Momentum exchange coefficient (resistance coefficient) which is an index of momentum exchange between the air-sea surface has been treated as monotonically increasing with the wind speed. However, wind speed profile is deferent from a logarithmic law of wind speed because under severe storm turbulent flow is suppressed by sea spray generated from the sea surface. Moreover, from observational studies, it was found that the momentum exchange coefficient has a peak at about 33 m/s. Wave conditions also vary when sea spray exists under a severe storm. Liu et al. (2012) proposed a momentum exchange coefficient taking account of the effects of sea spray and wave age. In this study, the heat exchange coefficient is derived based on the bulk transport equation useful in the numerical meteorological model from the same momentum exchange coefficient. The latent and sensible heat exchange coefficient have the peak when the wave age is 0.4 and the wind speed is 25 33 m/s. This new coefficient allows us to discuss the effects of sea spray and wave age effects.

 The role of soil moisture and groundwater is important to reveal how land surface water balance is determined by long-term mean climate. The discusstion about how to define equilibrium state of soil moisture and groundwater table in hydrological simulation have been continued to understand terrestrial water balance. The aim of this study is to clarify how equilibrium soil moisture and groundwater table is explained by hydro-climate on global scale by using land surface model with explicit representation of groundwdater table dynamics. The new concept for defineing climatological equilibrium state of soil mositrue and groundwater table under assumpition that a similar climate pattern has been repeated for a long term period is proposed in this study. The analysis showed that around 80[％] of land surface area have climatological equilibrium state though the groundwater table and soil moisture did not reach climatological equilibrium state through a thousand simulation at arid and semi-arid region. It suggested that soil moisture and groundwater table are transient at arid and semi-arid region under current climate.

 This research aims to expend knowledge of the mechanism of slowly dissipating typhoons which are called “the long-lived typhoon” over Indochina. We analyzed the landing position of typhoons and decadal and monthly change in typhoon lifetime from 1958 to 2016. The typhoon lifetime seems to be related to landing position. The Self-Organizing Map （SOM）was used for classification based on the environmental field of precipitable water, wind velocity at 850hPa and sea level barometric pressure . The SOM result shows that the condition where the positive deviation field of precipitable water exists in the whole peninsula or the south part might cause long-lived typhoons.

 The use of satellite-based passive microwave brightness temperatures (TBs) is an effective way to retrieve the cloud water content (CWC) of broad cloud systems, but it is challenging to estimate CWC over land due to complexities of cloud processes and uncertainties in strong and heterogeneous land emissions. We proposed a method to estimate CWC over land at multiple-kilometer resolutions and to concurrently assimilate the estimated CWC into the model by using multi-frequency TBs and coupled land and atmosphere assimilation. The estimated CWC was in good accordance with vertical two-dimensional products of CloudSat in terms of cloud water path (CWP) and the vertical distribution of CWC. In addition, we examined the uncertainties of this method by sensitivity analysis of CWC estimates of TBs and cloud top height. The results suggested that the error in TBs is not large, and that cloud top height affects the estimated CWC more sensitively than TBs. The addition of cloud top height information from other satellite observations as a constraint of optimization allows further improvement of the vertical distributions of CWC. This study revealed that the proposed method has great potential to provide unprecedented data for CWC with adequate accuracy, which are continuously distributed over land and ocean.

 It is demonstrated that the inundation flows and loads on RC building of tsunamis after overflowing a chest wall, obtaind from the steady and unsteady experiments, could be significantly different each other. A relationship among the incident inundation depth of tsunami after overflowing a chest wall, overflow depth in the upstream region of the chest wall and overflow depth at the downstream end of the chest wall crown is examined using the distance from the downstream end of the chest wall to the falling position of nappe as a parameter, and it is enabled to evaluate the incident inundation depth from these overflow depths. Moreover, it is confirmed that the horizontal force on RC building caused by the tsunami inundation flow after overflowing the chest wall is estimated on a safety side by adopting the total hydrostatic pressure evaluated by using the incident inundation depth, incident inundation flow velocity and the coefficient of the inundation depth at the front of the building.

