This study was performed to clarify the spatial variation of habitat of Corbicula bivalves (C. japonica and C. leana). A series of field investigations were performed in the Kiso River estuary, in October – November, 2012, with particular references to the existence of a series of groins. We compared the differences of water environment, substrate and diet variables in longitudinal and transverse directions (Two-way ANONA) to grasp the habitat characteristics in different landscapes. Furthermore, correlation and multiple regression analyses for their densities and biomass were applied to clarify the crucial environment variables. As the results, it was clarified that salinity and water depth could be the controlling factors for the biomass of C. japonica, whereas the sediment and salinity factors would effect on promoting the biomass of C. leana and the density of C. japonica.

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The objective of this research is to develop a macrophyte model for the growth of submerged aquatic vegetation in the Condoriri River. The processes included in the macrophyte model are: photosynthesis,dark respiration, excretion and non-predatory mortality. The influence of the nutrients, the discharge, solar radiation, and the water temperature on the growth of the aquatic plants was considered. Macrophyte biomass and the specific nutrient transport of TN (0.02 g.s-1.km-2) and TP (0.0035 g.s-1.km-2) were greater during the wet season than during the dry season. Good agreements were achieved between field measurements and the model predictions of macrophyte biomass. The proposed model predicted seasonal changes in the growth of the aquatic plants, despite their high spatial and temporal variations.

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To control river regime from ship wave attacks, porous structure have been built along the riverbank. The results are not as good as expected at all locations even though same structures are applied. This study firstly investigated the interaction between porous structure and waves under different volumetric porosity of structure (θ) by conducting physical experiments. Based on that, relationship between θ and drag coefficient was established by using a 1-D model. The optimal θ to mitigate wave attacks was then determined by a 2-D model taking into consideration not only cross slope behind groins (i) but also the gap between two neighboring groins (G). In cases of i =1/100, the combination of (θ) = 0.4 and L/G = 5 (L is the stream-wise length of a groin) could bring out the best wave energy reduction. It is necessary to consider both of i and G for designing stream-wise groins.

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Prediction of salinity is of significant importance to the water management in estuaries. Although nowadays advanced numerical three-dimensional models are available that can provide detailed information on the salinity and mixing processes, there is still a need for simple tools to be performed in order to investigate the resultant effects of physical quantities on the salinity distribution. The analytical analysis presented in this paper may serve these needs. A new analytical form of the salt intrusion model was developed for use in funnel shaped estuaries, where little known about the effects of the channel shape and hydraulic parameters on the salinity distribution. The newly developed analytical model was well-tested against observational salinity data in the Abashiri River estuary under different tidal conditions and river discharge rates.

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A new bulk parameter, Lagoon Richardson Number (RiL), was developed based on the Estuarine Richardson Number (RiE) to characterize the mixing/stratification process of permanently open choked coastal lagoons (POCCLs) in Sri Lanka. In addition to tidal induced mixing, wind induced mixing is also incorporated in RiL. Furthermore, the estuarine bulk model was modified by replacing RiE from RiL in order to make it more applicable to POCCLs. By using the energy terms included in RiL, a significant amount of potential energy reduction was able to identify in dry season with compared to rainy season which make the process of wind induce mixing more prominent in dry season for Koggala Lagoon. Bulk models application to Koggala Lagoon shows that the salinity stratification estimation capability of the modified bulk model is greater than Fischer’s model, particularly for dry season surveys.

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The 2011 tsunami flushed sand spit in front of the Nanakita River mouth, Sendai Coast, Miyagi Prefecture. It also caused severe erosion of sand barrier which is adjacent to the left side of the river mouth. These damages formed concave shoreline at this area after the tsunami. The morphological recovery of this area is presented through analysis of aerial photography. The recovery time of morphology is evaluated from analytical solution of one-line model. Results indicate that coastal structures at both ends have major impact on the shoreline evolution. Moreover, the dimensionless recovery time of morphology is depended on the ratio of total length of adjacent sandy coast to the concave width. A new analytical solution of one-line model, which describes the evolution of shoreline of concave landform bounded by rigid boundaries, has been introduced. Good agreement between measured shoreline positions and simulated results is also obtained.

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Inhabitants and pedestrians in an urban area are subjected to the air flow condition within it. The complexity of the buildings geometry and density of its arrangement may lead to the gusty environment. In order to understand the situation, a large eddy simulation (LES) over a huge and high resolution of an urban area was carried out. The Lattice Boltzmann method (LBM) applied in this LES for several advantages. The computational domain size is 19.2 km in streamwise by 4.8 km in spanwise and 1 km in the vertical while the grid resolution is 2 m. The maximum wind speed normalized to several representative wind speeds considered to gain the appropriate spatial gust factor definition. This non-dimensional factor calculated and its location of occurrence was mapped. Some events were highlighted to study the correlation between the high gust factor and the building geometry.

