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

The Red River dike system was built, and an emergency solution was implemented to protect Hanoi Capital city from flood disasters. In the solution, floodwater from the Red River is discharged through the Van Coc Gate, with an overflow point into Van Coc Lake, and is drained downstream through the Day Weir. However, an optimal scenario for the operating procedure of the emergency solution, based on a comprehensive evaluation of the flood risk level from the Red River to the residential areas located outside the protected areas of the dike system, has not been adequately addressed to date. In this study, we employed the latest digital elevation map in a high spatial resolution for the first time, and a two-dimensional depth-integrated hydrodynamic model was utilised to obtain the optimal operation for the emergency solution. The optimal scenario was determined to minimise the flood risk level to the residential areas and optimise the inflow discharge at the Van Coc Gate and the overflow point, and the outflow discharge at the Day Weir for ensuring the safety of the operating system. This study lays a promising foundation for designing risk-reduction strategies in Hanoi Capital.

DOI： 10.1111/jfr3.12661

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

DOI： 10.1061/(ASCE)WW.1943-5460.

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

Ho Chi Minh City gets severely inundated by upstream flooding and a combination of rising spring tides and rain, owing to the combined impacts of rapid urbanization and sea level changes. A sea dike to close Can Gio Bay has been proposed to regulate storage and control water levels in the drainage and sewer system of Ho Chi Minh City. However, this proposed sea dike and different gate operating modes could significantly change the hydrodynamic regime in Can Gio Bay. In this study, a two-dimensional hydrodynamic model was developed to assess changes in the hydrodynamic regime after construction of the sea dike, including fluctuations in the inundated areas in Can Gio Bay mangrove forests. The results show that sea dike construction is an effective solution for controlling water levels and reducing inundation, especially considering a sea level rise scenario in the year 2050. Further, the gate operation mode also affects the effectiveness of inundation reduction, which is approximately 10% better than the same sea dike type without gate operation. However, the sea dike was less effective in a sea water level rise scenario in 2100 for all scenarios.

DOI： 10.1080/21664250.2019.1579460

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

Located at the downstream end of the Dong Nai-Saigon river basin, near the mouth of the Saigon River, which is known as the "green lungs" of Ho Chi Minh City (HCMC) due to the ecosystem functions of the Can Gio mangrove forest, is a very complex hydrodynamic and geomorphic region with crossing estuaries, forming the so-called Can Gio Bay. Given its flat, low-lying topography, this area is strongly influenced by two main factors: (1) upstream flooding and (2) tidal regimes. The historical flood event of 2000 indicated that the downstream region of HCMC suffers from serious flooding, and that the Can Gio area is the worst affected, with approximately 90% of its area being inundated. This research aims to investigate the impact of tides and inflows in Can Gio Bay in the context of sea level rise and a sea dike structure connecting Go Cong to Vung Tau. A two-dimensional hydrodynamic model combined with a wetting and drying scheme is used to determine the locations of inundated areas. This research also shows how sea level rise and upstream flows cause flooding in Can Gio Bay, and identifies the negative and positive impacts of sea dike construction on Can Gio Bay.

DOI： 10.6090/jarq.52.229

Publisher：Paddy and Water Environment  

The Yamadazeki Barrage, located in Fukuoka Prefecture, Japan, is an oblique weir that was constructed at the middle reach of the Chikugo River in 1790 and is still operational. The weir was recognized as a World Heritage Irrigation Structures by the International Commission on Irrigation and Drainage. This study used hydraulic analyses of the Yamadazeki Barrage to understand its function. Two-dimensional shallow water equations were utilized for the hydraulic analyses, and the calculated velocity distribution under ordinary flow conditions (approximately 40 m3/s) showed good agreement with the measured data. In addition, the bedload transport rate was calculated from the water velocity and depth distributions using the Ashida-Michiue formula to simulate riverbed variations. The results suggested that there was slight erosion and deposition in the vicinity of the weir under ordinary flow conditions. In contrast, under flood flows of approximately 3500 m3/s, riverbed variations occurred in most of the calculation area, with extensive erosion and deposition of more than 2.0 m over 24 h. To reevaluate the structural functions of the Yamadazeki Barrage, elimination scenarios of both the Southern Ship Way and the Sand Sluiceway, which are considered important sand removers, were determined and analyzed. These scenarios revealed that the flow became unstable, and riverbed variations were significant. Therefore, these structural elements stabilized the water flow and maintained a safe and reliable water withdrawal. Additionally, the relevance of the weir structures, which was carefully calculated and designed to match the river flow rate and water level, was evaluated numerically.

