In this paper, we conducted model tests to observe the process of ground deformation referred to an open-cut investigation of the Kita River levee in Miyazaki Prefecture, where sand boil and collapse repeatedly occurred in 2016-2018 and 2022, and attempted to elucidate the mechanism of progression of ground damage that affects sand boil behaviors. As a result, it was revealed that sand chambers and sand channels generated below the collapse of the subsidence of impermeable surface layers. It was also suggested that a single sand boil in the inside area may not cause damage to the entire foundation if the ground is sufficiently compacted. The evaluation method of sand boils-deformation behaviors was discussed.

 The present study aims to investigate the effect of protection work for slope and toe of slope on embankment erosion due to overflow by laboratory experiments. For four cases with different lengths of protection work, we examined the depth of scour hole and embankment collapse due to overflow. Next, PIV measurements were performed to investigate the flow velocity in scour hole.

 For long protection work case, the angle of the overflow at toe of slope decreases and scour hole depth was reduced. Consequently, the sediment of embankment was not sucked out and the collapse time of embankment increases. For short protection work case, after the scour hole depth increases, the angle of the overflow at toe of slope decreases and the erosion speed reduces.

 In this study, we developed an overtopping erosion analysis model of levees considering a suction effect by a seepage flow and conducted numerical investigations assuming a case of rapid rise of water level such as small to medium rivers to clarify the influence of the suction effect changes on the overtopping erosion. First, comparative numerical simulations with and without the suction effect showed that the amount of bank erosion without the effect was overestimated compared to that with the effect, indicating the importance of considering the shear resistance force due to the effect. In addition, numerical simulations using different permeability coefficients showed that the small differences in permeability coefficients contributed to the suction effect, and that the larger the grain size, the greater the effect on the erosion process and the amount of erosion. This result suggests that the unique permeability coefficient may have a large error in the prediction of overtopping erosion of actual river levees.

 This study quantitatively evaluated the reduction rate of expected annual damage and the amount of CO₂ reduction achieved by cutting trees within river channels in Class A river systems across Japan. The mitigation effect of tree cutting was calculated as the amount of CO₂ emission reduction, including CO₂ emission from the transportation of the cut trees. The mitigation rate of flood damage by tree cutting was 2.1% for the Joganji River and 0.9% for the Kurobe River, indicating that tree cutting in the downstream section of a swift-flowing river is efficient. The CO₂ emission reductions by logging category are 564 ×10³ t-CO₂ upstream, 621 ×10³ t-CO₂ midstream, and 618 ×10³ t-CO₂downstream, indicating that tree logging in the upstream is inefficient for CO₂ emission reduction. The water systems with high effectiveness in both adaptation and mitigation by in-channel tree felling were the Tokachi River, Teshio River, and Kiso River systems.

 In the Seto Inland Sea (SIS), nutrient management plans are being considered for each sea area, and it is necessary to accurately estimate the amount of pollutant loads from the land area. In this study, we constructed a distributed runoff model and analyzed the characteristics and amount of pollutant loads from the land area to the SIS; in addition, the L-Q equations were estimated for each sea area from the model's result. The model simulated the discharge (Q) and pollutant load (L) in the normal and flood flow conditions of major large rivers with good reproducibility. We evaluated the amount of pollutant loads and identified that the pollutant loads in flood flow conditions contributed a large proportion, thus indicating the importance of considering the loads during the flood when the simulations in coastal areas were conducted. Estimations of the L-Q equations (L=_aQ^b, a and b are coefficients) from the distributed runoff model’s results showed that the coefficient b was less than 1 in normal flow conditions. In the flood flow condition, b became larger for COD and TP. In addition, the pollutant loads entering the sea area in the SIS were estimated with good accuracy by substituting the observed discharge data of major large rivers into the L-Q equations.

 This study aimed to quantify and index the risk of geological weathering based on chemical composition using water quality in a watershed. We attempted to derive the risk by comparing the chemical composition and components of the baseflow in relation to the slope failure rate in granitic regions of the Japanese archipelago where mass movement due to heavy rainfall has occurred frequently in recent years. The study area included eight granitic areas, which were included in the previous studies, and data were compared for 64 basins. The main results show that the chemical composition of the granitoids is different depending on the formation age of the granitoids. The chemical reactions involved in weathering were different depending on the age, with Mg, Ca, and Sr in the Early Cretaceous and Fe in the Late Cretaceous and Middle and Early Jurassic showing a strong correlation with the rate of slope failure.

