This paper illustrates a statistical downscaling technique considering the spatial correlation structure of precipitation. Downscaling target is 60-km resolution of daily precipitation for 20-km resolution data. We have considered a window having (3x60-km)x(3x60-km) of area, and the downscaling target is the 3x3 of 20-km resolution grids in the center of the downscaling window. For the evaluation of the proposed method, we have prepared 15 years (1979-1993) of observation data, and identify the parameters with the square root information filter scheme. We optimize the parameters on a monthly basis, and apply the regression model to 10 more years of testing period (1994-2004). The proposed regression model provides very effective and efficient results with a certain level of estimation error.

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In this study, the risk assessment technique of pathogens was applied to a compound disaster of a large earthquake with a flood and an evaluation method of the infection risk was proposed. The infection risks of the norovirus and cholera vibrio were calculated quantitatively using the Kanda River basin as the study area. The spatial distribution of the infection risk was created and the visualization of the infection risk was investigated. The results showed that the infection risk changes in a range of 1.2 to 10 times higher than usual in the case of a large earthquake with a flood and subsequent inland inundation.

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Experimental investigations were conducted on the process of surface erosion and channel network formation on the bare slope. This is the process of sediment yields on the river basin. Some experiments were conducted to clarify the process of the erosion by varying both the gradient of slope and the width of mouth at the downstream end. It was found that characteristics of channels were different among the experiments, such as length, width, branches and interruptions. As a result, it became clear that the steepness of slope affects the length of the channel network in longitudinal direction. The width of the mouth, on the other hand, affected the width and the pattern of channel network in lateral direction.

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Fundamental process of surface erosion on bare slope which is caused by artificial rainfall was studied in this study. Numerical simulation was attempted under the same condition as the experiment that we conducted at the same time. Investigations were carried out for two type of the bare slope. Erosion process of the bare slope of sand which contains clay by 12% was one of the targets of this study. Numerical predictions technique was newly developed in consideration of being a non-equilibrium sediment transport process. Results of the numerical computation agreed well with experimental results, and the validity of the technique was confirmed.

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Although several physically based sediment runoff models had been proposed, sediment production and sediment supply to the river channel hadn't been considered in detail. In this paper, we introduced freeze-thaw action model and gully erosion model for sediment production, and talus erosion model for sediment supply. Each numerical model was connected to sediment transport model proposed by Egashira and Matsuki.
Applying this combined model to a real mountainous basin, we confirm that this model can express some of sediment runoff characteristics in a mountainous basin, for example seasonal variation of sediment runoff, temporal variation of the deposited sediment amount in talus, and difference of riverbed deformation between upstream and downstream.

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Debris flow can be trapped in a steel-grid sabo dam, due to the blockade of coarse woody debris without large stones. In addition, the permeable width of the barricade is not determined by the grain-size accumulation rate, but rather by the grain-size frequency. Information on the grain-size distribution characteristics in mountain streams is needed before construction of the dam. In this study, to identify the ideal structure for controlling sediment runoff, we experimented with the structure of the dam to show how the capture rate is affected under different conditions. The capture effect was evaluated for several grain-size distributions of real mountain stream beds to determine the relationship between grain size and the capture rate.

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In the Asahi River, heavy rainfall from 12th typhoon(2011) had caused the river channel blockade by sediment discharge due to slope failure and debris flow. These phenomena make large amount of sediment flow into the river shortly, and it changes the river channel characteristics, such as channel shape, aggradation, and grain size distribution. So, it is important to evaluate the sediment transport in river basin scale. In this study, first, we clarified the points of slope failure and the characteristic change in river channel by large-scale sediment discharge using observed data and air photographs. In order to estimate the quantity of sediment discharge, numerical analysis of flood flow, slope failure and debris flow was made. Furthermore, we evaluated sediment budget in the Asahi River basin, and suggested the effectiveness of sediment bypass tunnel.