DOI： 10.1007/s10333-023-00956-4

Web of Science

Scopus

Language：Japanese   Publisher：Faculty of Agriculture, Kyushu University  

本研究では，東南アジア新興諸国のようにデータが寡少な地域でも適用可能で，将来的な地域開発や気候変動に対する流出量の長期的変化を予測可能な降雨流出モデルの開発を目的とし，対象流域として，ベトナム南部に位置するCan Don流域を選択し，降雨の時空間的な不均一性や将来的な土地利用変化を反映可能なモデルとするため，分布型降雨流出モデルを構築した．さらに，分布型降雨流出モデルのメッシュサイズが計算流量に及ぼす影響にも着目し，7 種類のメッシュサイズを用いた流出解析を行い，それぞれの降雨流出特性や地形特性との関連から検討した．これらの結果を踏まえて，対象流域における最適メッシュサイズを提案した．まず，対象流域の流域境界，標高，土地利用，降雨量，貯水池流入量のデータを入手し，分布型降雨流出モデルへの入力データを作成した．この際，メッシュサイズの違いによる計算流量への影響を比較するため，450m，900m，1800m，2700m，3600m，4500m，9000mの7種類のメッシュデータを作成した．土地利用面積をより的確に反映させるため，流域を表現した各メッシュには森林，水田，畑地，市街地の土地利用別タンクモデルを導入した．さらに安定的な基底流成分を表現するため，流域全体に1つの流域地下水タンクを設けた．メッシュ間の雨水流動モデルの基礎方程式にはKinematic Wave法を採用し，運動方程式と連続式より，対象流域の貯水池流入量を日単位で計算した．計算期間は，各種データが揃った2004年～ 2010年の7年間とし，1年間ごとに流出計算を行った．降雨流出特性を調べた結果，大きく三つのことが分かった．一つ目に1 間の流量波形は450m〜4500mではほぼ変化せず，9000mで変化が目立ったこと．二つ目に，ピーク流量は，450m 〜 4500m で微小に減少し，4500m から9000mにかけての減少が大きくなっているということ．三つ目に，メッシュサイズによる累積流量の差はほぼないということである．また，計算時間はメッシュサイズが小さい程飛躍的に増大するということが分かった．以上の結果を踏まえて，計算時間も短く，1年間の流量波形，ピーク流量，総流量も適切に表現可能である4500mメッシュでの計算がCan Don流域においては最適と言える．以上のように本研究では，分布型降雨流出モデルに土地利用別タンクモデルを導入することで，東南アジアのデータ寡少地域で，降雨量，標高，土地利用といった少ないデータで流出量を計算できるモデルを開発できた．入力データを変えることで，他のデータが寡少な地域にも適用可能な，汎用性があるモデルが構築できたと言える．また，本モデルは，メッシュサイズにかかわらず，各土地利用の割合を一定に保つことができるので，450m〜4500mまではメッシュサイズの影響はほぼ受けず，流出解析を行うことができるとわかった．今後の課題としては，次の二点が挙げられる．まず，本研究の対象流域では観測降雨データは日データしか得ることが出来なかったので，洪水時の降雨流出特性を検討するためには時間データの比較検討が必要である．二つ目に，本研究では精度の高い観測流量が得られず，メッシュサイズによる流量再現精度の検討ができなかったので，精度が高い観測データが得られる流域での検討を通じ，メッシュサイズが分布型降雨流出モデルに及ぼす影響についてより詳しく検討し，再現精度がより高いモデルの構築を目指す．

