. Therefore, the cooperating sediment flushing of Unazuki dam and Dashidaira dam is made in the latter period of floods to maintain the capacity of dam reservior water storage from 2001. After stopping gravel dredging in the downstream of Kurobe river, vegetation growth on sand bank has gradually begun. And then dense vegetation growth cause bed scouring of channel thalweg in downstream reach. The purpose of this study is to deepen the understanding of river channel change by investigating relationship between flood flows, gravel dredging, bed variations and vegetation growth over time in the Kurobe river and to conducts a proper river management.

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It is an important issue to determine the river cross-section which is satisfied with functions of the flood control and the river environment. Fukuoka has derived the relationships of dimensionless width and depth versus dimensionless discharge considering floods and river basin characteristics.The purpose of this study is to show the application method of Fukuoka's equation to rivers at design and improvement stages. At first, we determine desirable range which dimensionless width and depth versus dimensionless discharge holds for rivers with various cross-sections. Secondly, we suggest that river width and cross section at an improvement stage should be improved up to the safety level of 1/30.

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The numerical simulations of rainfall-runoff and flood flows in the Onga river basin were performed.The rain-fall runoffs were simulated by a distributed hydrological model using a high-resolution scheme.The flood flows in the main river and plural tributaries were simulated simultaneously by the 2D unsteadyfree-surface flow model with treatment of parallel computation and sink term semi-implicitly. Theflooding event in the Onga river basin in July 2003, 2009 and 2010 were simulated by the model. Thesimulated results were compared with the observed water level. It shows that the model is a useful tool forexamining the process of runoff and flooding in the Onga river basin. The effects of river improvementworks on the water level in the Onga river and improvement of computational speed were also examined.

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Recently, in the wake of drought occurrence, the necessity of promoting comprehensive water resources development not only including river water, also groundwater and reuse of treated domestic wastewater has pointed out. Regarding reuse of treated domestic wastewater, as its water resources is relying on rain water and life sewage water, in case of drought, it has lower safety degree of water use due to scarce rainfall and the implementation of water conservation. This study shows the safety of water utility about the reuse of treated domestic wastewater. We have modeled the status of Fukuoka City water project promoting the use of reclaimed wastewater and the rainwater utilization. We numerically evaluate the effects of reuse of treated domestic wastewater and estimated the available amount of it in the future.

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We propose the method of quantifying mitigating effect of water conservation policy on shortage during drought. Because it is difficult to forecast effect of water conservation policy, evaluating effect and changing the way of policy is important. In Matsuyama City, the city has subsidized purchasing a washing machine with pump for reuse of water, a pump used as a single agent and a dish washer to conserve domestic water. It is estimated that this project decreases the domestic use of water by 1.5% but the damage resulting from drought by more than 10%.This result indicates the fractionation of water use is vital to estimate the effect on the damage during drought.

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In this study, the reduction on the environmental load by the replacement of conventional toilets with low environmental load toilets at highway service areas in Japan was quantified and a cost-benefit analysis concerning introducing low environmental load toilet such as waterless urinals and urine diversion toilets were performed. As for the results, the environmental loads from the service area, water consumption and energy consumption were reduced greatly by introducing low environmental load toilets. In addition, it is found that this system can be easily paid back in 3 years regarding the burden of the energy and cost when it is introduced into large service areas where the wastewater is treated by the sewage system.

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In this research, we gathered the Historical Maximum Discharge (HMD) of A class rivers in Japan after World War 2nd (1945) and classify these data into the topography-meteorological area. We used Creager curve for analyzing the regional characteristics of HMD. From this analysis, we explained the difference of the flood specific discharge among geographic regions. And we compared the historical maximum specific discharge between as of 1975 and 2009, so we could explain Creager curves in 3 region was updated and the flood specific discharge in most of river converged to Creager curve.

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To evaluate effect of flood and inundation of the Mekong River to land fertilization in Cambodia, we estimated amounts of nutrient transported by flood and inundation. A local-scale model based on observation and a large-scale model based on the hydraulic phenomenon were used. Amounts of nutrient estimated by the local-scale model was almost same as the amounts of nutrient estimated by the large-scale model. Relationship between the estimated amounts of nutrient and rice production in Cambodia were compared with the relationship between amounts of fertilizer and rice production in Japan. We conclude that the amounts of nutrient transported by flood and inundation are enough to rice production in Cambodia.