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Soil erosion and runoff have led to environment problems in Babeldaob Island, Republic of Palau, and practical simulation model which can evaluate soil erosion and sediment runoff in watershed area is necessary. This paper aims to quantify the sediment movements in a watershed through continuous field observation for two years and numerical simulation using GeoWEPP model. We focused the small catchment in Ngerikiil watershed which has 2.7ha of developing bare land. The following three points were clarified. First, field observed results showed that severe soil erosion at the land development zone affects the behavior of sediment movements in the watershed. Second, GeoWEPP model has high applicability in predicting sediment runoff at two distinctive watersheds. One has no land development and another has developing bare land. Third, the GeoWEPP model gave the reasonable spatial distribution of soil erosion in the watershed.

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We aimed to propose a combined simulation model of lahar triggered by snowmelt and examined effects of erupted sediment and snow in northwest of Mt. Yake, central Japan. By composing three models (one dimensional heat transfer and snowmelt model, drainage model of snowmelt water in source area, and two dimensional lahar model), we could simulate not only inundation and changes in ground level due to lahar but their timings. Supply of erupted sediment on snow layer caused exponential decreases in thickness of snow layer and very high initial peak of snowmelt water. Although volume of snowmelt water was sufficient, snowmelt water drained from the source area (= initial lahar) was very small under conditions in which snow layer partially remained after snowmelt process.

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The objective of this study is to clarify the deformation process of river bed which is composed of extremely wide range of sediment. The frame of bed is constituted by the larger rock or stone which cannot move at all. In this study, "the dynamic equilibrium state of river bed" was investigated experimentally. The flow discharge and the sediment discharge of supply were the parameters in experiment. The sand and gravel existing in a void of the stones of the large particle size is affected by the stones. It is called a hiding effect. It was found from this study that the riverbed reaches different dynamic equilibrium state according to a supplying rate of the sand or gravel, and the surface elevation of sand and gravel exposed on the riverbed surface changes.

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Gravel bed rivers are composed of particles of various shapes and sizes. However, effects of particle shapes on sediment transportation and bed variation have not been clarified, because it is difficult to observe particle motion and sediment discharge rate in gravel-bed river during flood flows. This paper demonstrates the effects of particles shape by comparing particle motions between spheres and gravels which are simulated in a numerical movable-bed channel. The result is concluded that gravel particles of shape differing from spheres tend to make all size particles move together by the engagement with the neighboring particles and shapes of particles should be considered for predictor of sediment discharge rate and bed variations.

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Particles with large variety of sizes and shapes are seen in gravel-bed rivers. However the effect of collision between different size particles on motion of particles and bed structure are hardly clarified. This paper presents the result of the movable bed experiment with the numerical movable-bed channel which simulates three-dimensional motion of flow and particles of different sizes and shapes. The result of the numerical experiment revealed the characteristic difference in direction of contact forces of different size particles and the effect of particle volume concentration on the collisions. This paper shows that characteristics of collisions between different size particles strongly affect the motion of particles and bed structures.

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In this study, we investigated the reduction in sediment transport by the addition of short fibers to silica sand at various mix ratios. The experiment results revealed when a fibrillary material gets mixed with riverbed materials, the sediment transport changes depending on a mixed rate. Based on the experiment results, the relation between a mixed rate and the reduction rate in sediment transport was modeled by an exponential function as the vertical distribution of reduction rates in sediment transport at the surface layer of riverbed. Numerical experiments using two-dimensional analysis of riverbed evolution were conducted, and the analysis results reproduced experiment results very well.

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We evaluated freshwater discharge and suspended sediment(SS) transport into Pacific Ocean from Tohoku and Kanto districts. Measured discharge for class A rivers were collected while discharge for class B rivers was evaluated by using a runoff model (MIKE11). SS transport was calculated using the river discharge obtained here and a sediment rating curve(L=aQb) in which the coefficients were estimated with a new approach presented by the authors.The results indicate that 71 and 29 % of the total freshwater discharge were flowed from the class A and B rivers, resprctively, showing the siginicant sources of the class B rivers for freshwater discharge. 95 % of the total SS transport was on the whole outflowed from the class A rivers, while in the Tohoku district, 18 % of the total SS transport was flowed from the class B rivers.

