Rivermouth blockade has been occurred for a long period at Monobe River of Shikoku-island in Japan. The rivermouth blockade causes serious environmental problems for river control and ecosystem such as spawn of sweetfish. In this study, amount of sediment discharge from upstream is analyzed by surveying the morphology data of Monobe River for 32 years (1973-2005) and by means of aerial photographs to find the causes of rivermouth blockade. In addition, numerical simulation by 3D k-ε turbulence model and sediment discharge formulas by Van Rijn and Sunamura are applied for simulating the bed variation of sand bar near rivermouth considering with the flood/normal discharges, flow depth, wave direction, wave height and period of ocean wave. The phenomena of formation and destruction of the sand bar are reasonably simulated for conditions of winter and summer seasons.

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This study aims to develop a physically-based morphodynamic model in order to reproduce incision of tidal creek networks as well as evolution of geomorphology in the tidal environments. The process of incision and long-term geomorphologic evolution on tidal flats and marsh is of practical significance from the environmental view point. Generally, it is postulated that tidal creeks are developed as a result of ecomorphologic processes of tidal system driven by tidal energy. Some previous investigations have provided significant insight to this problem. However, there is still lack of a physically-based modeling approach that can replicate the initiation and evolution process of this phenomenon. In this study, physically-based model was applied to a narrow area referred to as tidal flats in order to provide quantitative and qualitative evaluation of its reproducibility. Calculation was conducted for different time scale up to 350 days. Calculation results revealed that the incision of tidal network and its initial development process can satisfactorily be reproduced by a physically-based computational model.

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Because the intake of the run-off-river hydro power plant faces the river, sediment in the riverbed flows in the waterway through intake when the flood occurs. At a very large-scale flood, power generation stops because of the inflow of sediment. In this study, we constructed the numerical model that reproduces this sedimentation process. This model is composed of two model, the model of upstream area and the model of river around intake of hydro power plant. The first model can evaluate sediment runoff from upstream channel bed. Secondary model can calculated bed variation around intake by using 2-dimensional numerical model. The result of sediment runoff is used as the upper boundary condition of this 2- dimensional model. This model is applied to the actual watershed of hydro power plant, and the calculated results by this model mostly agree with field survey.

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The flow and bed variation in channels with diversion and confluence was investigated experimentally and numerically. The experiments were conducted to obtain the bed variation data of a flow and bed variation in channel with diversion and confluence for verification of the numerical models. The effects of channel width on the bed variation and diversion discharge as well as sediment discharge were also examined from the experimental results. A numerical simulation were also performed by twodimensional bed variation model and verified against the obtained data. It shows that the model has ability to reproduce the bed variation in the channel with diversion and confluence with reasonable accuracy.

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In the case of the stony bed river with wide grain size distribution, boulders, which would not move during a flood, act as strong resistance element to the fluid. The other side, sand and gravel can stay in the bed irregularities formed by boulders. Therefore, the stony bed river will be in the stationary equilibrium condition of no sediment transport when the river bed form and grain size distribution corresponding to tractive force are established. However, in the past river bed variation analysis, this essential mechanism in the stony bed river can not be taken into consideration. In this study, we developed a new method of 1-D bed variation analysis in the stony rivers with well graded sediment stony rivers by considering the riverbed's stability mechanism by boulders, and we verify the applicability of the present model by the field experiment carried out in the Joganji River.

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This paper shows the experimental results on the river-bed configuration caused by a single permeable groin made of stone gabions. The local scour around the permeable groin is proved to be very small, whereas the bed-configuration of the downstream region far from the groin largely changes forming sand waves. The characteristics of the bed configuration downstream of a single permeable groin are experimentally revealed to be influenced by the permeability and the scale of the groin of stone gabions as well as the flow conditions such as submerged or emerged flow over the groin.

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Continuous submerged groynes can be used to create diverse riverbed configuration. However, scour holes were too large to make groynes unstable in case of impermeable and rigid structures. In order to reduce the scour depth, we used permeable and flexible groynes, that is, gabions. Model groynes with various characteristics were set on a laboratory open channel and velocity distributions and bed configurations were measured. The permeability and embedding effects were investigated experimentally. Three groynes were laid on movable sand bed without embedding. The permeability is necessary to prevent sinking of groynes and can reduce front scour drastically. The third groyne was folded at halfway because of the head sinking by erosion. The permeability decreases the velocity behind groynes and changes the flow structures slightly, but the bed configurations created by groynes were very similar to those of rigid, impermeable and embedded groynes.