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This study attempts to create regional divisions for environmental flow assessment based on net primary productivity (NPP). First, the world is categorized into six hydro-climatic regions according to seasonal flow variability and average monthly temperature. Second, a trophic level index is built in order to describe the potential richness of ecological structures of river channel. This model describes biomass flux in the river channel and rate of dependency on upper reaches. In poor productive areas such as desert or high latitudes biomass supplied from upper reaches contributes to sustain ecological richness. The hydro-climatic regions and the trophic levels highlight the regional characteristics of riverine ecosystems and indicate the priorities for setting the environmental flow objectives.

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This study aims to clarify the factors affecting water level variations in the Kahayan River in Indonesia, and aims to forecast the water level of that river. In recent years, peat land has been drying as a result of agricultural development, and such drying has increased the frequency of large-scale wildfires. To analyze the factors affecting water level variation, we examined the relationships between global weather phenomena, rainfall in the study area and water levels of the river. It was found that rainfall was scant and the water level was low during El Nino events. In addition, it was found to be possible to forecast water level fluctuations with a one-month lead time by using the Nearest-Neighbor Method. The results promise to be useful for controlling the hydrological conditions in peat land restoration in the future.

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This paper addresses the optimal operation of a group of dam reservoirs in a snowy region for adaptation to the water shortages that are expected to result from climate change. In snowy regions, climate change is likely to cause snow accumulation to decrease. This is expected to shift the snow-melting season earlier, to decrease river discharge and, consequently, to reduce water availability. Thus, the operation of existing dams should be improved. Research was made on the operation of two multipurpose dams in the Toyohira river basin, which supplies water to Sapporo (population 2 million). Using reproductions (1981-2000) and projections (2081-2100) provided by the Regional Climate Model (RCM20) of the Japan Meteorological Agency, we estimated the optimal operation of a group of reservoirs by dynamic programming. The simulation suggests that shortages of dam storage will occur if each dam is operated separately, but that coordinating the discharge operations of two dams can make up for those shortages.

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Itis an objective of the study that the author research on a possible methods due to increase for waterpower generation, with reviewing for control manual in the Kusaki dam of multo-porpose . Namely, it is significant that to make decreasing an invalidated outflow discharge at flood outflow , and also to make increasing an effective outflow discharge that change into waterpower generation. As following, we had suggested new system that is said to be beforehand outflow methods in dam control,and simulated base on the hydrological data of Kusaki dam managemwnt during 15 years. Run-off analysis of heavy rain using tank model,a quantitative of an effective outflow discharge and waterpower generation was carried out. Results of this study, it is found that beforehand outflow metod is not only an effective for waterpower generation, but also for flood control.

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We suggest a new flood control concept called 'Cascade method' which permits a dam to overflow around an upstream region with plural dams set in series in a river basin. We recommend plural small scale dry dams set in series instead of a large scale dam in order to prevent flood disaster and preserve a natural environment. In this study, the new flood control concept is applied to single and double peak flood events in a numerical simulation. Under the condition of common reservoir capacities, new flood control method permitting upstream dams to overflow except for a downstream dam is compared with the conventional one not to overflow in each dam. In addition, appropriate design high water discharges for plural dry dams are investigated. As a result of this study, it is made clear that the new method is more effective than the conventional one for double peak flood events as well as for single ones, and uniform design high water discharge for each dry dam is practically appropriate in the Cascade method.

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This study examined a peak discharge reduction function and a flood adjustment ability of flood control facility and basin management facility through a runoff analysis for recent major floods in Yamato River basin in Nara Prefecture, where see a rapid urbanization, by application of a hydrological distributed runoff model.As a result, the discharge reduction effect of flood control and basin management facilitation and occurrence of inland flood was estimated as approximately 15-20%. Also, it was estimated that basin management facility has equal or more effectiveness for flood adjustment than flood control facilities. Furthermore, it was indicated that the flood adjustment effect might be further improved by optimizing excess capacity of facility to the leveraged outflow facility specifications.

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