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Development of meandering streams in bank erodible channels has been observed in the Otofuke River since the construction of straight low-water-channel in 1975, in contrast to a braided streams which was the typical bed configuration of the river before. In this study, numerical experiments with a field-scale channel were performed in order to reproduce the characteristics of the development process of meandering streams observed in the Otofuke River. It is found that meandering streams caused by alternate bar formation can be appeared in widening process of low-water-channel with local bank erosion at scouring points. The numerical experiments also suggest that the meandering streams can be changed to the braided streams after the low-water-channel widened to a certain extent.

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In rivers which formed multi-row bars or braided rivers, riverbanks often have wavy shape on a scale of several times of river width. In such rivers, a wide width part (anti-node) and a narrow part (node) appear by turns in the longitudinal direction. The elucidation of this phenomenon accompanied by bank erosion is very important on river management works. However, the formation mechanism of a gourd type channel has not been clarified. This research conducts a linear stability analysis as the first step which clarifies the formation mechanism of such channels. As a result, it became clear that a gourd type wavelength is changed with hydraulic conditions.

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The purpose of this paper is to deal with influence on channel form by regulated river width artificially in small and middle-sized river. Firstly, we surveyed about 100 rivers and evaluated the some parameters related to channel form, width (B), representative grain-diameter (dr), bed slope (I) and so on, with GIS data and survey data. Secondly, we calculated flow discharge(Q), flow depth (H), Froude number (Fr) and so on using the existing formula. Finally, we investigated the relationship between those channel characteristics and channel forms. As a result, there were highly correlations between the sandbar generation area classification (Kuroki et.al. 1984) and channel forms. we found that the types of those river channels can be classified 4 groups by Fr - BI0.2/H.
In conclusion, the results of this study were found to have effects on the ratio of the river width and the depth of water (B/H) which were set up artificially has affected the river channel through change of a stream bed form.

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For the purpose of understanding the thickness of riverbed material exchange at multiple places with different bed topography, we conducted cross-section surveys, gravel size surveys and buried markers surveys in the Toyohira River before and after snowmelt flooding. The surveys showed that the thicknesses of the bed material that is exchanged are more diverse around gravel bars than at narrowed sections of the river, and that the thicknesses increase at places with high flow rate and decrease at the middle and upper areas of each gravel bar front. At the narrowed river sections and at the gravel bars that were exposed to high flow rate where a thick layer of bed material was exchanged, scouring at the time of peak flood and deposition at the time of floodwater recession were considered to be key factors of bed material exchange. Deep scouring due to the presence of dune also affects bed material exchange. At places around the gravel bar front where the thickness of the exchanged bed material was successfully obtained, the thickness is likely to have been affected mainly by deep scouring during the time of peak flood and by deposition during time of floodwater recession.

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Numerical simulations for flood flows and bed variation in a diversion of a river were performed using a quasi-three dimensional numerical model. The vertically averaged and moment equations was used as governing equations to allow for the incorporation of pre-assumed linear distribution of horizontal velocity distributions. The model is based on finite volume method using HLLC(Harten, Lax and van Leer and Contact(2004)) numerical flux, which is one of a Riemann solver. The model is verified against two experimental data of flows and bed variation in a diversion of a river. It shows that the model has ability to reproduce the flow and bed variation in a diversion of a river, but the more improvement is needed to predict reasonable accuracy.

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Riverbed degradation and subsequent exposure of clay layer have occurred in the Kiso River due to less supply of sediment materials from upstream basins. The loss of the clay layer resulted in acute erosions of underlying sandy deposits. Ultimately, local scouring with about 20 m in maximum water depth was occurred.
In this study, we investigated the riverbed morphology and found a broad exposure of the clay layer and two large-sized local scouring in the Kiso River. In addition, we simulated the two-dimensional bed variation to evaluate the generating factor and process of the local scouring. The simulation indicated that the local scouring became enlarged because the edge of the clay layer has same function as riverbed girdle.

