Daily snow water equivalent, snow depth and snow density distribution were estimated form SWE model with the meteorological data, satellite data and DEM. The SWE model was composed of snowfall model and the snowmelt model. The daily snowfall was estimated using weighted average distance method from AMeDAS data. The daily snowmelt was estimated using the degree-day method in the snowmelt model. Comparing snow distribution from the SWE model, the snowmelt rate factor was not much different in east and west Japan. As a result, the snowmelt rate factor was about 4 to 5 millimeter per day per degree in one snow season. The process of snowfall-accumulated was also evaluated in the different regions.

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Forecasting a snow phenomenon in the cold districts is a very important countermeasure to realize the repression of the natural disaster and the altitude use of the water resources. On the other hand, there are few examples that all necessary weather data are observed with a superficial spread in every time in the applicable basin. Therefore, the strict forecasting model of a snow phenomenon has low practicality in the present condition of such weather data observation. The model can forecast a change of snow depth and snowmelt rate of the snow layer by using only temperature is developed based on such conditions, and it aims at contributing to building of the safe society economic base it can be relieved, and reported here.

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Effect of snow on vegetation activity in snowmelt season and after disappearance of snow is analyzed using climate data, snow accumulation-snowmelt model and distributed hydrological model. Vegetation activity is evaluated with NDVI (Normalized Difference Vegetation Index) derived from AVHRR/NOAA data. The Snow accumulation-snowmelt model can estimate snow water equivalence and snowmelt. The distributed hydrological model, which consists of 2 layers (snow and surface) and 2 tanks (soil and ground water), can estimate runoff, soil moisture and so forth.
It is shown that firstly, vegetation activity decreases if the snow water equivalence is higher than 500 mm, secondly, accumulated snowmelt for 10 days is estimated 15 days before from observed day and vegetation is more active if the snowmelt is higher than 20mm, finally, vegetation is more active if the soil wetness index is higher than 70%.

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This study developed a satellite algorithm for snow depth and snow grain size basedon the microwave radiative transfer theory used the dense media model and the 4-stream fast model and validated by using the in-situ snow depth data at the 75 ground-based stations in the northern hemisphere and the Advanced Microwave Scanning Radiometer for the Earth Observation System (AMSR-E) on Aqua launched by NASA in 2002. The results of validation were show good correspondence of observation value and estimation value.

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This paper introduces microwave radiometric data, snow pack properties and meteorological forcing data observation collected during the winter season '02/'03 in Fraser, Colorado, USA. The observation was part of the NASA Cold Land Processes Field Experiment (CLPX) at the Local Scale Observation Site (LSOS). Apart from continuous observation of meteorological data, which can be used to constrain physically based snow models, intensive ground-based passive microwave observations have been implemented during the winter season. Furthermore regular observations of snow pit properties have been conducted, including the snow density and snow grain size profiles. The data set provides the possibility to evaluate and improve radiative transfer models for snow and satisfactory modeling results have been achieved using the dense media radiative transfer theory (DMRT). All data will be released to the public on October 1, 2004 and are available from the website of the National Snow and Ice Data Center.

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This paper introduces a remote sensing based snowmelt model and its coupling with a metrological based distributed hydrological model in the Upper Yellow River Basin in China. Until the availability of earth resources satellites, no really efficient way of obtaining snow-covered area existed. This situation is more severe in inaccessible rugged mountainous regions. Snowcover is important hydrological phenomenon and it is clearly discernible using satellite-obtained optical data because of high albedo of snow. Present study is to estimate snow cover quantitatively on a catchment scalefrom satellite remote sensing data along with ground-based metrological and hydrological data. Its suitability to snowmelt runoff forecasting has been investigated. This may contribute to management and utilization of water resources in remote and less developed areas.

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A phenomenological model (Hino 2003, 2004) on the stomatal mechanisms has been applied to calclate the daytime changes of transpiration, sensible and latent heats, CO₂ absorption and phtosynthetic products.
The model is constituted of the several plant-physiological processes such as water storage changes in plant cell, water uptake from soil through root and trunk, osmatic pressure change due to photosynthesis, CO₂ absorption through stomata and CO₂ concentration change in plant cell.
Finally, the recently found phenomenon of'noon's nap of leaves' is explained from the present model.

