Water control is essential to Japan, as more than half of its invested capital is concentrated in elevations under sea level and the majority of the island nation is exceptionally vulnerable to flooding. To avoid potential crisis, the Japanese have developed exceptionally innovative water management practices. Offering the unique perspective of Dutch engineers, considered the world’s most progressive urban water experts, this volume provide a detailed look at how Japan has developed its modern water system. It looks at the system of Tokyo city, discusses river management practices and urban flood control throughout the country, and considers the impact that these innovations have had on delta regions.
Chapter 1: Introduction
Urban water management in Japan is dominated by extremes. Extreme waves, typhoons, extreme droughts, flashy floods in rivers and, certainly in the past, extreme pollution loads. Rivers in Japan are short and steep, their floodplain often densely occupied. The rapid increase in population and the economic rise resulted in swift urbanization of the limited space fit to build on. This puts high stress on flood protection and on water resources management, certainly if we take into account that agriculture and urban development often occur on soft soils, sometimes significantly below mean sea level. Polders have been created to control the local water systems and protect these areas from flooding. In view of the dense concentrations of population and invested capital Japan is reconsidering its approach to flood protection and is applying new types of structures and ways to cope with flooding and disaster relief. Water resources availability requires sufficient water quality. And water quality demands for pollution control, both from point sources and from non-point sources, and intensive wastewater treatment. The shortage of water resources, certainly in Japans mega cities, stimulates creative solutions, including treatment plant effluent reuse and storm water use for specific purposes. And due to the shortage of land for agricultural production also the surface waters and wetlands are used for food production. Water management in Japan is a very complex task due to the many stakeholders and the distributed rights and responsibilities. Ongoing economic development and urbanization, climate change, land subsidence and ecological decay however require new approaches to water management. In this chapter the technology for Greenfield development, the water supply and the urban flood protection will be introduced in its context: Japan.
Chapter 2: Urban development versus the water system in Tokyo
The relation between urban development and water management in Japan is as prominent as in the Netherlands. The struggle to keep dry feet and at the same time living in prosperity because of the water is very similar. It is an historical relation that keeps on continuing in the future, especially with the climate change. This chapter is contributing to a greater understanding of the urban planning tradition of the Japanese cities in general and of Tokyo specifically. What is the relation between the way the Japanese dealt with the organisation of their urbanisation and the approach towards urban water management? In comparison to the Netherlands there could not be a greater difference. In Japan urban planning is reduced to a centrally organised activity that can be characterized as a communistic-capitalist approach while the Netherlands is world famous for its sensitive urban design approach. What is the result on the design of the urban water system when urban design is absent? The rules of water management are the same, but the design of the cities is as different in the Netherlands and Japan as possible. However, some same similar patterns come about and a study after these makes a very interesting compassion.
Chapter 3: The Urban Water System in Tokyo
This chapter elaborates four components of the Japanese urban water system: water supply, waste water, stormwater, and groundwater. The urban water system of Tokyo is taken as an example. Although the amount of precipitation in Japan is very high, the amount of precipitation per capita is very low, about 5200 m3/capita which is less than one fifth of the world average. Because Japan has no water supply from international rivers and because natural water resources distribution varies considerably in time and space, management of these resources is essential. Although, water supply in Japan is predominantly supplied by large river based centralized supply and distribution infrastructure, increasingly new approaches such as rainwater harvesting and water recycling are used. Examples of innovative solutions are given in this chapter. In addition, to secure water resources of large metropolitan areas, wastewater treatment plants have been built and basin management measures are taken, such as infiltration facilities and reforestation programs. In this chapter water use and resources of the Tokyo Metropolitan Area are elaborated and river basins measures to secure water resources are investigated. Industrialization and groundwater extraction led to rapid subsidence of Japanese urban lowland areas. Groundwater withdrawal started in the beginning of the 20th century. The accumulated subsidence was more than 4.5 meters before regulations on groundwater withdrawal were issued in the 1960’s. In Tokyo it has resulted in an area of 124 square kilometres of land that is lower than the high tide level. The restrictions on groundwater use have now resulted in higher groundwater tables which case problems in deep subway stations, for instance under Tokyo railway station and Ueno station. Most sewer systems (about 70%) in Japan are combined sewer systems. These systems transport both runoff and wastewater. Combined sewer overflows occur which threat the river water quality. Since the 1970’s separated sewer systems have been constructed in Japan and the focus has shifted to source control and stormwater infiltration. This chapter gives an inventory of the most important stormwater Best Management Practices in Tokyo.
