The present paper describes a new method to precisely calculate hourly evaporation flux under quasi-unsteady wind velocity using the wind tunnel that can supply a set of high/low speed winds by turns for every set-up period. Soil columns was used for the evaporation experiment and Chao soil and Toyoura standard sand were used for the experiment. The difference in the hourly evaporation flux, E_vh, became no less than 12-18% by changing the combination of the high/low speed winds, regardless of the kind of soil, although the average wind velocity, V_wm, was the same for all the wind-velocity combinations. This fact is attributed to the nonlinearity of the relation between the evaporation coefficient, α_v, and wind velocity. It is found that E_vh calculated using α_v for the high and low wind velocities is more accurate than that calculated using α_v for V_wm.

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This paper shows the effects of building height variation on momentum and heat transfer characteristics using Comprehensive Outdoor Scale Model (COSMO) . Turbulent fluctuations and radiations were monitored on the two different type arrays at the same time to investigate the essential effects of building height heterogeneity; the normal model included an aligned array of only 15cm concrete cubes, and the variable model had a geometrically same array but with two building heights of 15cm±50% (i. e. 7.5cm and 22.5cm) . The uneven building array produced relatively strong mixing, and consequently the large drag coefficient. On the other hand, it showed a little difference in sensible heat transfer; there may exist a trade-off between the mixing intensity and the surface heating. The net radiations on the two sites were almost the same so that the building height variation was likely to have little influence on the heat balance as far as the current experimental condition is concerned.

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In this study, a Large-Eddy Simulation model that is capable of resolving urban buildings was used to investigate the influence over turbulence statistics caused by the existence of urban geometry.
In the convective boundary layer, the horizontal temperature variances from both flat and urban geometry are smaller than the field observation results. And the horizontal velocity variances in the urban ABL are slightly smaller than those for a flat throughout the whole range of height. In the surface layer, the results of the urban simulation are not in agreement with the results from observations. And that is partly caused by the disability of current SGS model.

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A summer heavy rainfall event in Japan is a part of large-scale circulation field. But, heavy rainfall research has not been done from large-scale viewpoint because it is difficult to get high-integrity long-term data. In 2006, Japanese 25-year Re-analysis (JRA-25) data was begun to be published.
In this study, by using JRA-25 data, trajectory analysis was carried out and anomalous field of atmospheric conditions about the 35 events in which heavy rainfall occurred in Japan in Baiu season was investigated. Some features of synoptic scale atmospheric structure of summer heavy rainfall was found out. ; intention of Pacific high, westward spread of Pacific high, intension of cyclone near Japan, intension of MA-3, increase of water vapor of moist tongue, pressure variation of Okhotsk Sea. When dry year events were analyzed, they show opposite tendency to the features.

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In this study, verification is performed for the accuracy of 24-hour forecast of pinpoint precipitation using the mesoscale meteorological model MM5 with a high-resolution grid spacing of 2 km through comparisons with the precipitation measured at 9 weather stations in Gifu Prefecture over one-year period from June 2005 to May 2006. It is shown that the values of correlation coefficient of 3-hourly accumulated rainfall between the predicted values and the measured ones become almost 0.4 or more over one year although they are about 0.7 during the period from January to May. In addition, a radar data assimilation system to initialize 3-dimensional cloud microphysical fields accurately is newly developed based on the template matching technique. The forecast accuracy is improved not only in the large-area distribution of precipitation fields but also in the time series of the pinpoint precipitation.

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A nonlinear effect ofnon-orographic rainfall on orographic rainfall is introduced into a short-term rainfall predictionmethod which uses Tatehira's orographic rainfall model. In the previous paper, orographic rainfall is assumed tobe simply proportional to non-orographic rainfall. In the seeder-feeder mechanism, which is themost importantpart in the generation of orographic rainfall, ratio of capturingcloud drops by raindrops (by non-orographic rainfall) c is taking a vital role. However, c is not proportional to the non-or0graphic rainfall intensity. In this paper, therefore, c is assumed to be anonlinear function in terms of the non-orographic rainfall and a method ofsolving simultaneous equationscomposed of the nonlinear function and theconservation equation of clouddrop is proposed. As a result, it is found that, when the nonlinear effect is taken into account, computedorographic rainfall becomesmuch smaller and that assumed depth of atmospheric layer ofhundred meters is not enough. Therefore, the computation method is further modified so thatorographic rainfall can be generated frommulti layers.

