The present paper introduces the first steps done towards the development of a land data assimilation system for snow, based on the assimilation of passive microwave brightness temperature (TB) observation. It introduces the coupling of a land surface model (JMA-SiB) used by the Japanese Meteorological Agency (JMA) and a radiative transfer model for snow.
In a first step JMA-SiB was extended to consider the change of the snow grain during the winter season, which have a significant impact on the TB observation and the radiative transfer in snow. The model results indicate, that the new version is capable to predict the snow grain size. Furthermore a first version of the coupled system was applied to data observed during the Cold Land Processes Field Experiment (CLPX) in Boulder Colorado (2003), to assimilate the TB change at 89 GHz after snowfall events and the results are in agreement with the observed change of the snow water equivalent at the site.

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Ground-based microwave radiometric field observations were conducted by using the Ground Based Passive Microwave Radiometer (GBMR) at frequencies of 6.9, 10.65 and 18.7 GHz to gain a better understanding of the physical mechanism of the radiative transfer process taken place in dry soil media. A metal plate was used as a bottom boundary and dry soil was put on it by increasing its depth one centimeter by one centimeter. The observed brightness temperature increased as the dry soil depth increased, while the increment of brightness temperature per one centimeter increase of soil depth was getting smaller. This behavior demonstrated the existence of volume scattering effects in the dry soil. Three models: surface emission model, Mie-scattering model and dense media radiative transfer model, were applied to the experiment results. The dense media radiative transfer model shows the best agreement with the observed data.

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Different multivariate statistical techniques were used to evaluate temporal and spatial variations of surface water-quality of Fuji river basin using data sets of 8 years monitoring at 13 different sites. The hierarchical cluster analysis grouped thirteen sampling sites into three clusters i.e. relatively less polluted (LP), medium polluted (MP) and highly polluted (HP) sites based on the similarity of water quality characteristics. The principal component analysis/factor analysis indicated that the parameters responsible for water quality variations are mainly related to temperature (natural), organic pollution (point sources) in LP areas; organic pollution (point sources) and nutrients (non point sources) in MP areas; and organic pollution and nutrients (point sources) in HP areas. The discriminant analysis showed that five water quality parameters account for most of the expected temporal variations whereas six water quality parameters account for most of the expected spatial varitations in surface water quality of Fuji river basin.

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Since suspended sediment and organic matter loads were extremely high in Nhue River (Hanoi, Vietnam), a 2-D depth-average model was constructed to simulate hydrodynamic state, suspended sediment transport and environmental change around the confluence between Nhue River and its tributary, To Lich River. The biochemical conversions were constructed based on the QUAL2E conceptual scheme. The model is capable of backwater simulation that was frequently seen there. The simulation results indicated a strong suspended sediment deposition. A clear deterioration of environment was simulated. Within few hundred meters from the confluence two water masses were incompletely mixed in normal discharge condition.

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This paper deals with the use of Monte Carlo optimization and Artificial Neural Networks (ANNs) for deriving monthly reservoir operating rules. The procedure generates synthetic inflow scenarios which are used by a deterministic optimization model to find optimal releases. The ensemble of optimal release data is related to storage and inflow in order to form allocation rules. Different from the common use of regression analysis to define equations relating releases to the other variables, this paper uses ANNs to calculate the releases to be implemented at each period. Simulations based on the use of numerical interpolation instead of ANNs are used for comparison. The procedure is applied to the multipurpose reservoir that supplies the city of Matsuyama in Japan and the results show high correlation with those using optimization under perfect forecast.

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In this study, the surface energy and water balance components and related hydrological variables of the Seyhan River basin Turkey are estimated through off-line simulation of the land surface model. The simulation domain is 2.75 degree × 2.75 degree area (E34.25-37.0, N36.5-N39.25) with 5 min resolution (33 × 33 grids). As for the atmospheric forcing data, the products from RCM (Regional Climate Model) for both present and future (warm-up) condition are used. Based on the field survey and NDVI time series analysis, landcover dataset of this target basin is improved and utilized in the numerical simulation. In terms of basin average annual water balance, precipitation is projected to decrease about 210mm, while evapotranspiration increases about 30mm by the higher evaporation demand. This means that the reduction in runoff is about 240mm. Furthermore, irrigation water demand will increase about 10mm. Considering the amount of present water balance, these impacts are thought to be significantly large.