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Quantity of Sediment transport from the rivermouth is not well known. However, it is very important in order to calculate sediment transport and beach profile change in coastal zone. Many research activities by using ADCP to estimate sediment transport quantity were made. However, it is difficult to conduct field observations by using ADCP at the flood. Then, in this study, sediment transport quantity form the Naka River in the Ibaraki prefecture was estimated by using ADCP, the turbidity meter, and STD. Furthermore, sediment transport off the rivermouth was observed. In conclusion, the sediment transport quantity due to suspended component was well estimated and it was carried to the direction of southwest, the port of Ooarai.

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Recently, climate change has resulted in an increasing number of heavy rainfall events. Heavy rainfalls tend to cause large-scale landslides and create large landslide dams. Large landslide dams retain a large amount of water and often burst causing floods and catastrophic damage in the downstream area. Therefore, the study of landslide dam deformation is essential for predicting potential floods to implement effective flood risk management. To understand the landslide dam deformation process and dam outflow discharge characteristics, we carried out flume experiments of landslide dam erosion by overtopping flow. In the flume experiments, we observed the landslide dam deformation process directly. We found that dam height and inflow discharge affect to outflow discharge. Secondly, we developed a numerical model to simulate landslide dam erosion by overtopping flow. To improve the prediction of the outflow discharge, we incorporated the inertial debris flow model, the side bank erosion model, and the slope collapse model into our numerical model. The resulting proposed model is tested by comparing the results of simulation with experiment data. In addition, we organized experimental data by dimensionless quantity and it may indicated that peak outflow is expressed by dam height and inflow discharge.

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Propagation characteristics of surges in a straight channel with mild slope have been researched under small water discharge conditions by many researchers, because tsunami and tidal bores are observed near the coastal area. However, it is difficult by these studies to figure out that Nagatono power station was damaged by typhoon No.12 in 2011, since their assumed conditions such as geography and discharge are very different. In this study, propagation characteristics of surges produced by landslides in the mountainous river have been examined by two-dimensional bed deformation analysis and experiments of a meandering and linear channel. As a result, as for these surges, it was shown to propagate to upstream in flood at mountain area and to be dispersed in a meandering channel, it is very different from linear one. Furthermore, when another landslide dam had formed at downstream neighborhood where the surge produced, it is considered that propagation velocity of the surge become faster, more destructive surge is produced and propagated to upstream, that the erosion of the downstream landslide dam gives large effects of water depth change in downstream of the channel.

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Natural bedrock rivers form diverse erosional morphologies. The results of recent investigations have suggested that the bedrock erosion rate depends on discharge, slope, width, bedrock roughness and sediment supply. However, little is known about how these parameters affect spatial patterns of bedrock channel morphology. In this study, we conducted numerical simulations to evaluate the influence of sediment supply on bedrock bed state. The numerical results suggest that the increase of sediment supply leads to the formation of a single inner channel in a bedrock river.

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A single strong meandering stream is often observed in double-row bars rivers which attacks river bank and causes local scouring and bank erosion in even medium-size flood.Therefore,to maintain the safety against flood in double-row bars,we need knowledge on mechanism of such formation process and factors which bring about a single strong meandering stream.In this study,a depth-averaged flow and bed-variation analysis is carried out under the regime condition in double-row bars.Results of the simulation show formation of a single strong meandering channel and bank erosion and invasion of excessive vegetation in bars are factors which strengthen such a single meandering stream.

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The bank-full channel characteristics for gravel bed and sand bed alluvial rivers are investigated theoretically and empirically. Two sets of equations for describing the bank-full channel width and average depth for gravel bed and sand bed alluvial rivers are obtained. One satisfies rational regime relations, the other satisfies a dynamic equilibrium condition for stable channels. Using these sets of equations, a dynamic equilibrium condition for stable channels is identified. Then existing data of natural rivers in Japan is used to verify these sets of equations as well as the dynamic equilibrium condition for stable channels. The condition is found to well match with the data of natural rivers with sediment size ranging from sand to gravel.