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The current study conducted some investigations into the relationship between the form of topography and the fields of precipitation and wind velocity in linear convective systems, through a physically-based numerical approach using a mesoscale meteorological model with virtually-created atmospheric conditions. In order to clarify the mechanism of localized torrential precipitation, sensibility analysis of precipitation systems was conducted by modifying the form of topography at the point where convective cells were mainly generated by orographic trigger effects. The results show that the modification of topography tends to affect the organization of convective cells, which leads to the formation of a linear convective system. Areal maximum precipitation from a linear convective system largely fluctuates by around ±20 % with the modification of topography and can be decreased in some cases as the topographic elevation increases, although areal average precipitation shows a slight change of -5 to 5 %. A streamline analysis of the wind field shows that the decrease of maximum precipitation can be attributed to greater temporal fluctuations of the wind field caused by the modification of topography.

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A Doppler radar data assimilation system based on an ensemble Kalman filter (EnKF) method is developed. The system employs a meso-scale hydrostatic model, which includes the conceptual model of the efficiency of the water vapor conversion. A case of the rainfall occurred in Kinki region in 2003 is chosen as an application. Radial velocity and reflectivity observed by Miyama Doppler radar and Jogamori conventional radar are assimilated. The rainfall predicted by our developed system is compared with the prediction results of the four dimensional variational method (4D-VAR) and those of the conditional Kalman filter method. It is demonstrated that our system has equal accuracy to the 4D-VAR method. Also by the comparison of the EnKF method and the conditional Kalman filter method, it is made clear that the spatial correlation in error cannot be ignored.

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Improvement of quantitative precipitation estimation (QPE) is one of the primary benefits providedbypolarization radars. Ministryof Land, Infrastructure and Transportation Japan (MLIT) put Shakadakeoperational Cband Radar to practical use in1992. However, large improvement hadnotbeenrealizedbecause of its initial technical stage.
Under these circumstances, first, this paper compares the performance of the conventional R (Z_HH) relation and three polarimetric relations, which are R (Z_HH, Z_DR), R (K_DP), R (K_DP, Z_DR) . At lower rainrates, the combinationof K_DP and Z_DR is less efficient because K_DP becomes noisy. Next in order to improveQPE, a few combinations of estimation equations for operational purpose is proposed, considering thecharacteristic ofthose relations. Also validations with some other algorithms are conducted. As a result, the proposed algorithms improve the estimationof hourly rainfall and accumulated total rainfall.

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In these days, several kinds of global precipitation maps derived from satellite observations have become available. Some of them have resolutions of 1 hour and 0.1 degree, which seem to be good enough to be used for hydrological purposes including flood detection. As a basic research to develop operational flood detection systems by using satellite precipitation maps mainly for developing countries in near future, we conducted river discharge simulations all over Japan by using several precipitation dataset and evaluated the ability of flood detection. The simulation system is based on “Today's Japan” developed by Yoshimura et al. The GSMaP product can detect the precipitation events which caused flood disasters, but the precipitation amount is generally underestimated, consequently the river discharge is not well simulated in many cases. The GSMaP product adjusted by using monthly and 1 degree rain gauge information can be used to detect flood events as well as hourly rain gauge observations. The underestimation in precipitation estimates by the GSMaP product should be physically modified.

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Urban development causes serious changes to watershed conditions by decreasing storage area, introducing pavement and channeling. As a result, the peak discharge has been increasing and the arrival time of peak becomes early. The purpose of this study is to investigate the state of retention facilities such as irrigation ponds and paddy area in Mikasa River watershed. The result of investigation shows the rate of the capacity of flood control of dam, ponds and paddy area are 37.1%, 14.6%, 48.3% and total capacity is 3, 063, 000m³.
For the estimate of the storage facility effects, we applied the distributed runoff model considering ponds and paddy area effects. The result of calculation showed that the peak discharge at Sanno Bridge decreased 36m³/s by dam, 31m³/s by ponds and 36m³/s by paddy area.

