Date：4 Aug. 2008 (Mon) 10:00-12:00
|" The Relationship between Groundwater under Hino Terrace and Asakawa (river)"
Professor, Hosei University
1. "River Water and Groundwater of Asakawa Left Bank Areas"
We set up an observation well in areas between upstream to downstream of Asakawa which runs through the edge of Hino Terrace, to estimate the underground flow. The survey results show that the flow volume decreased in the upstream areas because the river flow runs into groundwater; on the contrary, groundwater flows into the river in the downstream area. The vertical distribution of groundwater temperature shows that the change of water temperature caused by the flow into the groundwater has a correlation with the temperature change of Asakawa. The observation using OCD camera clarified the general flow direction of the groundwater. As a whole, the situations of incoming and outgoing flows across old river flow and groundwater became evident.
2. Recharge Area of Hino Spring Waters
I gave advices on recharge area surveys conducted by the Tokyo Metropolitan Government. I wrote an article on spring waters under the central library, and Kurokawa spring waters in the survey report. The data obtained by drilling including land surface contour lines, contour lines at the top surface of gravel layer, and groundwater level, show that the flow of groundwater of spring water under the library is assumed to be derived from Asakawa. On the other hand, Kurokawa spring waters do not relate with Asakawa. The overall groundwater system is recharged from rainwater on the terrace; and the groundwater and the river flow is considered to be exchanged via the old river flow.
< Summary of Questions and Answers>
Participants were particularly interested in the origin of Asakawa subsoil water and discussions were focused on this theme. Some of the examples are as follows:
・Even if there is the difference of elevation between inflow part and the spring water under the library, I think it is not enough to determine that the flow joined with the spring water.
・The coliform detected under the library seemed to be derived from local factors.
・Nitrate-nitrogen is derived from agricultural factors.
・It is necessary to analyze the flows based on wide water cycle including Tamagawa.
・The organic chlorine detected in concentrated amounts in Kurokawa spring waters, is derived from factories.
・The biota around the Fureai Bridge is different from surrounding areas because of the inflow of groundwater.
In the second meeting, we will invite Mr. Kiyomi Tsunoda (Tokyo Metropolitan Kitatama High School). Furthermore, we will conduct a pilot program on our model district: Tokoji spring water, in cooperation with Ministry of Land, Infrastructure, Transport and Tourism.
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