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In this paper, we try to simulate a bed-deformation using numerical computation. For calculation of sand particles, we employed Distinct Element Method called DEM. This scheme calculates the sand particle collisions by mechanical elements, such as springs, dashpots, and sliders. DEM enable us to calculate "multi-particle collision". For flow calculation, the Unsteady Reynolds Averaged Navier Stokes model called URANS model was employed. In this model, we selected 2nd ordered non-liner k-ε model for turbulence scheme. To coupling between the particle calculation and flow calculation, we apply the two "two-way models", which incorporate the particle-fluid interaction terms of the drag force with/without the shielding effect. In previous results1) with one-way model, they could not simulate accurate dune characteristics, such as sand wave movement, wave length, and wave height which depend closely on fluid conditions. In order to improve the accuracy, we developed a new scheme using two-way model. We conduct a numerical computation under existing hydraulic experimental conditions, and evaluate the advantages of two-way modeling on the bed-formations.

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Recent years, slit Sabo dams have been installed for their function to prevent debris flow disaster and conserve continuity of water and sediment flow simultaneously. Because the sediment transportation is a phenomenon for a long term, numerical simulation models for sediment runoff are necessary to clarify the effect of the slit Sabo dams. However, though there are many simulation models to predicting the sediment runoff, the methods for modeling the slit dams have not been established. Therefore, the authors developed a numerical simulation model for sediment runoff simulation of the basin with slit Sabo dams by combining a rainfall runoff model and a quasi-2D bed variation model. It is applied to the Ogamo river basin in Tottori prefecture, Japan. This paper reports the method of developing the model and the results of the estimation of the sediment runoff.

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The Saba River in Yamaguchi Prefecture has many weirs and it induces a flood control problem due to breaking the continuity of water and sediment. The removal and integration of weirs have been executed in the Saba River. It is important to know the influence of the weir removal on the river bed deformation in the downstream area.
The purpose of this study is to estimate the sediment movement and river bed deformation due to the removal and integration of weir using two-dimensional numerical simulation. The results of numerical simulation indicate that two-dimensional simulation considering the effects of vegetation to the water flow is useful and the river bed deformation is to be complicated with progress of the time.

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This study experimentally and numerically investigates the flow structure to develop scour holes around a dam gate. First, we carry out a movable bed test of the scour. In the test, a weir with a rectangular slit is used to physically simulate the scour induced by sediment releasing through a dam gate. The stereo PIV method is applied to spatially and temporally measure flow velocity fields. Next, we carry out the three dimensional numerical analysis using the bed topography measured in the movable test. The numerical analysis solves the Reynolds-averaged Navier-Stokes (RANS) equations coupled with the VOF method and k-omega SST turbulence closure model. The analytical result is confirmed to agree well with the measurement. The measurement and numerical analysis show a tornado-like vortex in the vicinity of the slit. The vortex is found to highly contribute temporal evolution of the scour hole.

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Spur dykes have a variety of types in materials and shapes etc. In this paper, shapes of spur dykes, especially their head parts which are installed parallel to the main flow direction is studied. The laboratory experiments were conducted for 10 spur dykes in a straight flume with a movable bed and 10 spur dykes. Effects of the length of the head parts on bed configurations and the flow were determined and discussed. The equilibrium bed configurations and the velocity on surface flow were also measured. How the shapes of the spur dykes make geometric diversity in the embayment, and possibly diversity of habitats, is highlighted.

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There have been many bridges constructed over alluvial rivers in monsoon regions. However, the characteristics of local scour around bridge piers in such rivers have not been well analyzed. The past researches are all based on the assumption that flow is steady, sediment transport is under a certain equilibrium condition, and that the flood continues only during limited time. On the other hand, actual hydraulic conditions in the rivers are different; flow / sediment transport conditions are unsteady and high water levels continue for several months during wet season, which repeats every year. In this paper, authors clarified the change of the river bed topography around the bridge over Meghna River in Bangladesh, a typical of the rivers, using actual survey data between 1984 and 2007 for 23 years. The result shows that the local scouring progressed for 16 years after its construction in 1991. The values of scoured depth are larger than those estimated with the methods proposed by past papers. The facts founds research are practically important and will contribute to planning and maintenance of bridges over identical rivers.