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Distributed representation of spatial information and physical description of hydrological processes are necessary in large river basin because of the highly nonlinear hydrological processes and the variability of the spatial heterogeneity. It is important to represent both geomorphologic properties and land cover char acteristics in hydrological simulation in large river basin. The DBHM (distributed biosphere hydrological model) employs a flow intervals discretization scheme in the representation of geomorphologic properties and a simple biosphere model in the representation of land cover characteristics to simulate integrate hydrological processes in a large river basin. The geomorphologic properties are abstracted from digit elevation model. The hydrological part estimates the surface runoff and calculates the interlayer exchanges within the soil profile and interaction between soil water and groundwater. The land cover characteristics are described by satellite data and the flux transfer between atmosphere and vegetated surface is calculated by a realistic land surface model SiB2. The DBHM can represent the role of both topography and land cover characteristics in hydrological cycle. The model was applied to the Yellow River Basin to investigate its applicability to a region with large variations in topography, land cover and climate. The hydrological simulation has implemented by hourly time step with a spatial resolution of 10 km mesh. The simulated hydrographs were compared with observations for evaluation of the model performance. The results shows evaporation in irrigation districts is much larger than the evaporation in the surrounding area in semi-arid area, indicating human water regulation had affected the hydrological cycle in the Yellow River basin.

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New attempt of ensemble rainfall-runoff prediction is presented with radar rainfall prediction and spatial random error field simulation. A radar image extrapolation model gives deterministic rainfall predictions, and its prediction error structure is analyzed by comparing with the observed rainfall fields. With the analyzed error characteristics, spatial random error fields are simulated using covariance matrix decomposition method. The simulated random error fields successfully keep the analyzed error structure and improve the accuracy of the deterministic rainfall predictions; then the random error fields with the deterministic fields are given to a distributed hydrologic model to achieve an ensemble runoff prediction.

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Recent applications of the University of Yamanashi Hydrological Model (YHyM) to the Mekong and Yellow River basins reveal significant influence of snowmelt runoff on observed discharge during post-winter months. In additional, there is a need for the development of a new snow model that requires minimal data input, since the majority of data, especially snow data, is not available for these basins. The aim of this study is to give a description of the development of: 1) a distributed snow accumulation and ablation model; and 2) a new methodology of degree-day factors estimation. The developed snow model coupled with the method of degree-day factors estimation has been applied, as a test run, to the Yellow River basin.

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This paper tried to clarify the effects of capillary rise on subsurface runoff through a recently suggested water balance model for representative elementary watersheds (REWs). We focused on saturated zone water balance of a REW model effected by the capillary rise, in comparison with to the Tank model. The results and discussions on the comparison led the followings: (1) Capillary rise is effective under arid climate than humid climate. (2) This tendency is enhanced under climates with clear difference between wet and dry seasons. (3) REW models have potential to describe and diagnose basin's processes based on the mass and momentum balance equations better than Tank models and other lumped water balance models. (4) REW models can be more suitable than Richards equation based models under arid climate if user's requirement for model structure is only unsaturated and saturated zones.

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A distributed hydrological model was used to simulate hydrological processes in Agatsuma River basin at hourly time steps. By using interpreted radar products and rain gauge rainfall data, simulated inflow to Shimagawa dam have been used as input to a reservoir operation module running simultaneously with the distributed hydrological model. The reservoir operation module uses a storage function approach in order to update the actual volume dam at each time step. Volumes were translated into water levels by using an H-V curve. The operational rule uses the updated water level in order to decide release. The developed scheme offers an easy way to modify the operation rule; therefore, it allows for the incorporation of an optimization scheme in future research. To reduce potential damage of floods and droughts in Tone River basin an optimal reservoir operation scheme will play an important role in the protection of downstream areas and contribute to effective use of water resources.

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In July 2004, torrential rain induced by baiu.front caused devastating floods in the Asuwa River basin damaging five railway bridges between Fukui and Miyama stations on the JR Etsumi Hoku line. The Asuwa River basin has only one river gauging and two AMeDAS ground rainfall measuring stations. Those limited data are not sufficient to forecast the heavy floods caused by unprecedented downpours. A physically based distributed TOPMODEL with Muskingum-Cunge flow routing method and radar derived rainfall intensities are used to simulate hydrological processes of the basin. Results show good agreements with observed discharges at Tenjinbashi gauging river station. Simulated distributed discharge values are used to compute the bending stresses of the collapsed railway bridge piers and compared with respective bearing capacities. The main objective of this paper is to introduce the state of art of distributed hydrological modeling with radar derived rainfall inputs to identify the river structures along the river channel that are vulnerable to floods.

