Evaluation of change in subsurface thermal environment due to groundwater flow in the Tokyo Lowland,Japan |
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Authors: | Akinobu Miyakoshi Takeshi Hayashi Atsunao Marui Yasuo Sakura Shinichi Kawashima Masafumi Kawai |
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Institution: | (1) Geological Survey of Japan, National Institute of Advanced Industrial Science and Technology, 1-1-7 Higashi, Tsukuba 305-8567, Japan;(2) Faculty of Education and Human Studies, Akita University, Akita, Japan;(3) Faculty of Science, Chiba University, Chiba, Japan;(4) Civil Engineering Center, Tokyo Metropolitan Government, Tokyo, Japan |
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Abstract: | Information on the distribution of subsurface temperature and hydraulic heads at 24 observation wells in and around the Tokyo
Lowland, the eastern part of the Tokyo Metropolitan area, were examined to make clear the relationship between groundwater
and the subsurface thermal environment in the urban area. Minimums in temperature–depth logs due to subsurface temperature
increasing at shallow parts were recognized in 21 wells. This fact shows subsurface temperature is affected by ground surface
warming in almost all of this area. Deeper than minimums, where the effects of surface warming became relatively small, regional
variation is observed as follows: high temperatures are shown in the central part to the southern part, and low temperatures
shown in the inland to eastern part. The high temperature area corresponds to an area where the lower boundary of groundwater
flow is relatively shallow. This area corresponds also to an area with severe land subsidence resulting from excessive groundwater
pumping. It is considered that this high temperature area is formed by the effects of upward groundwater flow affected by
hydrogeological conditions and pumping. On the other hand, a comparison between past data (1956–1967) and present data (2001–2003)
revealed widespread decreasing temperature in the inland area. This is explained by downward groundwater flow based on an
analysis of temperature–depth logs. This fact suggests that subsurface temperature is not only increasing from the effects
of surface warming but also decreasing from the effects of groundwater environment change due to pumping. |
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Keywords: | Temperature– depth logs Subsurface temperature Groundwater flow Groundwater pumping Tokyo Lowland |
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