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When simulating the turbulent flow around urban structures with large-eddy simulation models it is often necessary to use non-cyclic boundary conditions in streamwise direction. In such cases a turbulent inflow condition at the inlet is favored although it is highly difficult to obtain. A synthetic turbulence generator, modelling turbulence statistics and correlations, is used to generate a turbulent inflow for large-eddy simulations. Results are compared with simulations using laminar inflow. An artificial urban canopy consisting of aligned buildings with cubical shape was used. Two simulations contained one additional tall building located at the center of the domain. The turbulence statistics show a well-developed urban boundary layer above the building arrays for each simulation. Higher turbulence intensity was found when using the turbulence inflow method resulting in faster development of an urban boundary layer.

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This paper presents a readily understandable hydrologic-based method to calculate the effective dose emerges from the intake of radioactivity on agricultural products derived from radioactive fallout on the soils. We discuss the intake of polished rice as an example of agricultural product. The authors have been studied internal dose calculation regarding to the human body. The scope of our research is expanded from the human body to the soils in this report. Our modeling of the radiocesium transfer from the soils to the human body is based on the previous research regarding the vertical infiltration, the transfer factor to plants, and the residence time of cesium in the soils. We calculate analytically in concise formalization the intensity of radioactivity on the soils per area and the effective dose derived from the intake of radioactivity on the rice using measured radioactive fallout after the Fukushima Daiichi NPP accident.

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The production of precipitation in a regional climate model (RCM) is handled primarily by the microphysics and cumulus physics parameterizations. Application of the WRF model as an RCM to a mid-latitude Japan case and tropical Philippine case using single-year simulation sensitivity experiment showed scheme sensitivity to simulation of precipitation and exploration of potential transferability of the schemes to different climate regime applications. Results show that simulations can capture seasonal 2-meter air temperature well and demonstrate capability in simulating seasonal precipitation for both application. Results show that cumulus (microphysics) scheme sensitivity is higher in simulating seasonal and monthly precipitation when larger fraction of precipitation is convective (non-convective). Precipitation sensitivity to cumulus scheme showed largest variation in warm season for Japan case and in all seasons in Philippine case. It has been found that Kain-Fritsch (KF) scheme tend to overestimate precipitation in hot humid climate regime application and Grell-3 (GR) scheme showed the most consistent good skill performance throughout the seasons for both applications. CU scheme selection showed higher impact for simulating precipitation in the model than the MP scheme selection.

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The objective of this study is to investigate the trend of hydrologic variable changes by applying the Mann-Kendall statistical trend test to daily historical record of reservoir operations data such as inflow to dam reservoirs, release from dam reservoirs, dam storage as well as precipitation and temperature. The five large scale dam reservoirs located in the northern, central and western parts of Thailand are selected to analyze the trend of the Ping River basin Bhumibol Dam, the Nan River basin having the Sirikit Dam, the Pasak River basin having the Pasak Jolasid Dam and the Mae Klong River basin having the Srinagarind and Vajiralongkorn dams. Through the analysis, we found that the temperature and precipitation show in-creasing trends except the Ping River basin; water resources availability in terms of inflow to the Bhumibol Dam and Pasak Jolasid Dam shows decreasing trend during dry season; the inflow of all reservoirs in rainy season had increasing trends; and dam releases of the all reservoirs shows significant increasing trends in dry season. Furthermore, water storage for Bhumibol dam were found dramatically decreasing trends throughout the year while the Srinagarind dam was detected increasing trends. Also, the increasing trends of water shortage in Bhumibol and Pasak Jolasid Dam and raising trend of excess storage volume in Sirikit dam and both dams in Mae Klong River Basin were observed.

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The physical based Water and Energy Budget - Distributed Hydrological Model with improved snow physics (WEB-DHM-S) was constructed to simulate the long-term hydrological processes in the Shubuto River Basin, Hokkaido, Japan. Long-term (1948-2006) simulation using high resolution JP-10 reanalysis data set showed slight to moderate decreasing trend in snow cover days and decline in snow water equivalent (SWE) in the basin. The model was forced with bias corrected Atmosphere-Ocean General Circulation Models (AOGCMs) outputs to explore the climate change impact on the basin hydrology. The AOGCMs predicted snowmelt induced peak flow to be occurred on average two weeks earlier with less snowmelt in the future. The paper delivered usable information of snow extent, snow depth and SWE and enhanced understanding of long term hydrological changes and uncertainties associated with the simulated climate signals. The present study provided direction for future research to reach more reliable conclusion.