 A long-term (63-year; 1961-2023) trend analysis of meteorological observation data in Japan revealed a statistically significant increase in equilibrium water temperature, which is an indicator of water temperature in rivers and lakes. This increase was found to be driven by two main factors: increases in solar radiation and air temperature. A seasonal analysis of the long-term trend of equilibrium water temperature and its contributing factors revealed that equilibrium water temperature exhibited an overall increase across all seasons. However, the magnitude of this increase varied considerably between seasons and regions. The contribution of increased solar radiation and increased air temperature to changes in equilibrium water temperature exhibited seasonal and regional variability.

 We conducted the eDNA and stable isotope samplings in order to evaluate the environmental conditions of two river basins (Takatsu and Takahashi rivers) with different land use in Japan in October of 2022.We used the quantitative eDNA metabarcoding to estimate the eDNA concentrations of fishes in the study sites. In addition, we used nitrogen stable isotope ratio of attached algae as the indicators of nutrient loads from the catchments. Our results showed that the river segments with higher restoration priority (e.g., river segments with higher species diversity and higher nutrient loads) were identified based on eDNA concentrations and nutrient stable isotope ratios.

 In this study, we estimated the habitat potential of multiple fish species in the Takatsu Basin using the MaxEnt model based on the presence information of fishes revealed by environmental DNA analysis. As a result, the AUC was more than 0.7 for all fish species that were selected for analysis, demonstrating that the constructed models were useful for estimating the distribution of target species. The results also revealed that the habitat potential of most fish species was strongly affected by the riverbed gradient and flow rate in the subwatersheds. On the other hand, the importance of river water temperature and land use was lower than that of riverbed gradient. The estimation of habitat potential using MaxEnt reproduced the distribution trends of fish species with high accuracy, indicating that the habitat potential of multiple fish species can be estimated comprehensively in a watershed by using the MaxEnt model with fish presence data obtained by environmental DNA analysis.

 Effective debris flow countermeasures require accurate predictions of sediment transport. Constitutive laws of debris flows have been proposed, and recently, theories of sediment transport were validated and modified by the motion of each grain obtained by a developed image analysis technique. However, data measured in laboratory experiments are still limited. In terms of numerical simulations, although Lagrange-Lagrange models have the potential to be applied to unsteady debris flows, there are few previous applications.

 This study used a DEM-MPS scheme to conduct three-dimensional simulations of steady sheet flow (immature debris flow), and the model was comparatively validated from the corresponding laboratory experiments. The simulation with non-spherical elements investigated sphericity effects on frictional/collisional stress, and the stress structure of an immature debris flow was investigated.

 This study aims to open up new horizons in the study of debris flows by examining the mechanisms of debris flow with erosion of valley beds and banks by debris flows from the viewpoints of both momentum and energy. First, the mechanism of growth and development of the debris flow head were clarified from the viewpoint of momentum by incorporating eroded gravel particles and the effect of the incorporation of gravel particles on the flow field of the debris flow head. Next, to obtain an overall view of the field of the debris flow, the temporal and spatial variation of the flow and gravel analyzed by the APM method was used to examine the energy perspective. The energy storage and release processes, such as the localized increase in the energy of the debris flow due to erosion and collapse and the accumulation of gravel and stones, and the release of the energy when the accumulated gravel particles are re-moved by the increased energy, were found to be important mechanisms of the debris flow.

 This study investigates and tests a method to define the "mean transport velocity" of sediment using the bed-load equation and to calculate the time scale required for sediment to pass river sections in gravel-bed rivers with a wide grain size distribution. The average transport velocity is calculated by the method based on the pick-up rate and step length, and the method based on the Ashida- Michiue equation. This method was tested on about 10 km section each of the valley bottom plain and the alluvial fan of the Nagara River in the Kisogawa River system in Mid-Japan. After comparing the methods for calculating the shear stress, a discharge hydrograph for 47 years was given, and the mean transport velocity and its time-integrated distance were calculated from the shear stress against the hourly flow rate in each section. The time required to pass through each section was estimated to be 100 to 101 years for fine gravels, and 103 to 104 years for large cobbles.