 Laboratory experiments were conducted to understand how a tsunami-like solitary wave energy can be reduced in one horizontal dimension against the effects of beach slope, sand dune height, depth and length of the lagoon in cross-shore direction. The wave height to depth ratio from 0.1 to 0.4 was used. The resultant wave transmission height and maximum runup for beach slope of 1/30 and 1/7 were measured using a slope of 1/4 at landward of the lagoon. The dimensional analysis was used to pick up important parameters for comparing the maximum runup effect. The plunging breaking, surging breaking and nonbreaking type of waves were observed on the beach slope. The undulations with no breaking, leading wave breaking and turbulent bores were observed inside lagoon with the change of wave transmission height to lagoon depth ratios. Thus, a coastal lagoon having gentle beach slope, larger sand dune and larger length in cross-shore distance helps to increase more resilience against tsunami attack.

 After the Great East Japan tsunami, against a Level 2 tsunamis, the goal of the coastal defence is not ‘disaster prevention’ but ‘disaster mitigation’ by compound defence system. As a compound defence system, double embankment structure was previously investigated by experiment and the flow structure in between two embankments was demonstrated to affect the reduction of tsunami energy. Especially, the flow structure which hydraulic jump occurs in between two embankments is suitable because the energy reduction is high and the oscillation of water level at the top of second embankment is not observed. Therefore, in this study, a theoretical equation to estimate the critical occurrence of hydraulic jump by double embankment system was proposed. By comparing the theoretical equation with the experimental data in a previous study, the applicability of the equation was validated. In addition, the friction loss equation was suggested not to be applicable for a run-up flow.

 After the Great East Japan Tsunami, tsunami mitigation method by strengthening the existing coastal forests were considered in Hokkaido. Effectiveness of tsunami energy reduction by the hybrid structures using an embankment, moat and vegetation from the seaside was tested using surge-type flow by quicky opening gate, and by numerical simulation in the real topography. The inflow volume to inland and the delay in tsunami arrival were measured, and fluid force index was estimated by the measured data. The effectiveness of the hybrid structures for tsunami energy reduction has clearly been shown. Especially, the collision to the ground utilizing the difference of height between embankment and moat, and the vegetation resistance were effective for reducing fluid force index in the experiment. Inundation area, the delay in arrival time and fluid force index were also compared in numerical simulation under different arrangement of hybrid structures in real topography. The effectiveness of the hybrid structure in the order of an embankment, moat and forest from the seaside for tsunami energy reduction is also shown. The importance to the countermeasures on the tsunami inundation through a river was also demonstrated as the tsunami arrival was more rapid and fluid force index was higher than the tsunami inundation through the hybrid structures.

 In August 2016, three typhoons sequentially landed on Hokkaido, and another typhoon approached Hokkaido. It caused heavy rainfall, severe floodings and sediment disasters in various part of Hokkaido. It is predicted that spatio-temporal distribution of rainfall will change because of global warming in the future. The flood risk can be increase if flood peak time will change because of the spatial distribution of rainfall will be different. In this study, we used a quasi two-dimensional unsteady flow model for a reproduction calculation of flood in 2016 and simulations assuming other rainfall patterns and uncertainty of discharge. The result show changes of peak discharge and peak water level affected by uncertainty of upstream discharge are different in place.

 The objective of this work was to investigate the relation between river-bed gradient and river bed configuration in a granitic headwater catchment. Further, we investigated the relationship between the step structure and controlling factors such as river course characteristics or slope angle of river bank. As a result of field survey, the transition of river bed configuration (transition of waterfall, cascade, step, and riffle from the upstream to the downstream) according to the river bed gradient was observed. The relation between the step height and maximum diameter of the step construction gravel was different between the antidune type and keystone type. In case of antidune type, maximum diameter of the step construction gravel was positively related with friction velocity. Whereas, maximum diameter of the step construction gravel of keystone type increased with the increment of river-bed gradient and step width.

 In this study, in the river channel of the hydraulic environment belonging to the formation area of double-row bar for meso-scale bed configurations, movable bed experiments aimed at investigating the formation of sediment accumulation caused by partial widening to form alcove was carried out. As a result, it became clear that the shape of the sandbar is different depending on the length of the widened part. In the case of the length of the widened part about 5 times the width of the channel, it was confirmed that even if free bar entered the forced bar, it did not affect the flowing down of the free bar. On the other hand, in the case of the length of the widened part about 10 times, the possibility that the alcove topography is formed along the river bank after the flow rate reduction was suggested.

 Better understanding of the process of bank erosion with vegetation destruction is an important issue for river dynamics. In this study, six cases experiments were conducted by changing the existence of vegetation, the density of vegetation and water level, in order to clarify how the bank erosion with vegetation destruction effect on river channel evolution. Particularly, we have applied the original making for vegetation model which destruct by river flow and topographic measurement of the laser displacement meter. In the result, it is resolved that the vegetation stops the bank erosion of upper side temporarily, and promotes a scour of underside bank. And after vegetation destruction, bank erosion restarts and widens channel intermittently.