DOI： 10.15017/6796278

CiNii Research

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

Language：Japanese   Publisher：Faculty of Agriculture, Kyushu University  

In this study, the accuracy of satellite meteorological data was firstly evaluated, and a bias correction method was developed to apply these satellite meteorological data to the rainfall-runoff analysis in scarce-data watersheds of southeast Asia. The Sai Gon-Dong Nai river basin located in the southern part of Vietnam and the lower Chao Phraya river basin in Thailand were the target watersheds for the evaluation of satellite data, and the Thac Mo basin, which is a sub-basin of the Sai Gon-Dong Nai river basin, was the target of rainfall runoff analyses. The error indices of mean absolute error, root mean square error, percent bias and correlation coefficient were calculated for 5 types of rainfall satellite data and 2 types of evapotranspiration satellite data. As a result, the IMERG was selected for rainfall and the AgMERRA was selected for evapotranspiration as the data with high estimation accuracy. Next, based on the results of evaluation using the spatial distribution index SPE and the spatial mapping, the AgMERRA and the MSWEP were selected for rainfall and the AgMERRA was selected for evapotranspiration as highly compatible data for the spatial distribution pattern The bias correction using the percent bias was performed on these satellite data, and as a result of using them as input values for the distributed rainfall-runoff model incorporating the tank models for several land utilizations, good simulation accuracy could be obtained. It was concluded that the satellite data with high estimation accuracy to ground-based observation data could be sufficiently applied to rainfall-runoff analysis, and that the satellite data that had high compatibility with the spatial distribution pattern of ground-based observation data could be also applied to rainfall-runoff analysis by introducing the bias correction.

DOI： 10.15017/4797837

CiNii Research

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

DOI： https://doi.org/10.1007/s10333-021-00883-2

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

DOI： https://doi.org/10.1007/s10333-021-00874-3

Publisher：Paddy and Water Environment  

To effectively manage a eutrophic reservoir, short-term predictions of algae class-differentiated chlorophyll a (Chl-a) were conducted. The study adopted a three-layered feedforward artificial neural network using discrete water environment datasets collected through weekly observations from May to November over seven years (2012–2018). This network was constructed using supervised learning, and the available datasets of a certain observation day were set as the input variables to determine the total Chl-a, Chlorophyceae Chl-a, and cyanobacteria Chl-a that would exist after one week. From the viewpoint of the simplification of the network’s complexity to suppress overfitting, input variables were carefully selected by identifying the important variables related to the seasonal changes in Chlorophyceae and cyanobacteria and eliminating the duplicated expressions of water-quality parameters. However, network downsizing was found insufficient to suppress overfitting. To improve prediction accuracy, dropout was introduced, which stochastically deactivated some nodes in the input and hidden layers in the learning process. The analysis results showed that sufficient short-term predictions of total Chl-a and Chlorophyceae Chl-a may be achieved. The insufficient prediction accuracy of cyanobacteria Chl-a may be overcome using meteorological data as close as possible to the desired prediction day. Consequently, this model may serve as a useful tool for the management of eutrophic reservoirs because short-term predictions of the dominant phytoplankton can be achieved, and the necessary mitigation measures may be accordingly planned.

DOI： 10.1007/s10333-021-00874-3

Web of Science

Scopus

Publisher：Paddy and Water Environment  

This study focuses on a method for improving water quality via anoxification recovery using underwater LED treatment in an organically polluted reservoir. The main aim was to evaluate the effects of the optical spectrum and light intensity of LED irradiation on the maintenance of healthy aerobic conditions, as well as anoxification recovery, by promoting oxygen production via phytoplankton photosynthesis. Water quality was monitored via beaker and water tank experiments while using LED irradiation for 24 h (12 h on/12 h off) for 2 months in anoxic water, where the anaerobic decomposition of organic matter progressed under strong reductive conditions. As a result, red–green–blue (RGB) light was advantageous for promoting rapid oxygen production by phytoplankton photosynthesis compared with the mixed red and blue light. In particular, LED irradiation, including the green color, preserved the healthy dissolved oxygen environment without lowering the oxygen level in the dark. In addition, RGB irradiation (R:B:G = 1:1:1) did not only assist in preserving a healthy aerobic state in spite of low light intensities but also evidently decreased concentrations of total nitrogen and total phosphorous. In conclusion, the spatial effect of water quality improvement via LED irradiation was not limited to the vicinity of the light source but was applicable to a wide range, in which the light intensity contributed to one-fifth of the optimum photon intensity for phytoplankton photosynthesis.

