We aim to develop the management technology of river-basin environment with a quantitative underpinning, and tried to evaluate the environment of birds’ habitats around the nation using ecological niche models(GLM). In the results, ecological niche models for birds showed the important environmental factors and spatial scales differed according to bird species, and detected the relative importance of river environment versus surrounding environment as birds habitats. Thus, this approach in the study can evaluate the river and basin environment integrally, and suggest the quantitative goal on the environmental managements of river basin.

The purpose of this paper is to develop the simulation tool to evaluate the results of hydrological regime and river habitats seamlessly. The evaluation tool can be visualized the results. The river habitats tool consists of habitat suitable index model of freshwater fish and the growth judgement model of river terrestrial plants in water. We examined validity of these tools by 3 models changed the width of a river. As a result, the model which widened the width of a river can be increased suitable habitats for fish, it however were covered with a plant too much. These tools will enable a river environmental planning to estimate quantitatively as well as a flood-control planning.

This paper discusses the influence of fine sediment discharge from paddy field on the river water turbidity being based on filed measurements conducted in the Eai River catchment in 2014: The data of continuous turbidity measurement in a drainage channel were formulated into an empirical relation for suspended sediment flux using the mathematical quantification theory classⅡby taking the stages of paddy field operation and the rainfall intensity as the influential parameters. The results successfully explained the variation of turbidity in the river reach where the paddy field discharge is comparatively large not only for the data obtained in 2014 but also the data for the four years from 2010 to 2013.

This study aims to acquire basic knowledge for the conservation of floodplain dependent species at the Kikuchi river. We investigated water quality, physical environment and fish of the artificial off-channel habitat inflow of groundwater has been constructed in March 2014. The artificial off-channel habitat was confirmed that it is functioning as the habitat of Cobitis kaibara and Lethenteron reissneri the floodplain dependent species by inflow of groundwater.

Water chestnut Trapa natans var. japonica causes pollution in marsh by making Hypoxic water and rot after withering. On the other hand, it prevents waterblooms and turbidity. Moreover, it provides habitat to organisms. In this report, we made some experiments by cutting or remaining water chestnut in Lake Inba-numa, Chiba Pref. and assessed the effects of improving water quality and economic efficiency. From result of survey, we proposed effective method of cutting water chestnut.

Environmental management of rivers (EMR) aims conservation and restoration of the natural and beautiful rivers. However, there are still many problems for EMR, e.g. to set environmental target and to obtain abundant environmental data. To promote EMR, this paper reviews the practice of EMR and discusses the issues and directions of EMR. The EMR can be divided into four parts, i.e. understanding of environmental status, appraisal of data, establishment of environmental target and implementation of management. Appraisal of data still needs the improvement of the basic science and methodology. Above all, establishment of environmental target remains the biggest difficulties for EMR. Therefore, we proposed to set the basic principle of EMR, “Preserve the existing environment and possibly improve it” instead of setting environmental target. To practice the EMR following the principle above, we propose to designate “good site”, where relatively ecologically a good site locates in the river. The “good site” is conserved and the other sites are restored referring “good site” as much as possible. We discussed the EMR based on this principle.

In order to grasp the relation between river wall structure and tidal biota distribution at a tidal river ,we surveyed 4 types of river wall structure (dry stone pitching, environmental conservation type, basket block, megaliths pitching) at the tidal area in Yoshino River which flows through the eastern paret of Shikoku Island in Japan. Distribution of tidal biota (Crassostrea gigas、Xenostrobus secures, Grapsoidea ,Caulacanthus okamurai) was observed .Tidal biota were more common at clearance gaps than the surface of river wall because gaps serve a function to maintain wet condition. Japanese oyster (Crassostrea gigas) and crabs (Grapsoidea) were more prevalent at the basket block than the other types of river wall, whilst Xenostrobus secures were less common at the basket block than the other types of river wall. Based on these results we suggest a new improved basket block for breeding Japanese oysters and crabs. And we suppose that this new river wall will control the distribution of the non-indigenous Mytilid Bivalve Xenostrobus which are prevalent in tidal rivers.

