Riverbed degradation and biodiversity loss downstream of dams are widely recognized; however, the extent to which tributaries with low sand availability can alter these impacts remains unclear. This study investigated longitudinal changes in environmental conditions and benthic macroinvertebrate communities in a dam-regulated river that receives inflow from a sand-poor tributary. Comprehensive surveys of water quality, plankton drift, riverbed substrate, and macroinvertebrates were conducted along the mainstem and the tributary. The results showed that immediately downstream of the dam, macroinvertebrate assemblages were dominated by lentic-associated filter feeders, such as Macrostemum radiatum and Spongillidae, due to increased plankton inputs and coarsened substrates. Downstream, tributary inflow partly altered these dam-associated conditions: dissolved oxygen increased, plankton densities decreased, and riverbed substrate shifted toward finer coarse material, supporting a rise in scraper taxa such as Heptageniidae. In contrast, inorganic case-bearing caddisflies did not respond, consistent with the tributary’s limited supply of coarse sand. The results indicate that even tributaries with low sand resupply may control certain dam-induced environmental changes and contribute to shifts in macroinvertebrate community structure; however, their influence remains constrained for sediment-dependent taxa. Understanding how sediment type shapes tributary effects is essential for managing ecological conditions downstream of dams.

Ecosystem-based Disaster Risk Reduction (Eco-DRR) is a new concept and yet to have a well-established classification system. While widely applied in developed countries, there is a pressing need to introduce and implement Eco-DRR in disaster-prone developing nations like Bangladesh. This approach could enhance the resilience while preserving environmental health of the country. The primary objective of this study is to classify existing Eco-DRR elements in Bangladesh based on their natural characteristics, geographical context, and disaster mitigation functions. The study results showed that the Eco-DRR of Bangladesh can be classified into four major groups: Coastal or Marine Eco-DRR, Inland Freshwater Eco-DRR, Terrestrial Forest Eco-DRR, and Manmade or Agri-based Eco-DRR for miscellaneous functions. This study proposes a reproducible methodological framework for the spatial classification of Eco-DRR elements, tailored to the deltaic context of Bangladesh. The emphasis of this research is to move beyond conceptual reviews by providing a spatially-explicit, functional classification that can be operationalized for disaster management. This study will help future research works on the Eco-DRR sector in Bangladesh and its neighboring countries.

Low-cost, robust multipoint velocity monitoring is essential for advancing watershed flood-management strategies. This study aims to validate the measurement principle of a low-cost, slit-type velocimeter by examining its internal physical mechanisms through computational fluid dynamics (CFD) analysis. First, the CFD model was validated against U-shaped flume experiments; high fidelity was confirmed, with both the afflux in front of the velocimeter and the internal pressure within the horizontal tube agreeing with experimental results within an error margin of 2

Abstract With the increasing frequency of extreme weather events driven by climate change, Nature-based Solutions (NbS) have attracted growing global attention; however, their engineering framework remains underdeveloped. This study defines river basin flood control as a two-tiered system—density management and energy management—and proposes an operational framework based on this structure. As an index for the first tier, density management, we introduce the spatio-temporal effective rainwater density $$\:{\rho\:}_{ster}={V}_{e}/(A\cdot\:{T}_{fd})$$ , where $$\:{V}_{e}$$ is the total volume of effective rainfall, $$\:A$$ is the catchment area, and $$\:{T}_{fd}$$ is the flood duration. Reducing $$\:{\rho\:}_{ster}\:$$ can be pursued by decreasing $$\:{V}_{e}$$ or extending $$\:{T}_{fd\:}$$ offering an interpretation of the “slowing the flow” concept advocated in NbS. The second tier, inundation flow control, addresses the management of kinetic energy and momentum of floodwater once inundation occurs. Based on these two tiers and three phases—conservation of soil structure, control of water mass and state, and control of flow energy and vector—ten technical elements for river basin flood control were identified and organized. Each element was drawn from physical laws, historical flood control practices, and the authors’ engineering experience. Water balance analyses of two Japanese flood events were compared using depth-equivalent values (mm). In the predominantly non-urban Kuma River basin, approximately 50% of total rainfall was retained as basin storage, whereas in the urbanized Zenpukuji River basin, approximately 18% was retained. In both basins, basin storage continued to increase until the cessation of rainfall, even under extreme precipitation. This result suggests that the functions of technical elements contributing to density management may not be entirely lost during heavy rainfall events. As flooding cannot be entirely prevented under climate change, inundation flow control technologies become increasingly important, and their effective implementation calls for co-creation with local communities.