 The discharge capacity of Kumozu River has evidently declined due to the sandbars development caused by vegetation growth on sandbars. By continuous monitoring the areas of sand deposit since 2013 and utilizing laser profiling (LP) data, it is now possible to accurately estimate the sandbar size (volume and area) and the vegetation distribution.

 In order to specify the area of growing sandbars from the viewpoint of river management, we have developed a method for grasping the vegetation density and distribution by utilizing LP data, and determining the variable-permeability coefficient with considering of vegetation height. The proposed variable-permeability coefficient is applied to riverbed variation analysis model from August 2014 historic flood.

 By comparing the analysis results and monitoring records, it was found that reproducibility improves with respect to riverbed variation height and the sediment volume. In addition, as a result of the sensitivity analysis on the relation between vegetation density and sandbar volume, the clear indication of vegetation density promoting sandbar deposition was found. The proposed method aims to contribute to predicting the area of deposition for efficient and effective river management.

 Tendency of vegetation overgrowth in three river systems was analyzed and compared by a vegetation dynamics model. Examined here were several river channels in Kinu River, Kako River, and Takatsu River, Japan, in which parts of the river courses have been well-vegetated. For applying the model to the river channels, the model parameters were determined for the flood generation, vegetation growth rate, and infant vegetation invasion. The model results showed that tendency of vegetation overgrowth would be stronger in order of Kako River, Kinu River, and Takatsu River, and that well-vegetated channel tended to have larger ratios of the bankfull/floodplain widths. Furthermore, vegetation activity, channel characteristics, and flood impacts were discussed in detail between the three river systems for examining the predominant factors of vegetation overgrowth tendency.

 Pre-disaster prevention actions such as wide-area evacuation is being considered in the downstream basin of Arakawa River, and it is necessary to forecast flooding for several days ahead in order to achieve steady implementation. However, uncertainly in flood forecasting is not clear, and it is difficult to determine the implementation of pre-disaster prevention actions based only on specific prediction values. Therefore, this paper focuses on observed rainfall pattern as indicators for evaluating uncertainty and presents the method of flood information presentation which indicates the occurrence frequency of the water level for arbitrary rainfall by flood forecasting using rainfall amount extended to arbitrary rainfall. In addition, it is confirmed that this method can be applied even when the actual rainfall is exceeded by comparing it with the occurrence frequency of the water level by flood forecasting using large-ensemble information of the rainfall by d4PDF.

 A two-dimensional flood model was applied to the middle reach of the Arakawa River basin, to clarify the change in the potential flooding risk area and the breaching timing of the embankment, under the condition that the breaching of river bank occurs when river water level exceeds high water level (HWL) or the embankment height. Three different rainfall patterns were selected for the analysis. It showed that the Ando River, which runs through the center of the town, flooded first in all of the three rainfall patterns, followed by the flooding from the Ichinogawa River. The sensible breaching location is dependent on the breaching condition. Moreover, the time allowance after breaching of the embankment was largely dependent on the rainfall pattern. When the difference in flood peak time between the main river and branch rivers was small, the allowance for escape was short. When the peak discharge was large, the flood inundation was more rapid. The centroids of the un-inundated houses were located around the right-side embankment of the Arakawa River and near the Kawajima Interchange on the east and west side of the Andogawa River, respectively. It is effective to evaluate these two areas, east and west, for urgent and the primary refugee before moving to long term evacuation sites, respectively.

 In order to consider effective evacuation strategies for nursery homes (NHs) in case of large-scale floods, a rescue model was developed which can calculate the number of stranded people, concerning the triage of NH residents, transferring cycles, etc. Simulation for Ara river was conducted to compare the reduction effect between different evacuation priorities, start times, and rescue participation rates. There were cases where approximately 100 to 400 people were less stranded when NHs estimated to be inundated sooner were prioritized compared to when NHs close from rescue bases were prioritized. The results showed how strategic evacuation priorities, prompt decisions, and high rescue participation rates contribute to greatly reducing the number of NH residents being left in severe conditions.