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Reliable assessment of Climate Change (CC) impacts on water resources of the Tone river basin is critically important due to its key role on Japan’s socio-economic systems. Hence, to increase the confidence level in CC projections, this study performed high-resolution Pseudo Global Warming Downscaling (PGW-DS) experiments on cautiously selected Coupled Ocean-Atmosphere General Circulation Models (CGCMs) outputs. Value added future climate datasets were developed at the basin scale by removing systematic biases from the PGW-DS outputs using gauged precipitations and a validated statistical bias correction method over this basin. Results showed that annual and monthly climatology of precipitation and corresponding discharges will be increased in the future climate, especially during the Baiu and typhoon periods. Flood-prone areas will be extended and peak discharges will be amplified during warming climate. Recurrence analysis revealed that peak discharges will be increased with increasing return periods, however, larger differences exist in rate of increments between a sub-basin outlet and the main basin outlet, indicating that future investigations should be focused at sub-basins including the effects of dams on discharges to quantify the CC impacts in detail.

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This research investigated the effectiveness of merging the remote sensing satellite precipitation, GSMaP-MVK (Global Satellite Mapping of Precipitation moving vector with Kalman filter), a very high spatial distribution product, with the local rainfall measurements for analysis of quantitative rainfall estimates and run-off prediction capability at basin scale. Three satellite-gauge merging methods stem from the idea of geo-statistical merging techniques were utilized to provide the precipitation input for conceptual hydrological model HBV for run-off simulation in two medium size river basins in different climate regions. The performance trends of three investigated merging approaches were similar in both two different climatic watersheds. The Bias reduction satellite-gauge merging method with good rainfall estimations and excellent stream-flow simulation skills is appropriate satellite-gauge blending method. It depicted the best performances, following by the monthly constant multiple factor and annual constant multiple factor respectively.

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The objective of this study is to propose a new calibration procedure for a basin-scale hydrological model using satellite-derived terrestrial water storage data and observed discharge data. The analysis was conducted in a step-wise calibration method within Differential Evolution Monte Carlo Markov Chain simulation framework. In comparison with conventional calibration method, this approach efficiently reduce parameter uncertainty, model can perform good discharge simulation and reasonable water storage simulation. We also found that based on this method, our model can enhance actual and potential evapotranspiration simulation in sub-basin scale. More important, this study demonstrated the potential for the joint use of available GRACE derived water storage data and discharge data to improve main hydrological flux simulations in hydrologic models.

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Accurate rainfall predictions, especially for tropical monsoonal rainfall, are among the most difficult tasks in hydrology. In this article, we discuss ANN-based long-term rainfall predictions for Oekabiti, West Timor, Indonesia. Due to the remoteness of the area, the only information available is historical rainfall data. However, by basing on previous studies into the time lag relationship between the El Nino Southern Oscillation (ENSO) and Indonesian rainfall, we utilized Sea Surface Temperature Anomaly (SSTA) Zone Nino 3.4 and the Southern Oscillation Index (SOI) to improve accuracy levels of rainfall prediction models efficiently. During our model development, it was revealed that rainfall fluctuation is more influenced by the lag 0 to lag -1 of the SOI than by the SSTA. We also found that the resulting models could dynamically predict long-term rainfall, but tended to underestimate some extreme values, which limited their utility for irrigation management planning.

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Antecedent soil moisture is a key factor to determine flood characteristics. Understanding the role of antecedent soil moisture for flood is needed for conservation of ecosystem and for damage mitigation as well. The aim of this study is to quantify the relationships of the antecedent soil moisture to flood volume, peak discharge and its duration. Discharge and soil moisture were simulated by a hydrological model. Then, multiple linear models quantified the relationships. Thirty-five floods were analyzed from 2005 to 2012 in Huong River, Vietnam. As a result, not only total precipitation volume but also soil moisture before flooding explained flood volume and its duration. Similarly, antecedent soil moisture increased the predictability of peak discharge with peak rainfall amount. The flood characteristics changed by reflecting wet/dry condition at top soil. We expect that consideration of antecedent soil moisture to identify the flood characteristics accurately leads to practical flood countermeasure.