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River cross sectional form had settled in the dynamic equilibrium form at the relationship between discharge, the river bed slope and bed material when river improvement is not progressing so much. But, river channels do not seem to satisfy the equilibrium condition of sediment transport due to river improvement work in progress. As the result, many problems have arisen on river management. Sediment transport became discontinuous by the dam and removing large size of bed materials as stones and gravel from rivers is mentioned. In this study, we describe the bed stabilization mechanism of the stony bed rivers found by the field experiment of the Joganji River and the difference in sediment transport mechanism of the stony bed river and the gravel bed river. Moreover, we insist on the problem on washing out of dam reservoir sediment and the necessity for the new bed variation analysis method in the stony bed rivers.

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For elucidating tree breakage condition with different breaking pattern, i. e. trunk breakage, tree overturn, local scour and degradation of the substrate of trees, and with different tree species, field investigation on tree damage situation after two flood events (October 2006 flood and September 2007 flood) were conducted in the Arakawa River and the Tamagawa River. Plant regeneration situation after 1year of the 2006 flood event was also conducted. If the breaking pattern is bending or partial breakage, the tree, Salix subfragilis, has a high productivity for regrowth. It implies that such breaking pattern is not so important if we consider the rehabilitation of gravel-bed river environment. The threshold moment of partial overturn of Robinia pseudo-acacia that has thin root zone was smaller compared with the previous experimental results by pulling trees because of a local scour. If severe scouring was occurred, threshold overturning moment can be quite small. The threshold moment can be found to be expressed as a function of the substrate condition.

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The management of the vegetation in the Oono and Ototsu River were examined using extended quasi 2D simulations. Firstly, the relation between the boundary mixing coefficients f and vegetation density in the Oono River is examined through comparison of numerical results between quasi 2D and 2D simulations. From the relation, a value of f is found to be 0.11 in the Oono River. And the effects of deforestation to the boundary mixing coefficient f were also examined. It showed that deforestation is not effected significantly on the value of f in the Oono River. Finally, management map of the vegetation in the Oono and Ototsu River was made using extended quasi 2D analysis.

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Field surveys, experiments and numerical calculations were conducted to examine driftwood accumulation in a river channel, with respect to the existence of sandbars. We investigated the areas where driftwood accumulated and captured from river channel is observed in two rivers. It seemed that factors such as the existence of riparian woods, sandbar configurations, and sandbar locations relative to the river flow determined the points of driftwood accumulation. Based on the field survey results, hydraulic model experiments investigated the flow path of driftwood in model river with alternate sandbars. The analysis related to flood flow indicates that when the flow velocity and the water depth of the main current differ greatly from the flow velocity and the water depth of the flow that is away from the main current, the force of the main current acting on driftwood pushes the driftwood outward. And we clarified the relationship between discharge and the locations of driftwood capture, traps were built at different points on a sandbar.

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This research deals with our investigation regarding the quantity and processing methods of driftwood, collected over a period of 5 years, from 2000 to 2004, by 395 offices of the national Ministry of Land, Infrastructure and Transport (the Cabinet Office for Okinawa Prefecture) and the civil engineering-related section stations at 47 prefectures. Also, the energy abundance of the driftwood based on this driftwood collection quantity was calculated. Next, regarding the 18 river systems of the entire nation, the following three factors were taken as parameters for a factor analysis: the river characteristics, the vegetation areas in the rivers, and the vegetation areas in the basins as calculated from GIS analysis. The results of the factor analysis were used to seek the relationship between the driftwood emission rate and the river characteristics as well as the basin characteristics.
Our results indicate that the driftwood emission rate and the river slope can be considered to be cofactors.

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Information on the velocity of inundated flow is necessary to investigate the actual situation of flood or tsunami disaster, to estimate the fluid force on individual building, the moving velocity of floating body, etc. Although a simplified method for estimating the velocity had been presented by authors (1998), there still remain problems to be examined, such as the velocity coefficient, the distribution of water edge on a building or other object, etc. These problems are examined through hydraulic experiments.

