Authorship：Lead author,　Corresponding author   Language：Japanese   Publishing type：Research paper (scientific journal)

DOI： 10.2208/jscejj.23-16101

DOI： 10.2208/jscejj.23-16101

Authorship：Lead author,　Last author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)

DOI： 10.1007/s12237-023-01248-0

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DOI： 10.1007/s10113-023-02098-z

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Dams have contributed to population growth and technological innovation by reducing the risk of flooding and allowing humans to cultivate productive alluvial soils on river floodplains. However, in countries where many dams have already been constructed, many problems have been observed, such as river environment degradation, aging of the embankments, and inadequate dam performance. As the social and natural environment surrounding dams is becoming more complex and diverse, it is necessary to understand the current overall status of dams and the history of their construction such that we may consider how social capital and dams are related to human society and the natural environment. In this study, the relationship of basic information of dams and the social background in which the dams exist was examined for Japan, where dam construction began in earnest in the late 1800s and became a driving force for economic development. The situations surrounding dams are drastically changing, as maintenance and management costs increase due to the aging of dams and water demand varies due to changes in the industrial structure of a region. Simultaneously, there are instances where dams are expected to reduce damage, such as in the presence of more severe and frequent droughts and floods caused by climate change. It is therefore necessary to remove or restructure dams while considering numerous complex and diverse factors, such as the local social conditions, potential future changes, and environmental impact of rivers.

DOI： 10.1002/rra.4129

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DOI： 10.1007/s12237-022-01097-3

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Language：English   Publishing type：Research paper (scientific journal)

DOI： 10.3390/w14091343

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Headstream areas, which are located in the uppermost reaches of mountain streams, are important sections for investigating the geomorphology of stream channels and their generative mechanisms, because they are close to sediment supply sources and generally suffer little anthropogenic impacts. In this study, the occurrences and characteristics of bed morphologies in a sandstone-dominated headstream area are explored at two scales—reach and unit—which are often overlooked. As a result of field investigations, cascades and step–pools were found to occupy the majority of the stream channel laterally at the reach scale. However, most of the elevation differences were accounted for by fall–pools, cascades, and step–pools, suggesting the importance of bed morphologies with large elevation losses in the headstream area. In addition, the characteristics of the bed morphologies at the reach scale were closely related to the longitudinal profiles of each stream. The mean gradients of the reach-scale bed morphologies were 46.9% for fall–pools, 23.9% for cascades, 16.8% for step–pools, and 5.9% for pool–riffles. At the unit scale, pools occupied the majority of the stream laterally, and > 80% of the elevation differences in all the studied rivers were occupied by falls, bedrock cascades, cascades, and steps. Although there have been no studies on the elevation loss functions and characteristics of falls, this study revealed the importance of fall–pool reaches and fall units in a sandstone-dominated headwater area in the Kantō Range of Japan.

DOI： 10.1007/s10201-021-00690-y

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Authorship：Lead author,　Last author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)

DOI： 10.1016/j.catena.2021.105760

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DOI： 10.1111/sum.12705

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DOI： 10.3897/BDJ.10.e83527

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The headstream area is an important channel segment for investigating the self-organization mechanism of a stream channel or the occurrence characteristics of stream bed morphology owing to its sediment source and low anthropogenic impact such as that from check dams or channel modifications. However, less work has been conducted on the transition of stream bed morphology in channels with very high gradients, unlike in step–pool channels. This study describes the field observation results of the stream bed morphological characteristics and the relationship between the step–pool structure and stream channel characteristics in the headstream areas of rhyolitic mountains. The transition of the stream bed morphology associated with different bed slopes was confirmed through field observations. The dominant stream bed morphology changed from a fall to a cascade to a step, from upstream to downstream. Furthermore, the relationship was different between the step formation processes (hydraulic control and keystone types) and the jamming state, which was caused either by the supply process of the step constituent boulder or the external force of the step. Mountainous streams are strongly affected by geology, and this tendency is likely to be more pronounced in headstream areas. Further, the factors influencing stream bed morphology or stream channel characteristics include the formation age of mountains and the climate, geology, and the absence of fault zones. Therefore, knowledge of the stream bed morphology of headstream areas under various geological and meteorological conditions is required.