Situated within one of the world's largest basins, the Ganges-Brahmaputra-Meghna (GBM), Bangladesh frequently experiences natural disasters due to itsgeomorphological setup. Situated along the southern edge of Bangladesh and open to the Bay of Bengal, this coastline experiences regular and diverse natural disasters. Owing to climate change, the coastline of Bangladesh is expected to become more vulnerable over time. Consequently, it is essential to understand the spatio-temporal dimensions of vulnerability and reinforce the resilience of coastal communities. This study utilized Remote Sensing and GIS techniques in combination with Multi-Criteria Decision Making (MCDM) and the Analytical Hierarchical Process (AHP) to establish a Coastal Vulnerability Index (CVI) of Bangladesh coast. AHP was conducted in ArcGIS version 10.5, using two geological parameters, five physical process variables, and three socio-economic parameters. Several thematic maps were created for each parameter using ArcGIS and reclassified according to vulnerability rankings. Ultimately, a CVI was developed, categorizing vulnerability into three classes: moderately vulnerable, vulnerable, and highly vulnerable. Results indicate that approximately 70 % of coastal areas are vulnerable, while 29 % area fall within moderate to high vulnerability zones. Around 1 % of the area in Khulna District, Satkhira District, and Char Fasson of Bhola District is classified as highly vulnerable. Considering the coastline, 28 km is highly vulnerable, 315 km moderately vulnerable, and 196 km vulnerable. This study will provide valuable insights for government officials, local administrators, coastal planners, and decision-makers in developing a risk management plan for sustainable long-term coastal management.

All raw data for "Tributary mitigates river discontinuity by dam depending on the distance from dam to the tributary confluence". The units of the variables were shown in the paper. "quadrate" means the number of each quadrate site in each study reach for measuring the variables.

本研究では，人吉市街地の堤内地に貯留・浸透及び氾濫流制御対策を講じた場合の支川のピーク流量及び浸水域の低減効果をシミュレーションにより評価した．田んぼダム（対象流域面積の1.4％），学校グラウンドと公園（対象流域面積の0.04％）を活用し雨水貯留を導入した場合，50年確率までの降雨に対して，山田川，西川内川，御溝川のピーク流量は現況より約1～8％低減し，福川ではさらに道路嵩上げ（総延長1.3km）を導入することで約51％低減した．氾濫域は，田んぼダム導入により30年確率までの降雨に対して低減し，さらにグラウンドや公園における雨水貯留及び道路嵩上げを局所的に導入することによって，50 年確率までの降雨に対して低減することができると推定された．

In recent years, climate change has led to an increased frequency and scale of heavy rainfall events, and subsequently, a rise in the occurrence of landslide induced by these rainfall events has been observed.Vegetation enhances slope stability by increasing soil strength through root systems.It is essential to quantitatively assess the influences that vegetation exerts on the occurrence of landslides and their depth to utilize vegetation to reduce disaster risk.Hence, in this study, we aimed to quantitatively evaluate the effects of vegetation diversity on the depth of landslides in the Aso region of Kumamoto Prefecture using statistical methods.We collected necessary data on topography, geology, vegetation, and rainfall and analysed them using a random forest.As a result of constructing the RF, the factors importance was the slope angle was the largest, followed by the landslide area, and the importance of vegetation was not large.As a result of creating partial dependence plots of the average landslide depth for each geology and vegetation type, the average landslide depth of secondary grasslands was approximately 20 cm smaller than that of broadleaf forests in all geological categories.This study could contribute substantially to future disaster mitigation efforts.