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In 2004, a sever drift wood hazard caused by fallen trees drifting in muddy flows and overflowing at river bridges happened in many steep small-scale rivers of Ehime Prefecture. In this paper, a countermeasure in which the rail on the bridge girder is removed and some of flowing flood water overflows on the bridge girder like a sinking bridge is proposed and the effect of the countermeasure is examined through runoff experiments in hydraulic steep channels. As a result, it was made clear that the countermeasure removing the rails is a very effective one which reduces a destructive power of overflooding water to one third.

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The purpose of this paper is to examine the trend of the riparian land-cover changes over the past 100 years quantitatively. We have analyzed the land-cover and the height of plants within riparian area in the year of 1890, 1947, 1961, 1974 and 1990 by using maps and aerial photos in the downstream part of Kokai river.
The ratio of land-cover and the height of plants did not change significantly until 1970's, suggesting that riparian environment was in equilibrium. However, the area of the forest increased by 18% and the height of trees increased up to 15-20m from 1970's to 1990's. This can be attributed to the decline of the human disturbance. We have characterized three typical processes which lead to the growth of forest in riparian area in Kokai river, as follows.
1) Reed area was transformed to forest area. 2) Trees in forest area have been no longer cut and used as fuel. 3) Cultivation activity has been lowered in riparian area. Above three processes seem to have been accelerated due to the change of the life style of people in the vicinity of the river.

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Morphological evolution of the topography of the reach with groins is investigated using a numerical model solving the two-dimensional shallow water equations in this study. A flood event is represented to discuss the dischargedependent change of the interaction between flow structure and sediment transport. The primary flow is meandering according to alternate or multiple bars formed in the channel during low-water and medium-water periods, and it is found that deposition of the fine sand and silt on vegetated area between groins is affected by the meander of primary flow. During a high-water period, on the contrary, the primary flow follows the large-scale topography of the river so that flow on the flood plain is also straightforward according to the large-scale channel form. This straightforward flow on the flood plain, formed between groins, induces three-dimensional flow structure (longitudinal vortex), develops streak go through the groins longitudinally, and forms the rib-shaped topography on the flood plain. This ribbed bathymetry is highly interacting with sediment transport not only within the flood plain but also between the channel and the flood plain.

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The effect of sediment transportation into the artificial embayment by tidal and flood flow on the environment of embayment is considered. Changing of flow velocity and water depth by tidal event, and depth of accumulated sediment by flood event were investigated. It is thought that accumulated sediments in the embayment are transported by tidal flow, and accumulation of silt leads sediment of embayment to the anaerobic condition. Direct inflow of sediment in flood can be prevented with good devised configuration of the embayment and appropriate arrangement of vegetation.
On the embayment in tidal area, there is some possibility that effect of daily tidal flow on ecoenvironment is larger than that of irregular flood event.

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Nature friendly hydraulic structures made of natural stones such as ripraps have attracted attention in recent years. However, those structures are subject to failure problem under flood flow. Therefore, the authors proposed connected stone to increase its stability against flood flow. Coefficients such as the drag and lift force are necessary in designing those structures. However, the authorized values for those coefficients are not established yet, the coefficients used for concrete structures are therefore applied in designing structures made of stones at present condition. This study aims to clarify the drag and lift coefficient for connected stones placed at the middle and upper reach of the bed protection works using connected stones.

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Bridges in upstream reaches of rivers have collapsed during floods in Japan. The authors investigated the field conditions of the collapsed truss bridges on the Mimi river and examined the causes of collapse of supports for girders of truss bridges by hydraulic model experiments. Fluid dynamic force exerted on girders of truss bridges is clarified.

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Nature oriented hydraulic structures made of natural stones such as ripraps have been used in Japan considering river environment. Negative aspect of these structures is easy to collapse under intense flow. Therefore, a connect stone is proposed to increase its stability against the intense flow. In this study, stability of two types connected stones, one is non-porous and the other is porous type, was investigated under rapidly varied flow conditions such as supercritical flow and hydraulic jump. Stability analysis using uplift and drag force acting on the connected stone shows that the non-porous type connected stone may collapse turn up and lift up mode. Furthermore, it is clarified that the porous type connected stone is more stable than the non-porous type.

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The total value of impulsive fluid forces acting on the partial part of composite breakwater model for breaking waves and the whole part of dam model for hydraulic bore were measured by using multi components load cells (LMC). The impulsive forces measured by the load cells include the inertia and damping forces produced by the response acceleration and velocity of these hydraulic structures attached on LMC. The net values of these impulsive fluid forces are evaluated by using the linear vibration equation which approximate the motion of the load cells attached these hydraulic structures.