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Since the elevation of flood plains in the lower Ota River floodway is located in the intertidal zone, tidal flats formed on the flood plains have become important as one of river functions. However, the tidal flats are gradually reducing in size due to bed scouring year by year. So, the cross-sectional shape in the lower floodway has changed gradually and naturally to the ship-bottom shaped channels at present from compound channels in the beginning by flood flows. Therefore, it is necessary to design the riprap for protecting against the erosion of the tidal flats. In this study, we evaluate effects of ripraps on the topographic changes and provide appropriately ripraps design by using numerical simulation for flood flows and bed variations in the lower Ota River floodway. Finally, issues to be considered in the design of a ship-bottom shaped channel which are found in the present study are summarized.

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Soil moisture is one of most important hydrological variables. Its redistribution have significant effects on evaporation, infiltration and groundwater recharge. Recently, its impacts on climate system is widely recognized. High non-linearity of Richards' equation makes its practical applications very difficult. Many soil moistue accounting hydrological models or land surface schemes (LSSs) take soil moisture into account conceptually as an index of wetness. Even Richards' equation based LSSs, used and evaluated in the global soil wetness project (GSWP) and/or the atmospheric model intercomparison project (AMIP), have only several soil layers. In order to develop a model to represent soil moisture redistribution in vertical direction for a better soil moisture accounting scheme, a high resolution numerical model solving vertical 1D Richards' equation is developed and applied to 9 soils in this study. By analyzing the soil moisture movement derived, two fomulae are proposed with parameters estimated from soil parameters. It is shown that these fomulae represented the behavior of soil water in soil column and at the surface fairly well.

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Laboratory-scale experiments on simplified heterogeneous porous media were conducted in a 100 × 100 × 3 cm sandbox with small blocks of fine or coarse sand. The use of visualization of dye solute and the measurement of NaCl concentration were applied to transitional estimates in longitudinal and transverse dispersivities caused by the presence of heterogeneities. Results showed a larger longitudinal dispersivity in the flow field with fine blocks than that in the flow field with coarse blocks while a continuous decrease in transverse dispersivity was shown despite of the heterogeneity. Laboratory study was extended by a random walk particle tracking and spatio-temporal moments to reflect experimental conditions, demonstrating a good agreement between the experimental and numerical results. Numerical simulations also exhibited that the transverse dispersivity depends on the magnitude of the initial solute distribution.

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Groundwater pollution by nitrate has become serious environmental issues in the Shirasu plateau of Kasanohara of Osumi peninsula, Kagoshima prefecture, Japan. We developed three-dimensional numerical simulation model to understand how the pollution diffused in the aquifer of the plateau. To evaluate the effects of countermeasures for the pollution source, the model was also used to simulate remediation stage. The numerical results showed that the nitrate concentration in the springwater from the edge of the plateau is very low. Therefore, the countermeasure against a contaminant source will be effective. Accourding to the results of the remediation simulation, it will take around 8 years to show the large effects of countermeasures of 80% reduction in nitrate concentration of the source zone. Even if the 50% reduction case, the nitrate concentration in the springwater reduced around half of the initial concentration after about 8 years.

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In order to evaluate effects of in-site bioremediation with groundwater circulation system on groundwater remediation of chlorinated ethenes, a numerical simulation of advective-dispersive multisolute transport was conducted at a contaminated site. First order rate constants of all chlorinated ethenes were calculated by using field monitoring data. The results showed that the first order rate constants were larger than those under natural aquifer conditions by more than a few orders. This finding provides evidence that this technology is very useful for accelerating the reductive dechlorination of chlorinated ethenes in an aquifer.

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Numerical simulation of heat convection in Boring hole using VOF scheme with Boussinesq approximation was performed. Comparison between results of numerical simulation and experiment indicated that effect of heat convection during Multipoint Temperature Logging is sufficiently small for detection of aquifer. Field observations at boring hole located in 30m distance from river were performed. Results of field observation performed before river-bed excavation showed existence of relatively remarkable river-bed water in shallow aquifer. The river-bed water showed vertical distribution of seepage velocity with depth. The generous river-bed water in shallow aquifer disappeared after river-bed excavation. After that, river-bed water restored gradually.

