1. Introduction

There are approximately 2,700 dams in Japan. Their total reservoir capacity is approximately 25 billion m³ (BCM), far less than the 34.4 BCM of Hoover Dam in the US or the 39.3 BCM of the Three Gorges Dam in China. Lake Biwa, with a capacity of 27.5 BCM, which has recently been used for multiple purposes by the Lake Biwa Comprehensive Development Project, is equivalent in scale to such artificial lakes. On the other hand, dams in Japan that were constructed on mountain rivers with considerable sediment deposits are decreasing their capacity more rapidly than those constructed on continental rivers, so they require measures against deposition to maintain their long-term reservoir capacity. In addition, extreme weather phenomena (increased rainfall and drought intensity) under climate changes increase high demand for storage capacity of dams. In order to effectively use these dams as limited resources and to hand them over to the next generation in healthy state, continuous investment and development of maintenance technology are required. Recently, to promote this investment and development, “A vision for upgrading dams (effective use of existing dams to mitigate damage from frequent floods and droughts and to generate renewable energy)” was established by the Ministry of Land, Infrastructure, Transport, and Tourism (MLIT) on June 27, 2017 [1]. This special issue is collecting the significance of the dam upgrading projects and important challenges from various aspects to be implemented.

Japan is subjected to harsh weather conditions, with a high overall annual rainfall, a rainy season, and concentrated torrential rains during the typhoon season. Moreover, rivers in Japan generally have a steep gradient and are characteristically subjected to sudden rises of water level that cause flooding, or the falling of water level over a short period when the rain ends, causing the water shortage. Although dams have been constructed according to river basin characteristics to handle flooding and water usage issues, the number of favorable dam sites in Japan is rather small. Thus, extensive dam upgrading, aimed at strengthening the function of existing dams, has recently been carried out. In this report, examples of past dam upgrading projects as well as the status of dam upgrading are reviewed. In particular, the technological issues of dam heightening and additional installation of discharge facilities are discussed for upgrading projects in which structural retrofitting is carried out while the dam is in operation. Moreover, the required measures are considered.

Among the dams managed by Japan’s Ministry of Land, Construction and Transport, Shin-Katsurazawa Dam is the first dam to be renewed by coaxially raising the embankment of an existent dam. Raising the embankment of an existent dam that is in operation involves various problems that are different from the ones involved in constructing a new dam, such as evaluation of the foundation base rock and integration of concrete of the old and new dam bodies. The technical features of Shin-Katsurazawa Dam as a coaxially raised dam and measures taken to solve the various problems involved are presented.

In general, redevelopment projects of existing dams can significantly reduce the social, financial, and environmental impacts on a community in comparison to the construction of new dams. In addition, as redevelopment projects of existing dams can accomplish the project purpose more quickly than new construction, the expectation is that such projects will be required more frequently. Tsuruta Dam was constructed in 1966 as a multipurpose dam on the first-class Sendai River. After an unprecedented flood in July 2006, a redevelopment project of the dam began in April of the following year (2007). The project was required to minimize the effect to the flood control function of Tsuruta Dam and to minimize the effects to the power generation company, the dam user. Construction work of the upstream-side cofferdam included a reservoir construction at a significant depth of 60 m or more and a dam body drilling work, and had to be conducted under a complicated and tight schedule. This paper is intended to summarize the Tsuruta Dam redevelopment project as an introduction of the experience and technology obtained and provide some lessons to future redevelopment projects of existing dams.

The Comprehensive Inspection of Dams was institutionalized by the Japanese Ministry of Land, Infrastructure, Transport and Tourism for the dams managed by it in long-term operation. In this paper, this inspection is outlined, and its practical procedures and methods with the important technical notices for its implementation are presented.

The Ministry of Land, Infrastructure, Transport and Tourism (MLIT) aims to perform underwater inspection of dams using vehicles instead of divers, to address the deterioration of infrastructures, considering the shortage of engineers and technicians in the near future, in order to improve inspection safety. To this end, the technology for underwater inspection vehicles was publicly invited to conduct the verification of the technology at the concrete gravity dams and concrete arch dams, managed by MLIT. This paper reports the contents of the field verification, evaluation of the technology, and the results of the trial introduction, assuming practical operation.