 Erosion experiments were performed on a cohesive beds, and three-dimensional numerical simulations were performed on investigate the experimental flow field. The simulation results successfully reproduced the water surface profiles observed in the experiments. Based on these simulation results, the energy acting on the cohesive bed was estimated, and the energy expended for both the characteristic surface erosion and mass erosion on cohesive beds was examined. The energy distribution analysis revealed that the energy is concentrated to the extent of the irregularities scale in the areas where mass erosion occurred, leading enhanced erosion. Furthermore, it was demostrated that for the same erosion depth, the energy expended for mass erosion was smaller compared to the energy expended for surface erosion sections, indicating that mass erosion progressed with less energy.

 Hydropower is important as a CO₂-free energy source that can maintain stable output in the long run. On the other hand, reservoir sedimentation management is one of the most important issues in ensuring the sustainability of hydropower operation. Additionally, “Dam Upgrading” that maximizes the use of the CO₂-free energy and “Sediment Environment Restoration” that both extends the life of dams and improves rivers and coasts are important. In this paper, we considered the relationship between sediment transportation and habitat environments in downstream of a dam, with the aim of improving reservoir sediment management that consider the river environment downstream of a dam. The study focuses on the Futatsuno Dam, where sediment replenishments is planned, we conducted 1D riverbed variation analysis, and analyzed the result of environmental research of the river. As a result, we found that it is possible to formulate an optimal sediment replenishment plan by understanding the required sediment grain size for a river.

 This study proposes a dynamic and integrated modeling approach to predict anthropogenic heat emissions (AHE), which are additional heat sources on the Earth's surface resulting from urban human energy consumption, by utilizing an integrated assessment model (IAM) and high-resolution heat emission datasets. Based on energy consumption data obtained from IAM and adjusted using heating degree days (HDD) and cooling degree days (CDD) acquired from climate models, we improved the accuracy and resolution of AHE predictions. This model integrates IAM outputs to enhance Shared Socioeconomic Pathway (SSP) scenarios, which were previously limited, enabling predictions under various future conditions. Our methodology provides an essential tool for simulating the impacts of policy changes and technological developments on urban heat emissions, supporting stakeholders in formulating effective urban and environmental policies. The results of this study emphasize the importance of considering urban expansion and climate change in future AHE predictions, setting new standards in urban environmental research and providing a framework for future urban climate adaptation strategies.

 Nagasaki Prefecture, located at the northwestern end of Kyushu, is more prone to localized heavy rainfall than other areas because it is strongly affected by rising sea surface temperatures in the East China Sea due to climate change. Therefore, we attempted to verify the “rate of change in heavy rainfall intensity”, which in necessary to consider flood control planning based on climate change, focusing on the Nagasaki Prefecture’s area. In addition to applying the rainfall data used in the study conducted by the Ministry of Land, Infrastructure, Transport and Tourism (Hereafter, the abbreviation "MLIT" will be used.), the study conditions were set based on the study conducted by the MLIT, taking into account the spatiotemporal scales of Nagasaki Prefecture. The results showed that the value for a 2°C rise in temperature was 1.16 times higher than the result of the MLIT’s study (1.14 times for the northwestern part of Kyushu reigon). On the other hand, the result for a 4°C rise in temperature was 1.32 times, which was slightly smaller than the result of the study conducted by the MLIT (1.36 times for the northwestern part of Kyushu region).

 Precipitation from two ensemble climate projections with different spatial resolution were compared. Comparisons were conducted for five river basins in Kyushu, Japan. Additionally, the river discharge estimated from numerical experiments using bias-adjusted precipitation as input values was also analyzed. The results indicate that the 20-km resolution experiment reproduced a variety of peak discharge at the same rainfall due to the large number of ensemble experiments. In contrast, the 5-km resolution experiment reproduced the designed peak discharge in each basin with a limited number of ensemble experiments, thereby demonstrating the advantages and disadvantages of using the 5-km resolution experiment in the evaluation of extreme discharge.

 The statistical relationship between peak discharge and extreme precipitation has been discussed and examined as an unavoidable issue in flood design, because on the background the physical climate process based on the temporal and spatial pattern of rainfall distribution and the rainfall runoff process are involved among them. For the evaluation of the appropriate frequency of discharge, synthesis probability method has been implemented, which is also known to be ascertained. This study handles with the several simplest forms for the conditional probabilities derived in the extreme value theory, gives a demonstration by employing the emsemble members by the climate model for the application and shows the dependence via those probability serve as the coverage developed in flood design, and return periods for the concomitant peak discharge are also obtained as the side effects of the dependence analysis.