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From the viewpoint of watershed management, paddy areas are regarded as having important functions beyond their role in food production; these include flood regulation, fostering of water resources, and prevention of soil erosion. These functions are commonly found in low-lying paddy areas such as in Japan, Cambodia, Vietnam, and other countries, where the levels of development of paddy irrigation are quite different. In this study, a flood inundation model, which covers floodplains of the Mekong River from Kratie in Cambodia to near the Vietnamese border, was developed by using the FEM technique with 2-D shallow water equations. The model was applied to the water flows over the years 1996 through 2003. Main roads, dikes, colmatages, and waterway-opening works in the study area, which enable water to be stored, were taken into account in the simulation. The flood regulation function of paddy fields in the study area was then assessed, using the results of the model simulation and land-use data. Namely, the volume of flooded water on paddies was estimated in order to evaluate the impact of flood storage by paddies on floods and water use. The results showed that about one-fifth of the total flood volume is stored on paddies in and around Tonle Sap Lake, and rice cultivation starting after the flood waters recede.

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An approach is presented to solve the Philip's equation with time compression approximation (TCA) for simulating infiltration under variable rainfall. This approach brings understanding into physical processes of infiltration and ponding during variable rainfall storms. In particular, we apply it into the Yamanashi Hydrological Model (YHyM) for analyzing the infiltration excess runoff in arid and semi-arid regions. The soil water redistribution is also included to simulate the soil moisture changing during the temporal gaps among storms. The modified YHyM was tested by a case study of Lushi River basin, China. Through comparisons of results from the modified YHyM with results from the unmodified YHyM, the presented TCA based infiltration model is proved to be able to improve the performance of YHyM in peak runoff calculation during variable rainfall multi-storms in arid and semi-arid regions.

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This study proposes the use of multiobjective optimization of a conceptual hydrological model with perturbed data as a sampling method to reproduce the posterior distribution of parameters for the quantification of uncertainty. The Pareto front is found to be sensitive to perturbed data, so model parameters are optimized with different combinations of perturbed data sets to sample behavioral parameters. Latin Hypercube Sampling (LHS) method was used to sample the behavioral parameters in order to evaluate the performance of the proposed method. The performance of simulation for all parameter sets sampled by both methods is evaluated and presented in objective space. The proposed method sampled large parameter sets more efficiently near optimal compared with LHS. The study demonstrates that the Elitist Non-dominated Sorting Genetic Algorithm (NSGA-II) a multiobjective optimizer, with perturbed data set can efficiently explore near optimal parameter space of a conceptual hydrological model.

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The aim of this study is to assess the uncertainty in precipitation using a distributed hydrological model. Firstly, a true model is established and then error is applied to true precipitation. The uncertainty is analyzed by using sensitivity analysis approach for systematic error and Monte Carlo approach for random error. Next, the parameters of the model are calibrated with erroneous data. Finally, the impact of low precipitation is assessed by neglecting different levels of low precipitation. The result of the study for a Nepalese river basin shows that a systematic error exceeding +/-10% causes significant impact on simulated flows. The impact of normally distributed random error with standard deviation equals to 10% of observed precipitation is not substantial. The calibration of parameters can adjust the low error, but the higher errors should not be compensated by just fitting the curve. Error on low precipitation of amount less than 0.5mm measured with some error does not affect the flood discharge.

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In this paper a blind test methodology is described and applied for inter-comparison of hydrological models using publicly available global data sets. The model inter-comparison involves making “blind”prediction of selected hydrological responses in the Mae Chaem basin (3853km²) which is located in the North West of Thailand. Moreover the value of the publicly available data sets (e.g. various satellite-based precipitations) is investigated to determine their suitability for Prediction in Ungauged Basin (PUB). The distributed hydrological model BTOPMC is applied for runoff simulation. Transfer parameters from proxy catchment and a limited measurement method are used for model parameters estimation. Though each of the satellite-based precipitations underestimated the flow, GPCP was found best among them and it showed that the application of satellite-based data in PUB is encouraging. The study also prepared a base for model inter-comparison in the Mae Chaem basin.

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A pseudo validation algorithm, which is capable of identifying the prediction uncertainty through recognizing and quantifying the different uncertainty sources in a hydrologic model, is manipulated as an instrument for hydrological model reliability assessment. For implementation, the pseudo validation algorithm is manipulated in order to compare TOPMODEL with different vertical flux calculation components, which have been applied to two Japanese basins. An index, which originates from the Nash-Sutcliffe efficiency, named Model Structure Indicating Index (MSII), is used to quantify the model reliability under different magnitudes of input uncertainty. The results show that within a small magnitude of input uncertainty, the reliability of a five parameter TOPMODEL is worse than a six parameter TOPMODEL. However, within larger magnitudes of the input uncertainty, the reliability of the five parameter TOPMODEL is better than that of the six parameter TOPMODEL, this shows that the pseudo validation algorithm can be used as a reference for hydrological modeling.