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Water footprints, or the total consumed water toproduce commodities, were estimated for imported food to Japan, using an integrated globalwater resources model that consists of a physically basedhydrological module and a cropgrowth module. In order to analyze the sustainability of water resources, the model was enhanced to quantify fourmajor sources: precipitation, river, reservoirs, and non-renewable groundwater. The results showed that the water footprint of Japan was 42.7km³/yr. The virtualwater, or the required amount of water that is needed toproduce the imported food domestically, wasestimated 62.7 km³/yr. Therefore, it indicates 20.0 km³/yr of water was saved through international trades. Among the total water footprint, 7.3 km³/yr (17%) was originated irrigation water, and 2.9 km³/yr (6.8%) was non-renewable groundwater.

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We investigated uncertainties in climate change impact assessment caused by general circulation models (GCMs), downscaling techniques, and hydrologic models. Two GCMs (MRI-CGCM2 and CCSR/NIES/ FRCGC-MIROC) under the Intergovernmental Panel on Climate Change (IPCC) Special Report on Emission Scenarios (SRES) A2 scenario were dynamically downscaled to the Seyhan River Basin in Turkey. The downscaled data covered 10-year present (1990s) and 10-year future (2070s) time-slices and were used as inputs for two hydrologic models: the Simple Biosphere including Urban Canopy (SiBUC) model and the Tank Model. Results are summarized as follows. (1) There were huge uncertainties in the future projections by the GCMs. Therefore, the range of future projections should be shown using results from various GCMs. (2) Since there were huge errors in the dynamically downscaled data, bias-correction was necessary when using such data to assess climate change. (3) Like GCMs, hydrologic models can cause uncertainties. The performance of hydrologic models should be examined using maximum past flood and drought data, or multiple hydrologic models should be used to show the range of projections.

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This study evaluates the flood reduction functions of five forested basins of the Yoshino river system covered with Japanese cedar and Japanese cypress. The functions are compared with that of the Meya dam basin covered with beech forest. The distributed runoff model is used, to eliminate the storage effect of the river channel that causes overestimation of the function. The functions of these basins are evaluated by the index of flood reduction function that considers resistance property of surface runoff and storage depth under the ground surface estimated by the model.
The indexes of flood reduction function evaluation of the forested basin of the Yoshino river system are higher than that of the Meya dam basin. The difference between basins appears in the equivalent roughness coefficient of surface runoff in the runoff model.

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A physically distributed hydrological model (WEP model) was coupled with a newly developed physically distributed model of heat transport in river water to simulate watershed scale hydrological and heat transport processes and resulting effects on stream environment. The model is characterized by the capability of simulating runoff from a highly urbanized watershed with a dual drainage system of river channels and a sewer network, which enables appropriate prediction of inflows to wastewater treatment plants and river floods. Also, this model is designed to investigate factors affecting spatial and temporal variations of stream temperature by incorporating anthropogenic heat impacts and urban canopy processes. Applying the model to the Kanda River Watershed, stream flow and temperature as well as inflows to a WWTP are well simulated. The anthropogenic heat impact on stream temperature was also simulated.

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We showed that the amount of irrigation water was 34.4 m³/s during irrigation period in the kinokawa river, Japan. This is very large compared to the river discharge in a normal flow condition. To take water use into account a runoff analysis using a distributed hydrological model, we proposed a new model that consider the water-intake from head works, inflow, storage and flood control by dams. It was found that the simulated river discharge using this model agreed with the observation data, especially for the low water flow in the irrigation period. In addition, the reduction rate of irrigation water from paddy fields to kinokawa river was inversely estimated. The rate was low in a small precipitation year and was high in a high precipitation year. This characteristic agrees with a traditional and empirical water uses of irrigation water.