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To investigate the instantaneous flow patterns around a single groyne, a scale model was installed in the shallow water channel and experiments were conducted by means of surface flow visualization technique. A particle tracking velocimetry (PTV) method has been developed for shallow flow conditions and has been adopted to estimate the instantaneous velocity fields to cope with the problem of a very high dynamic velocity range behind the groyne. Proper orthogonal decomposition (POD) is applied to obtain an effect of the fluctuating flow pattern and its coherent structures. Conditional sampling technique (CST) is also applied to reveal the advection properties of POD decomposed flow pattern. POD decomposed coherent patterns and their advection properties under submerged and emerged conditions. One of main results is the distribution of coherent vortices generated at the groyne tip due to high shear forces in the mixing layer between main stream and dead zone.

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Transport mechanism of suspended sediment is one of great interests in river engineering, because there are complicated interactions among flow structure, particle motion and bed forms. A lot of previous studies have been conducted on velocity measurements and numerical simulations in these suspended sediment flows. However, there are still many uncertainty about turbulence modulation, that is to say, the particle effects on flow structure. In order to reveal this significant topic, we conducted simultaneous measurements of fluid velocity, particle velocity and sediment concentration by using a discriminator particle tracking velocimetory (D-PTV) and a discriminator particle image velocimetory (D-PIV).
It was found from the present study that the larger sediment particles enhance the turbulence intensities and Reynolds stress, while the smaller size particles depress them. Furthermore, we also revealed that this tendency becomes more remarkable as the sediment concentration is larger.

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It is necessary in river environment and hydraulic engineering to investigate the hydrodynamic properties in vegetated canopy rivers, in which velocity distributions are largely changed in the vertical direction. In particular, the relative submergence, i. e., the ratio of the water depth H to the vegetation height h, influences velocity profiles significantly. For example, in high submergence, we can see an outer layer in which a logarithmic layer is formed. Whereas, in low submergence, the flow is directly influenced by the vegetation elements. So, in this study, turbulence measurements were conducted intensively in vegetated open-channel flows by changing the relative submergence, and consequently, mean-flow properties, turbulence structure and coherent motions were revealed and discussed in detail.

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In actual rivers, many aquatic plants are often observed and submerged canopy flow appears in floods. Submerged plants create complex flow patterns, in which wakes behind vegetation and coherent motions are generated. In particular, mass and momentum transfers and the mixing process are promoted significantly between the in-canopy layer and over-canopy layer. It is, therefore, of great importance for river ecosystem to reveal turbulent diffusion in submerged vegetated open-channel flows. In this study, both of PIV and laser induced fluorescence (LIF) measurements were conducted simultaneously with a pair of high-speed cameras in order to evaluate the relation between the turbulent diffusion property and the coherent motions.

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Conventionally, two-dimensional velocity distribution of model experiment with relatively shallow water depth has been measured by surface tracers because intrusion of probe itself will disturb the flow field significantly especially, in the case of movable bed experiment. However, surface flow is not always a good representation of mean flow when secondary flow effects are not negligible. On the other hand, the dye-injection method has been used for understanding general flow features by visualizing the depthwise flow. In this paper, a novel idea of utilizing dye-injected flow images for the measurement of depth-averaged velocity distribution is proposed. Through the particle simulation and experiments using straight and curved channels, the validity of the new idea was verified.

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It is well known that a surface oscillation is generated by installing a rectangular side-cavity structure to an open channel flow. The intensity of oscillation increases greatly as the increase of the Froude number. In addition, the type of oscillation changes easily depending on the shape of side-cavity and the width of ratio of the main channel to the depth of side-cavity. In our previous experiments, we categorized the oscillation pattern into four types. In the present study, the space-time correlation relations between the surface elevation and the velocity component at the inlet of the side-cavity is examined by the large eddy simulation that allows the water surface variation. It was found that the type of oscillation is largely divided into two types, i. e. with and without a strong depth-velocity correlation.

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Vegetation communities are often observed to grow in stripe pattern or patches within many stream channels. In such a situation, hydraulic engineers should examine an appropriate vegetation management system paying attention to flood control and vegetation ecosystem. In this paper, the flow resistance and momentum transport in open channel flow with discontinuous vegetation in longitudinal direction were examined experimentally. Velocity fluctuations were measured using a particle-image-velocimetry (PIV). Results showed that the flow resistance significantly depended on the longitudinal length of cavity between vegetation zones and the reason could be explained by the difference of momentum transport through the interaction among main flow, discontinuous vegetation and cavity.

