The 7th workshop of History Project

Date：26.May.2005　18:00-21:00
Place：Hosei Univ. Ichigaya Campus Boissonade Tower 26F Meeting roomA

"Problems and Their Transition in City Areas' Underground, Associated with Environmental Change of Groundwater -from the example of Tokyo-"
Tomohiro Tokunaga
Institute of Environmental Studies, Graduate School of Frontier Sciences, The University of Tokyo
The underground environment in the metropolitan area has undergone a major change, with the process of transition of groundwater as well as the ongoing development of underground spaces. The environmental change of groundwater and utilization of underground spaces have caused various environmental problems for the underground environment.
As seen in Fig. 1, the groundwater potential of artesian aquifer had decreased in the early 1970's; the water head dropped more than 50m lower. This caused a critical land subsidence in the large area of the Low City (Shitamachi) in the east of Tokyo (Fig. 2). Some artesian aquifers presented unconfined state, which would result to generate oxygen deficient air, causing several critical accidents. More specifically, the development work of underground space made oxygen deficient air move within the aquifer; this was the cause of the fatal accident by oxygen deficient air in the basement floor, etc.
The restriction of pumping was imposed in the period between 1961 and 1974, as a measure against the escalation of land subsidence resulted from the excessive pumping of groundwater. This allowed rapid recovery of the potential of artesian aquifer (Fig.1). It is thought that this recovery was realized because of the high water permeability in the relatively new aquifer in the Tokyo area, as well as the high infiltration rate in the Kanto area (:2-3mm/day) (Shimada, 1988; Shimada et al., 2002).
In the Tokyo area, the subsidence was alleviated by the regulation, and the groundwater potential has also been recovered. However, new problems have been posed.
The underground Tokyo station of East Japan Railway Company, was designed in 1965 and has been used since 1972. The well water level of confined groundwater was at the depth of 35m from the ground line when designed. However, the recovery of groundwater potential by the regulation described above, raised the water head of groundwater potential to the depth of 15m from the ground level until 1998. The East Japan Railway Corporation adopted the heavy-duty ground anchor system (Fig.3), which will allow the water level up to the depth of 12.8m from the ground level (Shimizu, 2004).
With the recovery of groundwater in the metropolitan area, the water leakage into underground structures was increasing. In general, the leakage into the structure is directly disposed as sewerage. However recently, several attempts have been made to use such leakage for the improvement of urban environment (Shimizu, 2004).
The Kokubunji Tunnel of JR Musashino Line has been used since 1973. This tunnel runs at right angle to the flowing direction of the groundwater and has faced troubles arose from the rapid rise of groundwater level between 1974 and 1991. The tunnel has 24 drain holes to control groundwater level. Since 2002, drained groundwater has been used for the restoration of small ponds of the area, and for increasing river flow rate. In consequence, the water environment of the Earth's surface of the area has been improved (Fig. 4).
Recently, Prof. Kajino and the research group (2004) have admitted the possibility of controlling the temperatures of pavement surface in the urban area, using the "surplus" groundwater, and further of alleviating heat-island phenomenon. These measures for improving urban environment by surplus groundwater will be important viewpoint for the sustainable development in urban areas.
As we have seen, I outlined the transition of underground environment along with the change of related issues in the areas around Tokyo. These changes in the metro area can be divided into to three stages. The first change was the environment deterioration of both Earth's surface and underground because of the excessive pumping; the second was the recovery of groundwater by the regulation of pumping; and the third was the occurrence of new issues associated with the groundwater recovery. It will be important to clarify appropriately the results of such process and to apply them to development plans of future urban areas, for realizing an environment-conscious urban development. Furthermore, the viewpoint for environmental improvement using surplus groundwater in the developed urban area, will be significant for the sustainable urban development.

"The Transition of Urban Water Environment from Geographical Viewpoints -focusing on the restoration of historical water environment in Tokyo"
Tomomasa Taniguchi
Department of Geography, Faculty of Geo-Environmental Science, Rissho University
Over the past century, the human activities have concentrated on cities; the rapid growth of population and developed infrastructure caused a dramatic shift in the nature within cities and surrounding areas. The natural environment of cities can be understood based both on present and past natural environments, as well as the formation process of present situation. Closely linking to human activities, "water" including the river is changing affected by artifacts; we need to figure out the natural condition of water, in addition to the process of human-induced effects, to understand the impact to water within a city. In other words, the relation between water and human should be comprehensively studied because various elements are connected with urban hydrological environment.
Now I will outline the urban hydrological study centered on rivers in Tokyo. Although various studies are made (e.g., present situation and issues of water environment in urban areas, effects on water circulation and environment caused by urban development process, etc.), historical studies of hydrological environment on the Edo, Meiji or Taisho Era are scarce because of the lack of hydrological observation data. Naturally, it is difficult to understand the environmental change of the periods without scientific data, and studies have centered on the Showa and Heisei Period with abundant numerical data. However, it is important to clarify historical water environment to understand the relationship between human and nature since the modern age. Therefore, referring to the descriptions in literary works and historical documents on rivers and waterways, I have restored the images of Tokyo's water environment of the early 20th century, and clarified the water quality distribution and the transformation of water quality of the Sumida River over the past century. This study aimed to figure out the river environment of the age without scientific analytical data.
The study showed that the water contamination problem occurred in rivers flowing across the city core, including the Sumida River and the Kanda River in the early 20th Century; in particular, the quality of waterways along the densely-populated areas like Asakusa and Hongo suffered serious deterioration because of the wastewater from households. The polluted waters were spreading over Musashino plateau and the left bank of the Sumida with the expansion of the city area; however, relatively good waters remained within the city, around pond springs of Musashino plateau, and the upper course of rivers flowing from those springs. In general, rivers and waterways were more and more polluted in the densely-settled area, and the deterioration was serious in the peripheral areas of lowlands and plateaus.
Furthermore, the general hydrological environment of the city would be clarified not only by rivers/quality (water quality and loading amount), but also by groundwater/volume (volume of water and water level). From this viewpoint, I reported on groundwater and volume of water for the historical reconstruction of hydrological environment.
This attempt can successfully show that the reconstruction of historical hydrological environment -based on text documents including descriptions on water, move of groundwater decrement point associated with lowering of the groundwater level, and hydrological landscapes including forms of wells, water and land utilization, etc.- is one of the effective ways to clarify the phenomenon or situation concerning water in the period or area without observation data.
Geography has traditionally analyzed the natural, human and social phenomenon respectively, as well as their relationship to know each region; however in recent years, "integration of the humanities and science", "environment", "nature" and "human" have been emphasized from the viewpoints of environment conservation and sustainable utilization. To understand each area, we should reevaluate our methods, documents, and analytical forms, in addition to the study on natural environment including cultural elements, or the one on cultural and social environments including natural elements. The waterfront environment has its original practice and landscape; recent waterfront renovations, urban planning and plans for the collective housing area have been required to utilize the history and tradition of the place, .which will lead to the recognition of immediate natural environment in the city. Such tendency also confirms the needs for a new method and analysis on urban waterfront environment, beyond traditional procedures.