 It is necessary to develop adaptation measures that take the nonstationarity of extreme rainfall into account. Therefore, we developed a methodology to evaluate nonstationarity in extreme rainfall time series data using the probability limit method test. In this study, we compared the testing power of this methodology with other hypothesis test theories. The results indicated that the probability limit method can estimate the degree of nonstationarity in extreme rainfall time series data more accurately than other methods. Additionally, applying this method to the annual maximum daily rainfall time series observed in Japan revealed a nationwide increasing trend in nonstationarity. Furthermore, it was shown that the rate of transition to nonstationarity increases over time, particularly in the Shikoku, Tohoku, Kinki, and Kyushu regions.

 Currently, the ensemble climate databases used in flood control planning and disaster risk assessments correspond to fixed warming levels in both past and future climates. However, continuous projections are crucial for discussions on adaptation measures over time. Performing continuous climate reproductions and projections from the past to the future with a large number of ensemble members is challenging. This study proposes a mathematical method that incorporates information theory and the conservation laws of the physical occurrence frequencies of extreme hydrological events, enabling the creation of time-continuous and large ensemble climate information.

 It is important to evaluate the probability of discharge in a water environment since the discharge is effected on the development and occurrence of hypoxia in the coastal area. However, in the previous studies, discharge observational data have uncertainties by the data-scarce and observation method relative to precipitation observational data. Therefore, few studies have evaluated the probability of discharge. Thus, this study aims to reveal the optimal discharge probability distribution in each river basin with d4PDF by developing the runoff model which is considered the inundation based on the current river channel in the main eight river basins in Kyushu. As a result, it is found that the goodness of fit of the Gumbel distribution which is used for precipitation distribution evaluation widely is also high in the discharge. However, it is suggested that the evaluation of optimal probability distribution in each river basin is important since there is the case that it is different in a river.

 In general, the designed flood discharge is established through statistical processing based on observed data and historical flood data. However, the hydrological and meteorological data needed to determine the designed flood discharge are limited for small and medium-sized rivers, and some river basins have not yet been observed. In this study, the future changes in rainfall and discharge considering climate change were analyzed for small and medium-sized rivers in Minami-town, Tokushima Prefecture, using d4PDF rainfall data corrected for bias at Hiwasa AMeDAS. The d4PDF can be used to calculate the planned scale discharge including various rainfall waveforms that are not included in the historical data. The results also suggest that it may be possible to calculate the probabilistic discharge rate of surrounding small rivers for which no observation data are available by using d4PDF rainfall data corrected for bias at AMeDAS.

 We investigated the flow structure and the sediment deposition rate between triangle roughness elements to reveal the effect of the roughness interval on the self-lining of sediments. The two kinds of flume experiments (cases) were conducted by changing the roughness intervals and channel slope. First, we examined the sediment deposition between roughness elements and evaluated the coverage rate by self-lining using a video camera. The results revealed the experimental cases that the sediments were deposited successfully between roughness elements. Next, PIV measurements were conducted during the sedimentation experiments. We revealed that the strong downward flow occurs at the point where the flow depth becomes smaller. The sediments were flushed by a sweep for large Froude number case.

 In this study, the characteristics of the flow field in an open channel in which a longitudinal ridge element with a suction function was installed on the bottom wall, with the suction operation in the upstream half region was examined. Regarding the pronounced upward flow and paired swirling flow that disappear with full-area suction operation, when the upstream half region operation is performed, the formation of upward flow remains at the half-water depth position, and the paired swirling flow disappears. It was also observed that the Reynolds shear stress (-uv) in the vertical direction was relatively small compared to the case without suction operation and with suction in all areas. Additionally, the distribution of the turbulence energy generation term (-uv(dU/dy) was found to be relatively small compared to the case of no suction operation and all area suction operation. These characteristics are thought to be due to the undeveloped longitudinal vortex structure formed downstream of the upstream half region.

 Flows containing fine sediment such as wash roads occur not only in high-sand rivers such as the Yellow River, but also as mudflows and debris flows that occur as landslide disasters during heavy rains. It is important to understand the flow characteristics of such high-concentration sediment flow in order to know the actual flood behavior and the impact on bridge piers, houses, etc. In this study, high-concentration sediment flow was reproduced in an open channel with columnar objects of various shapes using polymeric agents to experimentally investigate the differences in flow structure and shape resistance characteristics between a highly viscous flow corresponding to a sediment concentration of 7% by volume and a fresh water flow. As a result, it was clarified that the scale of detouring flow and wake vortex generated around a columnar object is suppressed in a highly viscous fluid compared to that in a fresh water flow. In addition, the relationship between the resistance coefficients of each shape and the shape resistance characteristics of highly viscous fluid was clarified.