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Heterogeneous surface conditions modify the flow structure of the convective boundary layer (CBL). We investigated this impact focusing on the spatial representativeness of eddy-covariance (EC) point observations. The typical daytime boundary layer was simulated using large eddy simulation (LES), where horizontal heterogeneity was imposed on the ground surface heating as one-dimensional sinusoidal variation. The effect of variation of the wavelength and amplitude on the vertical heat transport was examined.
The surface budged based on the point EC method is examined excluding the net vertical heat transport due to the mesoscale circulations invoked by surface heterogeneity. The mesoscale circulation is represented using a phase average. The result found that our simulated EC point measurements still underestimate this energy budget. However, this deficit gets close to zero when the surface heterogeneity is strong. This underestimate can be strongly attributed to the turbulent organized structure (TOS) developed parallel to the mesoscale circulation.

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A Simple 3-dimensional Urban canopy Model for Meso-scale simulation (SUMM) was proposed. The model predicts the energy balance of constituent faces (roof, floor and 4 vertical walls) without time-consuming iterations. In the model, complex 3-dimensional radiation processes (multi-reflection processes) are theoretically solved, resulting in a large reduction of computational time. As for the turbulent transfers, the network of resistance is adopted. We also conducted outdoor scale model experiments having the similar geometric structure with SUMM, to construct the databases (energy balances and surface temperatures) for model validation, and to examine unknown model parameters (e. g. turbulent transfer coefficients).

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The Hargreaves equation has two parameters: one is an empirical coefficient for estimating solar radiation, and the other is a fitting parameter. This study aims to develop the calibration equation for the fitting parameter, which is useful to analyze monthly water balance throughout Japan. The followings are clarified: 1) the fitting parameter is estimated by a multiple linear regression model with the square root of the annual mean range between mean monthly maximum and minimum temperatures, the proximity to a coast, and the annual mean temperature; 2) the modified Hargreaves equation with the above-mentioned model gives a good estimation accuracy with a root mean square error of 0.34 mm ± 0.10 mm (Ave.±S. D.).

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Based on one year of field measurements, we described the annual fluxes of energy and CO₂ at a residential area of Tokyo. The major findings are as follows. 1) The total of Rn, H, and LE was 2.36, 1.35, and 0.90 GJ m^-2, respectively. The latent heat flux LE was large despite the small areal fraction of natural coverage (trees and bare soil). The estimated local latent heat flux per unit natural coverage was two times larger than the available energy (Rn+A), which indicates that the '‘oasis effect’ was significant. 2) The annual CO₂ flux was upward due to fossil fuel consumption in houses and traffic and human bodily exhalations. The total CO₂ flux was 3352 gC m^-2 and was six times larger than the downward CO₂ flux at a typical temperate deciduous forest.

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The social experiment was carried out for the purpose of the mitigation of the heat island effect by watering on August 18th to 25th. The microclimate observation has been carried out at watering area in Eastern Tokyo. As the results, the effect of the watering on the thermal environment in urban area was evaluated as decreasing effect on temperature. The following results were obtained; 1) The temperature variation in the daytime is included to be different every site because of the dispersion of surface temperature. 2) The air temperature in the experiment area is from 2 to 9 [degree] higher than temperature in thermometer shelter by the effect of long radiation. 3) The temperature decrease instantaneously when watering starts. 4) The temperature decreases 0.66 [degree] on average, 1.93 [degree] on maximum after the watering. 5) Total amount of decreasing temperature is decreased linearly by the distance from the point of watering.

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The Huaihe River Lasin is vast granary in China, therefore landuse and cropping cycle information is important for water usage and hydrological analysis. In this study, landuse and cropping pattern classification in the Huaihe River Basin is produced from satellite derived vegetation indices (30sec resolution) and surface meteorological data. And agricultural statistic data of 187 prefectures in Henan Province is used for validation. Firstly, using some notable features in the NDVI and NDWI time series, all meshes (1320 × 600) are classified into 7 categories. Secondly, accumulated degree-days temperature data during growing period is calculated from NDVI time series and surface air temperature data, and it is used for cropping type classification. Lastly, VSW (Vegetation, Soil and Water) index is applied for evaluation of the mixed-cell effect. The results of this study show the importance of mixed-cell effect and the availability of VSW index for cropland classification.

