GSFS Faculty

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(Professor/Division of Environmental Studies)

Department of Socio-Cultural Environmental Studies/Estuarine and coastal environment, Coastal engineering, Hydro-environmental engineering, Coastal zone management

Career Summary

1991: Received B.S. in Engineering (The University of Tokyo)
1993: Received M.S. in Engineering (The University of Tokyo)
1996: Received Ph.D. in Engineering (The University of Tokyo)
1995: JSPS Research Fellow (The University of Tokyo)
1997: Research Associate (The University of Tokyo)
1999: Associate Professor (The University of Tokyo)
1999-00: Visiting Researcher (Asian Institute of Technology)
2002: Associate Professor (Yokohama National University)
2007: Visiting Researcher (University of Florida)
2009: Professor (Yokohama National University)
2013: Professor (The University of Tokyo)

Educational Activities

Graduate School: Coastal Environment Infrastructure Studies

Research Activities

Evaluation and Social Implementation of Blue Carbon:
Are you familiar with blue carbon? It is a relatively new term. In 2009, the United Nations Environment Program (UNEP) defined blue carbon as ?gcarbon sequestered and stored by the action of marine life.?h Phytoplankton, seagrass (eelgrass), seaweed (kelp, sargassum, brown seaweed, laver), mangrove, and tidal marsh are thought to absorb carbon dioxide (CO2) by photosynthesis and suppress the increase in atmospheric CO2 concentration. Although this has been common knowledge for quite some time, in recent years it has attracted attention as a potential measure for CO2 sinking source. The measures for absorption of CO2 by blue carbon are restoration and creation of seagrass and seaweed beds, tidal flats, tidal marshes, and mangrove forests. Through their enhancement of coastal ecosystems, they also contribute to ecosystem services (supply of food through fishery resources, purification of water quality, tourism and recreation, prevention and mitigation of coastal disasters) and enhancement of the value of coastal environments. In addition, due to ecosystem-based measures, there are features such as high sustainability and low ethical barrier in social implementation.
In the Nationally Determined Contribution (NDC), which was announced in the Paris Agreement in 2015, Australia, India, Bahrain, and the United Arab Emirates declared the utilization of blue carbon as a measure to mitigate and adapt to climate change. Although Japan does not declare the use of blue carbon, we will clarify the features of blue carbon and estimate its potential, and will continue research strategies for its social implementation.
With blue carbon, it is important to estimate how much carbon dioxide has been sequestered and stored as blue carbon along with its time scale for returning to the atmosphere. Marine phytoplankton actively absorb carbon dioxide by photosynthesis, but at the same time, a large portion of them are decomposed into carbon dioxide in a short time, returning to the atmosphere. In contrast, part of the organic carbon in seagrass beds (not only seagrass itself but also the organic carbon present in the ecosystem of the beds) accumulates in sediment for a long time, and blue carbon is thus considered to have a high retention function. It is necessary to quantitatively evaluate the potential carbon storage expected by creating these seagrass beds. Further, some of seagrass leaves are transported offshore and reach the deep ocean. Consequently, the return of carbon to the atmosphere can be extensively delayed for hundreds of years or more. It is necessary to clarify what kinds of carbon sequestration and storage functions are performed on various time scales and to what extent they are effective. For this purpose, we are planning to conduct research utilizing field data on many existing marine ecosystems.
From the viewpoint of social implementation, it is necessary to know the expected time, area, and amount of sediment resources (dredged sediment in ports and navigation channels and steelmaking slag) that can be utilized to create seagrass and seaweed beds. Using these data, we will consider strategies for creating and restoring seagrass and seaweed beds. Also, it is important to clarify how much blue carbon in the coastal area of Japan or any country can be expected in cases where there is no constraint on the amount of available sediment. Furthermore, from the perspective of how to secure financial resources and human resources, we can expect a framework of public-private partnership, such as the Public-Private Forum for Tokyo Bay Restoration, established in 2013, to implement in the society.