 The structures of the forced circulation flow generated by a pump and the associated sediment transport characteristics were investigated by hydraulic model experiments and the three-dimensional numerical analysis for a square planar tank and a rectangular tank that simulate an aquaculture farm. In case of square shaped basin, one large recirculation cell is generated. On the other hand, two recirculation cells are generated in cases of rectangular shaped water basin with the aspect ratio 2:1. The accumulation area of sediment is affected by the secondary current of the first kind due to the unbalance of the centrifugal force associated with the recirculation flows. The scale of the secondary flow cells increases as the depth increases. If the pump discharge is enough large to exert enough traction form larger than the critical value, the deposition area becomes smaller as the depth increases. The accumulation area changes after the stop of the pump due to the change of the recirculation flow pattern in case of the rectangular shaped basin.

 Wave breaking by submerged breakwaters in coastal areas enhance the transport of oxygen and carbon dioxide gases into the ocean. However, the mechanisms of sub-surface gas transport are still unclear. In this study, we quantitatively investigated waves, turbulence, and dissolved gas transport in a wave-making flume. In particular, we clarified the spatial-temporal variation of the reaeration coefficient using multiple optical DO meters and the structure of wave breaking turbulence using PIV visualization measurements. Based on their information, the hydraulic quantities that seem to dominate the phenomena, such as wave period, waveform, and turbulence statistics, are summarized, and the mechanism of gas transport enhancement by submerged wave breaking is discussed.

 Jet pump type flow device is used as a countermeasure against water pollution in closed water bodies such as lakes and resevoirs. In the conventional study, the theoretical formula of the flow velocity ratio of driving water, absorption water, discharging water is derived under the assumption that it is thoroughly mixed in the mixing pipe and then discharged. In conclusion, there is a condition of the optimal pipe diameter ratio that can obtain the maximum discharge water flow rate from the balance between the two factors, that is, the reduction of the drive water flow rate and the increase of the absorption water flow rate to the drive water flow rate. However, a more than 10 times mixing pipe length is required under the condition of the optimum pipe diameter ratio.

 The transport and establishment of seeds during floods contributes to our understanding of seed dispersal processes in riverine environments and provides important insights that form the basis of ecological research. However, the phenomena that occur during the establishment process remain unclear. In this study, flow experiments were conducted over an inclined drop, modelled on the leading edge of a sandbank, to investigate the turbulent structures and behaviour of floating seeds. Particle Image Velocimetry (PIV) measurements were used to visualise the flow and turbulent structures near the shear boundary layer created by the drop. Furthermore, in seed transport experiments, the trajectories of tracked seeds were compared with the PIV measurements to investigate the effects of flow field changes induced by the drop on seed transport mechanisms.

 In recent years, Japanese eel population has been declining significantly, which is thought to be due in part to the discontinuity of the water level caused by dams and weirs. In order to remedy this situation, fishways are installed in river crossing structures. Fishway is also expected to support the upstream reaction force and improve fish migration rate by installing pier roughness. In this study, the wooden cleats installed on the bottom of an open channel were varied into four types of roughness shapes, and the total length times velocity was varied from 1-4 (1/s) to investigate the suitable cleat shape for migration of Japanese eels. The results showed that, under the experimental conditions, Japanese eels could easily adhere their trunks to cleats with a square cross section of 10 mm in height and 10 mm in width in downstream direction and with 20 mm wide and 5 mm deep recesses at 20 mm intervals in crosswise direction. Japanese eels were found to adhere to cleat roughness easily and to use it as a resting place and an object to support upstream reaction force.

 Most fishladders in Japan are designed for swimming fish and are not effective for benthic one such as eels. In Europe, ramp-type fishladders are sometimes installed for eels, but the optimum geometrical shape has not been clarified. In this study, the channel slope and fishladder length were changed. It was found that the migration and success rate decreased with increasing the fishladder length from 0.4 to 2.0m, and the migration rate was about 0.7 for fisladder length between 0.4 and 0.8m when the channel slope was 30 degree. The migration swimming speed and sinuosity increased with increasing the fishladder length, and the stagnation rate decreased. In the range of the experimental conditions, the optimum fishladder length was in the rage between 0.4 and 0.8m and channel slope is 30 degree for the 200mm total length of Anguilla japonica.