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It is found that basin hydrological response and model effective parameter identification in relations with the drainage basin dominating geomorphological parameters is directly influenced by the scale of DEM resolution. Thus a scale independent relationship in flood routing models is necessary for consistency in rainfall runoff translation at a scale of interest. To overcome this problem downscaling methods of dominating geomorphometric parameters are used to obtain the scale invariant distribution function of cross-section, depth, discharge and wave celerity from different DEM resolutions. The downscaling methods of the flow variables is then coupled with the Muskingum-Cunge routing method to develop a scale invariant routing model.

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A nonlinear analysis procedure has been proposed to simulate the spatial variation of velocity profile of pressurized laminar flows between wavy boundaries as an idealized flow model in rock fractures. The main objective of this analysis is to refine the depth averaged flow model for a rock joint, reflecting the results of this analysis. The analysis is based on an assumed general form of velocity profile in the direction of flow, whereby the unknowns are determined through the use of the continuity and momentum equations. Comparison is made between the 2D-vertical model's results and the nonlinear solution through which the applicability of the analysis is verified. The nonlinear solution shows good agreement with the 2D-vertical model's results especially for small amplitude-to-wavelength ratio of the wavy boundaries, but enough to reveal the velocity profile's deformation.

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Ocean waves in reality often have a strong non-linear shape when propagating to shallow water, and the gap from the sinusoidal wave become remarkable. Therefore, it is generally believed that wave boundary layers, bottom shear stress and sediment transport behaviors actualizing the effect of non-linearity are different from sinusoidal wave. However, the example of research treating such turbulent boundary layer and sediment transport characteristic is very few. Therefore, the accuracy of bottom shear stress and amount of sediment transport used to evaluate the beach morphological change obtained from the wave motion model of sinusoidal is necessary to be clarified by that of non-linear.
In this present study, turbulent boundary layer characteristics for asymmetric or non-linear waves according to the non-linearity effect is examined through both experimental and BSL turbulence model. Moreover, a new calculation method of bottom shear stress based on incorporating acceleration and velocity terms is used to examine both the experimental and BSL model results of bottom shear stress.

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To numerically simulate “bedload transport” of sediment by a turbulent flow over an erodible bed, our group has been developing “fictitious domain” methods to handle dense-phase particulate flow in turbulent flow of liquid. We report on efforts to check our simulation method against experiment for a dense-phase particulate flow in liquid, namely a rotating drum half-filled with spherical particles. Overall agreement between experimental and simulated values of static and dynamic angle of repose is found to be quite satisfactory, both in air and in oil.

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A 3-D numerical model, which employs the large eddy simulation (LES) and the modified Smagorinsky model, is used to simulate the motion and diffusion of 3D suspension gravity currents under the presence of a turbidity fence. The model constants are determined using the existing data of 2D suspension clouds, and then the validated model is applied for newly obtained experimental results on 3D suspension gravity currents under the presence of a fence. It is confirmed that the model is capable of predicting the complex behavior of the currents to a reasonable accuracy, and the amount of sediments contained within the fence to a good accuracy. In addition, numerical experiments are conducted to demonstrate that the model is a useful tool to examine the placement of a fence to effectively reduce diffusion of turbidity in aquatic environments.

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Salinity intrusion into estuaries, in general, is mostly affected by river water discharge and tidal level. In addition, the change of salinity can also be influenced by other external forces such as wave height, river mouth morphology. However, there has been none of the study considering this kind of aspect. In fact, the rapid change of river mouth morphology can strongly effect on salinity distribution. Hereby, we carried out the study at the Nanakita river mouth for considering the effect of morphology and wave height. One maneuver to escape the situation of lacking in morphology data is to use the digital camera for taking and collecting oblique photographs. Once this technique is utilized, the highly frequent morphological data can be obtained. These data are useful to the simulation of salinity intrusion into the river mouth with a short time interval. Furthermore, effectiveness of each external force also will be examined by sensitivity analysis .