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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 but also chemical parameters. 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, laboratory experiment of solute transport in heterogeneous field with cation exchange reaction was carried out. Electric conductivities (EC) were measured by time domain reflectometry (TDR) using small printed circuit board probes (PCBP) . Transient concentrations of cations and anions of eluted water were analyzed by ion chromatography. Breakthrough curves (BTC) of injected K⁺ and Cl^- showed split peeks that may be the effect of heterogeneity of the flow field. According to cations BTC, Ca and Mg were exchanged with K and then flushed out. Both of chemical and physical heterogeneity affects on solute transport clearly.

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Dispersivity is a medium-dependent hydrodynamic parameter that characterizes solute dispersion in a porous medium. Under saturated unidirectional flow condition, laboratory tracer experiments with a pulse source were conducted in homogeneous flow field as well as in less heterogeneous porous formation, which was comprised by a few combinations with three types of soil particles. Mean grain sizes and flow velocities in a region were varied in order to investigate a linear relation between grain size and longitudinal dispersivity under the approximately one order range of Reynolds and Peclet numbers, which were non-linearly expressed as a function of longitudinal dispersion coefficient. Laboratory study was extended by a comprehensive literature search to compare the new results with earlier work, demonstrating good agreement between the experimental and published empirical relations in heterogeneous porous media of concern.

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This study aimed at determining the distribution of hydraulic conductivity and radius of influence from the results of multi-well pumping test and natural distribution of piezometric head in a non-uniform phreatic aquifer. The inverse analysis was performed by using the Fast Fourier Transform (FFT) and the constrained simplex method. These results showed that the method presented here could estimate mean value of hydraulic conductivity and the radius of influence more accurately than the conventional method using an analytical model of aquifer flow. And the distribution of hydraulic conductivity were well reproduced except the case of that the heterogeneity of hydraulic conductivity was not reflected in the distribution of drawdown and piezopmetric head.

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We performed a series of column tests of the air-sparging method, and thereby compare the experimental results with the simulation results of the continuous-time random-walk (CTRW) model. In the experiments, we found that the concentration of the retrieved gas (CO₂) decreases in time by the power-law of the elapsed time, which agrees with previous studies. We also fitted the experimental results with the CTRW successfully. The procedures of determining the three model parameters (α, Δt, and Δx) is explained in detail. This study is, as far as the authors concern, the first trial to apply the CTRW to the two-phase flow.

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Generally, deeper 300m depth part of subsurface is expected as the high-level radioactive waste (HLW) disposal site due to low mobility of chemical species and reductive condition. It can be assumed that deep subsurface environment becomes oxidative condition by excavation for geological disposal of HLW. It is important that oxidative condition returns to the previous reductive condition after backfilling the pit.
In this study, to evaluate whether once oxidized core sample changes to reductive condition again, the column experiments for rock-water interaction were carried out. In the experiments, granodiorite and crystalline schist were used, and they were filled with seawater or distilled water as pore water, respectively. From the results of the experiments using seawater and distilled water, both ORP values were shown to decrease.

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Analyses using a logical hierarchical model, such as Evidential Support Logic, are useful tools to assess complicated hydrogeological and groundwater conditions in decision making. However, in most cases, parameters in the model are not determined explicitly, which prevents more objective evaluation. In this study, in order to identify weight parameters between propositions in different layers in a hierarchical model, a method to calculate the parameters based on distribution of many people's opinion was proposed. An example of hierarchical model for logic structure to evaluate risk of groundwater environment change under a hypothetical condition was developed, and some of the weight parameters were calculated by using Genetic Algorithm with distribution data of opinions collected through questionnaires.

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Flood damages were estimated by the flood simulation model and cost-benefit for land use types. Economical value in each land use is obtained from the flood control and the economic research manual (The Ministry of Land, Infrastructure and Transport, 2005) . The results obtained are as follows; 1) the economic damage by flood proportionally increases with increasing return period. 2) the expectation value of mean damage for 100 years return period is about 11 trillion yen per year, and 3) the estimated amount of damage in Niigata prefecture in 2004 is comparatively same with the values estimated by government.