This study aims to obtain valuable insights into forest management that can reduce the risk of shallow landslides. We developed shallow landslide susceptibility maps (SLSMs) incorporating tree height and the relative spacing index as indicators of forest management for Cryptomeria japonica and Chamaecyparis obtusa plantations, focusing on the shallow landslides that occurred during the July 2012 Northern Kyushu heavy rain in the Aso region of Kumamoto Prefecture. We created SLSMs by developing a Random Forest model. The explanatory variables included tree height and relative spacing index, topography, geology, rainfall, and other factors totaling eleven factors. The area under the curve for the model was 0.94, indicating very high accuracy. The importance of the relative spacing index was comparatively low. The impact of forest management on shallow landslides was quantitatively assessed via a partial dependence plot for the relative spacing index. The results indicated that the relative spacing index that minimized the landslide probability was 23.7, below the cut-off value that distinguishes between landslide and non-landslide. In addition, the SLSMs indicated that implementing forest management with a uniform relative spacing index of 23.7 could reduce the ‘Very High' susceptibility area by 77.76 ha compared to the case without forest management. The threshold of the relative spacing index obtained in this study are crucial for future plantation forest management practices aimed at reducing the risk of shallow landslides.

Climate change has increased the frequency and scale of heavy rainfall, increasing the risk of shallow landslides due to heavy rainfall. In recent years, ecosystem-based disaster risk reduction (Eco-DRR) has attracted attention as one way to reduce disaster risks. Vegetation is known to increase soil strength through its root system and reduce the risk of shallow landslides. To reduce the risk of shallow landslides using vegetation, it is necessary to quantitatively evaluate the effects that vegetation has on shallow landslides. In this study, we constructed a generalized linear model (GLM) and random forest (RF) model to quantitatively evaluate the impact of differences in the vegetation, such as grasslands and forests, on the occurrence of shallow landslides using statistical methods. The model that resulted in the lowest AIC in the GLM included elevation, slope angle, slope aspect, undulation, TWI, geology, and vegetation as primary factors, and the hourly rainfall as a trigger factor. The slope angle, undulation, and hourly rainfall were selected as significant explanatory variables that contribute positively to shallow landslides. On the other hand, elevation and TWI were selected as significant explanatory variables that contribute negatively to shallow landslides. Significant differences were observed among multiple categories of vegetation. The probability of shallow landslide in secondary grasslands was approximately three times that of coniferous and broadleaf forests, and approximately nine times that of broadleaf secondary forests. The landslide probability of shrubs was approximately four times that of coniferous and broadleaf forests, and approximately ten times that of broadleaf secondary forests. The results of constructing the RF model showed that the importance was highest for the hourly rainfall, followed by geology, then elevation. AUC values for the GLM and RF model were 0.91 and 0.95, respectively, indicating that highly accurate models were constructed. We quantitatively showed the impact of differences in vegetation on shallow landslides. The knowledge obtained in this study will be essential for considering appropriate vegetation management to reduce the risk of future shallow landslides.

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.

海・河川域双方を生息場とする通し回遊魚3種(カマキリ,シマウキゴリ,スミウキゴリ)を対象に,海・河川水温を加味した気候変動による影響を評価した.1980年代~2010年代の水温の公共観測値を1級水系ごとに整理し,沿岸・河川河口域の月別の平均値と変動勾配を得た.水温を含む生息環境条件を説明変数とし,生息有無を評価するモデルを構築し,変数の重要度を比較した.また,構築したモデルで将来の想定水温での生息可能性を評価した.その結果,カマキリ,スミウキゴリでは2月海水温,シマウキゴリでは4月河川水温が生息確率へ最も強く影響する水温に抽出された.水温の変動勾配は海域(+1.29℃/100yrs)よりも河川河口域(+3.93℃/100yrs)で大きく,将来の想定水温では3種ともに河川水温上昇による制限がより強いことが示唆された.