DOI： 10.1007/s10333-021-00883-2

Web of Science

Scopus

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

Repository Public URL： http://hdl.handle.net/2324/4363557

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

Language：English   Publishing type：Research paper (international conference proceedings)  

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

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

Language：English   Publishing type：Research paper (international conference proceedings)  

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

Language：English   Publishing type：Research paper (international conference proceedings)  

DOI： 10.3850/38WC092019-1240

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

Van Coc Lake located in the Dan Phuong and Phuc Tho, Hanoi, Vietnam, has an area of 30.83 km2. It is usually dry and includes arable land and residential areas. However, to protect Hanoi City from catastrophic floods, in emergency situations, it receives the floodwater from the Red River as a regulating reservoir and drains the floodwater to the downstream Day River through the Day Weir. We performed numerical simulations to assess the movement of floodwater in this lake and evaluated the impact of floodwater on its residential areas. A two-dimensional depth-integrated hydrodynamic model was constructed to simulate inundation in this lake. The model was validated and the effects of Manning's coefficient of roughness were examined. In case of emergency, it has to receive an inflow of 2,500 m³/s into the area. Inflow rates of 1,200 and 600 m³/s were also examined to compare the results. The simulation results indicate that this lake was entirely inundated in 13, 28, and 56 h by inflow rates of 2,500, 1,200, and 600 m³/s, respectively. Between 66% and 99% of residential areas were inundated. The areas with highest velocity were primarily focused behind the gate with a velocity of 1.5-1.8 m/s.

DOI： 10.6090/jarq.53.181

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

Water scarcity and flooding constitute major problems for developing countries located within the tropical climatic region of Southeast Asia. In addition, regional water consumption is increasing, and water usage patterns have been changing recently. Therefore, an advanced water resource management framework that considers both water supply and flood control is needed. Multipurpose reservoirs are widely used to manage water resources efficiently; however, water-related problems occur with reservoirs in Southeast Asian watersheds because of inadequate operation rule curves. We developed a method for constructing optimal operation rule curves for Dau Tieng Reservoir, which is one of the largest multipurpose reservoirs in Vietnam. The reservoir is used for flood control, domestic water supply, industrial uses, environmental flows, and agricultural uses, in the order of priority. The operation rule curves of the Dau Tieng Reservoir comprise five reference water levels: the retarding water level, upper water level, lower water level, critical water level, and dead water level. Water release from the reservoir is determined based on the relationship between the reservoir level and the rule curves. In this study, the rule curves were newly determined using the shuffled complex evolution method of the University of Arizona (SCE-UA method). The objective function for optimization was defined by focusing on the improvement in insufficient supply for agricultural uses and environmental flow downstream of the Dau Tieng Reservoir. Inadequate solutions were prevented by introducing penalty functions into the objective function. Experimental results indicate that the proposed optimization method efficiently searches for optimal rule curves.

DOI： 10.1007/s10333-019-00711-8

Language：English   Publishing type：Research paper (international conference proceedings)  

Ho Chi Minh City gets severely inundated by upstream flooding and a combination of rising spring tides and rain, owing to the combined impacts of rapid urbanization and sea level changes. A sea dike to close Can Gio Bay has been proposed to regulate storage and control water levels in the drainage and sewer system of Ho Chi Minh City. However, this proposed sea dike and different gate operating modes could significantly change the hydrodynamic regime in Can Gio Bay. In this study, a two-dimensional hydrodynamic model was developed to assess changes in the hydrodynamic regime after construction of the sea dike, including fluctuations in the inundated areas in Can Gio Bay mangrove forests. The results show that sea dike construction is an effective solution for controlling water levels and reducing inundation, especially considering a sea level rise scenario in the year 2050. Further, the gate operation mode also affects the effectiveness of inundation reduction, which is approximately
10% better than the same sea dike type without gate operation. However, the sea dike
was less effective in a sea water level rise scenario in 2100 for all scenarios.