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A zoomable irregular mesh editor is developed which is capable of constructing irregular mesh networks for flooding simulations. The software is written in a computer programming language, Java. This means that it is independent of computer platforms and does not need proprietary (commercial) software. The software provides a graphical mouse-driven mesh editing environment with a zoomable user interface, in which the user can smoothly zoom in, to get more detailed information, and zoom out for an overview. The software also allows the user to suspend and resume the operation, by saving and reading text files which describe the network structure.

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Understanding of Internet users for real-time precipitation or water level information was researched based on Internet questionary survey in February 2007. The percentage of recognition for “River Disaster Prevention Information”, administrated by River Bureau, was only 4.7%. It is hardly different from the result of similar survey in 2004. Even if real-time heavy rainfall disaster information Web pages were introduced to respondents, the answer with a clear use intention was about 10%. The use intention of cellular phone web pages was still lower. “The television is more useful for an emergency” etc. was mentioned as the reason. It is possible that even if well-known to these pages, many people may not use. There is no doubt about public presentation of information is important. However, it is also important to develop simple information communication system to general public for heavy rainfall disaster prevention.

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There are two measures to reduce human damage resulting from a flood flow, that is, preventive public facilities as hardware-like aspect and residents' evacuation from inundation flow risk as software-like aspect. Since the former has a practical limit when the facilities are attacked by the flood flow beyond their strength, at that time the latter becomes important. From this viewpoint, we picked up six areas from the Sendai river basin affected by flood disaster at the latter half of July in 2006 and executed questionnaire survey to the residents about evacuation activities, needs of disaster information, understanding of flood hazard map and awareness to flood disaster. Moreover, we analyzed effects of disaster forces on evacuation activity. This paper showed that social cohesion played an important part in a community's ability to respond to flood disasters.

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To evalutate the residents' recognition about the flood risks in the urban area, we analysed the land prices at Tokyo and Osaka with the hedonic approach which relates land price to a variety of environmental factors. Two factors, elevation and inundation depth, that are assumed to reflect the flood risks, were adopted as the explanatory variables of the hedonic price function in Tokyo, while there were no in fluences on land prices due to the flood risks in Osaka. This difference of the residents' recognition between two cities might be caused by the geographical features and the eRectual informations such as hazard maps and news.

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The sediment hazard probability and the road economic damage due to snowmelt are estimated from a risk evaluation model. As results, we made risk maps of sediment hazard probability and the road economic damage in Japan. These maps show spatial-temporal risk distribution of sediment hazard due to some snowmelt condition. The sediment hazard probability was obtained by a multiple logistic regression analysis based on conditions of past hazard, relief energy, hydraulic gradient, and geology. Hydraulic gradient was analyzed by infiltration analysis with consideration of snowmelt. Moreover, we verified weather situation about sediment hazard due to snowmelt.

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In order to deal with recent change of runoff characteristics by urbanization of a river basin, construction of facilities for rainwater storage and infiltration has been planed as a flood control measure in the basin. However, the construction plan has not been in progress due to high costs and limited sites for the facilities. Then in this paper, we propose a new utilization method of paddy fields remained in the basin as an alternative measure. This research aims to evaluate rainwater storage function of paddy fields and to verify a new procedure to improve the function, through on-site experiments carried out in the Shin-kawa basin, Aichi prefecture. A hydraulic model on the water-balance of a paddy field is identified based on observed data of the experiments, and by using the model the storage-drainage processes in a paddy field are simulated on a probabilistic design rainfall. From results of the simulation, it is found out that paddy fields have applicability as the runoff control facilities.

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Oxygen isotopic ratios of river waters in the Yakushima Island show high in the east and low in the west. Especially, oxygen isotopic ratio was extremely low in the west October 2006 when precipitation is the lowest month in the Yakushima Island. Oxygen isotopic ratio increases with precipitation and decreases with distance from seaside. ^Cl- concentrations in the river water are uniform from March 2006 to February 2007. However, ^Na+ concentration was high and oxygen isotopic ratio was low in dry season, October 2006. Spring water is thought to be high ^Na+ concentration derived from Na+ feldspar in granite and low oxygen isotopic ratio derived from rain water in the upper catchment. Therefore, low oxygen isotopic ratio and high ^Na+ concentration river water in the dry season is thought to come from spring water.