Chapter 4: Flood control in an urban environment
This chapter will start with an explanation about the different types of flooding. A distinction will be made between flooded surfaces due to direct rainfall, the so-called pluvial flooding, and inundation of districts caused by insufficient capacity of rivers, the so-called fluvial flooding. Both types will be explained more thoroughly. The meteorological conditions of Japan are very important to understand the threat of flooding. Large precipitation during the rain season and typhoons lead to heavy rainfall in a short period of time. In urban areas it is difficult to drain this large amount of water. A large percentage of the surface is macadamised and is therefore impenetrable for rainwater. Water has to be drained towards channels and rivers. Flooded surfaces are therefore no exception. In cities like Tokyo and Saga smart solutions have been constructed to minimize the threat of flooded streets. Examples are the permeable pavement and multifunctional gutters. These solutions will be explained in this chapter. The characteristics of Japanese rivers are important to understand the fluvial flooding problems in Japan. In this chapter the discharge pattern, the size of catchment areas and the river profile will be discussed. The cause of river floods will be explained and which effects they can have on cities like Tokyo and Osaka. To illustrate the problems of flooding in Japanese cities one section will especially deal with historical floods. What caused them and what damage did they cause. In order to cope with these floods the Japanese government has drawn up a safety policy. This safety policy will be explained after which several measures will be discussed; measures like adjustments in the river profile, horizontal and vertical bypasses and superlevees. Each measure will be explained with one or more examples. For instance, superlevees are already constructed along the Ara river and the Sumida river along the densely populated river shore in Tokyo. The conclusion of this chapter will be a comparison of the Dutch and the Japanese flood management approach in urban areas.
Chapter 5: Urbanisation in lowland areas
In Japan after World War II many polders have been reclaimed from the sea. Most of them are used as paddy fields but also much land was reclaimed as cheap industrial and residential area. Nowadays, most economical activity and more than half of the Japanese population are concentrated in low situated areas that are prone to flooding. These areas face typical lowland problems such as land subsidence, salinity and high flood risks. Comparable to the Netherlands, in Japan areas below sea level have emerged because of continuous land subsidence. In these areas the water level is controlled artificially by installing storage capacity and pumps. In Japan urbanization in concentrated in lowland areas because the Japanese are not used to build cities on higher grounds. In this chapter, the building process of greenfield development in polder areas is described. The best moment to implement new urban water management concepts is at the moment of Greenfield development. That is the phase in which changes in the concepts of water supply, sanitation, flood protection, pollution control can be applied. Greenfield development includes the technical and organisational aspects of the urban development process. It includes clearing sites, the main earthwork, installing drainage-systems, storm water and sewerage disposal systems and the construction of open water, civil engineering constructions and building lanes/paths. Moreover, Greenfield development has a relation to the spatial design, making arrangements between the stakeholders, amenities and recreational facilities, installing cables and piping, installing street-lighting, etc. It is the complex process of realizing a new town section or reconstructing. In this chapter the process of Greenfield development in low-lying areas in relation to the development of urban water system in Japan is described and a comparison to the Netherlands is made. Studying urbanization in Japanese polders from a Dutch perspective is particularly interesting because the Dutch water management approach can still be recognized in the polders in Japan. Moreover, more intensive rainfall, similar to the current situation in Japan, can be expected in the Netherlands as a result of climate change. An overview will be given of methods to make polders with poor soil conditions suitable for the construction of urban areas. Techniques, design methods, design standards and criteria are described of building site planning and preparation.