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Manning's roughness coefficient is influenced by roughness condition of perimeter, shapes of longitudinal and cross sections, flow conditions represented by parameters such as the Reynolds Number and so on. There are few preceding studies dealing with relationship between the roughness coefficient and other factors than the roughness condition. The purpose of this study is to examine relationship between the Manning's overall roughness coefficient and configurations of river channels which have different roughness perimeters by numerical simulation. Characteristics of variations in the Manning's coefficient according to water depth and applicability of composite roughness coefficient are discussed.

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This paper deals with hydraulic characteristics of two lane flow in a steep channel composed of large bed materials. After the recognition of the regime, field investigation and also numerical experiment were made in the case of kinu-river. As results of the study, the regime of this meandering system was found to be one of the stable condition of meandering system and also discussed about the disturbing factors.

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Field observations on characteristics of discharge were conducted in an urban tidal river, the Horikawa River. Velocity distributions and discharges on various cross sections were measured by acoustic Doppler profiler (ADP). The longitudinal distribution of maximum discharge caused by tidal flow was revealed. The velocity structures in a falling stage were different from those in a rising stage. In the falling stage, the surface-layer velocity is higher and the lower-layer velocity is lower than the log-law profile. In the rising stage, the medium-layer velocity indicates maximum value. In a concavity zone of the tidal river, horizontal vortices were observed in both the falling and rising stages. The flow structures in the concavity zone indicate three-dimensional feature. The surface vortex structures were different between falling and rising stage.

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Stepped channels are effective for dissipating the energy of supercritical flow that occurs at steep channels. Generally, the flow conditions in stepped channels have been classified into skimming flow, transition flow, and nappe flow. Also, stepped channel flows have been characterized as aerated flows. For design purposes, it is important to predict the aerated flow velocity, the air-concentration, and the energy head of aerated flows in skimming, transition, and nappe flows.
In this paper, aerated flow characteristics of skimming, transition, and nappe flows have been investigated for a wide range of relative step height S/dc under a given channel slope θ=19°. It was found that the velocity and air-concentration profiles characterize each flow condition. The energy head of aerated flows E in skimming, transition, and nappe flows has been determined from the air-concentration C and the aerated flow velocity u.

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The hysteresis phemena which can occur in transition between gated flow and free flow are experimentally clarified, and the profile and the fluctuation of water surface and the velocity profile under the relationship among the water hight, the gate opening and the discharge is described as the discontinuous condition in transition. And then, the unsteady discharge characteristics in transition are experimentally analyzed, and the validiity of the propose equation is confirmed though the comparision with the discharge based on the velocity. In addition, it appears that the numerical simulation model using the incompressible fluid analysis and VOF can simulate the hysteresis phenomena in transition.

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The flood disaster in a stream valley is discussed with experimental results by water surface flow visualization and water level measurement. From a field survey, it is found that the magnitude of damage is dependent on valley width, which implies the change of flood flow depth on the alluvial plain, and river width at the bend apex. As experimental results, the magnitudes of water surface velocity and divergence around the apex are large for deep condition on the flood plain and narrow channel width at the bend apex, implying that significant erosion can occur around a bend. Thus it is important to understand the effect of configuration on flood flows and appropriate river width at the bend apex to reduce flood damages in a stream valley.

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Recently, a heavy rainfall in a short period of time occurs often and causes severe damage from a flood in various regions. The heavy rainfall due to the Baiu front gave severe damage to the southern region of Kyushu Island from July 19 to 23 in 2006. In this paper, an outline of flood disasters for the Sendai river basin in Kagoshima Prefecture from this heavy rainfall was reported. Furthermore, an improvement of the flood control operation of Tsuruda Dam in Kagoshima Prefecture was considered. By introducing the improved operation technique, it is expected that the flood control of Tsuruda Dam works well not only under usual flood conditions but also under unexpected heavy flood conditions.