 Railway operators enforce train operation control based on actual precipitation observed by rain gauges to ensure safe train operation in the times of heavy rainfall. Now by utilizing rainfall prediction information they may make train operation safer. In this paper, we evaluate accuracies of predicted rainfall values by translation model developed by Kyoto university and the high-resolution precipitation nowcast distributed by Japan Meteorological Agency to utilize rainfall prediction information. As a result, it is found that, predicted rainfall values of translation model tend to be smaller than precipitation observed by rain gauges, and those of the high-resolution precipitation nowcast tend to be larger than it. And the translation model show higher accuracy in rainfall prediction after ten minutes to twenty minutes, and the high-resolution nowcast show higher accuracy in longer prediction time.

 Some people approach riversides flooded with curiosity being swept away by floodwaters. Social media was used to investigate actual patterns of this high-risk behaviour and to understand its temporal and spatial distribution. Among various social media, Instagram was chosen for its real-time nature and low-noise characteristics. The selected study areas included Tama river, Kinu river, Edo river, Tone river, Sagami river, and Hirose river in Japan, which were all affected by heavy rain from the 7th to the 12th of Sept., 2015. Data was collected by Instagram API detecting hash-tag search of the river names, such as “#Tama river”.The collected data was dealt with by time series analysis, text analysis, and image analysis. The results indicated that usage of the relevant hashtags increased following a Rivers Designated for Flood Forecasting being issued. Additionally, the number fo posts and recognition were influenced by the number of warnings issued in the past Thirdly, results revealed that many people continued to remain on the riverbanks in spite of their awareness of the increasing risk. Finaly, people approaching rivers during heavy rain was affected by the use of automobiles.

 Recently, urban inundation due to torrential rains exceeded by design strength of the drainage system is increasing in various urban area. Because of such condition, it becomes more and more important to offer people the correct information immediately as the software countermeasure in addition to the hardware countermeasure. In this study, we applied our method of prediction of urban inundation intended for Tokyo to another city for the first time. We tried to figure out the risk of inundation in Eastern Yokohama City, which has “the especially urbanized area” same as Tokyo, by using the torrential rains. On the other hands, we are advancing the research in social implementation project of a real-time inundation forecast. As the part of the research, the 3D-map providing the visually clear information is presented in this study.

 The usage of the ECMWF ensemble forecasts of precipitation for reservoir operation was considered. The most applicable index is an average of 6th to 15th ranking members by cumulative rain. Actual rainfall was located between an average of 1st to 5th ranking values by every 3hours and an average of 37th to 46th ranking members by cumulative rain. The proposed index was applied to the simplified calculation, demonstrating the effectives to consider operational ensemble forecasts of precipitation in reservoir for pre-discharge.

 It is important to accurately predict the amount of dam inflow in order to implement dam operation precisely and reliably during a flood. A dam administrator can obtain the flood prediction data from some flood prediction models such as the storage function method, and then a flood control operation plan is finally decided referring experience and capacity of staff. In this study, we investigated the availability of the flood prediction model utilizing deep learning which has been highlighted in various fields recently to predict the inflow amount at the time of flooding and the downstream water level of the river. At the study, we set up multiple methods for prediction, hyperparameters and more, groping for a method with the least prediction error. As a result, we succeeded in predicting the amount of dam inflow 48 hours beforehand, and the river water level at the downstream of the dam up to the practical level with high accuracy if the data of the predicted rainfall amount is accurate.

 It is required to evaluate climate change impacts on flood control and water utilization functions of dams after releasing MLIT vision for dam upgrading under operation. Up to now, however, there is no suitable evaluation methods to clarify those impacts, it is important to establish appropriate screening criteria in order to select high priority existing dams for upgrading. In this research, we firstly predicted changed in flow regime curves under climate change impact. Secondly, several criteria has been proposed to evaluate both changes in flood intensity and water shortage volume as well as available capacity for flood control and possibility for flexible dam operation. Based these evaluation criterias, we found that it is necessary to mitigate climate change in order to maintain necessary functions at about 90% dams.

 In recent years, dysfunction or malfunction of dam spillways or bottom outlets have been reported because of aging and sedimentation in existing dams worldwide. They affect discharge capacity of dams which may decrease suitable flood control functions. Therefore, in this research, risk factors for Japanese multipurpose dams operated by MLIT, prefectural governments and JWA that cause functional deterioration of flood control ability in order to extract high-risk dams have been discussed. The risk factors for bottom outlets include elevation comparing sedimentation level and number of outlet structures. In the risk assessment procedure, "n-1 rule" (n: number of gate) which is the design criteria for securing the safety of dams in Switzerland. We conducted case studies on the Susobana Dam, Nagano Prefecture, to clarify actual risk after losing flood control capacity.