Numerical Prediction of Long-Term Environmental Change in Estuarine and Enclosed Coastal Waters:
In recent years, the overall water quality in Tokyo Bay, one of the most polluted bays in the world, has been improved (actually, the pollutant load, including total nitrogen (TN) and total phosphorus (TP), has significantly decreased), but hypoxia and anoxia often occur at the bottom water during summer. In addition, upwelling of the bottom hypoxic and anoxic waters and their intrusion into the surrounding tidal flats and shallow water areas sometimes lead to mortality of benthic animals, such as short-necked clams (a major fishery resource). Since there has been almost no decrease in the amount of bottom hypoxic waters for a long time, it is important to propose effective and practical countermeasures against it. In addition, the fish catch in Tokyo Bay, formerly called Edo-Mae (fresh fish caught in the sea near Edo, the former name of Tokyo), has decreased to less than one tenth compared to the 1960s. Although the total pollutant load control system (TPLCS) has been implemented since 1979, leading to overall improvement of water quality, hypoxia and anoxia have not been mitigated and the fish catch has declined continuously. Some researchers in fishery science claim that the decline in fish catch may be partially caused by nutritional deficiency due to the TPLCS while other researchers say that further decrease in TN and TP may restore past desirable ecosystems. Thus, now would be the time to reconsider the management and control of water quality in the bay to achieve a balanced and flourishing coastal marine environment. Furthermore, it is speculated that climate change impacts may also be associated with long-term water quality fluctuations. Using monthly field monitoring data in public waters collected by local governments for more than 40 years, statistical modeling and analyses are required for identifying seasonal components, eventual factors (disturbance caused by typhoons, effects of river floods, etc.), and trends.
In light of these issues, monitoring water quality as well as sediment quality, and full-scratch numerical modeling and prediction of long-term hydrodynamic and biogeochemical processes, have been performed through the integration of circulation, wave-hindcasting, pelagic ecosystems, and multilayered sediment processes. We will also research effective measures for environmental restoration, rehabilitation, and mitigation along with their effectiveness and feasibility. In addition, we actively apply open source numerical models, such as FVCOM, for seeking better management in estuarine and coastal waters.

Environmental Restoration, Rehabilitation and Mitigation in Estuarine and Coastal Environments:
Factors associated with degradation of water quality and ecosystems in coastal environments include not only pollutant loads but also environmental infrastructure, such as topography and sediment grain size. For example, short-necked clams inhabit sandy tidal flats and shallow water beds, feeding phytoplankton by filtering seawater. Some of the organic matter taken up constitutes their body, some is used for respiration and decomposed, and some is deposited on the sediment. As a result, the existence of the habitat of clams has a function of suppressing the deposition of organic matter originating from phytoplankton on the offshore deep beds where hypoxic and anoxic waters tend to appear in Tokyo Bay. Owing to the long-term reclamation of the foreshore in Tokyo Bay, tidal flats and shallow water areas have decreased, leading to a decline in water purification function, including its decomposition and storage, in coastal waters. Restoration, rehabilitation, and mitigation of tidal flats and shallow water areas are expected to restore sound material cycling and lead to restoration of the coastal marine environment. In order to examine such environmental restoration measures and predict their effect, we have been performing field observation and numerical modeling and simulation. In addition, through activities in the Public-Private Forum for Tokyo Bay Restoration and a project team on the Restoration and Creation of Habitat under the forum, we will develop new ideas for environmental restoration measures on the basis of scientific evidence and their effective and feasible implementation in society. It has been necessary to renovate aging coastal structures, such as seawalls, and further consideration for balanced and environmentally friendly structures is becoming important.

Local Water Quality Improvement Using Technical Countermeasures:
Dredged pits made by mining sediment resources are sometimes distributed in coastal waters. In Tokyo Bay, such dredged pits exist off Urayasu, off Akanehama, off Makuhari, and off Kemigawa. Waters in dredged pits are often stagnant and as a result their water quality is sometimes extremely degraded, leading to the generation of anoxia.
At the Tokyo Olympics and Paralympic Games in 2020, Odaiba Seashore Park is planned to be the venue for triathlons and swimming competitions (10-km marathon swimming). As the Tokyo Metropolitan area has a combined sewer system where rainwater and sewage are collected in the same sewer pipes, the flow rate increases drastically during heavy rain, often exceeding the processing capacity and discharging untreated water into the environment. There is thus a concern that the amount of coliform bacteria in the water may exceed the standards of the competition.
Regarding such local water quality problems, we have been performing field and numerical investigation on effective countermeasures using various technical devices and methods of controlling the discharges of adjacent rivers.