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A distributed biosphere hydrological model with energy balance based multilayer snow physics (WEB-DHM-S) was implemented to investigate the hydrologic response of the current dam operation system to future climate in a snowy river basin (Yattajima basin) of Japan considering the impacts on flood, drought and dam behavior. Dynamic downscaled data (6 km and hourly) for past and future climate were archived from Data Integration and Analysis System (DIAS). Dam operation modules for 6 dams were formulated based on observed patterns of dam inflow/outflow and were validated in 2001-2005. The climatological average analysis of past (1981-2010) vs future (2081-2110) simulation results indicate that a remarkable decrease in runoff in May at Yagisawa, Naramata, Fujiwara and Aimata dam is observed due to shift of snowmelt towards April. Top 20 flood analysis reveals that future peak flow will increase in all gauges and dams except Fujiwara dam. Flood risk is reduced by Fujiwara dam due to the projected changes in snow seasonality. Future low flow will increase reducing the likeliness of the drought; however the number of days with low water level in Yagisawa dam will certainly increase in future.

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Soil in the Kuchibuto River catchment was contaminated by Cs-137 which was released by the Fukushima Daiichi Nuclear Power Plant (FDNPP) in 2011. The contaminated soil particles will transport and redistribute during flood storms. In this study, we simulated soil erosion and transport by a multi-class soil erosion and transport model. Flood storms in 2011 were used for calibrating the model. Simulated suspended solid flux both in the calibration and validation period show a good agreement with the observed data at the monitoring sites. Our simulation results also show, from Mar. 11, 2011, when the FDNPP exploded, to Jan. 1, 2014, an estimated 6211 t of clay (<3μm), 36210 t of silt (3-63μm) and 8880 t of sand (>63μm) were eroded and transport to the Abukuma River. In the study period, soil erosion mainly occurred in the middle portion of the catchment.

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Due to the high sedimentation rate in reservoirs located along the Kurobe River (e.g. Dashidaira reservoir), sediment flushing with water level drawdown is employed to preserve the effective storage capacity. During a flushing operation with full drawdown, the incoming flood erodes a flushing channel into the deposited sediment. The flushing channel evolution procedure is a complex phenomenon especially in steep reservoirs owing to the dynamic interaction between the unsteady flow field and bed variations. The flushing channel formation and evolution procedure were investigated in meandering channel of Dashidaira reservoir utilizing field measurements and numerical simulations. A 3D numerical model which applies the Finite Volume Method (FVM) in ombination with a wetting/drying algorithm was used together with different bed load transport formulas. Numericaloutcomes disclosed a reasonable agreement with the field measurements. In addition, a further insight in the correlation between the flushed out sediment discharge and the water discharge as well as the water level was found.

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Linear stability analysis of sand fluvial bars with bank erosion is performed with the use of the shallow-water equations. We assume that the average total channel width is constant, and the bank erosion takes place due to increases in the bed shear stress in the vicinity of banks. We obtain analytical solution by the use of asymptotic expansions around the state of no bank erosion (the bank erosion coefficient γequals 0) in order to clarify the effect of bank erosion on the instability of sand bars with different lateral wavenumbers. We obtain instability diagram for γ evaluated from field and experimental data, and found that bank erosion stabilizes the bed in the ranges of small wavenumbers, and of large wavenumbers and aspect ratios.

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Overhanging failure is a major problem in river morphology, and it affects the riverbank geometry. Several studies have investigated different types of riverbank failure; however, uncertainty remains regarding to the process of overhanging failure. We carried out experiments on the mechanism of overhanging failure by using three types of cohesive materials classified by the percentage of silt-clay content. The experiments showed that the dominant factor in the failure process was hydraulic erosion in the initial stage. After that, tension cracks developed in the upper surface of banks and beam failure occurred afterward. Furthermore, we developed a numerical model for overhanging failure that uses a triple-grid approach to simulate overhanging behavior within the framework of hydraulic erosion and overhanging failure. The simulated results showed good agreement with the experimental results in terms of the spatially averaged bank width and water level along the bank.

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Stability of hypothetical riverbank subjected to five different flood hydrographs is discussed using the results of numerical simulation. Three models of hydraulic fluvial erosion, seepage flow, and slope stability are coupled to discuss the effect of the seepage flow and river bed deformation on riverbank stability. The three models are based on the finite element method with moving boundaries. The response of riverbank to the oscillated water level in the river and the consequent groundwater table is analyzed. The trend of factor of safety through time is presented. The influence of relevant geometrical, internal and external forces are also discussed.

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The continuous measurements of flow velocity/rate and suspended sediment concentration (SSC) in tidal rivers are crucial in estuarine studies. However, the accurate estimates of these terms are difficult and labor-intensive procedures are needed; thus, a robust and efficient method of the measurements is required. The changes of cross-sectional average suspended sediment concentration, tidal bore celerity and flow velocity were measured in the Qiantang River by using acoustic tomography systems. The results showed that the amount of SSC increased more than threefold during tidal bores. The acoustic systems could successfully measure the cross-sectional average velocity in the unsteady flows though the high SSC bred a short missing period after the bore arrival.