 In recent years, flood disasters of unprecedented scale have frequently occurred in mountainous rivers in various parts of Japan, and necessary measures, such as introduction of warning and evacuation systems, need to be taken urgently. Among them, flood early warning systems (FEWS) are considered to be one of the effective measures to mitigate the impact of flood disasters. For FEWS to operate effectively, two capabilities are crucial: they should be able to predict the water levels of river channels as early as possible so as to ensure sufficient time for evacuation, and they should also be able to be easily installed even in locations without sufficient data on past floods. In this study, employing a flood early warning system using a rational formula with standard parameters, which is used for river channel design without parameter identification, we conducted simulations for two recent cases of large-scale floods in different mountainous rivers to examine the effectiveness of the flood early warning system in terms of the length of the lead time (the time between when a sign of a disaster is detected and when the disaster actually occurs).

 We proposed a Nash coefficient equivalent to the information criterion WAIC that can evaluate the generalization of the flood prediction model. Using this Nash coefficient, we evaluated the generalization of the water level prediction model consisting of the storage function model of one basin. Engineers involved in runoff analysis can empirically evaluate the accuracy of the model with the Nash coefficient, so that they can evaluate the generalization of the model in the same way as the accuracy with this Nash coefficient.

 Under the increasing trend of the heavy rainfall with the magnitude exceeding the designed control level, it is necessary to comprehensively operate existing available stock of flood reduction measures such as flood control facilities in a river and a management system of sewer network. It is also necessary to evaluate how the drained water through sewer network would affect the water level in rivers particularly during the flooding event. In this study, the integrated river and sewer network model was developed in the Tsurumi river, one of designated urbanized rivers, to evaluate the impact of drainage on the river water level. The results show that the drained water through sewer network elevates the peak river water level by approximately 50cm during the flood event and also show that changes in the river water level affects natural and pumping drainage and eventually alters the flow system in drainage network.

 In rivers throughout in Japan, a flood prediction system using a rainfall outflow model, such as a distributed parameter runoff model and a one-dimensional unsteady flow analysis model has been introduced and is used for flood control activities and evacuation guidance. Many problems persist regarding the simulation error, but it is possible to minimize this by using actual flood data after flooding. To predict flooding in real time, prediction system should be complementarily adapted to the system error to predict rainfall and real flooding situations.

 The purpose of this study is to develop a method for calculating the upper limit and the lower limit of predicted rainfall using probabilistic statistical analysis. In the filtering method for the flood tracking model, which is effective as a method of correcting the prediction error caused by the actual rainfall error, multipoint sequential filtering was proposed as a method for improving the predicted flow accuracy for each branch.

 Recently, machine learning technologies such as deep neural networks have increasingly applied for floodwater-level prediction. However, in many of these studies, water level time series data were modeled inappropriate. In this paper, we propose a flood prediction method using recurrent neural networks (RNNs) that can process time series data. We evaluated water level prediction model using the RNNs model to predict the Tokoro River’s water level during the heavy rainfall disaster in Hokkaido in August 2016. Moreover, we generated a multi-node output model that simultaneously predicts the water level at five points. For performance evaluation, we compared conventional fully connected neural networks (FCNNs) and RNNs using the root mean square error (RMSE) between the measured and predicted water levels. With a lead time of 6 hour, the RMSE of the RNNs model and FCNNs model are 0.29 m and 0.40 m, respectively. The above results demonstrate the effectiveness of flood prediction using an RNNs with a time series structure.

 Recently, large-scale floods are increasing in Japan. In Accordingly, we aim to improve the performance of water level prediction to large-scale floods. In this study, we generated water level prediction modelss were using hydrological information on the upper reaches of forecast locations on the Ishikari River and the Tokachi River. At first, we used the Random Forest (RF) method, which is a machine learning method, and we generated water level prediction model were generated with lead times of 6 hours and 12 hours. Next, we selected explanatory variables that are strongly correlated with objective variables were extracted from the RF model. Then, we used this variable to calculate a multiple regression model which named the related factor correlation method. As a result, we could generate a high performance multiple regression model which is Nash-Sutcliffe coefficient score was 0.7 or more on both rivers. Through this study, we have obtained practical and highly accurate findings for forecasts of peak water level and water level rises.