Although fish habitat investigations were conducted before Pirika Dam was completed (1977-1982), under dam construction (1983-1989), after Pirika Dam was completed (1990-2004), and after fishway was completed (2005-2014), the impact of the dam project on fish has not been comprehensively evaluated post- under-after dam and fishway construction. Therefore, the results of previous investigations for 38 years on masu salmon population, spawning bed distribution, population density of juveniles and number of fish migrating upstream were evaluated. It was found that masu salmon have been stably inhabiting reaches downstream of the dam for a long period. Although fish fauna, spawning bed distribution and juvenile population density upstream of the dam were found to be reduced after dam construction, all these were restored after fishway installation. Every year (after 2007), about 40 to 150 adult masu salmon migrate upstream past the dam to spawn. The fishway at Pirika Dam was found to be able to reverse the divided connectivity that was created by the dam.

This study was conducted to clarify the mechanism of anchor ice formation on the river bed and to understand the impact of anchor ice on material transport in ice-covered river. Field observations indicated that anchor ice formation was significantly affected by the air temperatures and water temperatures as well as by the hydraulic conditions, such as the water depth and the flow velocity. We tried to simulate anchor ice formation in the actual river. The simulation results showed that accurate estimation of the temperature of river bed material that incorporated the influence of solar radiation and ground heat was critical for enhancing calculation precision. We could estimate that the anchor ice pulled away the algae from the river bed and flushed them to downstream, similar to a bed load transport in summer flood. This study proved that the river used for simulation had a specific material circulation due to frazil ice and anchor ice.

In recent years, technology for measuring the concentration of suspended solids using ultrasonic waves has been studied. Particles of suspended solids have an irregular shape, and the distribution of particle size varies with time and space. Further, suspended solids include volatile suspended solids such as vegetable pieces and plankton. In this study, we proposed equivalent spherical scatterer models that take into account the shape, particle-size distribution, and density of suspended solids. We measured the concentration of suspended solids in the Rokkaku River estuary and confirmed the usefulness of these models. As a result, we proved that equivalent spherical scatterer models could accurately measure the concentration and particle-size distribution of suspended solids.

Recently, there were cases that the monitoring of the water surface elevation accidentally stopped since water gauges were destroyed during large flooding causing missing data without any alternates; e.g., the case of northern Kyusyu heavy rains in July 2012. Those events highlighted the serious issues of current hydrological observational system. For preparing alternative measurement system, authors investigate how to improve measurement accuracy of reading the staff gauges, and how to implement automatic reading system with using the high-quality CCTV camera, which is operationally used in Yatsushiro River Office. This study reports the results and the future tasks.

An orientation measurement method which used auxiliary recording instruments was developed to enhance applicability and operating efficiency of the Large Scale Particle Image Velocimetry (LSPIV) and the Spatio-Temporal Image Velocimetry (STIV), the non-contact current measurement methods which applied image analysis techniques. The method allows a video camera to obtain necessary parameters using the conventional orientation method which requires predetermined control points at an observation site.

With this method, field observations can be carried out without the reference marks at the time of observation, consequently saving the efforts of orientation measurement.

The purpose of this study is to clarify the elemental compositions of sand and stone in the rivers using the X-ray fluorescence analysis (XRF). The Kurobe, the Joganji, the Sho and the Oyabe Rivers were selected for this study. Total 379 samples of sand and rock of 4 rivers were analyzed and the spatial characteristics of sand and rock were clarified using the cluster analysis.

In the lower Kurobe River, the characteristics of the elementary compositions of the beach sand agreed with sand and stone which deposited in the Unazuki reservoir lake well.

egional distribution characteristics of sand and rock in the rivers could be clarified according to ultimate analysis by the XRF and the cluster analysis.

In this study, the authors showed the discharge calculating method in the high runoff using Space-Time-Image-Velocimetry (STIV) and Dynamic Interpolation and Extrapolation (DIEX) method. We could measure the flood surface flow under the low light and bad weather condition using extended ISO sensitive camera in actual river. This reason was that surface wave image was capable to clearly analyzed at the night time and rainy condition. But, it was difficult to measure the Space-Time-Image (STI) at the low water. The water ripples corresponds to the brightness distribution. For the successful analysis using STIV was needed to require more than 10 standard deviations of brightness distribution. The calculated discharge by STIV and DIEX method had a higher correlation with H-Q equation. We showed it was possible to observe to the quickly observation and manpower saving.

