Search

This study attempts to back-calculate Manning's roughness coefficients by repeating a two-dimensional flow simulation to fit the spatially and temporally dense river water-level data observed in Japan's Yamatsuki River, a typical mountainous river with an average riverbed gradient of 1/50 and an average river width of 17.9 m. Furthermore, we aim to clarify the influence of the in-channel physical parameters on the coefficient of roughness obtained through the above method. In the Yamatsuki River, 16 water-level gauges were installed at intervals of about 40~80 m in the longitudinal direction in the study reach. Manning's roughness coefficients were back-calculated by repeating two-dimensional flow simulations to match the observed water levels of a flood in 2021 (the estimated maximum flow rate is 11.5 m3/s). The back-calculated roughness coefficients approached a constant value in the range of 0.05 to 0.1 s/m1/3 as the relative water depth increased, indicating that the roughness coefficient can be considered a constant value when performing plane two-dimensional flow calculations for flooding. The roughness coefficient during flooding was found to be correlated with the slope and step height (H)-step length (L)- channel slope (S) ratios (H/L/S). An equation for predicting the roughness coefficient during flooding based on the physical parameters of the channel is also proposed. [ABSTRACT FROM AUTHOR]

In recent years, climate change has occurred on a global scale, causing frequent flooding in many regions. In response to this situation, watershed-wide flood management is attracting attention around the world as a promising approach. Under these situations, Japan has also made a policy shift to watershed-based flood management, which aims to manage floods and control runoff in the entire watershed. For this management, it is essential to obtain areal hydraulic information, especially flow information, from each location in the watershed. To measure river flow, it is necessary to measure water level and velocity. While it is becoming possible to make area-based observations of water levels using simple methods, various attempts have been made to measure the velocity, but continuous data cannot be obtained using simple methods. Low-cost flow velocity meters would facilitate the simultaneous and continuous accumulation of data at multiple points and enable the acquisition of areal flow information for watersheds, which is important for watershed-based flood management. This study aims to develop an inexpensive, simple velocity meter that can be used to make areal measurements within watersheds, and to make this velocity meter usable by residents, thereby contributing to citizen science. Therefore, experimental studies were conducted on a method of measuring flow velocity based on the simple physical phenomenon of rising water surface elevations due to increased pressure at the stagnation point. First, we placed the cylinders in the river or waterway, observed the afflux, and compared the velocities calculated using Bernoulli's theorem with the velocities at the experimental site. By multiplying the calculated flow velocity by 0.9, the average flow velocity was found to be obtained. Then, by using a large pitot tube with a hole diameter of about 5 mm, the rise in water level in the pitot tube was measured using a pressure-type water level meter, and the flow velocity was calculated using the pitot tube theory and compared with the flow velocity at the location of the hole at the experimental site. By multiplying the calculated velocity by 1.04, the velocity at the location of the hole can be obtained. In addition, the same experiment was conducted using a pitot tube with a slit. The slit tube was placed vertically with the slit facing upstream. Measurements were taken in the same method as for the pitot tube velocity meter and compared to the velocity at that point. By multiplying the calculated flow velocity by 0.99, the average flow velocity at that location can be obtained. These results indicate that a flow velocity measurement method utilizing stagnation points can lead to the development of inexpensive velocity meters. Because of the simplicity of this meter, there is a possibility that citizens can participate in the observation to obtain information on the flow velocity during floods and areal information within a watershed. [ABSTRACT FROM AUTHOR]