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In order to clarify the runoff mechanism in urban catchment area, field observation of discharge and application of runoff analysis to the urban catchments are reported in this paper. Land-use in urban area has become more complicated by urbanization during the last several decades. As a result of urbanization, the peak discharge increases and the concentration time of flood decreases. It makes flood disasters in urban area more serious problem. On the other hand, discharge data in urban catchments are very few. In this paper, field observation of discharge are carried out and runoff analysis method for land surface area based on morphological and geological properties is applied several urban catchments to evaluate the effects of urbanization on runoff characteristics in urban area.

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Through meteorological and hydrological observations in a small mountainous watershed, melting runoff processes in this area are investigated and the following is clarified. When solar radiation only caused snow-melting, lowering of snow deposition was successfully calculated using accumulation of solar radiation. In such a stage, that melting did not caused increase in the river-water discharge because most of melting water was considered to be stored within the snow deposition layer. From late winter to early spring, a daily periodic variation in the river-water discharge was seen. Main energy of its snow-melting is solar radiation and sensible heat flux. Based on analyses on that periodic characteristic, the former is known to be roughly five times higher than the latter. Also roughly 90% of snow-melting water infiltrates into the soil layer in the slope and causes increase in base-flow discharge, while the residual water, approximately 10% of that water, contributes to increment of daily varying discharge as a direct runoff.

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Snowmelt runoff is a precious water resource in cold region. However it causes disasters by influence of a warm air and a rainfall in spring. Therefore accurate estimation of snow water equivalent and forecast of snowmelt discharge are vital for river management. We investigated how snow water equivalent changes with time in the Jozankei Dam basin and on the premises of the Ishikari Experiment Laboratory. It was done by continuously monitoring of snowcover weight and snowmelt discharge using snowcover weightmeters and lysimeters. We observed time-lag of snowmelt runoff and excessive snowmelt runoff. It was caused by structure of snowcover layer. We proposed a simple equation for estimation of snow density by multiple linear regression analysis. We estimated snow water equivalent in the Jozankei dam basin by using the equation. The result of estimation is almost satisfactory.

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In cold region, many rivers and lakes are freeze up in winter season. Frazil ice is a small particle that generated in supercooled and turbulent water surface. They are casual factor of freeze up the water surface of rives. In addition, the water intakes that located at riverside are often clogged by accretion of frazil ice at midwinter. To overcome about these types of ice problem, it is important to know about the property of the frazil ice flow down in a cold stream. In this study, in order to collect frazil ice, field observations were carried out at the Teshio River in winter season. The distribution of frazil ice in the stream and the volume of generated frazil ice were measured.

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It is difficult to determine the normal flow discharge stated in the basic policy for river improvement and the river improvement plan even in cases of large-sized rivers, especially in medium to small-sized ones which spread as networks in river basins and have an important share in water environment there. The normal flow discharge covers both of the water use and the maintenance flow discharge, the latter of which satisfies multi-purpose functions required ordinarily for rivers. The maintenance flow discharge of a small-sized river called the Shinborigawa draining a narrow low-laying area including the main campus of Gifu University is discussed in this study from the viewpoints of historical changes of the river and its basin, verifications of the river modification plan, and water quality improvement based on the use of rainfall and a shallow water analysis.

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A new method of flood control by gate operation based on runoff characteristics of a basin is proposed in this paper. This method is based on an anticipatory release approach and the idea that there is no risk in reducing reservoir levels if the amount of anticipatory release is equal to the amount of inflow which will flow into the dam for certain from the rainfall that has already fallen. In this method, rainfall prediction or weather forecasting will not be necessary for flood control. The amount of anticipatory release will be calculated by the real time inflow into the reservoir or accumulated rainfall. And reservoir levels will certainly be restored to there former condition, because the amount of discharge is based on the area under the recession part of the hydrograph.