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Water shortage has been becoming one of the most crucial issues in China, because of the rapidly increasing water demand for economic development. One way of alleviating water scarcity is to increase the efficiency of water use without developing additional water supplies. Therefore it is essential to develop a holistic policy tool which can help the policy-makers to decide the usage of water wisely. The fundamental work is to explicitly quantify the agricultural water use efficiency in target areas. In this study, the agriculture water use efficiency is measured by the Data Envelopment Analysis (DEA) method, and recommendations of sustainable water use are provided.

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The majority of water catchments in Japan are located in mountainous areas that can produce large quantities of runoff, which may lead to flooding, erosion, and landslides. Thus, it is important to know the minimum total rainfall required to generate surface runoff by estimating the water storage capacity of each catchment. The threshold of minimum total rainfall required to generate surface runoff occurs when at least 95% of total rainfall becomes total loss rainfall such as infiltrates into the ground. The variation in this value is dependent on the catchment characteristics. Based on the relationship between total rainfall and total loss rainfall, the average values of minimum total rainfall required to generate surface runoff and total loss of saturated rainfall were 51.3 mm and 108.5 mm, respectively. Catchments consisting of a smaller area of sedimentary rock and higher values of drainage density, elongation ratio, and catchment width tended to have smaller values of minimum total rainfall required to generate surface runoff.

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Central Vietnam is highly vulnerable to flood disasters. Due to the trend of increased weather extremes, the vulnerability keeps to be further exacerbated causing high risk of casualties and damages. Also, the complication of the physical processes and socio-economic issues in this area is great challenge for practitioners and communities to have full understand flood pattern and associated risk. Therefore, this study selected Vu Gia . Thu Bon river basin, one of the largest system in Vietnam, to apply an integrated approach, including 1D flood simulation (using MIKE NAM and MIKE-11), Arc-GIS based mapping and conceptual DPSIR (Driver-Pressure-State-Impact-Response) framework to develop inundation maps of 10%, 5% and 1% frequencies and potential impacts in the study area. These results are considered as primary information to tailor effective flood disaster management plan in the long run.

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Scouring downstream of hydraulic structures is a complex phenomenon that causes the instability and even the failure of the structures. This experiment-based research was conducted to study the effect of the protection work length, L, along the embankment landside slope on the relationship between non-dimensional scour depth (S_D/Lsinθ) and its location (S_P/Lcosθ) under various overtopping flow depths (S_D: maximum scour depth, S_P: the location of S_D, and θ: the landside slope angle). For evaluating the possibility of the fragility of the embankment landside slope, a schematic diagram based on the angle of repose of foundation behind embankment toe is proposed in this study. The result shows that the effect of the protection work length on the risk of the embankment landside slope fragility are classified into 3 types according to the variation of the overtopping flow depths.

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The research regarding side weirs of stormwater storage systems which can be considered as effective hydraulic structure to mitigate the urban flooding and estimation of overflowing discharge over the side weir into those storage systems are significant. The De Marchi’s equation seems appropriate for the open channel flow condition to understand hydraulic behavior of the side weir but there are no studies that identify its suitability under the pressurized flow condition. Hence in this study, the overflow discharge coefficient in the De Marchi’s equation is evaluated for pressurized flow condition with different side weir length and height to verify the variation of discharge coefficient. The process of proposing discharge coefficient for each different side weir condition in circular channel is discussed through comparisons between experiment and simulation.

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Levee overtopping creates large scoured region at the landside, which greatly affects the levee performance. Both 3D and 2D experiments were conducted to analyze the downstream scour profile after levee overtopping. For elucidating the difference of scour pattern under various overtopping water depth and width conditions, 3D scour profiles are investigated. In addition, vertical 2D scour profiles are also investigated to compare the 3D scour profiles with 2D experiment results. From the analysis, it has been observed that for overtopping width (W_bank) to levee height (h_bank) ratio of 6 to 8, multiple scour holes appear with overtopping height (d_bank) to levee height (h_bank) ratio of 0.1 to 0.2, while for same W_bank/h_bank, two scour holes are created when d_bank/h_bank=0.25 to 0.3. Comparison of 2D and 3D scour data sets at downstream scour profiles shows that 3D experiments tend to create larger scour depth and shorter scour length than 2D cases. This result indicates the importance of 3D experimental analysis for levee design.