DOI： 10.1016/j.catena.2021.105427

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Article, review, commentary, editorial, etc. (scientific journal)

DOI： 10.1007/s10113-021-01820-z

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Increasing water demand due to population growth, economic development, and changes in rainfall patterns due to climate change are likely to alter the duration and magnitude of droughts. Understanding the relationship between low-flow conditions and controlling factors relative to the magnitude of a drought is important for establishing sustainable water resource management based on changes in future drought risk. This study demonstrates the relationship between low-flow and controlling factors under different severities of drought. I calculated the drought runoff coefficient for six types of occurrence probability, using past observation data of annual total discharge and precipitation in the Japanese archipelago, where multiple climate zones exist. Furthermore, I investigated the pattern of change in the drought runoff coefficient in accordance with the probability of occurrence of drought, and relationships among the coefficient and geological, land use, and topographical factors. The drought runoff coefficient for multiple drought magnitudes exhibited three behaviors, corresponding to the pattern of precipitation. Results from a generalized linear model (GLM) revealed that the controlling factors differed depending on the magnitude of the drought. During high-frequency droughts, the drought runoff coefficient was influenced by geological and vegetation factors, whereas land use and topographical factors influenced the drought runoff coefficient during low-frequency droughts. These differences were caused by differences in runoff, which dominated stream discharge, depending on the magnitude of the drought. Therefore, for effective water resource management, estimation of the volume of drought runoff needs to consider the pattern of precipitation, geology, land use, and topography.

DOI： 10.3390/w13091259

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The alteration of hydrologic systems due to urbanization causes many problems including urban flood inundation, water quality degradation, and stream ecosystem damage related to river channel modifications such as stream burial. The purpose of this study was, therefore, to clarify the factors affecting the process of stream burial by performing a time series investigation of the changes in six river systems flowing through the Tokyo Metropolitan Area from 1909 to 2020 using historical topographic maps. The observed changes revealed that the stream burial process consists of: (1) river improvements such as meander cutoff and integration of flow channels by branch abolishment, (2) stream burial of relatively small tributaries, and (3) stream burial of large tributaries and part of the mainstream. Stream burial was remarkable in the center of the Tokyo Metropolitan Area, where the river channels and condition of stream burial were nearly the same in 2020 as they were in 1945. However, meandering channels partly remained in the tributaries of relatively large stream systems. Straight channels constituted about 10% of all channels in 1909, but constituted greater than 40% in 2020, suggesting that the remaining open channels were considerably influenced by river improvements such as meander cutoff. Furthermore, the degree of stream burial was observed to be strongly related to the proportion of urbanization and the scale of the target river system. Stream burial was found to be advanced not only by changes in land use, but also by social factors including earthquake and war damage reconstruction projects as well as measures to counter flooding and improve water quality. The findings of this study advance research into evaluating measures and goals for urban river restoration projects.

DOI： 10.1007/s12665-021-09524-7

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The conservation and restoration of freshwater ecosystems require the understanding of potential biota of the target area. My ultimate study goal was to clarify the potential fauna of the watershed unit of the Japanese archipelago, a hotspot of biodiversity. Here, I attempted to classify the macroinvertebrate community of the major rivers within the Japanese archipelago, thereby elucidating its biogeography, and to investigate the extent to which environmental factors drive the watershed’s macroinvertebrate community. I classified the rivers located in the northern region of the Japanese archipelago geographically, but did not group the geographically adjacent rivers in the western region together. Differences in watershed size, geological history (including river conflict), and paleo-drainage systems seem to affect the classification results. Moreover, Indicator Species Analysis results suggest that river groups in the northern part of the Japanese archipelago had highly endemic species, whereas, the river groups in the western part of the Japanese archipelago had few highly endemic species. The result of the canonical correspondence analysis indicated that topographic factors, the flow regime, geology, water quality, and anthropogenic factors were significantly correlated with macroinvertebrate classification and distribution. The results of the decision tree model indicated that water temperature and maximum specific discharge were explanatory factors in the classification of the macroinvertebrate community. Further, my results also suggest that environmental factors at a smaller scale than that of the watershed were needed to explain further subdivisions in classification of the macroinvertebrate community.