Preliminary release conducted at multipurpose dams is the operation which aims to temporarily increase their flood control capacity by releasing water stored for water utilization ahead of a flood based on rainfall forecasts. However, if rainfall forecasts overestimate actual rainfall, there is a risk that the volume needed for water utilization may not fully recover after preliminary release. Consequently, because of apprehension of such a risk, preliminary release has been seldom operated in Japan. This paper introduces the determination of preliminary release based on ensemble rainfall forecasts. First, the two risks related to preliminary release were defined at first. One is the flood control operation for extreme floods, which is conducted when preliminary release has not been conducted or inadequately conducted, whereas the other is the water level may not fully recover to the level needed for water utilization if preliminary release is decided based on rainfall forecasts overestimating actual rainfall. Next, these two risks were quantified using the results from ensemble rainfall forecasting and hydrological simulation. Finally, based on the quantified risks, the operation of preliminary release was decided. The experimental simulation of preliminary release based on ensemble rainfall forecasts was conducted. The flood caused by Typhoon Man-yi in 2013 is selected as the experimental flood, and the Hiyoshi Dam as the experimental dam, where the flood control operation for extreme floods was conducted during the flood. The simulation results of the experimental flood showed that flood control operation for extreme floods would still be required notwithstanding the increased flood control capacity generated by preliminary release. However, the results also showed the possibility that preliminary release can delay flood control operation for extreme floods and considerably reduce the maximum outflow compared with the maximum outflow that would be required when no preliminary release is conducted. In addition, the study found that ensemble rainfall forecasting can be an effective tool to support the formation of a consensus among stakeholders such as dam managers and water users by quantifying and visualizing the risks associated with preliminary release, which cannot be accomplished with the conventional deterministic rainfall forecasting.

This paper presents approaches and case studies for the introduction of ensemble hydrological predictions to reservoir operation for water supply. Medium-term operational ensemble forecasts of precipitation are employed to improve the real-time reservoir operation for drought management considering longer prospects with respect to future hydrological conditions in the target river basin. Real-time optimization of the water release strategy is conducted using dynamic programming approaches considering ensemble hydrological predictions. A case study on the application of ensemble hydrological predictions to reservoir operation for water use is reported as an example, with a hypothetical target river basin whose hydrological characteristics are derived from an actual reservoir and river basin.

Flood control by a dam is generally executed to follow the predetermined operation rule, which can determine the required outflow discharge in accordance with the change in inflow. However, when flood damage could be reduced by using the dam flood control capacity to its limit, the dam would be expected to store as much water as possible without any regard to the predetermined operation. Occasionally, an adaptive operation for flood control would be effective in such cases, for example, to reduce dam outflow discharge compared to the predetermined outflow discharge to match river flow capacity, which is low in some downstream parts of a dam, or to ease one river to flow down quickly by storing and retarding another river flow by dams. However, such an adaptive operation is non-typical and requires extra effort in addition to being risky to dam managers and the people along the rivers. This paper introduces two cases of adaptive flood control for the flood control executed in the Yodo river in 2009 and 2013 and then describes the systems applied in the Kizugawa Dams Integrated Operation and Management Office (KDIIMO), Japan Water Agency (JWA) to execute an adaptive operation for flood control in a safer manner.

Herein, we summarized the current and future study topics of sediment management using bypass tunnels based on the discussions at the Second International Workshop on Sediment Bypass Tunnels (SBTs) at Kyoto in May 2017. Although reservoir sediment management using bypass tunnels has appeared since the beginning of the 20th century in Kobe, the number of SBTs worldwide is still limited. To promote the installation of SBTs as an effective sediment management measure, it is essential to appropriately evaluate their long-term advantages economically and for the restoration of the aquatic ecosystem. An abrasion model has been developed to predict the abrasion rate of tunnels from the volume of sediment transport. Further, methods to monitor sediment transport in tunnels have advanced. With a significant amount of sediment supply by SBTs, the ecosystems in the downstream reaches of dams can be restored within a few years. A precise rainfall and runoff model for predicting the inflow hydrograph and sediment is essential for the efficient operation of dam gates and SBT (e.g., diverting minimum amount of water for sediment transport). Further studies are needed to clarify the suitable grain size for transportation through SBTs in terms of both the mitigation of tunnel abrasion and promotion of the restoration of downstream ecosystems.