本研究では,熊本県白川水系黒川流域を対象に,機能分離型田んぼダム導入による本川への流出抑制及び浸水軽減効果,水田地区ごとの流出抑制の特徴をシミュレーションにより推定した.その結果,水田1,687ha(流域水田の32%)に田んぼダムを導入した場合,10年,30年,50年確率に対しては50mmの流出孔が最も本川への流出抑制効果を発揮し,50年確率降雨に対してピーク流量を33.7m³/s(5%),浸水域を54ha(7.1%)低減させる効果があると評価された.また,各水田地区における流出抑制効果は,地形勾配,背水の有無が関与し,背水がなく地形勾配が大きいほど1ha当たりのピークカット量は大きいと推定された.

Bangladesh is a small developing country in South Asia with a densely populated crisis and is prone to several natural hazards.Due to climate change, the frequency of devastating events increasing.Coastal low-lying poor people are the worst victim of severe cyclones.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 have been taken to quantify the capacity of an existing Pandanus Forest on Saint Martin's Island to reduce the storm surge disaster risk.For this, historical data were collected and processed with ArcGIS software, and mean wind speed and cyclonic average wind were analyzed to determine the reduction of wind speed by Pandanus trees.Average storm wind speed was analyzed using the IDW interpolation method.The results showed that the average wind speed faced during a cyclone was 11-15 km/hrs and Pandanus trees can reduce the wind speed by almost 52%, which ultimately protect the island and helped the wind speed range around 7 km/hrs.

本研究は, 多くの人的被害が生じた令和2年7月球磨川豪雨時の御溝川流域に着目した人吉市市街地の氾濫状況及び人的被害の要因を明らかにするため,氾濫シミュレーションによる当時の再現及び地域住民に対するヒアリングを行った.その結果,御溝川周辺では最大浸水深2.7m,最大流速2.4m/sの氾濫被害が生じている場所があったことが明らかとなった.また,御溝川流域では,山地谷筋を流下する河川からの氾濫や水田地域に整備された道路が横堤防の役割を果たしたことが確認された.さらに,御溝川周辺の犠牲者5名の被災場所の豪雨時の氾濫状況を推定した結果,南から球磨川,北から御溝川,西から福川の3方向の氾濫流が発生していたこと,水中歩行が可能な浸水深・流速限界以下であっても犠牲者が発生する危険性があることを示した.

堤体高 15 m を越えるハイダム撤去に対する河口域の生態系の応答を調査した事例は世界的に限られている．本研究では荒瀬ダム撤去前に該当する 2011 年から撤去後の 2018 にかけて調査を行い，球磨川水系の河口域の底質と生物相の変化を評価した．調査期間の秋季と春季に調査を計 14 回実施し，球磨川と前川に設置した 178 定点が調査された．このうち，本研究では 138 定点を解析に使用した．底質変化の指標として，調査定点のシルトと粘土の割合を算出した．結果，2012 年の春と 2014 年の春にそれぞれ粗粒化が認められた．これらの粗粒化は主に 2010 年の荒瀬ダムゲートの開放と 2011 年の大規模出水と関連すると考えられる．底生生物群集の変動を解析した結果，定点ごとの生物相の変動は，特定の調査時期，あるいは季節性に基づかないことが示唆された．この結果から，ダム撤去が河口域の底生生物群集に与えた影響は決して大きくなかったと考えられる．一方，球磨川と前川の両河川では内在性種が 2012 年の秋季から 2013 年，あるいは 2014 年の秋季にかけて顕著に増加した．同時期に，内在性種のアナジャコとニホンスナモグリ，およびこれらの巣穴を利用する共生種の出現定点数の増加が認められた．アナジャコとニホンスナモグリは砂泥質，および砂質環境に生息するため，底質の粗粒化が本種らの生息地の拡大を促進した可能性が示唆される．しかしながら，本調査を開始する前には河口域で底質のかく乱が既に観測されている点，本調査域では河川改修や自然再生事業に伴い直接的な土砂の投入が行われている点などから，本研究で観察された底生生物の出現パターンの変化が荒瀬ダム撤去とどの程度直接的に関係しているのかは十分に検証できていない．この関係を明らかにするために，今後，荒瀬ダムの堆積土砂の動態を評価すべきであろう．

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.