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SiBUC (Simple Biosphere including Urban Canopy) is one of the participants of the Second Global Soil Wetness Project (GSWP2). It uses mosaic approach to incorporate all kind of land-use into LSS. As for farmland, 4 types of crops are considered; spring wheat, winter wheat, corn, and soybean. Not a small part of the world's cropland is irrigated. In order to estimate global soil moisture field as accurately as possible, it is necessary to prepare some parameters which the irrigation scheme needs. The purpose in this study are to prepare a global dataset of crop type and cropping calendar with 1-degree resolution. Through the time series analysis of NDVI, farmland is classified into 4 types and global distribution of cropping calendar (seeding, harvesting, etc.) is produced. In this study, the original index is introduced: Normalized NDVI.

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A geo-referenced global dam reservoir database is constructed by assembling several published dam inventories and latitude/longitude coordinates that are digital obtained or decided from printed maps. This database is designed for hydrological applications on river basin scale to the global scale, and 15, 317 dams with 29 dam reservoir attributes are registered in it. A shoreline polygon data of the reservoir/lake is also provided for 4, 204 dams. The total storage capacity of the registered dams is 5, 594km³, which is equivalent to the 70% of total storage capacity of all reservoirs and lakes over the world (7, 000 km³). Since geo-referenced reservoir database which covers whole global area is rarely available, the database will greatly contribute for global scale water resources analysis and impact assessment of reservoirs on the freshwater systems.

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Environmental flow requirement is estimated in global scale. The estimation is based on 0.5 degree grid river network dataset and river runoff calculation result provided by IIS, University of Tokyo. The whole world is divided into 4 groups by river runoff seasonality. For wet and seasonal dry region, flood pulses are also taken into account. Base flow is supposed to be 10% of mean monthly flow, except for wet months (>10 mm/month) which 30% of mean monthly flow is applied. Flushes are supposed to account for 1/3 of base flow. In extremely dry months (<1 mm/month), no environmental flow is required.
As a result, global averaged value turned out to be 88.17mm or 26% of total runoff.

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We have developed a new regional climate model based on the Regional Atmospheric Modeling System (RAMS), and conducted present and future Asian regional climate simulations nested in the CCSR/NIES Atmospheric General Circulation Model (AGCM). The general simulated features of the AGCM and some regional phenomena such as orographic precipitation, which were notappeared in the outcome of the AGCM simulation, were successfully produced by the nested regionalclimate model. Annual mean precipitation, evapotranspiration and surface runoff are projected to increase in a lot of Asian regions. Those indicate faster and stronger hydrological cycles. There is growing apprehension that the risk of floods will increase under the global warming and the associated hydrological changes such as the intensification of convective precipitation in summer, the reduction of snow cover in winter, and earlier snow melting in spring.

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A global river discharge simulation is conducted taking into account irrigation water intake and reservoir operation. The monthly irrigation water demand is calculated globally by a modeling approach, and it is withdrawn from the river section in the same calculating cell. Four simulation runs (with/without irrigation intake × with/without reservoir operation) are compared, to clarify the effect of irrigation water intake on the river discharge simulation.
In the latter part, irrigation water demand and supply is assessed in monthly interval for nine basins in the world. The result suggests that the irrigation water intake significantly decreases the river discharge in specific period and affects the water resources in the whole river basin.

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Long-term simulation of terrestrial water cycle is estimated using a Land Surface Model (LSM). There are no observations long enough to drive LSM except for monthly precipitation and monthly temperature; therefore daily atmospheric forcing which is indispensable to run the LSM is statistically and/or empirically constructed from monthly precipitation and monthly temperature. High correlations of annual runoff variations are obtained at many basins globally, however, the correlations of annual runoff are low in dry areas and cold regions. It was also showed that the model successfully replicated the annual snow covered area in North America and summer soil moisture in Mongolia. Flood and drought indices are then extracted from the estimated 100-year river discharge and compared with those extracted from available runoff observations at large basins. Results showed that the historical large drought and flood were well simulated in the model.