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Groundwater observation wells have been bored in 42 sites in Tokyo Metropolis. Large fluctuations of groundwater levels were observed after the 2011 off the Pacific coast of Tohoku earthquake at 102 observation wells in Tokyo. In this study, the fluctuation patterns of monthly groundwater levels caused by the earthquake were investigated using Self-Organizing Map (SOM). The SOM application classified the groundwater level fluctuation pattern into four clusters showing exclusively distinguishable patterns. sequently, the results show that the monthly fluctuation pattern of more than half observation wells changed after the earthquake. Additionally, an increase can be seen in the confined groundwater level in Musashino Plateau following a lower amount of groundwater being pumped due to the earthquake. Furthermore, all unconfined observation wells, and most of the observation wells at depths above 70m and those south of Tama River showed no significant changes following the earthquake.

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In order to evaluate groundwater environment for appropriate and sustainable use, impact assessment should be carried out with considering global climate change in future by using groundwater flow and water quality model. In this study, generally used type of two dimensional saturated groundwater flow model and advection-dispersion equation for Total Nitrogen (T-N) are used. Precipitation data is supplied from GCM calculation results (MRI-AGCM3.2s), where single mesh can almost cover study area because spatial resolution of this data is 20km. In consideration of GCM's spatial accuracy and in order to obtain probabilistic estimation from simulation results calculated by a lot of precipitation information, rainfall data surrounding meshes of target area are applied. A risk of groundwater drawdown and water quality deterioration is evaluated with time and space domain by using multiple calculation results. These results are analyzed by using of probabilistic distribution function (PDF).

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Trapping mechanism of floating objects during tsunami due to aligned trees was investigated through field surveys and hydraulic experiments. From the hydraulic experiment, the physical factors related to roadside trees and explaining the capture of floating objects were obtained. In addition, we show the maximum momentum limit at which trees fall when floating objects were trapped. Using the floating objects capture evaluation method of the trees that considered falling of trees, a verification case was performed knowing the specifications of the trees and floating objects in Tagajo city in case of the 2011 Tohoku earthquake and tsunami. We proved that the trees in Tagajo city did not fall even if it trapped floating objects during tsunami, generally agreeing on the quantity of the trapping ratio.

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2011 Great East Japan Earthquake Tsunami destroyed many coastal dikes located along the Pacific coast in Tohoku Region. From many field observations, it is found that most of the damages of coastal dikes were caused by scouring at a landward toe induced by the tsunami overflow. Characteristics of scouring around the landward toe of coastal dikes were discussed through hydraulic experiments. Bed shapes and water levels were detected from video images, and two types of flow patterns were observed; hydraulic jump and submerged flow. The flow types strongly affected the scouring processes resulting in significant differences of scouring depths. Relation between overflow heights and scouring processes was also discussed in this paper.

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On March 11, 2011, a mega tsunami hit the Sendai Bay Coast, and broke 80% of the coastal levees. The areas around breached levees were scoured deeply, causing serious adverse effects on post-disaster reconstruction efforts. This motivates us to analyze the mechanism of the local scour in the areas around breached levees. We collected and investigated various data such as aerial photographs and tsunami videos. As the results of the investigation, we found the breach points progressing in two steps: Firstly, the brittle structure was destroyed by the first leading wave. Secondly, the concentration of the return flow eroded and breached levees with the broken points from the first step. In order to understand the details of the second step, a numerical simulation was conducted using a finite volume method. From the result of the simulation, the scouring mechanism around breached levees was analyzed and discussed.

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We investigated saltwater intrusion in coastal farmland in Japan near a river mouth that underwent subsidence after the 11 March 2011 earthquake and extensive inundation by the ensuing tsunami. Although land drainage was complete in part of the study area, full restoration of the land was still incomplete. Our measurements of electrical conductivity using a Geonics EM38 instrument in the area subjected to drainage showed that salt concentrations in lower soil layers were higher than at the surface, and they suggested continuing intrusion of seawater. Groundwater storage in farmland and the force drainage technique have been proposed as measures against saltwater intrusion in subsided coastal farmland. Our numerical analysis showed that it is possible to drain crop fields by these methods without shoaling the freshwater-saltwater interface.