Free-flow sediment flushing operation offers viable means to preserve the storage capacity of dam reservoirs as the incoming flood erodes the flushing channel, and the deposited sediment is flushed from the reservoir. This method involves complex flow patterns and flushing channel formation procedures owing to the dynamic interaction between varying flow conditions (e.g., shallow and deep flows) and moveable bed variations notably when the non-uniform sediments exist in the complex geometry of reservoirs. In the present study, first, the numerical simulation of a previously conducted free-flow sediment flushing operation in the Dashidaira and the target segment of Unazuki reservoirs using the available field-measured data were presented. Then, to improve the flushing efficiency in the Dashidaira reservoir, the effects of using a groyne were studied. A fully 3D numerical model using the finite volume method in combination with a wetting/draying algorithm was utilized to reproduce the flow velocity field and morphological bed changes. While the characteristics of the flow field can be captured by the numerical model in Dashidaira and Unazuki reservoirs, simulated bed changes in upstream areas covered with the coarser materials (e.g., study zone of Unazuki reservoir) showed some discrepancies. The outcomes also revealed that implementing a groyne at the entrance of the wide midstream of Dashidaira reservoir can locally increase the sediment erosion chance from this area and thereby can improve the flushing efficiency by approximately 10%. Therefore, the risks associated with the accumulation of distorted sediments in the wide midstream of Dashidaira reservoir within a long-term period could be reduced.

A field demonstration project on flexible dam operation at the Managawa dam in the Kuzuryu River Basin has been implemented since 2000. The goal is to restore flow and sediment regimes in the Managawa River, which flows along the Ono-city and is located below the dam. Flexible dam operation stores inflow discharge into a reservoir, which generally uses part of the flood control capacity and appropriately discharges the stored water to the river, also known as the “flood pulse,” for restoring dynamic fluvial systems and the resulting ecological processes. In addition, other options have been carried out in combination with flexible dam operation, for example, sediment replenishment since 2003 and channel rehabilitation since 2007. This article reveals the positive impacts and effectiveness of flexible dam operation, sediment replenishment, and channel rehabilitation, and discusses challenges and future prospects toward translating the field demonstration project into dam management on the ground level. First, we classified reach types to identify the impact of various management options, e.g., flexible dam operation, sediment replenishment, and channel rehabilitation. These management options can influence respected reaches. We conducted a macro-scale analysis to understand the relationship between the aforementioned management options and dynamic fluvial systems, addressing changes in gravel riverbed, vegetation, and habitat types (riffles and pools). Second, a micro-scale analysis was conducted to understand the relationship between the management option and changes in attached algae to sediment and macro-invertebrates, etc. The results show the effectiveness of the middle-scale flood pulse to restore dynamic fluvial systems, increase habitat diversity, and sustain ecological processes. Furthermore, we discussed the impacts of such options on the flow and sediment regimes in Managawa River and revealed that flexible dam operation reduces the occurrence of low flow and midscale floods. It was also revealed methods such as sediment replenishment and channel rehabilitation play an important role in increasing the effectiveness of the middle-scale flood pulse and restoring dynamic fluvial systems, even though sediment replenishment is not sufficient to restore sediment regimes (i.e., bring then back to pre-dam conditions).