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

In closed water bodies with significant organic pollution, anoxification due to thermal stratification leads to the elution of nitrogen and phosphorus from the bottom sediment and the generation of sulfide, resulting in further degradation of the water environment. This study focuses on the water quality dynamics in an organically polluted reservoir exhibiting long-term anoxification using two approaches: (1) field observations of seasonal changes in vertical profiles of dissolved oxygen, nitrogen, phosphorus, and sulfide and (2) construction of a water quality prediction model based on an ecosystem model incorporated with anaerobic biochemical processes. Iron and sulfate reduction occurred simultaneously because nitrate–nitrogen was reduced by denitrifying bacteria after the anoxification, and iron reduction became the main factor of the increase in ammonium–nitrogen and phosphate–phosphorus. The redox state of the bottom sediment surface, when anoxification began to occur, greatly affected the water quality dynamics caused by gradual reductive reactions under anaerobic conditions. Furthermore, the calculation accuracy of ammonium–nitrogen, phosphate–phosphorus, and sulfide was highly improved by modifying the conventional model based on the field observations. The characteristics of water quality under anaerobic conditions were sufficiently reflected in the upgraded ecosystem model. The proposed water quality prediction model could be used to quantitatively estimate the water environment dynamics in organically polluted water bodies. The model could be developed further in the future to solve the problems caused by long-term anoxification.

DOI： 10.1007/s10333-018-0659-6

Language：English   Publishing type：Research paper (international conference proceedings)  

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

DOI： 10.1007/s10333-017-0600-4

Language：English   Publishing type：Research paper (international conference proceedings)  

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

In this study, numerical simulation of a two-dimensional convective-dispersive model in Hakata Bay, Japan, is performed to analyze the impact of major river discharges due to torrential rain in Fukuoka City. Tank models are applied to calculate river discharges, which are taken into consideration as river inflow in the hydrodynamic model of Hakata Bay. A two-way nesting “edge” technique is developed and applied in the model in order to consider the influence of narrow and complex geographical features. The area around “Island City” and Imazu Bay are calculated in high resolution. The resulting model has high reproducibility since the calculated river discharges, tidal current, and salinity show good agreement with observed data. To analyze the impact of large river discharges, the calculation period is set from 11 September 2002 to 21 September 2002 since there was torrential rain on September 16 in the given year in Fukuoka City (163.5 mm/d). The results show that low-salinity water covered the whole of the inner part of Hakata Bay, and water of lower salinity than outer sea water (<34.0 psu) spread out to the bay’s mouth two days after the torrential rain event. Fresh water covered the entire area of Imazu Bay and flowed out from the mouth of the Bay after the torrential rain event. The behavior of fresh water after a few days of torrential rain was remarkably different from normal discharge river flow. These results indicate that the environment in Imazu Bay can be degraded severely by torrential rain. Therefore, countermeasures to protect ecosystems in Hakata Bay must be examined immediately.

DOI： 10.4236/jwarp.2017.96036

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

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

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

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

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

DOI： 10.7763/IJESD.2015.V6.568

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

DOI： 10.4236/jwarp.2015.71003

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

DOI： 10.1016/j.ecoleng.2013.04.018

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

Event date： 2022.11

Language：English   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2022.11

Language：English   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2022.10

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2022.8 - 2022.9

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2021.10

Language：English   Presentation type：Oral presentation (general)  

Venue：Web開催   Country：Japan  

Event date： 2021.8 - 2021.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：Web開催   Country：Japan  

Event date： 2021.8 - 2021.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：Web開催   Country：Japan  

Event date： 2021.8

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：Web開催   Country：Japan  

Event date： 2020.11

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：Web開催  

Event date： 2020.8

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：Web開催  

Event date： 2019.11 - 2022.11

Language：English   Presentation type：Symposium, workshop panel (public)  

Venue：Vietnam National University of Agriculture   Country：Viet Nam  

Event date： 2019.11

Language：English   Presentation type：Symposium, workshop panel (public)  

Venue：Vietnam National University of Agriculture   Country：Viet Nam  

Event date： 2019.11

Language：English   Presentation type：Symposium, workshop panel (public)  

Venue：Vietnam National University of Agriculture   Country：Viet Nam  

Event date： 2019.11

Language：Japanese   Presentation type：Symposium, workshop panel (public)  

