Harmony between aquatic environment engineering and disaster prevention/risk reduction

Clarify the complex environmental systems of the hydrosphere and develop measures to prevent and reduce disasters in it.

Profile

Norio Tanaka

Professor, Graduate School of Science and Engineering and the International Institute for Resilient Society, Saitama University

Doctor of Engineering: Aquatic environment engineering, applied ecological engineering, aquatic disaster prevention/disaster risk reduction engineering

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Career

1991	Graduation from the Doctoral Course, Graduate School of Engineering, the University of Tokyo
2000-	Saitama University, after working in a private company
2007-2013	Professor, Graduate School of Science and Engineering and the Institute for Environmental Science and Technology (IEST), Saitama University
2014-	Professor, Graduate School of Science and Engineering and the International Institute for Resilient Society, Saitama University

 

Publication

• “Environments in the Biosphere” (2007): Co-authored, Tokyo Denki University Press
• “Leaflet on Aquatic Environments” (2006): Co-authored, Asakura Publishing Co., Ltd.
• “Encyclopedia of Rivers” (2009): Co-authored, Maruzen Company, Limited
• “Wetlands for Tropical Applications: Wastewater Treatment by Constructed Wetlands”(2011): Co-authored, Imperial College Press
• “Learning about Japanese Rivers and River-related Technologies: By the Committee on Hydroscience and Hydraulic Engineering” (December 2012): (Tonegawa) Editorial Committee (Chairperson: Tadashi Yamada of Chuo University), Co-authored by Tanaka as an editorial committee member
• “Tsunami and Coastal Forests – The Effects of Bio-shields to Reduce Disaster Risks -” (2013): Co-authored, Kyoritsu Shuppan Co., Ltd.
• “Fifty-eight chapters to understand Sri Lanka” (2013): Co-authored, Akashi Shoten

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Clarify the complex environmental systems of the hydrosphere and develop measures to prevent disasters and reduce disaster risks in it.

– Including an analysis of the effects of coastal forests to reduce damage caused by a tsunami –

The hydrosphere, including rivers and coastlines, consists of environmental systems in which hydraulic (such as water flows and waves) and biological (including the acts of individual organisms and transitions of biological communities) phenomena occur on various time and space scales while influencing each other in a complicated manner. It has become increasingly important to understand the effects and influences of the systems on hydraulic (such as floods and tsunami) and man-caused (including changes in the hydrological environment and contamination) disturbances to develop a sustainable society.

My laboratory conducts research on the following subjects: methods for reducing disturbance effects on mangroves and lagoons, the behaviors of aquatic insects living in the downstream of dams, development of measures to respond to trees and plants growing in the courses of rivers (attributed to a decrease in the frequency and extent of disturbances due to floods), which interferes with water flows and causes drifts, protection of riverfront vegetation (such as reed) from the waves generated by running boats, and purification of water (to improve its quality) using emergent plants. Following the giant tsunami in the Indian Ocean, we conducted a study to determine its damage by defining sand dunes and, lagoons, and woodland as bio-shields, and developed a method for assessing their disaster-prevention effect quantitatively. We also proposed methods for designing/operating sustainable bio-shields to developing countries in South and Southeast Asia. Following the tsunami that caused severe damage in the Great East Japan Earthquake, increasingly higher expectations are raised in Japan for dunes and coastal forests to reduce damage caused by tsunami that would overflow banks.

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Process

1. Identify physical, chemical, and biological factors that are dominant on time and space scales specific to phenomena and tasks as research subjects (Interesting findings are obtained from complex hydraulic phenomena).
2. Make decisions on appropriate combinations of methods, including on-site survey, hydraulic experiments, and numerical analyses, for clarifying phenomena or solving problems. In most cases, a hypothesis is formed, and research plans are designed to examine its validity.
3. The development of experimental equipment, selection of experimental methods, creation of numerical analysis models, and implementation of on-site surveys, using a variety of techniques.
4. The validity of the hypothesis is examined again. Even if a hypothesis is not supported, unexpected findings may be obtained.
5. Proposition of response measures, design methods, and planning theories

An image of the research field as a whole

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An image of the research field as a whole

In relation to technological development for life in harmony with the environment, we conduct research on the following subjects: a combination of coastal forests, sand dunes, and banks to reduce tsunami risks in coastal areas, analyses of secondary disasters due to driftwood and the development of response measures, proposition of an urban structure designed to reduce disaster risks, prevention of the erosion of riverfront and bank vegetation attributed to the waves generated by running boats in the downstream areas of rivers, clarification of the relationship between the characteristics of floods and vegetational dynamics in midstream areas and the proposition of methods for the maintenance and management of rivers and their vegetation based on the results, and clarification of the relationships between the operation of dams and riverbed materials/aquatic insects in upstream areas.

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Propositions for the sustainable management of coastal forests

Our suggestions include the forestation of native species, planting mixed species to increase their mechanical strength, and the necessity of increasing residents’ motivation to maintain and manage the forests for a long period, such as social forestation.

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Matara forestation project

(by Saitama University, the University of Peradeniya, and Matara City) 

 

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Numerical simulation of tsunami propagating upstream along the Abukuma River

(tsunami diffraction around sand spits and tsunami overflow from the river embankment)

When the earthquake occurred in the Pacific Ocean of the Tohoku region, tsunami propagates propagated upstream along rivers in many regions, and damage was particularly severe in those areas hit by tsunami from the ocean and river sides.

The figure shows a result obtained from a simulation of tsunami propagating upstream along the Abukuma River and overflowing the bank. In this region, the severity of damage significantly varied from area to area, presumably depending on the structure of the river mouth and its geographical shape, including sand spits, bridges, and winding waterway. It is important to clarify the causes and identify rivers with a similar structure as important roles played by engineering.