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This study preliminarily examines potential use of the dynamical seasonal prediction with an atmosphere-ocean coupled model for the drought management in the upstream of the Tone River basin. first, likage between water storage in reservoirs for August and six accumulated-value predictors as precursor is revealed based on the observation data with non-parametric correlation test. In addition, correlation beween drought and El Niõo and Southern Oscillation phenomena years is examined to be not significant. The ensemble mean of the dynamical seasonal prediction outputs satisfactorily captures the drought years. This result suggests that the dynamical seasonal prediction may provide significant information about improvement in the cost-effectiveness of the weather modification operations to practitioners

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There are some problems in heavy rain disasters. Especially, it is difficult to grasp the damage situation at the time of a disaster. It is important to grasp the accurate information quickly and to share theinformation among administrators in times of disaster, in order to operate in real time, during disasters to minimize damages. We established an immediate action support system, based on the GIS to operate in real time, during disasters. The purpose of this system is to get the accurate information on the disaster situations and to display the appropriate measures, for immediate action. This system consists of two parts. One is a collecting-information support system and the other is an action support system.

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In order to implement policy measures on practical water management for the influences of rainfall characteristic variation arising from global warming, it is important to assess risks due to global warming from a practical point of view and develop actual water management measures including those related to floods and droughts. These risks are evaluated using the results of GCM20 high resolution general circulation model developed by Japan Meteorological Agency (JMA) and Meteorological Research Institute (MRI), calculated by using the super computer named the Earth Simulator. The horizontal resolution of the model is about 20km and the model output is expected to be useful for the flood and drought risk assessment of the future, in Shikoku Region Japan.

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In this study, a survey was conducted in the cities of Moriguchi and Neyagawa in Osaka Prefecture, where flooding occurred during heavy rains in 1997, regarding levels of knowledge and concern about urban flooding, awareness of self-help procedures, and participation in disaster preparedness activities. The survey data led to the findings about the nature and importance of disaster preparedness information. We found that even in a flood-prone area, self-help awareness is low. Information about the local area is an influencing factor on awareness of self-help measures and participation in voluntary disaster preparedness activities. Therefore the government should actively encourage public awareness of the importance of self-help during an urban flood, and conduct public information campaigns on what area residents can do for themselves and on subsidy programs.

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The erosion rate of naturally deposited cohesive sediment on river beds was investigated experimentally. In this study, we tried to establish reasonably the preparation procedure of a test sample which has almost same property of deposited cohesive sediment in an actual field of each river. After some detailed investigations about the preparation of test sample, a series of experiments were conducted in a laboratory flume in a same manner as that of our previous work. As a result of this erosion experiments, it was found that the measured data has the same tendency as that obtained by previous work.

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In this research, we have taken into account the necessity of technical scheme in order to see the movements of two big different sized grain groups, gravel in size 100 millimeter and sand in size below 1 millimeter. And we concentrated on the situation that sand passed over the bed laying big-sized-gravels in a state of suspended and predominant, and gave experimental consideration to the phenomenon of sand deposition into the gaps of gravels. We focused on the point that the sand suspension occurred on the sand bed that existed partly, and were based on the phenomenal analysis of suspended load and the past knowledge about integration into bed variation, examined methods of calculation about the relation between the concentration of suspended load and the ratio of area that covered with sand.

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Turbidity was measured continuously and suspended sediment samples were collected at the 17 gage stations in the Chikugogawa River basin, the suspended sediment budget and the characteristics of sediment rating curve were studied. The relationship between turbidity and suspended sediment concentration were analyzed for each stream, the nephelometric backscatter became much weaker with steep and small stream. The suspended sediment load was integrated for flood period of 2006, the sediment budget in the whole basin, the reservoir sedimentation by fine solids and the additional sediment supply to the flood water by river bed erosion in the estuarine channel were explained. The sediment rating curve for each stream were developed, it is shown that the coefficients of power function were affected by the watershed conditions such as topography, land use, rainfall and area.

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In this study, the effect of vegetation root system on surface erosion was investigated by conducting a series of experiments on slope erosion by artificial rainfall. Both a bare slope of sand and that with various densities of vegetation roots were set in the experiment flume, and oats were used here. As a result, it was found that the amount of eroded sediment from the slope with vegetation was considerably smaller than that from bare slope, and it was also proved that the surface erosion was obviously reduced by the root system. It was also found that the extension of eroded channel network was strongly affected by the arrangement of vegetations.