Venue：Vietnam National University of Agriculture   Country：Viet Nam  

Event date： 2019.11

Language：English   Presentation type：Symposium, workshop panel (public)  

Venue：Vietnam National University of Agriculture   Country：Viet Nam  

Event date： 2019.11

Language：English   Presentation type：Symposium, workshop panel (public)  

Venue：Vietnam National University of Agriculture   Country：Viet Nam  

Event date： 2019.11

Language：English   Presentation type：Symposium, workshop panel (public)  

Venue：Vietnam National University of Agriculture   Country：Viet Nam  

Event date： 2019.11

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：島根大学   Country：Japan  

Event date： 2019.11

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：島根大学   Country：Japan  

Event date： 2019.11

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：島根大学   Country：Japan  

Event date： 2019.9 - 2020.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：東京農工大   Country：Japan  

Event date： 2019.9

Language：English   Presentation type：Oral presentation (general)  

Venue：東京農工大   Country：Japan  

Event date： 2019.9

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2019.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：東京農工大   Country：Japan  

Event date： 2019.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：東京農工大   Country：Japan  

Event date： 2019.9 - 2019.6

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：東京農工大   Country：Japan  

Event date： 2019.9

Language：English   Presentation type：Oral presentation (general)  

Venue：Panama city   Country：Panama  

Event date： 2018.9

Language：English  

Venue：Yogyakarta   Country：Indonesia  

In this study, a numerical simulation consisting of a two-dimensional model of Hakata Bay, Kyushu Island. Japan, was conducted to analyze the impact oflarge river discharges due to torrential rain. Since Fukuoka city, one of the largest cities in Japan, surrounds Hakata Bay, the bay has a very complex environment, including an artificial island (Island City) in its eastern region and small bay (Imazu Bay) where tideland is spread with rich ecosystems in its western region. Tank models were applied to calculate the discharges of the 38 rivers that flow into Hakata Bay, and a two-way nesting technique, "edge nesting," was developed and applied in the model to capture the influence of complex geographical features, such as the Island City area and the Imazu Bay area, which were nested with a high-resolution mesh. The model accurately reproduced the observed tidal current and salinity data. To simulate the behavior oflarge river discharges, a historical simulation period including a torrential rain event (163.5 mm/d) was input into the model. The results showed that after the rain event, low-salinity water covered the entire inner part of Hakata Bay, and freshwater covered the entire area of the tidal flats and flowed out from the mouth of Imazu Bay. The behavior of this large mass of fresh water was remarkably different from usual discharge river flow. These results indicate that the environment in the bay can be significantly changed by torrential rain events.

Event date： 2018.9

Language：English  

Venue：Yogyakarta   Country：Indonesia  

Anoxic conditions, occurring in enclosed water bodies from an overabundance of organic matter, cause further deterioration of the aquatic environment through nutrient elution and hydrogen sulfide production. The quantises of biochemical reactions under anaerobic states, such as denitnfication, iron reduction and sulfate reduction are important research topics when considering conservation and improvement of water quality environment. This study involved regular observations for two years in the reservoir, in which overabundant organic matter was prominent due to humic acid, to evaluate the water quality dynamic near the bottom during long-term anoxic periods. Based on the temporal changes of dissolved oxygen, nitrate-nitrogen, ammonia-nitrogen, phosphate-phosphorus, sulfide, total iron ions, and sulfate, this study focused specifically on the influence of the redox state of the sediment surface during the early stage of thermal stratification on the anaerobic biochemical reactions. As a result, nitrate-nitrogen started to decrease to zero due to denitnfication as soon as the anoxic state occurred, and then both ammonia-nitrogen and phosphate-phosphorus increased linearly with time due to iron reduction after nitrate-nitrogen had decreased to zero. Sulfide began to increase linearly due to sulfate reduction as soon as nitrate-nitrogen disappeared. Also, the initial redox state of sediment impacted on the change characteristics of phosphate-phosphorus, ammonia-nitrogen and sulfide in the points of increasing timings, duration, and rates. It was concluded that our results would provide important finding about the mechanisms of aqueous environmental deterioration due to organic pollution as well as beneficial information for the modification of water quality prediction model.