DOI： 10.1016/j.limno.2020.125844

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DOI： 10.3897/BDJ.9.e67168

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Authorship：Lead author,　Last author,　Corresponding author   Language：Japanese   Publishing type：Research paper (scientific journal)

<p> This study investigates the relationship between distribution characteristics of fluvial morphology and geomorphic characteristics of the headstream area. The gradient of the fluvial morphology at the reach scale is large in the order of fall-pool, cascade, step-pool and pool-riffle. Slope relief and drainage density were selected as mountainous characteristic quantities that affect the longitudinal profile and the distribution characteristics of the fluvial morphology. These indices are considered to be important factors because they are related to sediment production and specific height difference of the stream bed.</p>

DOI： 10.2208/jscejhe.77.2_i_1009

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Other Link： https://www.jstage.jst.go.jp/article/jscejhe/77/2/77_I_1009/_pdf

Language：English   Publishing type：Research paper (scientific journal)

DOI： 10.3825/ECE.23.161

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)

DOI： 10.3390/SU12010065

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DOI： 10.1002/rra.3524

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DOI： 10.3390/w11040716

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DOI： 10.1016/j.ecss.2019.01.001

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Authorship：Lead author,　Last author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)

DOI： 10.1016/j.ecolind.2018.08.057

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Language：Japanese   Publishing type：Research paper (scientific journal)

CiNii Article

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Authorship：Lead author,　Last author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)

DOI： 10.1016/j.ejrh.2018.10.001

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Language：Japanese   Publishing type：Research paper (bulletin of university, research institution)

application/pdf

DOI： 10.14945/00025035

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)

DOI： 10.3390/su10020407

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DOI： 10.3897/BDJ.6.e26101

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 Nature friendly river improvement technology of high gradient river is not established due to occur exessive river bed scour and erosion during flood. We conducted physical, movable-bed model to design nature friendly river channel of the Oide River (located in Nagasaki city) which is high gradient river. As a result of the experiment, masonry groin system protected river bank and rive bed in high gradient river with limited river width and complex environmental structures was formed in river channels by considering the arrangement of groin system. Further, we compared the experiment result with the past findings and examined the relationship between groin structures and scour depth.

DOI： 10.2208/jscejhe.74.i_1141

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 Estuaries are distinctive environment which fluctuates continually by mixing fresh water and sea water due to the influence of the tide and waves. However, disappearance of habitats is a serious problem in estuaries since river improvement technology in consideration of the environment has not been established. In this study, we investigated the relation between the habitat structure and river course characteristic based on the classification result of river estuaries by the energy of tide, wave and river. As a result of the classification, river estuaries were classified into three groups (wave and river dominated, low wave and tide dominated). The river course characteristic influenced habitat structure was different among groups. Habitat structures of the wave and river dominated estuaries were influenced by sinuosity, low wave estuaries were affected by relative elevation difference in water channel and tide dominated estuaries were influenced by width depth ratio.

DOI： 10.2208/jscejhe.74.i_601

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<p> 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.</p>

DOI： 10.2208/jscejhe.74.5_i_1255

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 The sediment release and deposition characteristics associated with sediment replenishment by outlet gate operation of check dam in the step-pool structured small stream (Kamogawa River in Fukuoka Pref.) were investigated. The basin was mainly consisted of sandy weathered granite and the check dam had been trapped 13,700 m3 of sediment in a mutual layer with sand and cohesive cray since establishment 29 years ago. After the gate opening on March 2017, approximately 12.1% of total sediment volume was immediately released and further 6.6% flowed out in the subsequent floods. Estimated suspended sediment (SS) concentration was reached to about 1200 mg/L in downstream. The sediment from upstream filled some pools in the steep section. It suggest that sediment release can influenced in change of land form and substrate characteristics even in the step-pool section.