Currently, sediment removal method using suction pipe is researched as an effective method for discharge of accumulated sediment in dam reservoir. Vertical multi-holes double-pipes system is one of the method and has been researched for practical application in dam site. This paper shows the laboratory tests of the system and the verification of the result of the tests. Firstly, the laboratory tests by small model and nearly full-scale prototype system was carried out to check the suction ability. Secondly, the hydraulics model was constructed with results of the tests. Finally, the estimation method of discharging sediment concentration with the flow and the loss of pressure in the pipe has been developed.

We have recently developed a new monitoring system using H-ADCP measurements and river flow simulation based on a DIEX method. This system has been applied to continuous discharge monitoring in the middle reach of the Edo River over 8 years. This study presents the fundamental validity and applicability of this system. The results indicate that this system can completely evaluate river discharge without the conditions of unexpected accident for H-ADCP and low water elevation in which H-ADCP can not measure river velocities. The comparison of the calculated and observed discharges shows that the averaged relative error of the calculated discharge is 4.8 %. These facts suggest the high accuracy and robustness of this system for automatic continuous monitoring of river discharge.

In the present study, to build a river-discharge measurement system without floats in upstream, we have attempted to apply a radio current meter in a flood-flow measurement in Tone River. The observed results indicate that the water-surface velocity using a radio current meter has an influence of the wind. However, the measurement accuracy of the velocity using a radio current meter considered by the effect of wind are good agreements with those of ADCP. It is noteworthy that the coefficient of float show increasing and decreasing trend as water depth and the averaged coefficient of float are as same as the standard value. Therefore we can apply the standard value of the coefficient of float to the velocity using a radio current meter.

Space-time image velocimetry (STIV) is a promising tool for river-discharge monitoring, from the viewpoint of reliability and accuracy. Closed-circuit television (CCTV) cameras have been installed in high position along the rivers. Therefore, we tried to build a river-discharge monitoring system with high reliability and accuracy, by combination with CCTV camera and STIV. The results indicate that 59 units of CCTV cameras can be used for river-discharge monitoring in Kyushu region. In addition, present systems are automatic, continuous and give good agreements with the observed data using floats.

This purpose of this paper is to show the application of the small-medium river survey by using aerial survey technologies. We surveyed the Umetani river using Digital Aerial Cameras (DAC), Helicopter Laser Profiler (LP) and Unmanned Aerial Vehicle (UAV) in Gifu prefecture. We have also obtained the spots of surface elevation with topographical survey in river with VRS-GPS.

As a consequence of surveying, we proved that aerial survey technologies were relative high precise. DAC was suitable for survey riverine environment in watershed scale. LP could obtain most precise surface elevation. UAV could survey river channel not only under the terrain canopy but also under the water depth up to 70cm. We proposed to apply aerial survey technologies to river survey in consequence of some good points.

In this research, we conducted laboratory experiments using a basin model and artificial rainfall equipment and the characteristic of sediment discharge time duration were considered. An experiment using a basin model and rainfall equipment was made and the special quality of the change was considered time of the sediment yield by this research. Experiments results are as follows. Seeing small rainfall intensity condition, large sediment discharge happened and clear peak sediment discharge showed in the case setting sediment on one main river, comparing to the case setting sediment on multiple branch streams. Seeing large rainfall intensity condition, clear peak sediment discharge showed in the case setting sediment on multiple branch streams and also in the main stream case. From experiment results, we found that the sediment yield location and volume relating to sediment discharge runoff were influenced by rainfall intensity.

For improving river environment, artificial sand supply is recently conducted in downstream of dam reservoirs. However, there are many unknowns regarding how the sediment supply affects the bed material size and its dynamics at a flood event. Therefore, the purpose of this study is to clarify quantitatively the dynamics of artificial supplied sand in armored bed by proposing new model for calculating bed shear stress in the cobble layer. Quasi-three dimensional model has been developed considering the sheltering effect by boulders and decrease of bed shear stress. 2D model and the quasi 3D model are compared at flood events in downstream of the Futase Dam. Dynamics of sedimentation height and the deposited mean diameter were analyzed in the simulation. The quasi 3D model can express well the sedimentation at an inner side of meandering part of the river. The size of deposited material in gravel layer is more than 4cm. The model has a possibility to express the dynamics of supplied sediment motion in armored rivers.