 In a typical alluvial river channel, the flow path changes in various ways depending on the magnitude of the flood. However, in rivers with exposures of mudstone, the flow channel becomes deeply incised and fixed in the mudstone(Dotan) by large floods, making it difficult to maintain and manage the river channel. In order to avoid such a situation, it is important to detect the signs of channel immobilization at an early stage and to clarify the mechanism of channel immobilization to avoid or prevent the progression of immobilization. In this study, the stabilization mechanism of Dotan exposure channels in the Tama River was clarified and measures for maintenance of the Dotan channel were discussed.

 This study aims to reveal temporal-spatial distribution of velocity in an actual river to clarify how to treat fluctuation in terms of stable accuracy of discharge observation. Simultaneous velocity measurements were conducted with radio wave current meter, ADCP and PIV. Time-series of velocities on water surface and underwater were analyzed, indicated that variation converges with 60 seconds of average time. Furthermore, vertical distribution of velocity is consistent with the Aki’s equation which gave coefficient of float. Besides, PIV analysis was conducted in order to obtain spatial distribution of water surface velocity. The velocity was compared with velocity by radio wave current meter, which showed a reasonable agreement. Based on the analysis above, discharge values with some measurement methods were calculated.

 Recent climate changes have resulted in frequent and extensive flooding in Japan, increasing the need for watershed-based flood management. Basic information, including the flow data of tributaries and waterways, is required for the introduction of such flood management; however, little data has been obtained accordingly thus far. In this study, a slit-type pitot tube velocity meter was developed considering a flow-velocity measurement method using the proposed afflux height, and its performance in the field was examined. As a result, the developed velocity meter can observe the flow velocity with high accuracy. The continuous flow velocity data obtained from the installation in the channel presented a good responsive relationship with the rainfall waveform, indicating the possibility of inexpensive continuous observation of flow velocity in the field in future.

 The water depth profile used for flood discharge measurement is usually surveyed during normal water conditions. However, since bathymetry may change during floods, it is necessary to obtain the depth profile in addition to the surface velocity during floods for accurate discharge estimation. We propose a new method to estimate the cross-sectional profile by fitting the wave dispersion relation to the wavenumber-frequency spectrum of the water-surface variation, which is estimated from space-time images of the river water surface. We applied the proposed method to a river, and the estimated water depth profile had an error of less than 20% relative to the directly surveyed cross-sectional profile. On the other hand, the accuracy of the depth estimation depends on the resolution of the spectrum as well as the parameters used in the estimation method. The estimation error becomes large when the resolution is insufficient, and abnormal values may be obtained under high-Froude number conditions.

 While a water level observation network is progressing, there is a shortage of river discharge data. This study aims to advance an image-based flow observation method that combines SfM (Structure from Motion) and STIV (Space-Time Image Velocimetry) as a simplified geometric correction technique to reduce survey load. We conducted field tests in the Ichinomiya River basin in Chiba Prefecture, and the accuracy of these observations was evaluated. Additionally, river discharge was calculated from construction-site cameras under huge flooding condition, and sensitivity analyses were performed by varying the periods of rising and falling water levels. The results indicated that during river floods, the discharge peak appeared before the water level peak, and subsequently, the discharge does not change even as the water level continued to rise. The necessary observational data to maintain the accuracy of the rating curve were also evaluated.

 In the future, it is expected that the amount and frequency of precipitation will increase due to climate change caused by increased greenhouse gas emissions, and the impact of this on railways is a concern. In this study, we used the output data from a numerical experiment under the conditions of the RCP8.5 scenario using a climate model to evaluate future changes in debris flow damage assessment based on flood sedimentation using a planning method, targeting the Yamagata Shinkansen. As a result of assessing the debris flows damage for daily rainfall with various exceedance probabilities, we found that the probability of exceeding the daily rainfall that will cause debris flow disasters will increase by 20% in the future compared to the present period, and the number of debris flow disasters occurring for the same daily rainfall exceedance probability will increase by 1.9 to 2.4 times, which will be the impact of climate change.