Event date： 2018.9

Language：English  

Venue：Yogyakarta   Country：Indonesia  

We propose a new long-term rainfall-runoff model for a Southeast Asian watershed. To reflect the impact of land use changes associated with rural development, and the nonuniformity of rainfall in tropical regions, a mesh-based distributed runoff model was constructed. Four tank models (paddy, upland field, urban, and forest) were incorporated into each mesh element, to capture the outflow from different land uses. Each mesh element was connected to the river network to reproduce the rainfall-runoff flow processes. By incorporating a watershed groundwater tank, we improved the representation of the baseflow component which is important in long-term runoff analysis. To shorten the calculation time and improve the application to other watersheds, we introduced an inflow/outflow matrix that defines the direction of rainwater flow between adjacent mesh elements. The model was applied to the Dau Tieng watershed in Southern Vietnam, with an area of 2,700 km
²
. The model was run for the period 1999-2009, and the calculated discharge was compared with the observed values, and a good model fit was achieved. As the model represents the flow processes from rainfall to river discharge with highly versatile tank models, it can be applied to watersheds where hydrological data for model verification are scarce, which is a common issue for many developing countries in Southeast Asia.

Event date： 2018.8

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：ホテル法華クラブ仙台（宮城）   Country：Japan  

Event date： 2017.10

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：ジェイドガーデンパレス（鹿児島）   Country：Japan  

Event date： 2017.10

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：ジェイドガーデンパレス（鹿児島）   Country：Japan  

Event date： 2017.8

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：日本大学（東京）   Country：Japan  

Event date： 2017.8

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：日本大学（東京）   Country：Japan  

Event date： 2017.8

Language：English   Presentation type：Oral presentation (general)  

Venue：日本大学（東京）   Country：Japan  

Event date： 2017.8

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：日本大学（東京）   Country：Japan  

Event date： 2016.10

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：ジェイドガーデンパレス（鹿児島）   Country：Japan  

Event date： 2016.9

Language：English   Presentation type：Oral presentation (general)  

Venue：伊都キャンパス   Country：Japan  

The purpose of the present study is a close examination of the relation between water environment quality factors and bivalve catch volumes in the Ariake Sea, and a quantitative assessment of the effect of changes over time in the water environment on fishery stock. To this end, we focused on hierarchical neural network modeling to build a bivalve catch volume estimation model based on the related factors of organic contamination and eutrophication. The model showed a good result for estimating Asari clams (see Fig.1). Furthermore, we used this model in a sensitivity analysis to assess the effect of changes in the marine environment of the Ariake Sea on bivalve catch volumes. Results suggested that the primary cause of reduced catch volumes for the Asari clam (Ruditapes philippinarum) in recent years are increased transparency and excessive COD reduction in the Kumamoto Prefecture coastal waters as shown in Fig.2 and Fig.3, respectively. On the other hand, this report does not as yet have a clear conclusion as to the reasons behind the trends of increased water transparency and reduced COD in the Ariake Sea at the Kumamoto Prefecture coast. These changes in water quality are a subject for future investigation.

Event date： 2016.8 - 2016.9

Language：English   Presentation type：Oral presentation (general)  

Venue：ホテル法華クラブ仙台（宮城）   Country：Japan  

Event date： 2016.8 - 2016.9

Language：English   Presentation type：Oral presentation (general)  

Venue：ホテル法華クラブ仙台（宮城）   Country：Japan  

Event date： 2016.8 - 2016.9

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2016.8 - 2016.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：ホテル法華クラブ仙台   Country：Japan  

有明海は日本最大の干潟と独特な生態系を有する閉鎖性海域で，古くからノリの養殖や貝類を中心とする漁業が盛んに行われてきた．しかし，近年様々な環境異変が発生し，漁業生産に大きな影響を与えている．そのため，有明海の海域環境を定量的かつ経年的に把握し，環境異変の解明が必要である．本研究では，マルチボックス生態系モデルを用い，近年の有明海における環境異変やその対策による海域への影響評価を行った．

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：ANAクラウンプラザホテル沖縄ハーバービュー   Country：Japan  

Language：Japanese  

Venue：岡山大学   Country：Japan  

Language：English   Presentation type：Oral presentation (general)  

Venue：Web開催