Wando have been artificially created in river channel because it sustain variety of aquatic species and form water landscape. However, it is difficult to keep ideal condition of Wando because river flow cause sedimentation of Wando. In this study, by referring documents, aerial photographs and field observation, we clarified the location, number, shape, origin, condition of Wando in target area. In addition, we monitored thickness of sedimentation in seven sites during two to seven months as well as measured the sediment size of bed material of Wando. As a result, we clarified Wando which has narrow opening toward downstream tend to be maintained against sedimentation by flood. In tidal area, fine sediment can be transported by tide and deposited in Wando. In such a situation, bed slope of Wando which is milder than 1/100 increase the sedimentation of fine material by tide. Considering these points, we proposed a shape of Wando which reduce sedimentation by flood and tide.

Abe River drifting to Middle Shizuoka holds each problem in sand production,outflow basin,mountainous river basin,the shore basin in this Abe River sediment Cell in Japanese outstanding fast flowing stream earth and sand river. Ministry of land.Infrastructure and Transport Chubu Regional Development Bureau Shizuoka River Work Office established the management aim of movement of fine sediment fixed its eyes on the sediment cell whole in March,2007,”the Abe River comprehensive sediment management plan examination committee” which examined the basic policy of the earth and sand management strategy to take necessary measures against problems in Abe River sediment cell.In July,2013,”the Abe River comprehensive sediment management plan” and ,after this examination Committee,announced it.At the point that set the quantitative earth and sand management targeted value,it is the national first plan.This report reports the summary of the plan and the follow-up system after the plan development and the sisuation

Recently, to solve the sediment problems in dam reservoir and to carry out comprehensive sediment management, many sediment supply measures have been examined (sediment discharge, placed sediment method at the lower reach of a dam, etc.). In these circumstances, it is required to develop the decision method of the quantity and quality of sediment supply for suitable lower reach condition. Therefore, we paid attention to the river comprised of the wide grain size distribution river bed materials. In this paper, we conducted the large scale hydraulic experiments and developed the river bed variation model based on the knowledge of the hydraulic experiments. We also improved the model considering porosity and exchange layer variation of bed materials. As a result, we confirmed the role of each grain size in river bed variation and river bed configurations by the hydraulic experiments. Furthermore we confirmed the high reproducibility of the river bed variation model.

The large local scouring of which maximum depth is up to 20 meters occurs in the Kiso river, and it is still expanding. In the scouring area, complicated flow condition, such as reverse flow, is observed, and it is supposed that it has possibility to drive expansion of the scouring. In this study, vortex structures and causes of expansion of the scouring are estimated by ADCP survey and three-dimensional numerical simulation. As the result, large vortex structures, such as horizontal and vertical vortex, were confirmed. And it is estimated that the vortex contribute little to the upstream expansion of the scouring area. On the other hand, it is confirmed that strong descending current on the upstream edge of the scouring occurs at small-to-medium flood. Then it is estimated that the current drive the increase of shear stress there and upstream expansion of the scouring area.

Downstream of cross river structure, such as dams, it is often investigated that the grain size distribution becomes coarsened because of interruption of sediment transportation. If fine sands supplied to the coarsened bed, the porosity is decreased and the bed material becomes finer without bed deformation. Furthermore, the change of void structure of river bed is very important issue for habitats.

It is necessary to evaluate the river bed deformation with change of porosity and its influence on habitats. However, the practical method to evaluate the process is not established.

In this study, bed-porosity variation model easily to apply to the actual river is constructed. Then this model is applied to numerical channel on actual river scale, and it is confirmed that the model is able to simulate the bed deformation and porosity change with selective sediment supply, such as supply only fine sand from dam.

Conventionally, the particle shape of bed-material has not been taking into account the modelling of channel bed with sediment transport in the fields of fluvial hydraulics and environmental management. The objectives of this study is to check the effects of particle shape not only on the sediment transport process, but also on the bed interstitial zone as a condition of habitat environments.

Firstly, it is examined whether the bed-material particle shapes are characterized as the properties of channels and their watersheds or not. Secondly, it is described that the bed interstitial zones are formed due to the difference of particle shapes. And then, the critical tractive force on bed load incipient motion could be reevaluated by using the classical hydraulic modelling with ellipsoidal particle approximated by its tri-axial lengths, finally.

Comprehensive flood observation around the diversion of the Edo River was conducted for the purpose of figuring out the flood phenomena. Temporal data of water levels and discharge rates were measured at many observation points during September 2007 flood. The cross-sectional bed forms were surveyed before and after the flood. Next, the quasi-3D unsteady flood flow and 2D bed variation analysis model using the observed temporal changes in water surface profiles was applied to the Edo River channel planning. On the other hand, local velocity distributions and water surface profiles were measured particularly in large scale hydraulic model experiment. Then the improvement design of the diversion of the Edo River was developed using a new river design technique centering on the leading numerical analysis.