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From July 15 to 24, a front stagnated over Japan, and the heavy rainfall was brought. Especially the Sendai River basin was severely and uniformly damaged from the upstream to the downstream. At four observatory stations, water level of the Sendai River exceeded the design high water level. Around the Torai area, one of the most severely damaged areas, a diversion channel is planned to construct. Therefore in this study, applying a two-dimensional numerical model, flood simulation is conducted in the Sendai River and the effect of this diversion channel is investigated. As the results, though a part of the water level of the Sendai River is not expressed successfully, it is found that this diversion channel has an effect of decreasing the water level around Torai area.

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In this study, we were the subject of the Izushi River catchment area that is a branch of the Maruyama River, made investigated into flood runoff prediction, and an inundation analysis with the typhoon No. 23. The rain response characteristics were clarified from two elements, namely, the catchment area and the rainfall distribution characteristics, and method of the flood runoff prediction was examined. As a result, three correlations on the two parameters in the runoff model and rainfall distribution characteristics were able to make analyzed. These were expressed with valid correlation formulas, and the prediction discharge of flood overflowing from river channel was estimated. Moreover, in order to prove the validity of these correlation formulas, flood analysis at the time of the typhoon No. 23 was conducted, and it was compared to the survey figure of inundation. The reproducibility of this flood analysis was very good, and the validity of three correlation formulas was showed.

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The overflow discharges, under the overflow as well as submerged overflow conditions, from a meandering channel with or without retarding plantations into a flood plain are investigated experimentally and numerically. The analysis is directed toward the examination of the overflow discharges by the overflow discharge formula as well as the numerical analysis, simultaneously solving flows in a channel and inundation flows in a flood plain. The dynamic inundation analysis model used in the analysis comprises the finite volume method on unstructured grid using fluxdifference splitting (FDS) technique. We found that the model is much superior to the formula in predicting the overflow discharges with or without retarding plantations.

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An analysis of behavior of over-land flows based on geophysical characteristics using geographic information system (GIS) was conducted. Firstly, the digital surface model (DSM), which is the data of the surface of ground, was verified against the data of bed elevation in the map of the city planning whose scale is 1/2500. Secondary, using digital surface model, a behavior of over-land flow was analyzed. Finally, the analyzed behavior of over-land flow was compared with the flood process examined in the field study and numerical simulation. It shows that the GIS and DSM are useful tool and data for examining the behavior of the inundation flows.

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River flooding, especially flash floods are a well known risk in Samoa where steep river catchments get frequent intense rainfall events especially in the wet season resulting in floods. On the other hand, there is few information about hydrological observation and flood control is not enough to prevent damages. Therefore, it is very important to predict the flood flow and the danger of the flood during such disaster. This paper will discuss the application of numerical simulation models to the rivers which flows through urban area of Apia. In this study, runoff model and flood calculation are combined to know characteristics of each flood Models have been used to simulate the flood propagation and thus verified against physical observations. The results have identified the inundated area and quantified flood hazard extent and intensity Future studies include fitting flood structures for flood mitigation measures.

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Risks of urban flood have been increasing in recent years. Heavy rainfalls that attacked Tokyo, Nagoya and Fukuoka cased the underground inundations. When the underground inundation occurs, people must evacuate to the ground as soon as possible. Therefore, it is necessary to evaluate when and where it becomes difficult for users to evacuate during the inundation. The difficulty of evacuation in stairs has been evaluated with momentum per unit width. However, this criterion can not be applied to a corridor. In this paper, specific force per unit width is introduced as a new criterion to evaluate safety evacuation in both cases. It is difficult to implement safety evacuation when the specific force per unit width is over 0.125m2.

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Evacuation process from an inundated underground space to a ground level was investigated in this study. Numerical model which was proposed in our previous paper was applied here to simulate the evacuation behavior of people from the actual underground space in Shibuya as well as the inundation itself. Several series of computation were made, and a possible evacuation route was found for crowd of people there to go out of this space safely and efficiently without walking in the coming water. This kind of computation must be needed before we make a plan of evacuation route from such an inundated underground space in order to make a human damage be minimized.

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Inundation analysis method has been used on measures for water disaster in many cities. In the inundation analysis method the various hard and soft measures are examined and applied to actual field. Recently, the detailed ground elevation data are obtained by development in the survey technology. However, as the usual analysis method treats average ground elevation and average water depth in analysis grid, the detailed ground level data is not used effectively. In this study, the new inundation analysis method is developed and the validity of this analysis model is examined by comparison between analysis results by using normal analysis model and that by using new analysis model presented here. The new analysis model presented here treats inundation water volume as unknown value. Therefore, continuity equation becomes the equation related with water volume. Next, inundation water depth is obtained from prepared function of water depth and water volume. Finally, the momentum equation without advection term and viscosity term is analyzed by considering the characteristics of ground elevation.