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Heavy rain was observed at Niigata, Fukushima and Fukui prefectures on 13th-19th Jul 2004. We had many flood damages accompaning this record-breaking rainfall. It was thought that the issue of this event was the horizontal heterogeneity of the rainfall because the heavy rainfall between 12th and 13th at Niigata was observed during long time at mountainous regions. We obtained maximum duration of record-breaking rainfall to use the gauge observation during 25 years and found that the duration near the region which had heavy rain was about 15-20 hours. Mean areal rainfall intensities at the catchment basin of Ikarashi river and Kariyata river were obtained with the Thiessen weighting scheme, the isohyet method and radar observations corrected by the gauge observations. It was found that the horizontal distribution in high resolution of the rainfall intensity was important to obtain the mean areal rainfall correctly in the case of this event.

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In this paper, we present a new type flood simulator for flood risk communication. The characteristics of presented simulator are:(1) Calculation speed of flood flow is very fast;(2) It offers a fully interactive user interface;(3) It provides the property damage assessment based on the simulated results;(4) It visualizes the simulated results with three-dimensional cityscapes. The shallow water equations are solved by using a combination of leapfrog scheme and staggered grid to accelerate the flood flow calculation. Meanwhile we develop an execution sequences controlling function that enable parallel processing the visualization of current state of simulated flow as well as the simulation, and it underlies the interactive user interface. Moreover in order to implement these characteristics, we apply four-dimensional Geographic Information System (4D-GIS), which is suitable to manage and to simulate flood events with 3D geographic data and the simulated time sequence. Through an experiment, presented simulator shows a very promising performance, which would significantly improve the flood damage understanding of society.

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The typhoon No.10 hit the Pacific cost in Hokkaido on August 9 in 2003. The casualties were 10 killed and 3 wounded. The missing person has not been found yet. This typhoon gave the biggest damage by flood to Hokkaido in the last twenty years. In Saru River basin and Appetu River basin in Ilidaka region, serious damages, such as flooded house, house failure and bridge fall, occurred by this typhoon. Farmland and flood plain were covered for the large sediment.
In this paper, we will report an outline of heavy rainfall disasters of Hidaka region in Hokkaido by the typhoon No.10. We hope that the result of this investigation helps to clarify the mechanisms of the heavy rainfall disasters with hydrologic and hydraulic knowledge.

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In the southwest of Sri Lanka, a heavy flood occurred on 17-18 May in 2003, which caused severe river inundations and landslides in a wide area. About 300 persons were killed, and houses, farm products and infrastructures were heavily damaged. In order to investigate this flood and sediment disaster from the hydrological and hydraulic aspects, the committee on Hydroscience and Hydraulic Engineering, Japan Society of Civil Engineers (JSCE) delegated its members whose major are hydrology, hydraulic engineering and river engineering as a flood investigation team by JSCE. In this paper, results of the field investigation are shown for three river basins in Sri Lanka that were severely damaged by flood and landslide disaster induced by the heavy rainfall.

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This paper presents the fragility function for wooden house obtained from the field investigation of the flood disaster in Nakanoshima town, Niigata prefecture due to the July 13, 2004 Niigata heavy rainfall. At the emergency phase of disasters, the early understanding of overview of damage is required for the management of emergency personnel and resource. To understand the overview of damage easily, fragility function which estimates damage from inundation depth is helpful. The inundation depth is measured at many points and the damage rank of each house is identified in the investigation of this disaster. The fragility function is constructed using these data. Additionally, we marshaled those data about building damage and reviewed documents about damages in past tsunami disaster. By comparing obtained data to fragility curve, we considered the influence of driftage on building damage and the adequacy of that curve.

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This paper examines the relationship between the warm season precipitation and the historical highest hourly and daily precipitations based on AMeDAS data during 25 years (1979-2003, 1088 observatories) for simple estimation method of heavy rainfall. The linear regression equation is obtained for the historical highest (25-year highest) precipitation and the warm season precipitation from April to October, which indicates highest correlation. The equation is used for mapping of 25 year precipitation estimates. The equation is also used to define the “heavy rainfall blank areas” in which some AMeDAS observatories have the historical highest precipitation smaller than one estimated by the equation. Defined “heavy rainfall blank areas” are especially Akita, Toyama, Ishikawa and Fukui prefectures and the neighborhood. This result is similar to our past research based on the data from 1979 to 1998. In future, there is a possibility of occurrence of heavy rainfall over past 25-year record in these areas. Actually, heavy rainfall events occurred on Niigata and Fukui prefectures in 2004. These areas were “heavy rainfall blank area” though the present precipitation amounts at several observatories were exceeded the estimated 25-year highest precipitation amounts.