In this study, mechanisms of woody debris transport and spatial flow structures on an existing river, Nukabira River of the Saru River system, were investigated by using numerical models and reexamining observational results. The results of the field observation that the number of debris were counted in each sub-region of a monitoring area during a flood event in 2010 show that locations of highly concentrated areas of woody debris vary widely in response to the discharge and the debris size. The particle based numerical model of woody debris was additionally applied in order to investigate the details of the debris motions. The results of the calculation show that the woody debris concentrated to the regions where the vorticity was relatively low in the existing channel. The results also imply that the inertia of debris is one of the important issues, in particular in the cases where the discharge and the size of debris are small, because it determines the responsiveness of woody debris motions to small flow structures which was generated by the exposed incised channels.

One of the main causes of bedrock erosion is saltating bedload on the bare bedrock. On the other hand, if bedrock is covered by gravel, bedrock erosion is restrained by decreased collision frequency of bedload particles against bedrock. We focus on use of “net” as counter measure for bedrock erosion. “Net” has two favorable effects in solving bedrock erosion. One is a cover effect of net itself, and other is an effect of capturing bedload particles and increasing the extent of alluvial cover. We have already confirmed the above effects by flume experiments in our previous study. However, method of predicting suitable thickness of “net” for real river has not been developed. And little is known about the effects on “net” for real river. In this study, we predicted suitable thickness to validate thickness of “net” used in MinaminosawaRiver by using constructed model. In addition, we observed changes of the extent of alluvial cover before and after setting net on bedrock in MinaminosawaRiver.

The main aim of this report is to investigate the measure for controlling inside-levee inundation by flexible sluice gate operation in the event of tsunami in rivers. In order to prove the validation of our two-dimensional model, it is first applied to the simulation of the flood inundation in the Shiribetsu River by the 1993 Earthquake Tsunami off the Southwest coast of Hokkaido. Then it is used for predictions of tsunami run-up and subsequent inundation in both varying tsunami height and gate openness. It is shown that complete gate closure can increase the inundation risk of residential area particularly in the flooding time. A new sluice operation, namely, keeping a loophole of inside-levee discharge is proposed to resolve this problem. Numerical experiments in the targeted river sluice gate show the effectiveness of the measure for a key solution for inhibiting flooding for a certain period of time.

The Kurobe river forms alternate bars at downstream of the Aimoto weir. In this section, longitudinal dikes have been installed for bank protections of the flood channel. In 1995, a large flood occurred. Meandering pattern and flow attacking points of the main channel have been changed since 1995’s flood. Therefore, most of the longitudinal dikes have become not to work against bank erosions by flood flows. In this study, we considered that improvement of channels at downstream of the Aimoto weir was accomplished by recovering natural pattern of alternate bars. And, we carried out flood flow and river bed variation analysis in gravel-bed rivers in order to investigate the stability of the predetermined channels. As a result, it was confirmed that a proposed river improvement channel was useful and the existing longitudinal dikes were able to work against flood flows.

To prevent sediment disasters such as debris flows and landslides, it is important to characterize the damage that occurs to SABO facilities, and to carry out effective maintenance. Administration of these facilities requires monitoring of all damage, as well as evaluation of the soundness of the structures, in order to determine the greatest priority for engineering work. However, no method currently exists to evaluate soundness or to assess priority of engineering work for damaged SABO facilities. Here we describe a quantitative evaluation method for determining the soundness and maintenance priority of SABO structures, which takes into account budgetary limitations. We discuss our approach using the example of a bridge in Europe, and describe the details of this specific case as well as identify directions for future work.

Sediment supply measures from a reservoir are required to reduce sedimentation and to preserve the downstream river bed environment. Then, we have been trying to develop a new sediment supply measures using the differential water head energy between upstream and downstream of a dam. We have proposed “the burrowing type sediment removal suction pipe method”. In this study, in order to obtain knowledge for practical application of the pipe, we carried out the sediment discharge field test using the 200mm and 300 mm diameter pipe at the actual reservoir. As a result, we understood the hydraulic characteristics, the applicability to the material, and the availability of the pipe. It was confirmed that the pipe could discharge sediment at almost the expected performance for reservoir material (almost non- cohesive debris-less sediment material).