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The winter current pattern in 2003 in the Ishikari Bay was investigated by using the Princeton Ocean Model (POM) and field observation data. The model was forced by six hour, spatially distributed wind and open boundary forcing. The later was obtained from larger scale model namely Japan Coastal Ocean Predictability Experiment (JCOPE). Through three numerical experiments with different driving forces the following conclusions have been deduced: (1) the open boundary forcing is the major driving force for current in deep water, the effect of wind in this region is limited in few surface layers (2) the flow along the shelf and current in shallow region are mainly driven by wind forcing (3) circulations occur in the shallow area during strong wind conditions. A comparison between observed and computed current velocities showed that the model is capable to reproduce current pattern in the bay.

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Rain induced landslide is increasingly becoming major natural disaster. Although pore-water rise in the soil domain is taken as the cause of the landslide, it is yet not clearly known the response of pore-water pressure in different complexities of the soil domain. Multiple layers of soil with different hydraulic properties is one of the common complexities found in the field. We have tried to find out the mechanisms of moisture content variation and landslides in single and two layered slopes. The results showed that the upper layer which has higher hydraulic conductivity experiences slide first in case of two layered slope while slide of whole depth occurred in the single layered slope. A numerical model was also prepared to simulate the infiltration and landslide due to rainfall. The results as timing of landslide and moisture movement pattern from experiment and numerical simulation are quite close. The results encourage further research towards making landslide predication model.

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The sources of sediment deposited in Sengguruh and Sutami reservoirs are detected by qualitative analysis of grain size distribution and mineral composition resulted from x-ray powder diffraction (XRD). Grain size distribution of sediment in Sengguruh reservoir shows that Lesti sub-basin contributes higher percentage of sand particles than Brantas sub-basin. The most dominant minerals in Sengguruh reservoir are Feldspar and Carbonate (Calcite). In Sutami reservoir, the most dominant minerals are Feldspar, Mica and Chlorite. The difference of mineral composition both of reservoirs indicates the increasing of sedimentation from Metro-sub-basin. Now, it should be considered while it was neglected in the past.
Finally, the proposed method is applicable to assess sub-basins contribution of sediment origin and to evaluate the existing sedimentation countermeasures.

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An analytical model for the prediction of local scour depth around bandal-like structures is developed using the basic features of laboratory experiments under clear-water scour. The developed model is applied to available laboratory data as well as field data along the Jamuna river in Bangladesh. It is found that the model fits the experimental data having relatively shorter length but failed to predict the field data where length of the structure was relatively longer. The underlying reasons of such success and failures of the model for the prediction of local scour depth around BLS is discussed with the future target to develop more generalized prediction model.

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A vertical two-dimensional morphodynamic model with non-hydrostatic, free surface flow is reported herein. This numerical model can simulate flow and turbulence characteristics over sand waves. Likewise, model can reproduce the sand wave formation and migration process as well as free surface oscillation simultaneously in a moving boundary domain with the implication of generalized coordinate system. A nonlinear k-ε model is employed as a turbulence closure. CIP numerical technique is used to resolve advection term of momentum equations. An Eulerian stochastic formulation of sediment exchange process in terms of pick up and deposition function is incorporated to simulate non-equilibrium sediment transport that explicitly considers the flow variability during morphodynamic computation. The numerical model is validated with experimental data on flow and turbulence over fixed dunes as well as laboratory measurement and visualization of dune geometry and migration.

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The aim of this paper is to improve an understanding of physical processes involved in sediment transport mechanisms and bedform evolution in a two stage meandering channel. In this study, a laboratory flume was used since it is difficult to observe bedforms and to obtain sediment transport rates in natural rivers during flood. A series of experiments were conducted to measure stage-discharge data, sediment transport rates, and bedforms in a meandering channel with different roughened floodplains for overbank flows. Detailed measurements have shown that the bedforms considerably vary with different water depths and floodplain roughness. The sediment transport rate increases while the flow is inbank, and once the flow is overbank, it starts decreasing till at a certain water depth and then increasing again. The bedforms have ripples and dunes at a water depth when a minimum sediment transport rate occurs. The water depth at the minimum sediment transport rate also varies due to floodplain roughness.

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Accuracy of parameter estimation methods to be used in extreme value analyses for censored annual maximum samples is investigated using a Monte-Carlo simulation technique. The methods are maximum likelihood method (MLM), least square method (LSM) and partial probability weighted moment (PPWM) method, and probability distributions are Gumbel, shape parameter-fixed GEV and Weibull distributions. MLM yields more efficient estimates of quantiles than PPWM method and LSM even for censored samples. MLM-, LSM- and PPWM-based models are applied to extreme value analyses to several types of censored in-situ annual maximum samples. One finding is that inclusion of historical information in MLM- and PPWM-based models produces more efficient estimates of quantiles.