Saint Martin's Island is a tiny island located in Bangladesh that is rich in biodiversity but threatened by many natural disasters, and it is often neglected due to being far from the mainland. Ecosystem-based disaster risk reduction (Eco-DRR) is the most urgently required provision for Bangladesh as it is a very easy and inexpensive way to survive natural adversities. In this study, attempts were made to quantify the capacity of an existing Pandanus forest on Saint Martin's Island to reduce the storm surge disaster risk. For this, satellite images were processed with ErdasImagine and ArcGIS software, and land use and land cover changes were analyzed to determine the changes related to Pandanus trees over time. Storm surge wave height reduction was analyzed using the Bao regression model equation. The results show that the Pandanus tree population increased almost 3-fold from 2010 to 2021, and that the Pandanus trees can reduce the surge height, which will ultimately preserve 75% of the area of the island (2021). The minimum required patch width for the Pandanus tree belt was identified as 4.53 m. The areas highly vulnerable to flooding were also identified in this study. [ABSTRACT FROM AUTHOR]

Focusing on green infrastructure (GI), which utilizes nature's diverse resources, we developed urban flood control measures on three small-scale private tracts in Tokyo and Fukuoka in Japan, experiencing high rainfall. In addition, we implemented these measures and verified the possibility of introduction. Using a target rainfall of 100 mm/h and previous rainfall data, we set our goal of reducing runoff from each site below the capacity of a public sewage pipe. Implementation was conducted by assessing the soil infiltration rate and developing and installing rain gardens and storage layers using crushed stones. These measures satisfied the initially set goals, drastically reducing runoff at all three sites. The target installation cost was set at 100,000 yen per cubic meter of runoff reduction. The target costs were met in the two Fukuoka sites but not at the Tokyo site. The key reasons were the high costs of removing non-permeable surfaces or improving the soil of compacted surfaces, which called for a process to balance the runoff reduction and cost to determine the most effective plan for implementing GI in urban areas. The development and implementation processes were conducted in collaboration with the house owners and concerned parties; the workshops produced constructive ideas being unconstrained by conventional thinking. Visitors highly appreciated ideas related to using water because the techniques were derived from the Japanese culture of lifestyle. Thus, introducing attractive and effective GI may be possible through collaboration. Additionally, sharing experiences led to the formation of new community ties, supporting post-implementation site maintenance. [ABSTRACT FROM AUTHOR]

Water pollution is one of the most serious aquatic environmental problems worldwide. In China, recent agricultural and industrial development has resulted in rapid changes in aquatic ecosystems. Here, we reveal the effects of water pollution on the phylogenetic community structure of aquatic macrophytes in the Tiaoxi River, China.We placed a rectangular plot at 47 sites within the Tiaoxi River from the mouth of the river to 88.5 km upstream, in which we recorded species abundance and measured 22 physico‐chemical variables. Bayesian phylogeny using the rbcL and matK gene sequences was employed to quantify phylogenetic α‐ and β‐diversity, and test the phylogenetic signal in four growth forms: emergent, floating‐leaved, free‐floating, and submerged. Within communities, water contamination and phytoplankton abundance decreased species richness and phylogenetic diversity, which resulted in phylogenetic clustering; species within communities were more closely related to each other than expected. Between communities, differences in geographical distance and phytoplankton abundance resulted in phylogenetic dissimilarity among plots. Aquatic macrophytes showed phylogenetic signals in which related species responded more similarly to disturbance. Thus, the observed patterns could be explained by environmental filtering and suggested that water pollution by human activity has added more filters to the existing environmental filters that drive the species assembly of macrophyte communities. [ABSTRACT FROM AUTHOR]