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This paper presents an experimental and numerical study of transient flow from pressurized flow to open channel free surface flow in a horizontal circular pipe. A one-dimensional (1D) depth-averaged velocity model is developed to study the unsteady flow in mixed pressurized-free surface flow, which can be occurred due to the rapid movement of a gate. The numerical approach is an interface tracking and after finding the interface position, pressure drop is considered at the interface. To evaluate the numerical model performance, some experiments were conducted in a straight circular pipe using water and air as two fluids. In order to generate the undular bore, in some cases a weir was used at the open end of the pipe. The results of the comparisons lead to the conclusion that the pressure drop at the interface is very important. Results also showed that in the case of free overfall, the hydrostatic and Bouussinesq models can reproduce air cavity front shape with reasonably good agreement with experiments.

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In this paper, we investigated flow structure and bed deformation around a single spur dike downstream of a pile-group in an open channel. The purpose was to find out an optimum distance between pile-group and spur dike for reducing the local scour. For comparison, a single impermeable spur dike (conventional type) without the pile-group was also evaluated. A series of experiments under emerged flow and clear-water scour conditions were conducted. In the cases with an upstream pile-group, the local scour was faded with a noticeable decrease in the depth and amount of bed erosion. The scour depth and volume were decreased as the distance increased from zero to four times the spur dike length. Flow velocity near the nose of spur dike was higher in the conventional type spur dike. In the cases with a pile-group, flow near the spur dike became lower relative to the conventional case. But, in the main stream the flow increased as the pile-group and spur dike distance increased.

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A linear stability analysis of a laminar open-channel flow bounded in the bottom by a porous medium saturated with the same fluid is performed. The Brinkman equation is employed to account for the viscous shear in the transition between the flow in the fluid layer and the flow in and the underlying porous layer. The critical Reynolds number above which the flow is unstable is found to fall into three distinct modes of instability which are attributed to 1) the free surface, where long waves take place at the free surface; 2) the porous layer, where the instability triggered by shorter waves within the fluid layer extends to the porous layer; 3) the shear layer at the interface fluid-porous layer, where the active momentum transfer from the fluid layer to the porous layer causes the instabilities triggered at the fluid layer to extend further deep within the porous layer. We evaluate the correlation between the modes of instability and parameters such as channel bottom slope, permeability of the porous layer, wavenumber and phase velocity.

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In this paper, three-dimensional smoothed particle hydrodynamics (SPH) method is applied to simulate granular flow past simple types of obstacles. SPH is a mesh-free Lagrangian method and it has the ability to deal with problems with large deformations. An elastic-perfectly plastic model with Mohr-Coulomb failure criterion is applied to simulate the soil, and it describes the stress states of soil in the plastic flow regime. The model was validated by simulating the collapse of the three-dimensional axisymmetric column of sand with two different aspect ratios. The results showed that the SPH method is able to simulate granular flow. A small-scale granular avalanche experiment with different types of obstacles was simulated. The computational results showed a good agreement with the experimental results and the model is considered to be a capable tool for simulating the granular flow phenomena.

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We present a technique which allows determination of spatial modes oscillating at a single frequency. It is Koopman Mode Decomposition (KMD) which is based on spectral analysis of the Koopman operator, an infinite-dimensional linear operator. We performed two algorithms, Fourier-based and Arnoldi-based KMD, on 30-day beam velocities measured by an Horizontal Acoustic Doppler Current Profiler (HADCP) on the Hudson River Estuary. The flow is shown to be dominated by semidiurnal tide, supplemented by sub-harmonic (diurnal tide) and harmonics. Harmonic-average profiles (Fourier-based Koopman modes) correspond to a sinusoidal variation at a tidal frequency, whence a precise temporal rate of change. They also quantify the phase lags at different distances from the river bank. Results show that both algorithms provide quite similar phase lags at these dominant tidal modes.

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In this study, the fluctuation patterns of the long-term groundwater levels at 87 confined and 13 unconfined water observation wells in 42 sites in Tokyo Metropolis were investigated using Self-Organizing Maps (SOM). The SOM application classified the yearly groundwater level fluctuation patterns into eight clusters showing clearly distinguishable patterns which were then divided into 3 large groups. Consequently, the results show that the fluctuation patterns of natural groundwater levels were classified into Group-1. Most of the wells in the Tama region which showed regular fluctuation patterns caused by pumping were classified into Group-3. However, the majority of the wells were moved to Group-2 due to the pumping of drinking water being suspended or decreased. These results show that the SOM analysis was successful in extracting the unique long-term fluctuations of groundwater levels.