 We propose a methodology for assessing the impacts of climate change on sediment disasters characterized by numerous debris flows occurring within a single catchment. In this study, we first developed a probabilistic prediction method for debris flow affected areas by integrating a generalized ordered logistic regression model —trained on the information from the Heavy rain of July, Heisei 30 — using rainfall and topographic data as explanatory variables, with probabilistic predictions of sediment production from this model, and a debris flow runout model. Next, by inputting current and future rainfall conditions influenced by climate change into this method, we probabilistically evaluated the flood and deposition distribution of debris flows under each condition. This approach enables the assessment of future changes in quantitative indicators, such as the probability of flow depth exceeding a threshold or the probability of deposition thickness surpassing a threshold.

 In coastal low-lying areas, there exist risks of fluvial and pluvial inundations, as well as by storm surge. Their simultaneous occurrences caused by typhoons could exacerbate the inundation risk, and that might be intensified under under the future climate. In this study, using pseudo-global warming climate simulations, we estimated the changes in the past typhoon under the future climates, and conducted integrated analyses of storm surges, fluvial and pluvial flooding. In the analysis focusing on the Katabira River, there was a tendency for high tides to increase while there was variability in the increase in precipitation. The deviation in tidal levels by storm surge, combined with the tidal ranges, increased the river water levels. Tidal variations in storm surges, which are considered to be long period oscilation, were observed, high-lighting the need to consider regional characteristics.

 Impact of climate change on operation of reservoir systems for water supply and hydropower in the Tedori River basin, Japan, was investigated to understand possible climate change impacts on water resources management in heavy snowfall areas. Through the simulations of reservoir operation using the 150-year continuous climate experiment projected by MRI-AGCM3.2S of Meteorological Research Institute, Japan, based on RCP8.5 scenario and SST ensemble mean condition of CMIP5 models, it was shown that deficit of water supply significantly increased from summer to fall in the late 21^st century, corresponding to relatively great change in seasonal pattern of reservoir storage. The results also showed that power generation by run-of-river power stations may be more affected by climate change than storage stations.

 In a previous study, the authors developed a method for estimating 1-minute precipitation intensity from JMA rain gauge data. The previous method estimates the time of a tipping and calculates the precipitation intensity, assuming that the precipitation intensity between tippings is constant. In this study, the method was improved to estimate the change in precipitation intensity between tippings by referring to the XRAIN. Compared to the previous method, the accuracy was improved. Next, the correction coefficients are determined by viewing this as a correction to XRAIN. The correction coefficients were moving averaged in time and spatially interpolated to correct XRAIN in the absence of rain gauges, and it was found that it is better to set the confidence level of XRAIN according to the distance from the radar and the time scale of smoothing according to the distance from the rain gauge. The accuracy is generally improved compared to XRAIN before correction, but strong rainfall such as linear precipitation zones are underestimated.

 This paper proposes a new rainfall forecasting method that utilizes vertical wind estimates from MP-PAWR and incorporates an algorithm to suppress the source term in VIL Nowcast, a short-time rainfall forecasting method. Specifically, we integrated vertical wind data derived from Dual Doppler analysis into the VIL Nowcast and compared the forecast results with those of the conventional VIL Nowcast. The results demonstrated significant important during periods of rainfall intensity and observed downdrafts. The RMSE decreased across all lead times with more pronounced reductions at longer lead time.

 Consistent data on cloud and precipitation water content are crucial for initial precipitation forecasts and model evaluation but are extremely scarce. Microwaves, widely used for cloud water observation, interact with cloud and precipitation particles, varying by particle size, phase, and microwave wavelength and polarization. This study evaluates a liquid-phase water content estimation method using Ka band microwave, which is less affected by solid-phase scattering, and explores distinguishing cloud and rain water through synthetic experiments with satellite observations. Results showed that with appropriate cloud top height information allows for reasonable LWP estimation over a wide range of LWP. Additionally, though there are certain limitations in applicability, the polarization difference in brightness temperature is indicated to be effective for distinguishing between cloud and rain, demonstrating its feasibility.

 The authors have already proposed a multiple regression model for the rainfall interception based on the product of wind speed and rainfall intensity as horizontal micro-droplet fluxes under the assump-tion that the downwind transport of micro-droplets pre-dominantly contribute to the rainfall interception process. Since the rainfall was implicitly incorporated into horizontal micro-droplet fluxes in the model, it was inconvenient not only for the practical purposes but also to analyse the non-linearity between the rainfall and rainfall interception. A wind-rain-index, namely the ratio of rainfall to rainfall interception, was newly defined as a function of wind speed and rainfall intensity in this paper and stochastically modelled. The new regression model with the wind-rain-index was applied to the observation data. It was clarified that the regression coefficient and the wind-rain-index accounted for the characteristics of tree species and non-linearity in the rainfall interception process.