In this study, we collated the number of deaths caused by disasters that took place in the Chikugo River middle basin on the island of Kyushu, Japan, from the 1600s to 2017. The compilation of quantitative statistics of floods in Japan began in the modern era, while the statuses of previous disasters are described by vague indices and are thus difficult to quantify. In this study, we geographically restricted our investigation to the Chikugo River middle basin. We quantified the scale of each disaster by using the number of deaths recorded in historical documents. We then compared the disasters that took place in the area since the 1600s to identify the potential disaster risks harbored by our study area. During the period examined, the great famine from 1732 to 1733 was the greatest disaster and caused the most deaths. However, this is the only recorded famine for which fatalities were documented. Meanwhile, floods occurred frequently through this period, 26 of which resulted in fatalities: they had a total death toll of 292. Thus, famines occur infrequently but cause severe damage, whereas floods occur frequently but cause relatively minor damage. During the approximately 400 years examined, there were four floods with death tolls exceeding 30 people. Three of these occurred after 1868, when the modern era of Japan began. Meanwhile, there have been almost no small-scale floods during and after the modern era. By quantitatively assessing the disasters' scales, we were able to establish that the 2017 northern Kyushu torrential rainfall was the fourth gravest water-related disaster, in terms of its death, toll since the 1600s. If only the north bank of the Chikugo River middle basin is considered, it was the greatest flood disaster to occur in this period. [ABSTRACT FROM AUTHOR]

The Japanese archipelago extends over a large distance from north to south exposed to the effects of climate change. The aim of this study was to assess the impacts of climate change on environmental components by using hydrological indicators. The future climate change in the region was initially projected using HadGEM2-ES and MICRO5 models in three 20-year periods (2021–2040, 2041–2060 and 2061–2080), considering two representative concentration pathways (RCP4.5 & RCP8.5). The Kikuchi streamflow was then simulated using Soil and Water Assessment Tool modelling for the baseline (1986–2016) and future periods. Finally, the magnitude, duration, timing, and frequency of extreme flows were analysed using Indicators of Hydrologic Alteration software. The results showed a decrease in discharge under both models; however, a 2 m3/s increase was predicted under HadGEM2-ES (RCP4.5) in 2041–2060. Changes in river flow affect habitat suitability in aquatic ecosystems, and might have further impacts if the effects of water temperature are also considered. In our case study, water temperature was predicted to increase by up to 4 °C by 2080. This phenomenon will change habitat suitability, because important environmental flow components, such as the peaks of high flows and large flood frequency, will also increase. [ABSTRACT FROM AUTHOR]

Selecting sites for river restoration projects or performing ex post evaluation must be done in ecoregions with comparable biological integrity. Moreover, to evaluate the integrity of a river ecosystem that varies from the headwater to downstream regions, adjustments of the ecoregion according to the longitudinal change in biota must be made. We defined regions where biota are identical according to the direction of change along the stream path as “segment-based ecoregions.” We delineated segment-based ecoregions using fish fauna data for two ecoregions in Japan: the northeast Kyushu, and south Kyushu. The northeast Kyushu ecoregion was divided into three segment-based ecoregions, and south Kyushu ecoregion into five segment-based ecoregions. Classifying fish fauna within the same ecoregion enables classification by differences in the longitudinal change in the stream path rather than by differences in watersheds. Specific topographic regions such as the amphitheater areas of the south Kyushu ecoregion was classified as independent segment-based ecoregions. We further defined indicator fish species for each segment-based ecoregion. Indicator fish species reflected the fish fauna of each ecoregion in the midstream area, such as migratory Gobiidae of the south Kyushu ecoregion. Applying the segment-based ecoregion concept helps compare the biological integrity of fish fauna depending on a common environmental type between watersheds. [ABSTRACT FROM AUTHOR]