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River water level of prediction Real-time plays a very important part due to making early warning about a flooding that should be decrease a flooding disaster in small river basins within the Tokyo metropolis. It is a subject that security of urban river is to estimate an early warning about the flooding on real time, that because of a run-off phenomenon is a very short time in urban river basin.
River water level is predicted due to forecast a rainfall by using distributed rainfall-runoff model by inputting. The parameter recently could get from the data of 5 floods, an error less than 0.3m on water level is reproduced to accurate rainfall using by Genetic Algorithms, that have the ability to be excellent in untying an optimization problem are used to decide parameters of the model.

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The goal of our study is to clarify the effect of the human activities on water resources and water circulation. The Chao Phraya River basin was selected for this study. The Chao Phraya River basin, the largest basin in Kingdom of Thailand is located in central and northern part of Thailand. This basin has two large-scale dams named Bhumibol Dam across the Ping River and Sirikit Dam across the Nan Riven This large storage dams are beneficial to the country for generating electricity and discharging water for the irrigation project areas and flood mitigation on both banks of the Ping, Nan and the Chao Phraya rivers.
This paper has evaluated the water usage and flood control facilities of Bhumibol Dam. As the results of comparing the annual change of monthly runoff before and after dam construction, the minimum runoff increased drastically and the maximum runoff decreased.
As the results of numerical analysis, it is clarified the water usage has become stable and the high water has decreased by the operation of Bhumibol Dam.

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People living at Lake Biwa shoreline areas have suffered from inundation damages from the ancient time, they strongly desire to relieve themselves from these damages. The largest recorded flood in Lake Biwa basin after Meiji Restoration occurred in 1896, but it occurred long time ago so that little hydrological and hydraulic data such as rainfall data, discharge data of the rivers which are basic information for preparing a flood control plan are left. Therefore we can't take this flood into consideration when we make the flood control plan for Lake Biwa basin. Based on the importance of the analysis of the largest recorded flood, we tried to collect as much data as possible about this flood and simulate this flood correctly based on collected data. And we also analyzed the damage by this flood. Due to the results of the analysis, if this flood occurred now, the water level of Lake Biwa would be higher than the present design flood level even if Setagawa Barrage, which was constructed at the outlet of Lake Biwa, were totally opened. On the other hand, the precipitation in the Kizu and Katsura River basins would be not very large, so the present river-related facilities would be enough for the prevention of the flood damage even if Setagawa Barrage were totally opened. But for the Uji River basin, it is clear that further counter measures for this flood must be taken because the discharge in the river would exceed the actual capacity of flow.

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An algorithm to search the optimal solution, is proposed for the design problem of countermeasures taken in a floodplain against inundation. The design problem is formulated as to find the land augment pattern which maximizes the evacuation success rate under the constraint of total land level augmentation volume. Two-level random search method is developed to obtain the optimal solution for the problem avoiding impractical computational burden. The method comprises of two levels of searching: one is approximate solution search process based on simple estimation of inundation levels, and the other is strict optimization stage based on the actual simulation of flood inundation. The nested coupling of those two levels of searching has considerably deduced the computational burden caused by the inundation simulation and has enabled us to get practical solution for the design problem.
Using the optimization method proposed in this study, an attempt to estimate quantitatively the relation between facility-based countermeasures and so-called soft-ones for flood disaster mitigation.

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Water demand and water price are analyzed from disclosed information related to domestic water supply. Even though the number of each family decreases, total water demand in many cities tends to decrease since 1994, when the demand reached the highest peak. Water demand per person per day differed by the scales of domestic water supplies, but this difference has become smaller. Water demand has not increased so much and has become diversified all over the country. On the other hand, the price analysis of water supply shows the price elasticity of water demand has become relatively inelastic and approached to zero. This shows that there should be limitation on managing water through water price. Therefore, while water pricing can be effective in some water supplies with high price elasticity during droughts, more diversified needs, such as water quality or uncertainty in risks, such as drought risks for global climate changes, should be considered for water resources management.