DOI： 10.2208/jscejhe.74.i_913

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DOI： 10.3390/w9050356

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Authorship：Lead author,　Corresponding author   Language：Japanese   Publishing type：Research paper (scientific journal)

Here, we review existing knowledge about step-pool structures in mountain rivers with reference to their morphology, process of formation, destruction, hydraulic function, restoration, and ecological function. First, we present the constructive factors of steppool structures and their appearance, focusing on channel bed profile. Second, we summarize the processes driving the formation and destruction of step-pools, concentrating on current and sedimentation. The untidune and keystone theories are discussed as the key concepts of step-pool formation in relation to the installation of artificial step-pool structures. Third, with reference to previous studies, we discuss the relationship between step-pool structures and river course characteristics. Fourth, we describe the law of resistance and velocity in a mountain river. Finally, with reference to their ecological function, we discuss the use of step-pool structures in restoration projects. Based on earlier studies of step-pool structures, we discuss future issues and propose studies to technologize and standardize step-pool structures for river improvement and restoration.

DOI： 10.3825/ece.19.165

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CiNii Research

Authorship：Lead author,　Corresponding author   Language：Japanese   Publishing type：Research paper (scientific journal)

 The establishment of a conservation strategy or restoration goal for river estuaries requires knowledge of potential biota or possible habitat characteristics. We classified the Japanese river estuaries using physical indicators related to river energy, tide energy and wave energy, based on ecoregion decided by similarity of benthos. Japanese estuaries were classified into three ecoregions (Japan Sea, the Pacific Ocean and west Nankai). Finally, we classified nine types of estuary in three ecoregions by river energy, tide energy and wave energy. This classification is basic unit for conservation, because the potential biota or possible habitat is homogeneous in the same classification.

DOI： 10.2208/jscejhe.73.i_1171

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<p>Estuaries are distinctive environment which fluctuates continually by mixing fresh water and sea water due to the influence of the tide and waves. However, disappearance of habitats is a serious problem in estuaries since river improvement technology in consideration of the environment has not been established. In this study, we investigated the relation between shellfish fauna and physical factors of watershed scale and river course characteristics. As a result of single correlation analysis, sinuosity, river bed complexity, comparable height difference in low flow channel, depth ratio, bed slope and number of types of habitat had significant positive correlation to abundance of shellfish fauna. These results suggest that the securement or creation of high attitude area in low flow channel should be considered when conducting the river bed excavation, or diversity of shellfish fauna can be secured by increasing the depth ratio when conducting river improvement.</p>

DOI： 10.11532/river.23.0_657

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DOI： 10.1016/j.ecoleng.2016.10.024

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Authorship：Lead author,　Last author,　Corresponding author   Language：Japanese   Publishing type：Article, review, commentary, editorial, etc. (trade magazine, newspaper, online media)

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)

DOI： 10.1063/1.4948918

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Article, review, commentary, editorial, etc. (scientific journal)

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Authorship：Lead author,　Corresponding author   Language：Japanese   Publishing type：Research paper (scientific journal)

 A runoff model was applied to investigate outflow control effect of on-site storage and soil improvement for improving infiltration capacity. We calculated overflow amount of each manhole before and after measures at the Zenpukuji river in Tokyo using four types of hyetograph (occurrence probability 1/100). The result of simulation suggested the following: 1) large overflow amount and wide area of overflow was occurred in short term concentration rainfall, 2) effect of on-site storage and soil improvement was high in long term rainfall, although depression effect was different for each points, 3) effect of countermeasures was constant for short distance upstream and downstream form the measures point and reduction effect for upstream was high at place occurring overflow due to backwater, 4) effectiveness of countermeasures could be enhanced to intensively-introduce runoff control measures for sites overflow volume was large.