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It is almost impossible to know the process of a landslide occurrence by an investigation in landslide scar after the landslide had occurred. Therefore, it has been usually assumed that only one collapse occurred to become the final shape of the landslide scar. However, some of the recent landslides indicated that multiple soil masses collapsed one by one. It is not understood at all what kind of factor affects the multi-phased landslide occurrence, because it has never been studied. In this study, the effect of soil physical properties i. e., hydraulic properties and soil strength, on the process of the landslide occurrence including the multi-phased landslide are investigated by experimental and modeling approach. According to the results of these investigations, it is reveled that the soil layer with high internal friction angle and low cohesion tend to causes a small landslide and it might be followed multi-phased landslides.

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This study focuses on the influence of dam reservoir to cause excessive sediment disaster due to anomalous weather conditions by global warming. First, a sediment hazard probability model was developed and interpreted with observed sediment deposition records. Sediment yield was estimated for various return period and 5 year return period was found to be the best matched with the observed records. More over, it was observed that sediment production varies with particular land use in the region. Result of this study conform that the sediment hazard probability model is a much better tool to predict macroscale sediment storage in dam reservoirs.

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Red-soil erosion and runoff have led to agricultural and environmental problems in Okinawa, and effective measures which can reduce sediment yield in the farmland are necessary. For the purpose, advanced model for predicting sediment yield and transport is required. The authors carried out long-term continuous observation for sediment yield and transport at Nagura watershed, Ishigaki Island. Observation items were precipitation, water depth, flow velocity, turbidity, and SS concentration. Observed data contain 31 rainfall events for 1.5 years and some characteristics of sediment runoff were grasped such as sediment runoff variations due to timing of flood and tide. In these studies, the Water Erosion Prediction Project (WEPP) model was tested to verify their applicability in predicting sediment yield on farmland and sediment runoff at watershed. The calculated sediment runoff was reasonable compared with observed one. Consequently, the applied result of the model using the climate data for the past 13 years has specified the severe eroded hillslopes and the severe sediment runoff months.

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This paper presents quantitative energy and momentum exchanges between fluid and suspended sands via fluid-sand interactions in open channel flows over sandy dunes through comparisons of the sand-laden flow over movable bed and the single phase flows over the fixed bed, on the basis of double camera PIV measurements with an optical selection technique that is capable of measuring simultaneous velocities for the both water and sand phases at the same locations.
It was found that additional turbulent energy is induced during sand settlement process, which is over five times higher than in the fixed bed case. This additional turbulence may disturb the bed surface and enhance re-suspension of the disturbed sands. This recursive energy and momentum exchanges between the sand and water flows via the suspension, diffusion, settlement and re-suspension processes have important roles to characterize the sand-laden flows over the movable sandy dunes.

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Sediment control along river is very important for river management. These days, countermeasures to deal with rotational degradation, e. g. placing sand at the downstream of the dam, have been taken in some rivers in order to restore the continuity of sand interrupted by dam. To indicate significance of artificial sediment supply in river, we need know where supplied sediment deposit, how sediment supply let river morphology change, and so on. Therefore, we focus on the sediment transport on the bars which is typical landscape of river. We took the experiments to estimate sediment discharge on the bar and to indicate differences between sediment transport on the bars and on the flat bed. As results, characteristics of sediment discharge and sediment transport on the bars are shown.

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Effect of shape of sediment size distribution on alternate bar geometry is discussed by use of linear bed stability analysis and numerical analysis. Normal distribution, Talbot distribution, and bimodal distribution are chosen for sediment size distributions in the analysis. The results show that bar geometry on bed with bimodal type sediment has large difference from the others. Normal distribution with wide sediment size range is also tested and regularity of bar geometry is improved. Furthermore, bed load layer model is applied for reproduction of alternate bars and compared the results to those by exchange layer model. Spatiotemporal change of layers thickness is considered in bed load layer model and makes difference of reproduced bed geometry between two models.

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