Sedimentation in hydropower reservoirs is one of the most important problems facing power generation. Many of the reservoirs our company’s dams, built in the postwar reconstruction period, have been storing up sedimentation for decades. The percentage of sedimentation is now considerable, about 9%, because of a combination of a high degree of sediment production and the river flow regime. We have been trying to excavate the sedimentation from the reservoirs to avoid aggradations of upstream riverbeds and to eliminate obstacles to intake and outlet functions. Considering sediment properties, we have carried out representative five different ways of managing reservoir sediment. At the Sakuma dam, which is comparatively large, provisional transporting inside the reservoir is the main countermeasure, but radical management will be required in the near future. At the Futatsuno dam and Taki dam, which are medium-sized, the current volume of sedimentation excavation is not sufficient to maintain the size of the reservoir, due to flow sedimentation. Sediment routing methods, such as bypassing, will therefore be urgently planned. At the Setoishi and Yambara dams, the testing of sediment sluicing or hydro-suction sediment removal systems has already started. Regarding sedimentation sluicing, we have studied the feasibility of sediment bypass tunnels and gated outlets in the dam reservoir that is unsuitable for sluicing with the existing spillway. We found that gated outlet will be effective. Although there are no quick remedies that can reduce reservoir sedimentation dramatically, there are some methods that may be suitable, considering the size, life and basin of each reservoir. Not only the technical feasibility, but also the economic advantages and ecological acceptability should be considered. To sustain reservoirs and hydropower, sedimentation should be managed effectively and adaptively, based on the specific conditions of each reservoir.

The 2005 typhoon disasters taught us that the Mimikawa River system in Miyazaki Prefecture had various problems with sediments in the river basin (the riverbed in dam reservoirs rise so much that flooding risk increases, sediments captured at dams granulate the downstream river channel and destabilize the bridge piers in the downstream river channel). In one of the approaches to solve these problems simultaneously, since 2017, sediment sluicing at a series of dams has been operated cooperatively. Using this approach, we can expect that the river will recover its continuity of sediment movement, returning its physical environment and animal habitats to their original states. Based on environmental surveys and numerical analyses of the current conditions, we have predicted the environmental impacts due to sediment sluicing at dams and defined the method to assess them. This paper presents: 1) an overview of sediment sluicing at dams in the Mimikawa River system, 2) the analysis of the river environment prior to operating sediment sluicing at dams, 3) the prediction of the impacts of sediment sluicing at dams in the river environment, 4) the environmental impact assessment after operating sediment sluicing at dams.

Japan is suitable for hydropower generation because of its varying topology and abundant water resources. The use of natural energy resources has recently gained importance in Japan, and as such the subject of small- and medium-scale hydropower generation has drawn much attention. However, new developments have not advanced significantly. Hydropower has various advantages over other natural energy sources; it provides stable power output, and if construction and maintenance are implemented appropriately, it can provide electricity at low costs and over long timescales. Further, hydropower is environmentally friendly, and can protect and improve the environment when implemented in harmony with natural and social factors. Moreover, it has social benefits; it contributes to aspects such as regional revitalization, local attractiveness, and disaster prevention. The possibilities of hydropower are not fully understood, and methods have not yet been established for its comprehensive practical utilization. Hydropower in Japan has not been in full-scale development for a while. Therefore, there are currently only a few experts on hydropower development. Accordingly, technologies and institutions for the development of small- and medium-scale hydropower generation while ensuring harmony with the natural and social environment are required. Further, a system is also needed to allow experts to promote and support such technologies and institutions in a cross-sectional way.

The Science and Technology Research Partnership for Sustainable Development (SATREPS) is a Japanese government program that promotes international joint research. The program is structured as a collaboration between the Japan Science and Technology Agency (JST) and the Japan International Cooperation Agency (JICA). The program includes various fields, such as Environment and Energy, Bioresources, Disaster Prevention and Mitigation, and Infectious Disease Control, and a total 52 projects were currently in progress as of May, 2018.

It is expected that the promotion of international joint research under this program will enable Japanese research institutions to conduct research more effectively in fields and having targets that make it advantageous to do that research in developing countries, including countries in Latin America and the Caribbean, Asia, and Africa.

Recently, SATREPS projects in the field of Infectious Disease have been but under the control of the Japan Agency for Medical Research and Development (AMED). Although adult maladies, such as malignant tumors, heart disease, and cerebral apoplexy, are major causes of death in the developed countries including Japan, infectious diseases are still responsible for the high mortality rates in developing countries. Therefore, Infectious Disease Control is the important field of SATREPS.

Infectious Disease Control projects are progressing in several countries, including Kenya, Zambia, Bangladesh, the Philippines, and Brazil, and various infectious diseases and pathogens have been targeted.