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Flood disasters occurred in Niigata prefecture and Fukui prefecture on July 2004 caused by heavy rainfall which exceeded maximum data in the past. According to the field survey, the importance of information for disaster prevention which disseminate to inhabitants accurately, quickly, comprehensively was realized. In this study, information of flood risk potential which support self-help, mutual-help of inhabitants was developed. Information of flood risk potential, which is consisted of DEM and real-time rainfall data, estimate the flood risk potential along the river defined as ranking in the past. As the result of applications to the Niigata disaster and Fukui disaster, it was shown that it takes 1-5 hours from getting the warning to occurrence of disasters in the case of basin where the area is less than 300 km²

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This study presents a flood damage prediction model and a risk analysis method for flood protection level decision. The flood damage prediction model is composed of two models: a flood inundation prediction model (Model 1) and a flood damage estimation model (Model 2). Model 1 calculates the inundation depths of a river basin for any given storms. Model 2, using the depths obtained by Model 1, computes the damage amounts of the private properties as a function of inundation depth. In the calculation process, we fully utilize GIS as a tool for the damage calculations. The models were applied to flood damage simulations for the Kanda river basin with highly urbanized catchment located in the Tokyo Metropolis. The simulations yielded the flood damage for a set of several storms with different return periods. With the calculation results, we carried out a risk analysis for flood protection levels of the Tokyo metropolitan goverment and proved that the protection level is reasonable and acceptable for engineering viewpoint.

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The influence of global warming on hazard risk is estimated from the results of the regional climate model by Japan Meteorological Agency and Meteorological Research Institute. The horizontal resolution of the model is about 20km and the model outputs are expected to be useful for the risk assessment of the future. Before beginning the risk assessment, the model output values during 1981-2000 were verified by comparing with observed precipitation data. The verification shows that the precision of the models are generally well in representation of the precipitation, the normal value of the monthly precipitation and the annual maximum daily precipitation in each region. According to the analysis from the model outputs, the extreme daily precipitation in 100-yr time period will increase in some parts of western Hokkaido, northern Tohoku region, Hokuriku region and Nansei islands during 2081-2100. While, the result of the seasonal variation of precipitation shows that the precipitation will decrease especially in many areas in Japan except Hokkaido region from winter to spring, and the drought risk will increase there.

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Laboratory experiments were conducted using a two-component electromagnetic current-meter and a particle-image-velocimetry (PIV) to clarify the interaction between main flow and flexible artificial vegetation, which was attached to the central bottom of an open channel. In addition, interception plate 1mm thick was placed at the one-sided vegetation interface along the main flow direction.
Results show that in the main flow region of the equilibrium state, horizontal components of the secondary currents take the directions toward the vegetation zone near the bottom and toward the non-vegetation zone near the surface. From the measurements, it was shown that this thin plate significantly suppressed water surface oscillations, horizontal periodical velocity variations and spanwise momentum transport from main flow region to vegetation zone.

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This study describes an experimental investigation on turbulence characteristics and the water-surface fluctuations in adverse wind-driven open-channel flows by using both a laser Doppler Anemometer (LDA) and a wave gauge simultaneously. In this study, it was shown that the velocity fluctuations of water flow near the interface in not only cocurrent flow but also adverse flow are significantly affected by the water surface in every range of frequency. However turbulence characteristics in water layer in adverse wind-driven open-channel flows are different from those in cocurrent flow, and there exists a high correlation between turbulence and the surface fluctuations in predominant frequency due to high-sheared wind flow.

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Turbulent nature of near-bed flow field was investigated in an open channel over a rough-bed artificially arrayed with glass beads, where ratios of the glass diameter to flow depth are 03, 0.5 and 0.8. Detailed spatial measurements of streamwise and vertical velocity fluctuations were made using Particle Image Velocimetry (PIV) in a vertical plane along the completely rough bed surface. Results indicated significant degrees of spatially regular variation in the time-averaged velocities, in which the upflow generated over upper region of roughness top is about 8% of the cross sectional average velocity, much stronger than the downflow. In addition, Reynolds shear stress and turbulent intensity showed minimum values at the ridge of roughness elements and maximum ones at the trough. These organized flow structure were suggested to be due to the vortex shedding brought about by the roughness elements.

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Suspended sediment in open-channel flows has been paid great attention in river engineering. It has been pointed out that flow resistance is changed by the existence of sand particles. Moreover, knowledge of interaction between sand-particles (solid-phase) and water (fluid-phase) is necessary to improve sediment transport rate formula. However, the mechanism of particle-fluid interactions is not fully understood. In this study, simultaneous measurements were conducted with discriminator PTV in rough open-channel flows with suspended sediment. The roughness elements were set up on the channel-bed. Consequently, the relative velocity between particles and fluid and the turbulence modulation were investigated by changing the particle concentration systematically.