Statistical Identification and Stakeholders' Perception of climate change in Coastal Waters:
Phenomena that are considered to be the effects of climate change, such as an increase in air and water temperatures and a change in typhoon tracks, have been observed around the world. Engineers in construction companies involved in marine civil engineering have perceived and grown concerned about a decrease in the duration of a calm wave condition under which the installation work of a caisson (a huge concrete box used as a breakwater) can be performed. In fact, in some coastal areas, statistical analysis has revealed that the frequency of high waves and long waves (long waves increase the horizontal movement of the water mass even when the wave height is not so large, which makes construction difficult) has been increasing. Using statistical analysis of observation data and interview surveys of stakeholders?f perception and opinion as a basis, we are trying to identify long-term trends of the influence of climate change so that we can better develop adaptation measures, including the amendment of regulations for marine construction works.

Coastal Zone Management for Sustainable Coast in Developing Countries under Climate Change:
In coastal areas of Southeast Asia and South Asia, the impact of climate change is considered more apparent than in Japan. This impact may be getting worse as it is strengthened by land subsidence and mangrove deforestation. We have been conducting research aimed at contributing to the sustainable development and utilization of coastal areas in developing countries being affected by climate change.
Our current targets (and collaborators) are disaster mitigation using mangrove forests in the Mekong Delta in Vietnam (Can Tho University), sea level rise and sediment transport in Pondok Bali and the Cipunagara River mouth areas in Indonesia (Bandung Institute of Technology), mangrove restoration at the head of the Upper Gulf of Thailand in Thailand (Burapha University), coastal erosion in Marawila Beach in Sri Lanka (Coast Conservation Department, Sri Lanka), salinity intrusion and the resultant health crisis and environmental migration in the southwestern area of Bangladesh, environmental protection and sustainable use of coral reefs in El Nido, the Philippines, tsunami disaster mitigation in Oman Sea, Iran, and environmental management in Bohai Sea in China. In the near future, we will start evaluations of an ecosystem service in a river in Jessore, Bangladesh and begin restoration of a mangrove forest in Myanmar.
In these studies, we are conducting surveys to determine stakeholders?f perceptions and performing field measurements to propose possible countermeasures. We are also evaluating projects of mangrove restoration and analyzing the influences of salt intrusion and inundation caused by sea level rise (including ground subsidence).

Mitigation of Coastal Disasters, including Storm Surges and Tsunamis:
We have also been involved in studies on the mitigation of coastal disasters, including storm surges and tsunamis. Since participating in a reconnaissance field survey following the 2004 Indian Ocean Tsunami in the southern coasts of Sri Lanka and Banda Aceh, Indonesia, we have conducted several tsunami and storm surge disaster investigations, including one on the 2011 Great East Japan Earthquake and Tsunami. We have been developing a numerical system using the unstructured-grid, finite volume community ocean model (FVCOM) developed by Chen et al. (2003) that can precisely reproduce complex coastlines and structures. For the Great East Japan Earthquake and Tsunami, we conducted collaborative research with the development team of FVCOM in a study on the tsunami impact and spread of radioactive contaminated water due to the accident at the Fukushima Daiichi Nuclear Power Plant.