The bank protection works using sandbars with boulders which are local riverbed products have been developed and applied in the Jyoganji river, which is one of the most rapid stony rivers in Japan.

These works have two advantages compared to ordinary concrete revetment; 1) making its maintenance easy in the use local riverbed constituent material , 2) extending life-span of banks with existing bank protection works.

This paper shows technical investigation of securing functional maintenance of the bank protection works based on monitoring study and numerical simulation.

The new technology using sandbars with boulders for bank protection have been developed and applied in the Jyoganji river. These protection works have been found to contribute significantly to the stabilization of riverbed and banks against floods and river environments. On the other hand, it is difficult to use sandbars with boulders in some rivers where there are no boulders. Therefore, we need to develop secondary products useful for a substitution of boulders

This paper presents different kinds of secondary products developed for the bank protection in place of boulders and the results of field investigations monitoring their functional advantages and disadvantages in the Jyoganji river.

When the river tsunami occurs in the winter period, the operation of the gutter sluice gate can be prohibited by the influence of the drifting and jamming of ice floes, increasing the inundation risk inside the levee. Therefore, secure sluice gate operations are required against tsunami run-up during the ice- covered period. In this paper, demonstration experiments are performed in the Aikoku sluice gate of the Shinkushiro-river, showing the effectiveness of ice control measures using submerged pumps. The field test presented that submerged pumps inhibited ice formation within a radius of about 2~2.5 meters around the installation location. In addition, numerical ice-thickness estimation showed that the method guaranteed the ice control effect up to the thickness of 0.63 m. Based on these results, the applicability of the method is further investigated in other rivers around the coast of eastern Hokkaido. This paper succeeded in showing the effectiveness of our novel ice control measure for actual rivers.

This report presents a case study project of collaborative stream restoration work with installing timber log structures by citizens, researchers, students and administrative officer in Kamisaigo river. In order to reveal effects of this collaborative restoration work, questionnaire survey was conducted to citizen participants (=elementary students).

Following results were obtained.

Following results were obtained.

· Installed timber log structures work in safety and provide precious habitat for some aquatic species

· Collaborative stream restoration work create an intergenerational connection between citizens

· Citizens became more careful against Kamisaigo river than before

· Citizens’ interest for river management work was heightened.

· Citizens’ awareness about river environment was heightened

In recent years, on the Satsunai River, a tributary of the Tokachi River, the area of gravel dry riverbeds has been rapidly decreasing because of the invasion by riparian forests. The watercourses have concentrated into one main watercourse and many of the branched streams have already disappeared even at locations where double-row bars had existed. In this study, onsite surveys and theoretical analysis were done to clarify the characteristics of bifurcations in watercourses with double-row bars and to determine a method of selecting the optimum excavation locations for effectively restoring already closed former watercourses. It was found to clearly identify riffles and pools in the longitudinal profile of the watercourse in the Satsunai River. Excavation at locations slightly downstream of a pool, where a riffle starts to emerge, were found to be effective.

Understanding to sediment dynamics, especially in upstream, is not sufficient to precisely estimate amount and component of bed load. In this paper, two tributaries - Midaigawa River and Oomukawa River - having the same scale in high-sediment-producing Fujikawa River basin are compared. Flume experiment is held to clarify characteristics of mixed sand and influences of continuous drop structures. Thereafter how alluvial procedure determines riverbed materials and results to differences in grain size distribution is identified.

It is necessary to develop a method for efficient management to reduce the sediment deposition in the small-medium rivers. In this study, the maintenance method is proposed for the improvement of sediment transport by moving the deposited materials to the right place in the channel. At first, we show the method for finding the process of sediment deposition and characteristics of river channel by using both the two-dimensional riverbed variation analysis and Fukuoka’s formula. And, the method is proposed to design proper longitudinal and cross-sectional form to correct the sediment transport problem.

In the Kushiro Wetland, old river reconstruction project, which shifts the channel of the current straightened river to the old meandering one, started from 2006 and was completed in 2011. This study focuses on river bed fluctuation of the curved channel with channel width narrowing, where is located in the inlet of the old meandering river with 30(m) width from straightened one with 80(m). From field survey, in response to change in water and sediment discharges, significant streamwise variation in water flow width in the curved channel adjusts in order to establish the dynamic equilibrium. Along the outer bank of curved channel, the secular bed deposit beside the outer bank is increasing, and as a result, the main streamline flows into the old river along the inner bank as left bank. Moreover, this narrowing curved channel easily leads to overspill some flood water including rich suspended sediment and to deposit some fine sand near channel side flood plain. We intend to explain above significant bed variations by using movable bed experiments with the distorted model and the numerical simulations.