DOI： 10.2208/jscejhe.72.49

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 We examined relationship among specific discharge of flood and rainfall, geomorphology, land use and geology to reveal the influence of watershed characteristics on flood discharge. As a result of a correlation analysis, hourly rainfall depth was the most major factor to determine the flood discharge. Among the geomorphological factors, form factor and topographical gradient were major factors of increasing flood discharge. However, the effects of these factors differed by flood scale. In the land use factor, there was no clear relationship between broadleaf forest and flood discharge for each flood scale. Whereas, coniferous forest was factor to increase flood discharge at low frequency event.

DOI： 10.2208/jscejhe.72.i_1255

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 Nature friendly river improvement technology of upper reach is not established. We conducted physical, movable-bed model to design nature friendly river channel of the Oide River and investigate energy dissipating effect of step-pool structure.<br> As a result, river bed fluctuation and bank erosion could be minimized without using concrete river bank protection by appropriate arranging of groin and riprap. And, the experiment revealed that the step height and pool depth of 0.55m is the most appropriate structure of step - pool with the point of energy dissipation and river bed fluctuation in the Oide river.

DOI： 10.2208/jscejer.71.ii_397

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Other Link： https://www.jstage.jst.go.jp/article/jscejer/71/6/71_II_397/_pdf

Language：Japanese   Publishing type：Research paper (scientific journal)

<p>Combined Sewer Overflow(CSO) cause severe effect to river environment. In Japan, 200 Urban areas adopt the Combined Sewer and CSO is the nationwide problem.</p><p>In this study, We investigated the relationship between intensity of rainfall and number of occurrence of CSO in the Zenpukuji River. And, we developed the outflow simulation model of CSO by using Inforworks ICM. Then, we carried out the simulation on the assumption that infiltration facilities are set in the basins.</p><p>As a result, we reveal that over 1.1mm/5min or 2.0mm/10min, 4.3mm/30min, 6.4mm/hr rainfall caused the CSO at the upper reach of the Zenpukuji River. The simulation results indicated that the infiltration facilities can reduce the CSO peak flow when the peak discharge was under 12m3/s at the observation point.</p>

DOI： 10.11532/river.21.0_455

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Other Link： https://kyutech.repo.nii.ac.jp/records/2000528

Authorship：Lead author,　Corresponding author   Language：Japanese   Publishing type：Research paper (scientific journal)

River flow regime is important role in determining the river morphology, water use and biotic composition. In Japan, however, river management based on the concept of variation of flow regime is not taken. Because the knowledge of potential hydrological regime is lacking. In this study, we proposed the flow regime indicators which can explain seasonal change of stream flow at 52 watersheds in the Kyushu region. And, we investigated the relationship between flow regime indicators and factors that affect the hydrology (physiographic factors, geological factors and vegetation factors). Result of multiple regression analysis, flow regime indicators were well explained by the factors of physiography, geological and vegetation. The results indicated that geology of volcanic ejecta tends to stabilize the flow fluctuation, and urbanization and plantation tend to increase frequency of disturbance and drought.

DOI： 10.2208/jscejhe.71.i_1213

Kyutacar

CiNii Article

CiNii Research

Other Link： https://ndlsearch.ndl.go.jp/books/R000000004-I026355296

Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)

DOI： 10.1007/s11355-011-0171-2

Scopus

Other Link： https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=84872670260&origin=inward

Authorship：Lead author,　Corresponding author   Language：Japanese   Publishing type：Research paper (scientific journal)

Kyutacar

CiNii Article

CiNii Research

Other Link： https://ndlsearch.ndl.go.jp/books/R000000004-I024918739

Authorship：Lead author,　Corresponding author   Language：Japanese   Publishing type：Research paper (scientific journal)