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Inundation process in lowland areas of east Tokyo which is bordered by the Ara River and the Sumida River was investigated under the assumption that the overflow from the Ara River into this area occurred. Numerical simulation model was constructed by extending our previous computational model to evaluate the flows in vacant lands as well as on the road-networks in this area. The overflow point and its discharge were the assumed one in this stage. As a result of this simulation, the time series of information about the flow path of inundated water were obtained, and the characteristics of inundation in this area were made clear. This kind of information must be useful when we make a plan of evacuation route if we experience such serious inundation.

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Recently, we often experience the heavy rainfall whose intensity exceeds beyond the designed magnitude, because of the influence of a heat island phenomenon in urban area as well as a global climate change. On September, 2005, such a heavy rainfall caused the flood damage in Tokyo Kita Ward due to an overflow from the Shakujii-gawa River. In this study, numerical analysis was conducted to investigate how this inundation occurred. As a result of this analysis, the inundation which caused only by the heavy rainfall also happened simultaneously, and therefore the damage became more serious than that only caused by an overflow water of the river.

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In this study, taking up the area which is not put up city block data, calculation technique to calculate city block is developed according to combining digital map 2500 with city region digital map in Sendai City. Besides in these years digital sewage map is computerized in various regions. And so we can obtain from digital sewerage map the information, and the technique which can connect to the road network on the ground was developed. Furthermore the method to divide into pervious area and impervious area which has an effect on the landside inundation with laser profiler data is developed. Based on the above result, analytical model is applied to rainfall of August, 1986, and the result set against the questionnaire result.

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Preissmann Slot concept is one of the most extensively accepted numerical approaches in unsteady free surface pressurized flow. However Courant's stability condition has imposed this method with limitation on the size of the time step. The slot concept produces large wave celerity and a corresponding strict time step limitation with too small slot width, while inaccuracies may result with too large slot width. The equations for a surcharged flow which form the lateral model are derived incorporating the relaxation effect and compared with corresponding equations of slot model. The friction loss is evaluated in slot model by introducing the coefficient, which modifies the slot model. The pair of differential equations of Slot Model and Modified Slot Model are solved and presented in forms for direct substitution into FORTRAN programming for numerical analysis. The numerical result justifies Modified Slot Model to be more efficient for the modeling of transient flow in sewer network.

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Radio current meters were improved in a turbulence measurement version and pulsatory flow measurement was made every 0.3 sec in 7 reaches of 4 different rivers in order to applicability check of the version. 5 items (V, Vave, E, Eave, E0.3-3Hz ( E : Radio Reflection Intensity ))are chosen and succeeded in observation of periodical characteristics in some items and irregular signs because of bursting from the river bed.

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In case that we evaluate the effect of sediment replenishment during a flushing flow operation, there was no sophisticated measurement method to monitor gravel movements on the river bed. We have developed a tracer investigation technique on gravel movements that applied the IC-Tag technology. This system is composed of an ICTag that is inserted in each gravel, an antenna, an amplifier and a data logger. We have tested this system at the flushing operation of Managawa dam in 2005 and succeeded to find out flushed out gravels with IC-Tag in the downstream river bed.
In this paper, we present results of field tests on two different river channel conditions. One is Managawa river during flushing operation in 2006 and another is Hiru valley in Zintsu river during sediment flushing from a small sediment check dam. We have tested both a fixed type antenna to measure sediment passing time real-time basis and a movable type one to measure sediment movement after the event. Through these field tests, basic characteristics of the system and future challenges are discussed.

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Shallow Water depth is one of the important factors in science and coastal environmental management. However, in-situ measurement is quite costly and time-consuming. Past research efforts have provided a number of optically-based methods to estimate shallow water depth distribution from satellite image, but they cannot handle with the heterogeneity in bottom sediment distribution without the help of image-specific assumptions or additional information on bottom reflectivity. It is indispensable to develop a method that can be applied to water areas with inhomogeneous bottom material. In this paper, we present a generalized method over the previous methodologies by using remote sensing-based bottom feature information. The new method is applied to three coral reef areas, and as a result, is found to have improved accuracy and stability.

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