 The main objective of this study was the improvement of flood prediction. We combined a particle filter (PF), a type of data assimilation technology, with the RRI Model, and tested this model for effectiveness in flood prediction. The state space of the filtering target was water depth on the slope in the RRI Model, and the water depth was sequentially assimilated to the corresponding observed water level. The method was applied to the heavy rain in the northern Kyushu on July 2017 in Kagetsu River basin. The results of simulation under the condition of the perfect forecasted rainfall, found that the RRI Model with the particle filter achieved a better reproducibility of the water level predicted for the next 3 hours by evaluating likelihood by RMSE. Moreover, as a result of comparing PF with Non-PF using the forecasted rainfall, the prediction of water level was found to improve regardless of the length of lead-time; in particular, the water level predicted for the next 1 - 3 hours was improved 0.24 meters or lower. In conclusion, the present study has demonstrated the effectiveness of the RRI Model with PF in real-time flood prediction.

 In this study, to analize the relationship between rainfall and inundation damage, inner and river water simultaneous inundation analysis model considering sewerage system is ulitlized. As a result, (i) the relationship between the amount of rainfall, rainfall intensity and inundation damage is clarified. (ii) We proposed a method to plan effective countermeasures based on the inundation risk map considering uncertainty in rainfall and runoff process such as model parameters and observation errors.

 Due to the renewal of the basic disaster management plan, the transfer of flood risk to insurance is promoted by the Japanese government. An insurance company to which the flood risk is transferred needs to assess infrequent flood risks for managing the risk of company. Insurance systems may reach a peak risk when a high wind coincides with a high storm surge height, however, there are only few studies on the assessment of storm surges by stochastic approaches. In this study, economic loss on the Tokyo Bay coast due to the storm surge are predicted with return periods using stochastic approaches. Inundation depth data sets for 10,000 years, assets price distribution and damage functions provided by the Japanese government, are used to estimate the economic loss by typhoons with the return period. It was found that the economic losses of private and commercial sectors are 650 and 430 hundread millions in Japanese Yen with the 200 year return period, respectively.

 We evaluated the flood risks of 109 class-A river systems in Japan by calculating flood risk curves by Frequency-Damage method based on the flood disaster statistics. From the comparative study of probabilistic risk features, it is figured out that for some water systems the large part of flood risks are caused by the small damages occurring in short return period, and for others the large part of flood risks are caused by the big damages with long return period. As regional differences of risks, river systems in same region tend to have the same probabilistic risk features, while it is implicated that a same probabilistic risk feature may be based on natural and social conditions of each basins in different way. Rivers in north east Japan have large low laying terrain where small frequent flood damage are recorded, and are therefore featured by frequent small annual damage. Rivers in pacific ocean side of south west Japan are adjusted for frequent large flood, but sometimes they are damaged by extremely large flood. In contrast, rivers in east Hokkaido region are not adjusted to frequent large flood because of mild precipitation tendency, and therefore can be also damaged by extremely large flood as well as rivers in pacific ocean side of south west Japan.

 The role of non-structural countermeasures in the flood risk management is becoming more important in a situation of increasing frequency and magnitude of heavy rainfall which causes devastating flood disasters. At the time, structural countermeasures for alleviating the flooding damages are also essential. However, investment for infrastructures against the worst case assumption is impossible. A method with new perspective is desired to estimate hazard information which contribute to appropriate investment. In this research, heavy rainfalls with differente return periods were simulated by the pseudo global warming method. Then, hydrological and inundation simulations are implemented with the simulated rainfall as forcing, and inundation map were produced for different return periods. By using the information of flooding water depths and return periods, expectation of flooding water depth was estimated. The expection of flooding water depth reflects both depth and frequency information, and it is expected to contribute to optimum planning of infrastructures for flood risk management.

 In this study, the frequent inland inundation areas in Osaka City, Nagoya City and Wakayama City were extracted by using the maps of flood damage from 1993 to 2012. The maps were drawn manually for each city as paper-based flood records. Because of the unfixed patterns and methods of drawing the maps, these maps have not been used for flood damage vulnerability analyses. We have translated these paper-based maps into digitized maps on GIS database, and have extracted the frequent inland inundation area. After that, geophysical characteristics in the frequent inland inundation areas were quantified by principal component analysis and compared between three cities. As a result, it was clarified that the hazard of inland inundation can be explained by geophysical characteristics in order of Wakayama City, Nagoya City and Osaka City. Especially, the distribution of inundation areas from inland inundation in Oskaka City can’t be explained only with geographical characteristics.