Both hydropower dams and global warming pose threats to freshwater fish diversity. While the extent of global warming may be reduced by a shift towards energy generation by large dams in order to reduce fossil-fuel use, such dams profoundly modify riverine habitats. Furthermore, the threats posed by dams and global warming will interact: for example, dams constrain range adjustments by fishes that might compensate for warming temperatures. Evaluation of their combined or synergistic effects is thus essential for adequate assessment of the consequences of planned water-resource developments. We made projections of the responses of 363 fish species within the Indo-Burma global biodiversity hotspot to the separate and joint impacts of dams and global warming. The hotspot encompasses the Lower Mekong Basin, which is the world’s largest freshwater capture fishery. Projections for 81 dam-building scenarios revealed progressive impacts upon projected species richness, habitable area, and the proportion of threatened species as generating capacity increased. Projections from 126 global-warming scenarios included a rise in species richness, a reduction in habitable area, and an increase in the proportion of threatened species; however, there was substantial variation in the extent of these changes among warming projections. Projections from scenarios that combined the effects of dams and global warming were derived either by simply adding the two threats, or by combining them in a synergistic manner that took account of the likelihood that habitat shifts under global warming would be constrained by river fragmentation. Impacts on fish diversity under the synergistic projections were 10–20% higher than those attributable to additive scenarios, and were exacerbated as generating capacity increased—particularly if CO2 emissions remained high. The impacts of dams, especially those on river mainstreams, are likely to be greater, more predictable and more immediately pressing for fishes than the consequences of global warming. Limits upon dam construction should therefore be a priority action for conserving fish biodiversity in the Indo-Burma hotspot. This would minimize synergistic impacts attributable to dams plus global warming, and help ensure the continued provision of ecosystem services represented by the Lower Mekong fishery. [ABSTRACT FROM AUTHOR]

Small scale hydropower energy goes a long way to fire up community development. Until 1920-30s, Japanese hydropower techniques had been established on a global level in each local area. However, after the second World War, the main energy resource was changed. This has resulted in a local decline in micro-hydro technical expertise and fewer waterwheel makers throughout Japan. At the present, we are going to work to re-make small scale hydropower technologies and markets. In this paper, we discuss and propose improvements to the “Japanese” small scale hydropower technology and production techniques, especially Pelton type wheel. The Pelton wheel technology of Nepal was freely available in the public domain so we decided to design a system based on that. We decided to designed by 3D-CAD and to make our Pelton buckets using a 3D printer. We compared the power generation capacity of our waterwheel with one purchased from New Zealand to investigate its effectiveness and efficiency. In our results of the experiment, the power generation curves for each turbine are approximately equal. The power increases continuously with increases in the flow rate. The maximum power generated by each turbine is approximately the same. This shows that it is possible to design a Pelton bucket that has a power generation efficiency comparable to a purchased bucket. The next step, the Pelton turbine designed in this study was chosen to be included in the Itoshima micro-hydro power generation system. So we scaled up and redesigned the Pelton turbine. In addition, we conducted a survey involving waterwheel makers regarding connecting to cost reduction. Using a 3D printer has the following advantages: 1.) Design deficiencies and failed designs can be identified at an early stage. 2.) Different forms of waterwheel can be made at low cost and in a short amount of time, which can then be used to run water experiments. [ABSTRACT FROM AUTHOR]

To break the ‘carbon lock-in’ mindset adopted by policy makers, the potential for mass rural remigration, as an alternative to the current trend of moving from rural to urban areas was examined. The capacity of renewable energy to maintain populations in hilly and mountainous farming regions was evaluated from two perspectives: (1) an average nationwide estimate based on the future energy demand, and (2) a conservative estimate based on the current energy demand. Because estimate (2) indicated that Hokkaido has a huge capacity, a preliminary cost effectiveness analysis was conducted first for: (A) a Supply to Tokyo scenario, and second for (B) a Local Demand Generation scenario. Both renewable energy exodus scenarios were found to have merit in promoting a sustainable future. [ABSTRACT FROM AUTHOR]

The article presents research which assessed the distribution patterns of Teleostei: Cobitoidea or loaches that are found in the River East Tiaoxi in China. The researchers performed a macroscale analysis of the geographical distribution of the species which they have segregated based on longitudinal alterations along the river course. The detailed evaluation found that two Vanmanenia species, V. stenosoma, L. tchangi and V. pingchowensis stayed in the lotic habitats while C. sinensis and C. laterimaculata preferred the lentic habitats.