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We need to discuss that the well-precisely estimate of design rainfalls regarding design high and low water-level of a river is one of the most significant problems. Moreover, we have to consider about to improve the awareness of emergency from disaster for people who live along a river.
In this paper, we clarified the non-stationary properties of precipitation by a time series analysis. The sum of trend and period components of each of the 22 meteorological observatories in Hokkaido was shown to have 30%-67% variance of original series. Next, we decided the optimum probability distribution models of the annual precipitation, the annual maximum daily amount of rainfall and the annual maximum number of days with continuous non-rainfall in 17 models by the Standard Least-Squares Criterion. Finally, it was shown that the design rainfall for flood management changes extremely, as a result of the change of the T-year probable hydrological amount and its return period from 1989 to 2004 using the Generalized Extreme Value distribution. Especially, the Okhotsk Sea area indicated to decrease the safety factor for flood management.

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The objective of this study is to evaluate the effects of temporal resolution of rainfall on flood runoff analysis. When the temporal resolution of rainfall is lower than the time scale of the catchment, the calibrated model parameters may include the uncertainty caused by the poor temporal resolution. The calibrated parameters may different with the “true value”. Rainfall data with different temporal resolution are generated by a random cascade generator. Then, these data are used to investigate the effects of temporal resolution on the model parameters calibration. It is shown that the temporal resolution of the hydrological data has significant effects on flood runoff analysis. Furthermore, a method to eliminate the effects of temporal resolution of hydrological data is proposed. By using this method, their “true values”of the parameters invariant with temporal resolution can be estimated.

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This paper proposes a method of correcting variance of point monthly rainfall directly estimated as sample value with low frequent observations from space. First, expectation of sample variance of monthly rainfall is formulated as a function of frequency and length of observation. In the formulation, key parameter is correlation time length. Second, the formulation is validated using high frequent observations by a ground-based weather radar. Third, a method identifying the parameter when only low frequent observations are available. As a result from application to TRMM/PR observations, it is shown that the formulation and the method of identification work well and importance of incorporating spatial correlation in further correcting sample variance of areal mean monthly rainfall.

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We describe impacts of global warming on heavy precipitation characteristics and flood risk using the 2-day precipitation of the 12 General Circulation Models. The frequency analysis based on partial duration series was carried out. The model ensemble average 200-year quantiles in Tokyo during 2050-2300 under the climate condition of IPCC SRES-A1B scenario were 1.07-1.20 times as large as the one under the present climate condition. Those influences on runoff discharge and flood risk in the Tama river basin were investigated using the numerical simulations. The estimated high water discharge rise by 10-26%, and the flood volume increased by 46-131% if the precipitation with a 200-year return period occurred.

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We investigated several effects of global warming to hydrological and meteorological environment. JMA/MRI have carried out simulations of global warming due to doubled CO₂ by using their CGCM. They downscaled those results using a 20km scale regional meteorological model. We examined the effects of global warming on hydro-meteorological environment, viz; annual average temperature, annual maximum daily precipitation, annual precipitation and maximum dry duration, using Welch's test. As a result, mean of annual precipitation during 2080 and 2100 indicated an increasing trend that is significant at the 95% confidence level in some part of Japan, while no trend was detected in its variation. Moreover, we examined daily sea surface pressure and wind velocity at surface and 500 hPa in order to derive trend of tropical storm. The data show that percentage of intense tropical storms in total tropical storms increases when the global warming proceeds, as recently suggested by Webster et al. (2005).

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It is known that fingering flow may occur in unsaturated sandy soil. But numerical simulation cannot realize that if the soil is assumed to be uniform. In this study, conventional saturated-unsaturated seepage analysis coupled with 1/f^-ζ model as the geostatistical model of hydraulic conductivity are carried out. The results show that if the mean value of hydraulic conductivity is relatively high, the fingering flow can be simulated even though the variance of hydraulic conductivity is very low. It can be explained by the difference of water retention curves. The shapes of flow path can be characterized by fractal dimension. If the mean value of hydraulic conductivity is relatively low, the fingering flow rarely occurs except the case of the variance of hydraulic conductivity is very high.

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In solute transport through porous media in column experiment, increasing of apparent dispersion coefficient D as distance can be observed. This kind of phenomena has been thought by heterogeneous permeability. But Taylor theoretically explained by Lagrangian correlation function that constant coefficient D requires a time while solute particles go through various velocities. This concept can be used in porous media also.
As a phenomenon to simplify porous media flow, solute transport in laminar pipe flow is studied. Solute transport is simulated by stochastic-Eulerian approach and compared with previous theories from Lagrange or Euler view points. Results show good fitting to the Lagrangian correlation theory and time scale t₀, in which D changes. Furthermore, they indicate that D is underestimated by using 1-D Eulerian theory in time scale same as t₀.