In this special issue on Infectious Disease Control, the following reports from three projects have been selected: “The JICA-AMED SATREPS Project to Control Outbreaks of Yellow Fever and Rift Valley Fever in Kenya” by Nagasaki University, “Comprehensive Etiological and Epidemiological Study on Acute Respiratory Infections in Children in the Philippines” by Tohoku University, and “International Joint Research on Antifungal Resistant Fungi in Brazil” by Chiba University. These projects include viral, bacterial, and fungal infections.

If they become available, further supplementary reports from other projects in this field will be published in a future issue.

Nagasaki University has conducted a JICA-AMED SATREPS project entitled “Development of Rapid Diagnostics and the Establishment of an Alert System for Outbreaks of Yellow Fever and Rift Valley Fever in Kenya.” This project, which ran for the 5-year period from January 2012 to January 2017, aimed to tackle yellow fever and Rift Valley fever in Kenya, as the name implies. The project was carried out in conjunction with the Kenya Medical Research Institute (KEMRI) and the Ministry of Health (MOH) of Kenya. The specific aims of this project were (1) the development of new diagnostics, (2) the strengthening of reference laboratories, and (3) the development of a disease outbreak alert system, particularly to control outbreaks of yellow fever (YF) and Rift Valley fever (RVF). The RVF virus IgM-capture ICT kit, “ImmunoLine^TM,” and YF virus IgM-capture ELISA, “KemLisa^TM,” were developed as new point-of-care tests. A neutralization test for the confirmation of these arbovirus infections was introduced to the central and local reference laboratories. This project also developed a new disease outbreak alert system, “mSOS,” which the MOH of Kenya has extended nationwide by integrating it into the national health information system (DHIS2).

Childhood pneumonia has been the leading cause of morbidity and mortality for decades. Although substantial progress in the understanding of risk factors and etiology of pneumonia has been made, childhood pneumonia remains the major cause of death in children, accounting for 900,000 of the estimated 6.3 million child deaths worldwide in 2013. More than 90% of all episodes of clinical childhood pneumonia worldwide occur in low and middle-income countries. More effective and feasible interventions need to be developed and made widely available for such countries, including the Philippines. Comprehensive research, including etiological and epidemiological studies for assessments of risk factors and thereby, intervention studies to reduce the impact of childhood pneumonia are required in hospital settings, as well as community settings, consistently. A research project entitled “comprehensive etiological and epidemiological study on acute respiratory infections in children: providing evidence for the prevention and control of childhood pneumonia, the Philippines” was conducted under SATREPS (Science and Technology Research Partnership for Sustainable Development), which is a funding scheme to promote international joint research focusing on global issues. This project was implemented in four sentinel hospitals, with some community settings, in the Philippines between April 2011 and March 2017, incorporating five sub-components: etiological study, disease burden study, risk factor analysis, intervention study, and its evaluation. In this paper, we introduce the research project of SATREPS focusing on the methodologies, progress, and obtained evidence.

Increasing of detection rate of antifungal-resistant fungi is a serious global concern in public health. As few epidemiological data on resistant fungi in Brazil have been available, we planned an international joint project with the University of Campinas, São Paulo, Brazil to research antifungal-resistant fungi. This project, supported by the SATREPS program of the Japanese government, started in fiscal 2017.

This study examined the determinants of people’s participation in community-based disaster preparedness efforts. We administered surveys to residents of two communities in Japan: a neighborhood renowned for high proactivity in disaster preparedness efforts (N=443) and a relatively new, developing community of apartment complex residents (N=772). Results revealed that regardless of community type, people’s involvement therein predicts their engagement in disaster preparation actions. The effects were mediated by social factors (e.g., sense of responsibility, social influence) and disaster-specific factors (e.g., perceived costs/benefits of disaster preparedness, disaster attentiveness). We also identified several features that distinguished the two communities. Specifically, sense of community responsibility was a stronger predictor of people’s actions in the highly proactive community. Based on the results, we discuss the significance of promoting psychological attachment to the community to encourage disaster preparation actions among residents.