Chapter 6: Urban Water Landscape and Amenities
Japan has a long tradition of using water to create beautiful urban landscapes. This tradition almost died but like in the Netherlands the importance of ecology after the oil crisis in 1973 brought it back to life. The Japanese today are experts in combining functions and introducing water as a quality in their urban environment. A number of illustrative examples are give to provide insight on how water can contribute to an attractive living environment.
Chapter 7: Parallel plan making approach for urban water management
New methods of plan making approach are being developed in both Japan and the Netherlands. In relation to the past different players become important in the field. For example in Japan the communities become more influential on the urban development of their area. In contradiction to the Japanese tradition of central government determining everything, the communities have more opportunity to decide with the local government about the qualities and future of their neighbourhoods. For example the Kitazawa River in Tokyo that was changed to an underground combined sewer because of pollution. The neighbourhood wanted to have the river in sight again because of spatial qualities so the upper part of the sewer was changed into a nice stream with pedestrian path in a park like environment with clean water flow from a waste water treatment plant. It is a very successful example of participation of inhabitants in urban water planning. The inhabitants have become designers and water managers rather than consumers only. In this chapter Dutch and Japanese experiences with parallel plan making and dealing with complexity in urban water management are presented.
Chapter 8: Operation and Maintenance of Urban Water systems
This chapter elaborates on the operation and maintenance aspects of urban water systems in Japan. Attention will be paid to the organisational responsibilities, management plans and cost recovery mechanisms. Maintenance of the extensive urban water infrastructure is vital for the functioning of a large mega city such as Tokyo. Aging assets, urbanisation and climate change challenge the functioning of the urban water system. Restructuring and maintenance plans of the water system in Tokyo are evaluated to provide insight in how the Japanese are dealing with this challenge. The Japanese have built experience with managing disasters because in Japan disasters occur frequently. This chapter deals with methods and mechanisms to increase coping capacity of society in dealing with natural disasters in urban areas. Coping capacity of society is determined by the presence of effective emergency and evacuation plans, the availability of damage reducing measures, a communication plan to create risk awareness among inhabitants, and a clear organizational structure and responsibility for disaster management. For water supply, the availability of emergency and backup water facilities that can be used in case of droughts and disasters, are important determinants of coping capacity. The objective of developing coping capacity is reduction of damage. In Japan multiple actors are involved in improving coping capacity to reduce damage in case of disasters. Examples are fire fighters, water authorities, municipalities, and other government agencies are involved.
Chapter 9: Lessons for delta areas
Concluding in overview what lessons that can be learned from the Japanese example in comparison to the Dutch approach. What recommendations can be done for international problems in urbanized delta areas in general?
Biography
Rutger de Graaf studied Civil Engineering at Delft University of Technology. After his cum laude M.Sc. graduation on the transitions to more sustainable urban water management and water supply (2005), he worked on water management in the Jobaru river basin at Saga University, Japan. His dissertation work is part of the program ‘Living with Water' and focuses on developing new concepts for urban water systems to reduce the vulnerability of urban areas to floods and droughts. Moreover, it deals with the societal change and transition processes involved. Rutger is founding partner of Deltasync, a research and design group that was awarded first prizes for the design of the floating city 'IJmeer' in the international Royal Haskoning Deltacompetition (2006) and in the Dutch Climate Contest (2007).
Fransje Hooimeijer studied Art & Culture Science at the Erasmus University Rotterdam and specialized in the history and theory of architecture, urban design and landscape architecture. After seven years of independent practice she is currently working on ‘The New Dutch Water City’, at the faculty of Architecture of Delft University of Technology department Urbanism. She investigates past, present and future relationships between urban design and water management in polder cities.