The sediment balance in each segment of Class A rivers in Japan was studied as fundamental data for river management. The relationship between increase of river capacity and volume of river excavation for flood control and gravel mining was evaluated based on calculated sediment balance, and the trend of river capacity change was analyzed. As a result, the river excavation mainly cause the increase of river capacity and maintain the river channel volume which naturally decrease without river excavation.

We studied a changing process of river cross-sections and the resulting change of riparian vegetation after the excavation of a river channel. The study was conducted on how floods changed the cross sections and finally affected the vegetation environment, based on data and information accumulated for ten years after the excavation together with research on current conditions of vegetation and soil. As a result, the reproduction of a salix community was confirmed in the excavated area. The invasion and growth of the salix species in the river channel was analyzed in relation to the frequency, duration and depth of inundation. Floodplain pools on the uneven surface of the river channel after the excavation may have generated a favorable condition for the growth of the salix species.

This paper aims at examination of the effectiveness in Japan of the “Local River Widening” method mainly tried in Europe. About the example site of the small and medium-sized rivers which flows through the Kiso-river fan, the follow-up survey was conducted to consider the geographical feature change process. A point-bar was formed through two flood term after construction in the site. In order to generalize the knowledge acquired from the case study, the virtual river channels of alluvial fans were set up, numerical analysis were performed on varying plane conditions. The pattern of geographical feature change was arranged by four types, and the formation factors of each type were considered by the results of analysis. The considerations with the development domain of bed forms were performed. It was suggested that the fall of average shear stress of the widening section caused formation of bar-like geographical feature.

When it comes to flood, increased river flow causes stream diversion with bank erosion. Therefore, we have built revetments in order to keep the channel flow stable. However, the construction of the protection which narrows the flow width caused an increase of bed shear stress and a degradation of bed. In order to solve these problems, it is necessary to permit river channel change to some extent. However, the knowledge about the long-term movement of river channels accompanying bank erosion is insufficient.

This research investigates a river channel meandering process from the past to the present using the topographical maps. We found that river works revetments mitigate the degree of meandering in the present river. The width of channel is the almost same as the past meandering width in general. However, the old channel shown by the aerial photograph locates at protected area. Therefore, it is necessary to consider the danger of riverbank erosion on a long-term management plan.

Disaster possibility by mid-sized floods has not been focused much comparing to large-sized ones. In jurisdiction of Keihin River Office, mid-sized floods have caused disasters in the past. There are high possibilities that these types of disasters lead to serious disasters.

In this paper, we analyzed causes of a wide range of erosion at right bank upstream the Omaru weir by mid-sized flood brought by typhoon No.18,10.2014, which scale is 30m maximum breadth and 400m length. Moreover, we examined and proposed emergency countermeasure to mid-sized flood disasters, and the way of daily river-maintenance, considering other momentous mid-sized floods disasters occurring in jurisdiction of Keihin River Office in addition to erosion described above.

In the Hii River, there are some intake weirs which are made by river bed materials of sands. Since the sand intake weirs are eroded and scoured by flood flows, flushing of the sand intake weirs by a series of floods and rebuilding them after the floods induces formation of large scale sandbars and reduction of channel widths at downstream of the sand intake weirs. Therefore, first we investigated effects of flushing of the sand intake weirs on channel widths reduction by using observed annual data and the general Bottom Velocity Computation (GBVC) method which was developed by Uchida and Fukuoka. Next, we discussed how to rebuild the sand intake weirs after floods for minimizing effects of the sand intake weirs flushing on channel widths reduction.

Recently unprecedentedly rapid riverbed degradations are observed at several parts river channels on mudstone/alluvial cohesive soil layer in lower reaches of Kinugawa River, which has brought various problems upon river management.

To elucidate riverbed degradations mechanism at exposed river channels on mudstone/alluvial cohesive soil layers, this report focuses on the relationship between geological time of river sediment/geological structure and erosion, and implements factorial analysis regarding riverbed erosion types and characteristics based on the geological survey and measurement.