Large-scale disasters, such as hurricanes, cyclones, tsunamis, and forest fires, have caused considerable damage in recent years. This study investigated two case studies of discontinuous open levees (kasumi-tei), which are a traditional Japanese river technology, on the Matsuura River at the sites of Okawano and Azame-no-se, and evaluated the advantages of these levees from the perspective of ecosystem-based disaster risk reduction (Eco-DRR). These case studies were conducted through literature surveys, flood observations, and oral interviews. The systems in both the cases were flood control systems utilizing ecosystem services. The traditional river technology (the flood plain open levee) served as an effective Eco-DRR in both cases. Additionally, the flood plain levee technology enhanced the ecosystem services at both sites, including not only flood control capabilities, but also other ecosystem services. Furthermore, the open levees offered substantial cost advantages over their alternatives. These results suggest that other traditional Japanese river technologies may also be effective in strengthening Eco-DRR. [ABSTRACT FROM AUTHOR]

Although many significant policies and legislation have been put forth by the Chinese government aiming toward "ecological civilization" for the aquatic environment, in practice, the situation is still undesirable. A pioneering multi-year study has since been conducted on the East Tiaoxi River (a major tributary of the renowned Yangtze River), focusing on fish distribution, influencing factors and habitat requirements, and river health as well. This revealed certain key species, hotspot protection areas, negative impacts of local anthropogenic activities, and inappropriate perceptions and practices of conservation and restoration. We found that not all fish species were equally conserved and that the supposedly ecological engineering measures were initiated without regard for ecological integrity. Our exemplary study appreciates scientific basis and truly ecological notion, and urgently advocates comprehensive and continuous basin-scale scientific investigation of fish biodiversity, and "ecological river"-oriented conservation and restoration action for the Yangtze River Basin and broader areas of China. [ABSTRACT FROM AUTHOR]

For the utilization of renewable energy from sources widely distributed in low-density non-urban areas the grid augmentation for its transmission to urban areas of high population density is often discussed under the premise that the present demand distribution remains invariant. Instead of grid augmentation, this study examined an alternative option of creating a power demand close to renewable sources and inducing population movements (i.e., Renewable Energy Exodus). First, the capacity of renewable energy to maintain populations in hilly and mountainous farming areas of Japan was evaluated from two perspectives: Task (1) a challenging nationwide balance based on possible energy demand saving scenario for the future, and Task (2) a conservative nationwide balance based on the current per capita energy demand and on the region-by-region generation–consumption matching concept. Because Task (2) indicated that Hokkaido, the northern-most island, has a huge capacity, Task (3) was conducted for Hokkaido by examining both energy balance and economic evaluation including job creation for the following two scenarios: (A) a supply to Tokyo scenario and (B) a local demand generation scenario, keeping the same conservativeness as Task (2) by using the current data for energy consumption per capita. The nationwide Renewable Energy Exodus estimates gave 48 million people for Task (1) (with the future per capita energy demand) and 10 million people for Task (2) (with the current per capita energy demand and region-by-region self-sustained balance), respectively. For Hokkaido Task (3) (with an additional economic assessment) gave 1 million people. The Renewable Energy Exodus concept combined with the green economy promotion was found to have a significant merit for a sustainable future of countries like Japan where economic and social disparities are serious between urban areas and non-urban areas. [ABSTRACT FROM AUTHOR]

In July 2009, the city of Fukuoka, Japan experienced a flood disaster along the Hii River, which runs through densely populated, concrete-covered areas of the city. The drainage system was overwhelmed and the river overflowed due to heavy rainfall and rapid runoff. The event led citizens in its watershed to plan and implement comprehensive flood control. The plan aims not only to mitigate floods but also to revitalize the river environment and populated communities in urban areas. This study reports the activities led by the citizens. They organized and carried out civic forums, workshops, and fieldwork to share views as to how the flood disaster was caused, how floods in the watershed should be controlled, and how the river environment should be rehabilitated. This study illuminates how people, including the flood victims and municipal engineers, can change drastically and communicate effectively in the course of discussing and implementing the comprehensive flood control measures.