 In this study, the relationship between heavy rainfall and typhoon tracks brought by Typhoon Hagibis in 2019 to the upper Tone River Basin and Chikuma River Basin was analyzed using historical cases and high-resolution mass ensemble data (d4PDF) of typhoon events with similar tracks, with cases with east-west typhoon track deviations as comparators. It is shown that typhoon rainfall with similar tracks based on the same case event produces the maximum rainfall in both target regions. In both cases, rainfall under the future climate exceeds rainfall under the present climate. The rainfall amounts in the post-warming period are larger than the maximum rainfall amounts in the past climate, even when the typhoon tracks are shifted east-west, indicating that the frequency of typhoons bringing extreme rainfall to the region may increase.

 The relationship between land use and meteorological phenomena remains unclear, with exception of a few phenomena. In this study, we used Weather Research and Forecasting Model (WRF) to evaluate the effects of land use data from 1900, 1950, 1976, and 2016 on precipitation phenomena for August 2016 in the Kanto Plain. The result using land use in 2016, when the urban rate was the highest, showed area-averaged precipitation due to the typhoon is decreased about 50 mm than that using in 1900. It’s also showed less frequency of precipitation over 20 mm/h due to typhoon than that using in 1900.Those mean the typhoon external force are decreased by using land use in 2016. The latent heat at the time of typhoon passage did not vary among the land use data, and is considered to be caused by factors such as surface roughness and evaporation.. The observed decrease in typhoon precipitation due to urbanization indicates that land use management may contribute to the reduction of typhoon intensity.

 Effects of wind-driven currents on river surface flows have not investigated enough. It is very important in order to estimate river discharges by using floats or a radio current meter. In this study, according to field observation results by using the ADCP, wind speed meters and a radio current meter, effects of wind-driven currents on river surface flows in cases of follow flows between winds and river flows based on previous studies. In conclusions, wind-driven current components on river surface flows were estimated 6.9 % of U₁₀ which was the wind speed at the 10 m height. Surface current velocity was almost 1.2 m/s and the wind-driven current component was estimated almost 0.3 m/s, so that it was suggested as an unexpectedly large ratio of wind-driven curret conponet to the river surface velocity. However, the estimation of depths of wind-driven currents was so difficult that it was required to investigate effect depths of wind stress more carefully by using vertical profiles of river flows and wind speed data.

 In this study, we conducted flume experiments to reveal the change of floating log motions in wind blowing. First, we measured the drifting velocity of model logs by changing the model log diameter, specific gravity, and wind speed, and we examined the effect of wind drag forces on drifting velocity of logs. Secondly, we measured the drag forces acting on floating logs and evaluated the drag coefficient of wind drag forces. Results show that drifting velocity of the smaller diameter log increases significantly due to wind drag force, and for large specific density case the drifting velocity doesn’t increase. In addition, drag force measurements suggest that acceleration effect by wind drag forces is larger for smaller diameter log case, and conversely it is smaller for large specific gravity.

 We conducted the driftwood accumulation tests to investigate the formation of driftwood jam behind one bridge pier by changing the wood length. We examined the length in the streamwise and vertical directions and width of driftwood jam. The sink ratio of incoming wood pieces was also measured. Next, we measured the drag force exerted on the bridge pier and evaluated the increase in drag force and drag force coefficient of bridge pier due to driftwood accumulation. Finally, we focused on the failure of driftwood jam. We measured the times series of drag force when the vibration of jam occurred and examined the change of jam size before and after the failure.

 Extreme flood events cause complex three-dimensional flow fields influenced by river-crossing structures and channel shapes. These flow fields affect the water surface shape and the distribution of flow velocity, impacting flood risk and river environments. This study improves the Hy2-3D model, a low-cost three-dimensional flow model by incorporating non-hydrostatic effects and a two-equation turbulence model. By applying this model to a laboratory meandering compound channel and the 2020 Kuma River flood, it effectively reproduced the complex flow in meandering sections. Furthermore, the analysis of secondary flow in the Kuma River indicated that bridge resistance suppresses secondary flows, shifting the maximum velocity line.