1) Rakib, M. A., Sasaki, J., Palc, S., Md. Asif Newazd, Md. Bodrud-Dozae, and Mohammad Amir Hossain Bhuiyan: An investigation of coastal vulnerability and internal consistency of local perceptions under climate change risk in the southwest part of Bangladesh. J. Environmental Management, 231, 419-428, 2019. DOL

2) Samarasekara, R. S. M., Sasaki, J., Jayaratne, R., Suzuki, T., Ranawaka, R. A. S., and Pathmasiri, S. D.: Historical changes in the shoreline and management 1 of Marawila Beach, Sri Lanka, from 1980 to 2017. Ocean and Coastal Management, 165, 370-384, 2018. DOL

3) Amunugama, M. and Sasaki, J.: Numerical modeling of long-term biogeochemical processes and its application to sedimentary bed formation in Tokyo Bay. Water, 10(5), 572, 2018. DOL

4) Ratnayakage, S. M. S., Sasaki, J., Esteban, M., and Matsuda, H.: Assessment of the co-benefits of structures in coastal areas for tsunami mitigation and improving community resilience in Sri Lanka. Int. J. of Disaster Risk Reduction, 23, 80-92, 2017. DOL

5) Shimozono, T., Tajima, Y., Kennedy, A.B., Nobuoka, H., Sasaki, J., and Sato, S.: Combined infragravity wave and sea-swell runup over fringing reefs by super typhoon Haiyan. J. Geophys. Res. (Oceans), 120(6), 4463-4486, 2015. DOL

6) Chen, C., Lai, Z., Beardsley, R.C., Sasaki, J., Lin, J., Lin, H., Ji, R., and Sun, Y.: The March 11, 2011 Tohoku M9.0 Earthquake-induced tsunami and coastal inundation along the Japanese coast: A model assessment Prog. Oceanogr., 123, 84-104, 2014. DOL

7) Lai, Z., Chen, C., Beardsley, R., Lin, H., Ji, R., Sasaki, J., and Lin, J.: Initial spread of 137Cs from the Fukushima Dai-ichi Nuclear Power Plant over the Japan continental shelf: a study using a high-resolution, global-coastal nested ocean model. Biogeosciences, 10, 5439-5449, 2013. DOL

8) Sasaki, J., Ito, K., Suzuki, T., Wiyono, R.U.A., Oda, Y., Takayama, Y., Yokota, K., Furuta, A., and Takagi, H.: Behavior of the 2011 Tohoku earthquake tsunami and resultant damage in Tokyo Bay. Coastal Eng. J., 54(1), 1250012, 26pp., 2012.

9) Sasaki, J., Kanayama, S., Nakase, K., and Kino, S.: Effective application of mechanical circulator for reducing hypoxia in an estuarine trench. Coastal Eng. J., 51(4), 309-339, 2009.

10) Rasmeemasmuang, T. and Sasaki, J.: Modeling of mud accumulation and bed characteristics in Tokyo Bay. Coastal Eng. J., 50(3), 277-308, 2008.

Other Activities

Member and Secretary of the Japan Society of Civil Engineers (JSCE)
Managing Member, Coastal Engineering Committee, JSCE (2017.6-2019.6)
Executive Chair, Coastal Engineering Committee, JSCE (2013.6-2017.6)
Member of the Japan Association for Coastal Zone Management (JACZS)
Executive Board Member, JACZS (2017.5-2019.5)
Chair, Planning and Management Committee, JACZS (2013.5-2017.5)
Member of the Japan Society for International Development (JASID)
Member of the American Geophysical Union (AGU)
Advisory committee member of national and local governments, including Ministry of Land, Infrastructure, Transport and Tourism, Fisheries Agency, Ministry of the Environment, Chiba Prefectural Government, Kanagawa Prefectural Government, and Shizuoka Prefectural Government

Future Plan

My future plan is to continue studying coastal environments, coastal disaster mitigation, and sustainable use of coastal areas in developing countries. I will focus more on environmental restoration measures in polluted bays, including technological aspects, feasibility, and consensus building among stakeholders, which should be balanced with disaster mitigation and public and private use. I am also enthusiastic about accepting more foreign students from developing countries and promoting studies on the coastal problems facing their mother countries.

Messages to Students

One of our missions is to study practical problems in coastal areas and to come up with better solutions. I welcome students from developing countries to join forces with us in our struggle to conserve sustainable coastal areas. Also welcome are students and researchers who are interested in basic studies and pure technologies related to coastal engineering and hydro-environmental engineering, including the development of numerical models and/or the elucidation of physical processes. It is my great pleasure to construct a research network with former students studying in my laboratory.