 The Brazilian northeast semiarid region is vulnerable to severe droughts. Climate change scenarios indicate that the region will be affected by rainfall deficits and increased aridity in the second half of 21st century. In this study, the potential of drought assessment in the northeastern Brazil was investigated using the Coupled Land and Vegetation Data Assimilation System (CLVDAS). In consequence, we identified the 2005 historical agricultural drought, which is the conformability between the decreased major crop production (sugar cane, cassava, and corn) and CLVDAS’s LAI, output by eco-hydrological water cycle process, in the northeastern Brazil.

 In August 2016, during the heavy rain in Hokkaido, overflowing in the Tokoro River section under the jurisdiction, seven embankments were confirmed but one site was destroyed. It is also important to clarify factors that did not lead to the collapse despite overflowing, in considering damage mitigation techniques. In order to analyze these factors, we conducted an experiment focusing on soil and landside water. The results of the experiments are as follows: It was shown that when the surface coverage was applied to the gravel embankment with clay, the time from the overshoot to the collapse was long, but in the widening process there was no difference from the gravel embankment.

 The Satokawa low-water bridge in the Shimanto River has been washed away four times in the past and restored each time. However, its main cause of failure has not been clarified. Therefore, we clarified the hydrological cause of the washed away of the Satokawa low-water bridge and examined more effective countermeasures. Firstly, we selected the Jogu low-water bridge where has the similar specification as Satokawa low-water bridge and has no experience of washed away in the past to compare with the Satokawa low-water bridge. Then we conducted the two-dimensional flow analysis and hydraulic experiments of Satokawa section and Jogu section to clarify the flow characteristics. From these results, we revealed that the main cause of washed away of the Satokawa low-bridge was upward flow near slab and rocky area of left bank, and showed countermeasures.

 The general dynamic index governing the seepage flow: SF_n (Seepage Flow number) which provides the dynamic similarity condition of the seepage flow is derived by making the governing equation dimensionless, and the physical meaning of SF_n is discussed. In the case of levee, SF_n corresponding to levee vulnerability index t^* indicates the degree of concentration of seepage flow at the foot of back slope. t^* is also derived by solving the quasi-two dimensional equations of unsteady seepage flow described by assuming the similar seepage line in levee on permeable or impermeable foundation. It is proved that t^* is useful to categorize the degree of levee failure and failure pattern. Furthermore, t^* is the only dynamic similarity condition of levee failure due to the seepage flow in the model geometrically similar to the prototype.

 A Northern Kyushu heavy rain caused a lot of flooding and landslides. The disaster gave a great damage to Fukuoka and Oita prefecture on July 5 in 2017. In this study, for the purpose of analyzing the factor of the flooding damage expansion, I collected information from newspaper, confirmed state of the damaged houses and measured the inundation level in disaster area, and conducted numerical simulation. First of all, in this disaster, 40 people died and 2 people are missing. From newspaper I could find that 73% people of victims didn’t refuge. In field survey, I found that many disaster area damaged by flood, sediment and driftwood. Comprehensively judge from a lot of collected information, it is considered that a lot of people of victims injured by flood. This is one of the character of this disaster. Next, I conducted flood simulation in Akatani River and Myoken River using iRIC which is river simulation software. I could not reproduce the real flooding area and water depth in both river when using the topography before disaster, because the simulation model takes only the water flow into account without sediment transport. However, in Akatani River, I could resemble the flooding area and water depth in the real flooding area and water depth when using topography after filled the river with sand. As a result of this research, I concluded that one of the factor of flood expansion is caused by the sand and driftwood.

 It is necessary to reduce the cost for reinforcement technology of river levee against infiltration. This study aims to conduct 3D permeability numerical analysis to investigate the effect of discontinuous arrangement of drain layer in the longitudinal direction on the reduction of phreatic surface in river levee. In the numerical analysis, we set a model levee with 100 m long and 5.0 m high. The results indicated that discontinuous arrangement of drain layer can reduce the phreatic surface in the cross section with and without the drain layers, showing that the effect of the drain layer diffuses in the longitudinal direction. It was also found that appropriate arrangement of the drain layers in the longitudinal direction can be a cost-effective reinforcement technology against infiltration.

 Discahrge in sanitary sewer of separate sewer system extremely increases during rainfall. It has been recognized as a source of operating problems in wastewater collection. This is because of the rainwater inflowing sanitary sewer. It has become the cause of lowering performance of pump stations and treatment plants function. In addition, it leads to overflow from sanitary sewer at one or more locations. It is a very important problem to find the location which causes infiltration of stormwater. Conventionally, in order to clarify the location of infiltration water, a large number of flow meter in has been equipped in sewer pipeline network, and they has been discovering the location of infiltration by using their flow rate data. However, this method needs a lot of cost and time. Therefore, this study used time series analysis in order to analyze with relating time series of radar rain and flow. As a result, it was possible to narrow the location of infiltration of stormwater to a mesh size of rainfall data more efficiently.