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Groundwater model for understanding and predicting hydraulics and contaminant transport in aquifer make assumptions about the distribution and hydraulic properties of geologic features that may not always apply to karst aquifers. In this study, a finite difference groundwater model (MODFLOW-NWT) was applied to construct an equivalent single layer two-dimensional mathematical model of the Ryukyu limestone aquifer, which is located a southern part of Okinawa main islands. In order to handle problems at regional scale groundwater model in the aquifer, automated parameter estimation method (PEST) was used in this model. Groundwater level measurements collected in 1994 were used to calibrate a steady state model of the study area. This study shows the ability of MODFLOW-NWT and PEST to simulate regional groundwater flow in highly karstified aquifer such as Ryukyu limestone aquifer, which is important for water resource and groundwater management in the area.

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Macroscopic dispersivity is the most important factor to analyze advection-dispersion equation at the field scale. Any appropriate method for determining this parameter has not been established yet. If the pollutants exist on the ground surface, the behavior of solute is handled as an advection-dispersion phenomenon in the unsaturated vertical infiltration field. And it is known that fingering flow may occur in unsaturated sandy soil. In this study, conventional saturated-unsaturated seepage analysis coupled with 1/f ^-z model as the geostatistical model of hydraulic conductivity is carried out, and also the advection-dispersion analysis at such an unsaturated infiltration field is carried out. The property of macroscopic dispersivity which is obtained from numerical analysis is investigated.

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This paper presents a stochastic methodology using random walk particle tracking to estimate solute capture zones in a pumping well. Realizations of heterogeneous aquifer are represented as randomly correlated hydraulic conductivity and partition coefficient fields. By superposition of all solute capture zones, probability distributions are obtained that describe the probability of a certain grid space from which a solute particle will reach the well and the corresponding travel time. Proposed methodology demonstrated that a larger pumping rate and less heterogeneity of hydraulic conductivity lead to the decrease of the uncertainty factor, which is defined by the ratio of the area having the probability of non-zero and less than 1 to the area having the probability of 1. Chemical heterogeneity related to the retardation factor distribution has little influence on the both spatial distributions of solute capture zone and travel time.

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Electrokinetic remediation is recognized one of the effective technology to remediate contaminated soils and groundwater. A lot of field applications have been implemented in the world. Before conducting it in the actual field, numerical simulations are indispensable to optimize running conditions. The purpose of our research is to investigate imperative processes that have to be incorporated into numerical simulation. Three kinds of numerical models were compared in terms of reproductively electrochemical phenomenon. The results showed that most adequate model was the ion migration code with chemical equilibrium for ion exchange reaction and surface complexation. Simplification of the model may lead incorrect estimate for the effect of the electrokinetic remediation.

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Arsenic (As) contamination of groundwater has become problem in the world. Although arsenic removal by sand filtration can be used in various area of the world due to the low cost and easiness for maintenance and control, it have not been established how to use sand filtration effectively for arsenic removal. In this study, the groundwater contaminated by arsenic was reproduced by microbiological redox mechanism at first.Second, the reductive water with arsenic(III) was permeated through the column filled with dry sand while changing a condition for verifying performance of arsenic removal. This study showed the effective way of arsenic removal by sand filtration and one of the solution for problem of arsenic contamination of groundwater for drinking.

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A field observation was carried out to evaluate the salt removal performance in a rice paddy due to flooding in Natori city, Miyagi prefecture in September 2013. Salt concentrations in the paddy soil and flooding water were measured by six two-electrode salinity sensors and a soil sampling method for eight days of flooding, respectively. Salt mass content of the soil, Mss, at arbitrary time, t, and depth, z, can be obtained by a statistical analysis. Therefore, the amount of salt mass eluted from the rice paddy, which was calculated from the Mss-t-z relation, was in agreement with the observed value obtained by the sampling method. Salt mass content of flooding water, Msw, increased remarkably in the first three days of flooding, and then the increase rate became gradually smaller with time. It was seen from the present field experiment that 52% of the salt mass in the paddy soil was eluted at the end of flooding period.

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The promotion of heat island mitigation measures is an urgent need in Tokyo. This study simulated evapotranspiration, land surface temperature, and watershed averaged land surface temperature for each individual land-surface feature in the Upper Kanda River Watershed, implementing a water-permeable pavement for roads and green roofs as heat island mitigation measures. The simulation took an advantage of TET model that can express the amount of evapotranspiration, accounting for changes in soil moisture and permeable characteristics of individual land-surface features. As a result, it was found that the state of the soil moisture had a significant effect in the impact assessment of urban heat island mitigation measures.