In Japan, many restoration projects and efforts to conserve the river environment were carried out across the country. In spite of these efforts, effective measures to conserve the river ecosystem or post-evaluation of the restoration project were insufficient due to a lack of environmental indicators. We established biological indicators using fish fauna in the midstream segment-based ecoregions of the northwest ecoregions based on the concept that quality of biota can be compared in the same segment-based ecoregion. Furthermore, multiple regression analysis was carried out to explain the relationship between the index value and the physical characteristic of a habitat. As a result of the multiple regression analysis, it was found that embayment increased the number of fish species. On the other hand, weir and ponding decreased it. Establishing biological indicators using the ecoregion concept enabled to compare the integrity of fish fauna between watersheds, which had been previously difficult to examine.

DOI： 10.2208/jscejhe.69.i_1249

Kyutacar

CiNii Article

CiNii Research

Other Link： https://kyutech.repo.nii.ac.jp/records/2000549

Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)

CiNii Article

CiNii Research

Language：Japanese   Publishing type：Research paper (scientific journal)

<p>The restoration of river ecosystems is of worldwide interest. Although various techniques have been designed, an effective method for environmental evaluation is necessary. We report a new method for the evaluation of the riverine environment on the basis of simple fish ecological data. The 16 indexes studied were (1) native species, (2) alien species, (3) red list species, (4) genuine freshwater fish species, (5) amphidromous or brackish water fish species, (6) swimming species, (7) benthonic species, (8) flowing water species, (9) still water species, (10) permanent water species, (11) temporary water (flood plain) species, (12) spawning in vegetation area species, (13) spawning in muddy bottom species, (14) spawning in sandy-gravely bottom species, (15) spawning under rocks species, and (16) spawning in mussel species. The reference data is the maximum number of potential species . First, the fish fauna data of the evaluated point was obtained. Next, a radar chart was prepared with regard to the 16 indexes. Although this assessment method can be applied in the same ecoregion, it provided a good evaluation.</p>

DOI： 10.11532/river.16.0_449

Kyutacar

CiNii Article

CiNii Research

Other Link： https://kyutech.repo.nii.ac.jp/records/2000539

Authorship：Lead author,　Corresponding author   Language：Japanese   Publishing type：Research paper (scientific journal)

The biological indicator should be developed in the ecoregion where biota is relatively identical. Furthermore, as stream biota widely varies from headwater to downstream, it is necessary to define segment based ecoregions where biota is longitudinally identical. In this study, we delineated segment based ecoregions for ten rivers belonging to the northwest Kyushu ecoregion based on the degree of similarity of the fish fauna. The northwest Kyushu ecoregion was divided into five segment based ecoregions. As a result, fish fauna was more clearly characterized by the differences in community structure between segment based ecoregions than those between watersheds. Moreover, distinguishing segment based ecoregions, enabled us to compare the integrity of fish fauna between watersheds, which had been previously difficult to examine.

Kyutacar

CiNii Article

CiNii Research

Other Link： https://kyutech.repo.nii.ac.jp/records/2000542

Language：Japanese   Publishing type：Article, review, commentary, editorial, etc. (trade magazine, newspaper, online media)

CiNii Article

CiNii Research

Other Link： https://ndlsearch.ndl.go.jp/books/R000000004-I10381323

Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)

A large number of studies have been made on longitudinal changes of fish fauna, however, the relationship with the engineered viewpoint is little known. The purpose of this paper is to investigate relationship between longitudinal changes of fish fauna and segment classification defined from the viewpoint of flood control.<BR>We focused on 15 rivers in Kyushu and run TWINSPAN analysis to divide the fish fauna longitudinally and compared segment classification.<BR>The result of analysis showed that segment classification is largely corresponded with longitudinal changes of fish fauna and the values of longitudinal gradient which is the boundary of longitudinal fish fauna classification are 1/2000, 1/1000 and 1/100.

DOI： 10.2208/prohe.52.1147

Kyutacar

CiNii Article

CiNii Research

Other Link： https://kyutech.repo.nii.ac.jp/records/2000543