In the event of a tsunami, saltwater flows into rivers and water purification plants must stop taking water from rivers to prevent entry of saline water into the plant owing to potential damage to machinery and contamination of the system. This leads to interruption of water supply during disaster. In this study, a salinity transport simulation model that can carry out a three-dimensional salinity behavior analysis in a specific area and a horizontal two-dimensional tsunami propagation analysis simultaneously was developed to predict saltwater behavior in rivers during a tsunami. These models are structured so that the influence of the boundary of the 3D domain can be excluded without significantly increasing the calculation load. The model was used to simulate saltwater behavior in the Yodo River in Japan during a tsunami. The spatial distribution and temporal change of saltwater under various river flows were quantitatively predicted, and the effectiveness of possible countermeasures in diminishing the duration of water-intake shutdown and the presence of brackish water in upstream areas was assessed.

The north-eastern part of Bangladesh is very productive for agriculture and fishing, and the region involves several depressed (haor) areas. Flash floods during the pre-monsoon period bring devastating damage to agriculture in the haor region recurrently. To protect crops from flash floods, the Bangladesh Water Development Board constructed several ring-type submersible embankments. In this research, we have investigated the effectiveness of submersible embankments in controlling flash flooding in the Matian and Shanir haors in the Sunamganj district. A two-dimensional rainfall runoff inundation model was applied considering several scenarios for simulating heavy flash flood events in 2004, 2010, and 2016. Without an embankment, the river overflow would have entered the Matian haor 3 days, 22 days, and 9 days earlier in 2004, 2010, and 2016, respectively, whereas it would have been 7 days and 23 days earlier in 2004 and 2010 for the Shanir haor. The event in 2016 was successfully stopped by the Shanir haor embankment. To avoid river overflow entering into the Matian and Shanir haor completely, the embankment height must be elevated further by 1 m and 0.7 m, respectively. Providing proper drainage facilities for the accumulated rain water inside the hoar is still an important issue for protecting the crops effectively.

A large scale flood disaster occurred in Southern Thailand in December, 2016 and January, 2017, resulting in 95 deaths. The majority of the 15 provinces in Southern Thailand suffered from the disaster and extensive, long-term damage was caused which distinguished this flood event from previous flood disasters. This paper reports the findings of a field survey conducted in February, 2017 and analyzes the precipitation phenomena by using ground rainfall data as well as satellite rainfall data because there were not enough ground rain gauges set in this region. Results revealed that this precipitation event had the highest intensity out of all precipitation events occurring over the last 11 years.

On 5 May 2014, a Mw 6.1 earthquake occurred near Mae Lao (north Thailand), which damaged and disrupted healthcare services in the epicentral region because of structural and nonstructural damages. After providing a general summary of the observed ground motion and overall damages, a short description of the local healthcare system is addressed. Specific descriptions of the observed structural and nonstructural damages are provided based on a series of field surveys conducted between one and nine months after the mainshock. Although the observed structural damages were minimal, sustained nonstructural damages decreased the functionality of healthcare services for several weeks. Until recently, building regulations in Thailand and many other countries have aimed to preserve the structural integrity of buildings, and few studies have considered the seismic resistance of nonstructural components, particularly at hospitals. In addition, emergency planning should set functionality goals and develop plans for reaching them. This should include determination of the performance level expected of hospital buildings, medical equipment, and utility services to guarantee hospitals’ functionality during major disasters.

An M6.1 earthquake occurred in the northern part of Ōsaka-fu (Osaka Prefecture) on June 18, 2018, with many areas in the Kinki region experiencing intense shaking. In Ōsaka City and Takatsuki City seismic intensity 6 lower was observed, resulting in 4 deaths, 15 people sustaining serious injuries, 419 people sustaining minor injuries, 10 completely destroyed residence, 181 partially destroyed residences, and 32,989 residences partially damaged (as of July 17, 2018). There were 339 cases of people being trapped in elevators. At most, approximately 1700 people were evacuated. While there were no derailment incidents on the Shinkansen or local train lines, service was suspended on most railways. Following this earthquake, Ōsaka-fu took the decision to apply The Disaster Relief Act. Response was then enacted by the government local public bodies, and the private sector.