 This paper presents an investigation of the wind shear stress effect on flood inundation simulation. A 2D shallow water equation model DRR/FI and 3D Reynolds Equation model Fantom were used to estimate the effect of the wind shear stress on inundation simulation. First, 1D dam break simulation was selected as the case study. The results indicated that the wind effect is relatively large especially when the wind speed exceeds 30 m/s. Then, 2D dam break simulation and Arakawa inundation simulation were carried out to observe the effect of the wind on 2D inundation. As the results, it is implied that the wind effect is not necessarily negligible in inundation simulations, especially when the wind speed is high.

 Recently, the analysis model for inundation disaster in urban area has been considered detailed mechanisms of water behavior. And the analysis model is examined for high analysis accuracy. On the other hand, it is also very important to examine the usage of the numerical analysis for the pondering of the inundation situations. In this study, the visualization technique for fluid numerical analysis is developed by using of the idea of T-SAS presented by Sayama et al. The developed visualization technique applied to the urban inundation due to flood and heavy rain. From this study, it is found that the features of inundation water behavior and the individual spreading of the inundation due to flood and heavy rain. It was shown that the spread of water caused by rainfall is affected by the flood.

 In recent years, inundation damage caused by heavy rain has occurred frequently. Numerous researchers nave developed numerical analysis models for inundation due to heavy rain. But, observation data used for verification of analysis models are insufficient. In this study, water level gauges were installed in the sewer system of the Jizo river basin in Kasugai city, Aichi prefecture, and water levels of the sewer were measured. The relationship between the rainfalls and the water levels of the sewer was examined, and the importance of measuring the water levels on the sewer was shown. In addition, the computational results using the inundation analysis model were compared with the field observation results, and the accuracy of the inundation analysis model was verified. In this study, it was clarified that the analysis model has accuracy in case of heavy rainfall.

 In recent years, tremendous disaster due to climate change is increasing and countermeasure is becoming more important. In this study, the process of urban inundation due to huge storm surge was analyzed numerically . It was elucidated that the process of inundation becomes complex because Tokyo metropolitan city is highly urbanized area and infrastructures such as sewege system are organized densely. The risk of inundation exists not only in coastal area but also in urban rivers basin or areas that sewage systems are in close formation. Taking measures in advance is important to lessen damage caused by inundation due to huge storm surge.

 Flood risk of the Katura river basin, which was one of medium and small size rivers in the Tikugo river basin, on Kyushu-hokubu heavy rain in 2017 was examined by a numerical simulation for rainfall-runoff in watershed and flood inundation flows. The rain-fall runoff was simulated by a distributed hydrological model using radar rainfall. The flood flow in rivers and inundation flows on the ground were simulated simultaneously by the 2D flow model. The simulated results compared with the observed maximum inundation area. An inundation process and the relationship between amount of rainfall and flooding were also examined based on the numerical results.

 The present study discuss the effects of flood flow on the urban utility gas system in lowland city area located in alluvial plain. We conduct to simulate flood flow behavior with the iRIC Nays 2D Flood model for evaluating the inundation processes and spatiotemporal drag force distributions, quantitatively in the floodplain of the Shinkawa River, Aichi prefecture.

 By checking the relationship between the locations of governor of urban gas system in inundation area and these spatiotemporal hydraulic distributions, we could suggest the effects of catastrophic flood hazards, sufficiently.

 It is necessary to monitor and forecast an inland flood to prevent a city from it. A primary issue of the monitoring for the inland flood is how to calculate discharge and water-level distribution. The authors have developed the dynamic interpolation and extrapolation (DIEX) method which interpolate and extrapolate velocity in a cross-section, and DIEX method for flood prediction (DIEX-Flood) which interpolate and extrapolate water-level data into a streamwise direction with satisfying hydraulic principles. In this study, DIEX and DIEX-Flood models were improved to be applicable to a pipe flow. In order to verify the fundamental performance of the present method, laboratory experiments and numerical simulations were conducted. The results indicate that DIEX method can evaluate smooth cross-sectional velocity and discharge with high accuracy. DIEX-Flood evaluates streamwise distribution of water-level with high accuracy throughout the calculation area.