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This paper explained the uncertainty of discharge due to the uncertainty of rainfall theoretically and mathematically. The lumped rainfall-runoff model is represented by SDE (stochastic differential equation), because the temporal variation of rainfall is expressed by its average plus deviation, which is approximated by Gaussian distribution. As a result, this paper has shown that it is possible to evaluate the uncertainty of discharge by using the relationship between SDE and Fokker-Planck equation. Moreover, the results of this study show that the uncertainty of discharge increases as rainfall intensity rises and non-linearity about resistance grows strong. These results are clarified by PDFs (probability density function) that satisfy Fokker-Planck equation about discharge. It means the reasonable discharge can be estimated based on the theory of stochastic processes, and it can be applied to the probabilistic risk of flood management.

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In recent years, rainfall forecasting technologies and runoff simulation models have been advanced remarkably and some dam inflow prediction methods using a distributed runoff model have been applied to dam operations practically.In this study, the way to identify parameters of the distributed runoff model using the temporary parameters generated in the calculation process of the SCE-UA method (Shuffled Complex Evolution method developed at the University of Arizona) has been proposed and the applicability has been examined using the distributed runoff model applied to the Shingu river basin. Analyzed dam inflow identified parameters using this way shows good agreement with the observed one in many flood events.

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In general, the error sources of flood forecasting by a runoff model include input data, model structure, and parameter setting. The objective of this study was development of a method to minimize errors due to parameter setting. Hydrological parameters of a distributed runoff model were optimized for each of the fifteen past floods by a huge variety of optimization algorithms and three error assessment functions. Although optimized parameters were widely distributed in the search range, a high correlation was found between the optimized parameters and the runoff characteristics. Furthermore, the predictive accuracy of the optimized parameter sets was validated by applying them to an additional ten floods. The validation showed that the parameter sets optimized by floods similar to the target flood in terms of runoff rate can reproduce the measured discharge with high accuracy.

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This paper illustrates parameter identification examples of the distributed runoff model. Parameter optimization tool Colleo, Collection of parameter Optimization software, is developed to aid to exploit 74 different implementations of optimization algorithms by the same employing interface. Applying Colleo to 15 flood events of Gokase river in Miyazaki, the results are achieved as follows. (1) Colleo can find good parameter values to each flood event to reproduce the measured discharge. (2) 13 optimization implementations are specified to be suitable for the distributed runoff model. (3) Important parameters are investigated to improve the fitting by the regression tree analysis. (4) It turns out difficult to calculate the accurate discharge of all the 15 flood events with one set of parameter values. (5) Colleo outperforms SCE-UA optimization algorithm in the limited number of optimization iterations.

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We propose a new geophysical flow circulation model (GeoCIRC) based on object-oriented programming to compute surface and ground water flows. In this study, we focus on an infiltration processes and illustrate the basic structure of the model. The computational domain is discretized with vertical column objects that compute vertical infiltration processes within each column. They are horizontally interconnected and compute horizontal infiltration processes. The each column object consists of layer objects of different properties and resolutions to express weather, ground and geological characteristics. As a computational example, vertical circulation due to the horizontal density difference was reproduced. Then, to verify the accuracy of the model, GeoCIRC was applied to river discharge process in the Kushiro River. The computed results showed good agreements with the CoD of 0.95 and 0.81 for the Gojukkoku and Hirosato river discharge stations, respectively.

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This study attempted to improve a methodology for estimating watershed-scale storage changes from hourly discharge data and to verify its effect in the upper Abukuma River watershed in Japan. The previous methodology separate hydrographs into several discharge sub-components by a filter-separation method, and then it explored relationships between discharge sub-component Q and watershed-scale storage S, assuming power-law relationships between derivative of discharge sub-components dQ/dt and Q. The present study employed linear relationships between Q and S to be theoretically consistent with the filter-separation method in which linear relationships are assumed between Q and S. Based on this theoretical revision, we re-estimated watershed-scale storages to compare with those estimated by the previous methodology. As the result, we found instantaneous increases of storage after rainfall events become smaller and storage change become smoother. In addition, we confirmed the present methodology can estimates more realistic storage than previous one in terms of event-scale water balance.

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When an early rainfall precedes the main rainfall in a river basin,the runoff analysis must consider the change in the soil’s runoff characteristics due to non-rainfall periods and the rainfall’s scale.This study investigates how these factors influence the recovery level of the soil storage capability and proposes a new storage function model. In this paper, we consider the recovery of storage capability in the storage function model constants R and F to improve the conformity of the calculated flow discharges and the observed data.Based on our analytical results of the Honmyo River Basin in Nagasaki Prefecture, the calculated values and the observed data are in good agreement after changing both R and f. In addition,the calculated results are greatly influenced by the difference in the scale of the rainfall used to determine the initial model constants and the main rainfall which is the target of runoff analysis.

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