Date：10 Sep. 2008 (Wed) 14:00-16:00
|" The Geology
and Groundwater of Hino Terrace"
(Tokyo Metropolitan Kitatama High School)
1) Water Circulation
It is to be noted that sky and ground are linked with each other in water circulation. My study is based on the data on the level of groundwater, quantity of rain, temperature of groundwater, and temperature collected when I was in Tokyo Metropolitan Oume Nogyo High School. I made a diagram showing the level of groundwater based on the survey of wells on Akiruno Terrace. Because Mr. Hosono at National Research Institute of Fire and Disaster conducted researches on the eastern areas of Musashino, I selected the western areas of Musashino and Hino Terrace as subject of research.
*The report also included the geologic structure and research methods of groundwater around Hino Terrace.
2) Groundwater of Hino Terrace
A land use map drawn around the 15th year of Meiji (1882) shows that there were few settlements because water flow did not exist. This was the original landscape of Hino Terrace. After the 22nd year of Meiji (1889) when Kobu railway line was built, there were not so many inhabitants on the terrace. After that, Hino Motors advanced rapidly as a military plant. Hino offered several advantages for military industry, such as rich groundwater, and the location of terrace which was difficult to be looked over. The place-name, Izumizuka shows that spring water existed on the terrace.
Hino Terrace is a river terrace composed of four-level platforms (Hino terrace, Tama terrace, Toyoda terrace, Ishita terrace and Tamagawa valley), serving as reservoir of groundwater. The loam layers are composed of Tachikawa (Mt. Fuji), Musashino (Mt. Hakone), and Shimosueyoshi (which was built up 130,000 ago) loams. We conducted a survey on groundwater based on the general investigation of wells. At present half the number of those wells disappeared, therefore the similar investigation on groundwater has become impossible. Groundwater is confined beneath each terrace plain, and is spread out in a fan-like form beneath the ground where Kita-Hachioji station is located. The urbanization of terrace land has decreased groundwater.
The formation history of Hino Terrace: the gravel layer of the Tama River made up peninsular-shaped cay; in the next place, the Asakawa (river) has built up Tamadaira terrace plain and the terrace land has spread toward the south. The three-level layered terraces can be found around Tokoji area. The Kurokawa (river) was the result of the downcutting of spring water after the formation of Tamadaira terrace plain. The similar formation process can be observed around Hamura and Fussa. In Hamura, "maimaizu well" (a well on a lower ground reached from a higher place with a spiral-form approach) was built on the higher ground avoiding rainwater streams. In Fussa, the steam has become a drain, along which bars stand in a row. A low terrace plane with reverse inclination can be found in Nogawa.
The theory of Asakawa as subsoil flow (which was discussed in the previous research meeting): the section view in attached document shows that water of Kazusa layers is related with the subsoil flow on Toyoda terrace plane. The spring water in Shimizudani Park of Kurokawa was dried up two times over the past thirty years. It can be considered that this fact is not related to the Asakawa on Hino Terrace, because the diagram of groundwater level shows that the flow is derived from the north.
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