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In general, hydro-geochemical characteristics of field soil porous media are distributed with large heterogeneity. This heterogeneity affects not only physical parameters such as saturated hydraulic conductivity but also chemical parameters such as cation exchange capacity. Evaluation of chemical and physical heterogeneity effects on transport of contaminant species is important to understand basic transport characteristics of field soils. In this study, three kinds of heterogeneous fields were generated. We demonstrated acid flushing of lead contaminated soil in these heterogeneous fields. Then apparent dispersivities were evaluated for injected protons transport. The simulation results displayed preferential flow due to the heterogeneous distribution of hydraulic conductivity. Although clear relationship between dispersivity and correlation length was not obtained, the cation exchange reaction with heterogeneous CEC distribution and surface complexation reaction were seen to have a significant effect on the transport of dissolved species.

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Laboratory tracer experiments were conducted to investigate solute transport in 100-cm long, horizontally placed transmissivity field under steady saturated water flow condition. Uniformly packed homogeneous and layered formations of sand having cross-sectional areas of 50×6cm² were used under various hydraulic gradient conditions. NaCl breakthrough curves in the flow fields were measured with salt sensors inserted along flow direction. Dispersivity and dispersion coefficient were estimated through genetic algorithm (GA) linked with an analytical solution of the advection-dispersion equation and were identified using image analysis based on obtained images of tracer movement. The results show that dispersivity estimated from image analysis is about one order smaller than that GA estimates and the ratio of transverse dispersivity to longitudinal dispersivity ranges from 0.15 to 0.8 in an experimental field. Additionally, estimation of dispersivity in layered media depends on transport pathway of contaminant, suggesting the importance of observation location in parameter estimation.

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As river surface water permeates into sandbar and river bed, there is a process by which suspended load (organic matter, sand, etc.) infiltrate into soil pores. As suspended load infiltrates the pores, it causes clogging, and can become the cause of a degradation in permeability. Because such phenomena can influence the hydrological and chemical cycles, it is necessary to examine the mechanism by which clogging resulting from infiltration occurs. In the present research, an example of the permeability degradation as a result of clogging is presented. In order to model this process, an experiment in which only flow was changed so that fine particles passed through a sand column was conducted, and the relationship between permeability degradation and the clogging process was quantified. Then the phenomena was modeled with a numerical model considering permeability degradation and sedimentation of fine particles, and the experimental and numerical results were compared. With the experimental and numerical results, the process of permeability degradation due to the accumulation of fine sediment was illustrated, and the vertical distribution of fine sediment in sand column pores was expressed with the numerical model.

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To clarify the mechanism of water movement through a natural forest slope, its soil water content was measured and discussed on the relation between its change rate and unsaturated vertical flow, antecedent precipitation index (API) and slope discharge. Soil water content was measured during and after rainfall events by electric reflectometers at 3 depths (from 0.1 to 1.0m) of 3 places and its change rate was calculated. The relation between water content of shallow soil and its change rate suggested that the vertical water percolation was caused under conditions of unsaturated hydraulic conductivity proportional to (θ-θ_r)^n₁ (θ: volumetric water content, θ_r: residual volumetric water content, n1: constant) and hydraulic head gradient equal to 1. The relation between averaged water content and values of several types of API showed that API₂(t)=Σi^b₂ P(t-i) (P(t-i): precipitation on the i-th day before the t-th day, b₂:contant) is good as a slope API. The slope discharge could be expressed as a function proportional to (θ-θ_r)^n₂ (n₂:constant) with θ averaged spatially and this function could estimate the discharge from a slope during rainfall.

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Salt water intrusion in a coastal aquifer varies corresponding to the sea level and rainfalls. The influence of tidal river might be added to the behavior of salt water intrusion when the aquifer locates near the tidal river. Consequently it is easy to understand that the behavior of salt water bodies in such a situation will be quite complicated. The present study describes the findings about the salt water intrusion on the basis of the long-term field measurements conducted near a tidal river. Following findings were obtained: 1) The interface of fresh-salt water bodies in an aquifer consists of a wide mixing zone. 2) The depth of mixing zone varies cyclically and more largely during a spring tide than a neap tide. 3) Rainfalls may have the possibility to uplift the upper mixing zone remarkably for a short period after the rainfall event. Such possibility has to be verified in the future.