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It is important for river management to consider natural characteristics of the river. The upper reach of the KNU-river is characterized by the steep bed slope and the large channel width with sand bars. The purpose of this study is to analyze the flow that contains both sub-critical flow and super-critical flow on the sand bars numerically by using SIMPLE method. It is shown that the flow has super-critical area when the rate of discharge becomes small as for the obtained findings, and the water surface is found wavy in the super-critical area. The sub-critical flow and the super-critical flow are formed at the area of the downstream left side of slanting slope termination. The superficial hydraulic jump position is found in the central part of slanting slope termination.

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At the vicinity of river confluence, the complexity due to flow separations and velocity fluctuations has been the subject of interest for river engineers to understand its phenomena. Especially during the high discharge, this area is vulnerable to be flooded. Therefore, it is challenging to understand this mechanism. Field investigation had been conducted at the vicinity of river confluence of the Atsubetsu and the Biu Rivers, where the damage was most serious during the typhoon No.10, 2003. By this investigation, the situation of flood flow was estimated by the directions of fallen trees and the trace remained at the wall of houses. A flume experiment including river confluence was conducted. The flow velocity in the flume was measured precisely. The Numerical analysis using 0-equation model and κ-ε model was performed and the experimented results were compared with calculated results. The numerical analysis using κ-ε model was reproduced well rather than the numerical analysis using 0-equation model. This numerical model was applied to the vicinity of river confluence of the Atsubetsu and the Biu rivers. Calculated results showed the similar characteristics with the field investigation results. This model can be a powerful tool to analyze the flow at the vicinity of river confluences.

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When a relatively large side cavity zone is installed in an open channel, the influence of separated vortices and recirculation flow generated at the zone is sometimes exerted to the main flow as water surface oscillation. The mechanism of the oscillation is still not clearly understood because of the complexity of the phenomena. In this research, by using a stereoscopic surface measurement system developed by the authors, time-dependent water surface configurations are successfully measured at a sampling rate of 12Hz, from which general features of the surface oscillation is made clear for a wide range of the Froude number. We then applied the proper orthogonal decomposition (POD) method to the measured data and found out that the surface oscillation can be clearly decomposed into a Seiche-like major mode and sub-modes with smaller wavelengths.

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A multi-layer scanning 3-D PIV system was developed, in which the different elevated laser light sheets (LLS) were projected into the tilting flume almost simultaneously. This specially designed PIV system is able to measure time-dependent velocity components in the 3-D region at the same time. In this study, turbulence measurements were conducted in a compound open-channel flow, in which large-scale horizontal eddies were observed near the junction region between the main-channel and floodplain, and as the results, it was found that there were large correlation properties between the different elevated layers and the tube-like horizontal eddies were transported in the downstream.

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Field experiment on acoustic backscatter of suspended sediment was undertaken in Rokkakugawa-river estuary to establish the suspended sediment concentration (SSC) monitoring technique for measuring high concentrations exceeding 5, 000 mg/L and to obtain vertical distributions. A sound of 200 kHz frequency was emitted from the transducer, and it was detected in the direction of the suspended sediment; the transducer received the detected sound. A separate transducer and an integrated transducer were examined. The blank space after the separate transducer was 0.5 m, shorter than 2.5 m for the integrated transducer. The output power of 1-5 W for the sound is appropriate to measure concentrations of 100-20, 000 mg/L. Ambiguity of response was the minimum for 32-64 pulses. The relationship between the sound echo intensity and SSC was formulated in consideration of propagation loss; SSC profiles are successfully reproduced by echo intensity profiles for the frequency of 200 kHz, the sound power of 4.3 W, and the sound of 32 pulses.

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In curved channels, velocity distribution in the downstream direction is transformed by the secondary currents and the momentum transport is affected with redistribution of downstream velocity. Therefore, it is necessary.to include the transformation of downstream velocity in a depth averaged flow model in order to predict the river flows and channel processes effectively. In this study, 2-D model considering the transformation of the downstream velocity is derived and is verified by comparing with the experimental and 3-D results.