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On March 11, 2011, the Great East Japan Earthquake generated huge tsunami waves. Then, tsunami propagation occurred and expanded the flooded area. Tsunami propagation distance was collected and analyzed to estimate the area where we need the defense. It was found tsunami propagation distance in river is about 1.2 to 4.5 times as long as land area and, there is a good correlation between propagation distance in rivers and the bed slope. Furthermore, the dissipation coefficient of tsunami height was successfully estimated by applying the empirical equation and the general relation of wave height to distance.

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Comprehensive management for sandy beach is necessary to perform both the protection due to coastal hazard like tsunami and conservation of coastal environments. In the present study, we examined tsunami mitigation effects in sandy coasts and estimated sediment budget for sandy coasts. For these purposes, we conducted field measurements and data analysis in the Kujukuri beach with sandy coasts. The results indicated that 1) wide beach width (> 50 m), offshore breakwater and uniform dune height may decrease appreciably tsunami-overflowing erosion of the dunes, and 2)the sediment supply from inlands into Kujukuri beach was comparable to that from coastal cliff. This means that the comprehensive measures for beach erosion may have an important role for tsunami mitigation in sandy coasts.

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On March 11, 2011, huge tsunamis took place due to the Great East Japan Earthquake as large as Mw 9.0. It has been observed that an ocean bottom presimeter (OBP) and an ocean bottom seismometer (OBS) were sagged to the deep ocean by approximately 1 km, which suggests the possibility of the generation of a large scale line-source turbudity current taking place on the ocean floor off the coast of Tohoku. In this study, we reproduce the tsunami by the use of a tsunami simulation software, iRIC/ELIMO, evaluate the entrainment rate of suspended sediment, and estimate the source area of the turbidity current. It is found, from the results of the analysis, that a large amount of entrainment continuously took place from the north of Oshika Peninsula to the area within 40 km off the coast of Sendai Bay, which is assumed to be the source area of the turbidity current.

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Air-sea momentum and CO2 fluxes are estimated from observational data collected atsea observation towerbyusingthe eddy correlation method (ECM) together with the inertial dissipation method (IDM). Variability factors in the air-sea transfers can be investigated by using simultaneously both methods. The estimated fluxes are classified according to meteorological and oceanic conditions, i.e., the wave age, the unsteadiness of 10-m wind speed or the unsteadiness of CO2 concentration and the deflection of the wind stress vector from the mean wind direction. The present results show that the agreement between the fluxes from ECM and IDM is more sensitive to the deflection of the wind stress than the other factors. The wind stress deflection is found to be driven by the influence of swell on the air-sea momentum exchange process.

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During the 2011 Great Earthquake, ground subsidence of 20 cm occurred in Lake Hinuma. Since then, lakeshore erosion became dominant on Hiroura Beach located in the eastern part of the lake, with pine trees grown along the shoreline being damaged and the root of the pine trees being exposed to waves. In this study, long-term lakeshore changes of the area were investigated using an old map produced in 1885 and aerial photographs taken since 1947 along with the site observation on February 24, 2012. Although Hiroura Beach was a cuspate foreland before land reclamation, the lakeshore has eroded by wind waves and a marked change was triggered by ground subsidence associated with the Great Earthquake. To recover sandy beach, the effect of beach nourishment was investigated using the contour-line-change model considering the changes in grain size of bed materials.

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This study describes a horizontal circulation induced by the breaking of internal Kelvin waves over a uniform slope. In lakes or coastal regions, wind stress over a water surface or tide at the bay mouth may induce internal waves, which deform as internal Kelvin waves when the inertia radius is equal or less than the spatial scale of a lake or a bay. In general, internal Kelvin waves break due to the topographical features, such as a slope, which is revealed to cause horizontal circulation in the upper layer. The previous studies demonstrated that a horizontal circulation is induced due to the secondary lateral current due to the breaking of internal Kelvin waves over a slope. However, the development and damping of the horizontal circulation have not been clarified. Therefore, this study aims to investigate the occurrence of a horizontal circulation due to the internal Kelvin wave breaking over a slope by using laboratory experiments and numerical computations.

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