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With the development of urbanization since the 1960's, infiltration and recharge of rainwater into the aquifer systems decreased drastically. Increase in the population also created a difficult situation for supplying sufficient water resources to the urbanized area. Therefore, effective utilization of water resources and development of unused water in the regional scale should be studied. A conventional hydrological cycle model combining the rain water recharge tanks with the quasi-three dimensional groundwater flow model was developed taking account of the land use and geological conditions.
The development of regional water resources was discussed by using the present model. Various hydrological components of the water balance estimation in the study area were clarified. It was concluded from the present study that the proposed conventional model is useful and applicable for making a plan of water management.

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In the Marugame plain, recent variation in the hydrologic cycle due to landuse change has posed urgent need to develop new water resources in harmony with the sustainable water cycle. In this paper, measurement of confined and unconfined groundwater and data collection of water uses in the plain were carried out and a numerical analysis of the hydrologic processes for five years including dry and wet years was performed using the MIKE-SHE model, with special emphasis on agricultural water use. It was made clear that the numerical model can fairly reproduce the daily river discharge of the Doki River and the groundwater levels in the plain. And water balance analysis for 1996 showed that the evapotranspiration accounted three-quarters of the annual precipitation and that the domestic water use is heavily dependent on the groundwater and the water introduced through the Kagawa water conveyance channel.

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Physical understanding of subsurface water characteristics is quite important for the efficient use of water resources, since heavy rainfall infiltrates into the underground and much water is being used from the underground through the pump or the well in our lives. From this point of view, we developed a practical tool that can analyze the quantity of the water under water circulation. The model consists of three sub-models: surface model, subsurface model, and database model. In this integrated model, we have also incorporated a function which can precisely evaluate the interaction between river and subsurface and can assess the cultivation water for the paddy field. The model has been applied to the simulation for the Ryochiku plain, Japan. The numerical results on the groundwater level and the river discharge have been compared with corresponding field observations. Good agreements have been obtained.

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Contamination of unconfined groundwater by nitrate nitrogen has been reported at several locations in the Takamatsu plain. To understand the mechanism and the extent of groundwater contamination, a target region in the plain was selected where the nitrate nitrogen has shown high concentration throughout the year. Intensive field measurement of groundwater level, EC, pH and the analysis of major ions in the groundwater were performed seven times in 2004 at twenty four shallow wells. The rate of stable isotope of nitrogen was also analyzed at two different seasons. The obtained data clarified that the nitrogen in the unconfined groundwater from the ground surface has been not only inorganic nitrogen but organic. It was also indicated that the fertilizer in the greenhouses for vegetables and waste water from a cow barn in the target area have been the major sources of the nitrogen.

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In this study, a new method to detect the underground water path positions was developed. Water path position was estimated by the sound of ground water flow. As a first step, water flow through a single water pathway installed within an isotropic model soil layer was examined by this method. From the measured sound pressure, position of sound source was estimated. Results indicated that the estimated position of sound source corresponded to location of the installed actual water pathway. As a next step, this method was also applied both to natural hillslopes and road cut slopes. Water springs from lower part of every slope were observed, and the relationship between estimated water pathway within the slopes and the position of these springs were examined. Results indicated that the estimated water pathways were corresponded to springs position with accuracy of 0.5 m or less. From these results, it is obvious that we can detect underground water pathways with high accuracy using this new method.

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We have developed and implemented a real-time dam inflow prediction system based on a distributed rainfallrunoff model. The system predicts dam inflow for 6 hours every 10 minutes, receiving predicted rainfall data and calculating hillslope runoff and river flow on channel network. River flow is routed with the lumped kinematic wave model, of which state variables are updated by the Kalman filter with observed inflow data of the dams.
Additionally, to improve the accuracy of prediction for practical use, we estimate effective precipitation using a runoff coefficient which varies with cumulative rainfall, and introduce addition of base flow discharge considering influence of snow melt.
The system has been already installed into the dam administration offices on the Kurobe-River basin and is being used for practical purposes.

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The purpose of this study is to develop a upstream and downstream consistent distributed snowmelt runoff model including reservoir regulation, and carry out runoff analysis in the Sagurikawa River basin, which includes a reservoir. It aims at realizing reservoir operation in consideration of the action of the water in a basin, and grasping the amount of water resources of study basin by using the upstream and downstream consistent distributed snowmelt runoff model including reservoir regulation. The delineation of channel network used by the distributed hydrological model was created, and the upstream and downstream consistent distributed snowmelt runoff model includes reservoir regulation was developed. In this model, since the whole basin can be taken into account, it is possible to take various dam managements into consideration.

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