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This paper describes the comparisons of numerical models focusing on the water elevation around a bridge pier. Three different numerical models, namely, 2D plane model, Qasi-3D model (3D model with hydrostatic assumption) and Full-3D model, are considered. As turbulence models, a simple 0-equation model is used for the 2D plane model and a non-linear k-e model with effects of strain and rotation parameters are applied for the quasi-3D and full-3D models. First, laboratory test is carried out to obtain data for verification under Re=8400 and Fr=0.54. The computations are performed in the same conditions of the laboratory test. The numerical results show that the 2D and full 3D models can capture well the height of water elevation at the upstream region of the cylinder though the quasi-3D model under-predicts it. The 2D model overestimates the depth of the hollow behind the cylinder. The quasi-3D model considerably over-estimates the length of the re-circulation zone.

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In this study, a comprehensive inundation flow model, which comprises one-dimensional unsteady flow model, two-dimensional inundation flow model and runoff model using kinematic wave method, is developed and is applied to the Isahaya low-lying area, Nagasaki Prefecture. The validity of this model is considered by comparing with the actual records of inundated area and water level of the river network. Then, as the application example of this model to countermeasures against flood disaster, the effects by extending pump capacity and installing hypothetical pump stations are discussed.

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Typhoon No.10 approached Hokkaido on August 9^th, 2003. Because of incompleted embankment protection, floods, bank erosions, large amount of sediments, and drifiwoods occurred especially in the Appetsu River of Hidaka area. In this study, flood and deposition on the flood plain were reproduced by numerical calculation and their features were discovered. The steady flow calculation was conducted by selecting the peak discharge of this flood event. While, the unsteady calculation was simulated by the calculated hydrograph. The calculation of sediment transport was carried out by the transport equation of suspended load. The sediments were provided from the upstream end of the calculation region. The calculation for water flow, bed load and suspended load, and bed change of flood region were done in a generalized coordinate system. As a result, the characteristics of the flood during typhoon No.10 at the Appetsu River was clarified.

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Severe flood damage due to the levee break occurred in Nakanoshima area along Kariyata River in Niigata Pref. Especially many houses were broken and many people failed to escape in inundated area. Numerical analysis is important to reduce damage due to flooding flow. Numerical analysis for flooding flow is generally used to predict flooding water depth and to make hazard map for evacuation of people in river basin etc. Objects of the general numerical analysis are not to predict damage due to abrupt flooding flow like levee break.
In this paper, numerical analysis model for abrupt flooding flow and washout of houses is developed. The relationship among the flood in the Kariyata River, flooding flow and swept-away of houses due to levee break by the numerical model is described.

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Typhoon No.10, which struck Hokkaido Prefecture in August 2003, caused serious flood damage on the Saru River, which is in the easternmost part of the Iburi district. Driftwood washed into the river in great quantity. In this research, the flow velocity during the flood on the Saru River was estimated by measuring the critical turning moment at which trees are uprooted and applying it to partly uprooted trees. We also investigated how the influence of the tree crown on water flow depends on the tree crown form, and the relationship between the tree height and the bending arc. Although the calculated flow velocities did not closely correlate with values obtained from measurements, the calculated values can still serve as commonsense values that represent the flow conditions during the flood to some degree.

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Flood disaster caused by heavy rainfall occurred in Niigata prefecture on July 13^th, 2004. A numerical study of the flood flow from the Kariyata river in downtown of Nakanosima town, is carried out with fine numerical grid system for two cases of overflow rate from the river. The comparison of real field measurements with the numerical results shows that distribution of flood depth agrees with numerical results qualitatively. Fine tune up of the outflow rate is required for the qualitative agreement. The direction of the flood flow is consistent with the destruction of building structures and houses near the destruction point of the riverbank.

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Inundation process in underground space which connecting to a subway station in urban area was studied numerically. Actual data sets of (1) road network, (2) drainage network and (3) underground space in the area around Shibuya Station were considered here, and a simplified numerical model was constructed. Based on the results of numerical computation, the characteristics and the weak points of the drainage system in this area were quantitatively understood. It was revealed that (1) the local area whose ground elevation is relatively lower and (2) the undergournd space are the possible area where extensive damage will result if there happenes to be the rainfall whose intensity exceeds the designed one.

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