Japan Geoscience Union Meeting 2018

Presentation information

[EE] Oral

A (Atmospheric and Hydrospheric Sciences) » A-HW Hydrology & Water Environment

[A-HW22] Hydrological Cycle and Water Environment

Wed. May 23, 2018 3:30 PM - 5:00 PM 201A (2F International Conference Hall, Makuhari Messe)

convener:Seiya Nagao(Institute of Nature and Environmental Technology, Kanazawa University), Isao Machida(Geological Survey of Japan), Shin'ichi Iida(国立研究開発法人森林研究・整備機構森林総合研究所森林研究部門森林防災研究領域水保全研究室, 共同), Takeshi Hayashi(Faculty of Education and Human Studies, Akita University), Chairperson:Nagao Seiya(Institute of Nature and Environmental Technology, Kanazawa University), Iida Shin'ichi(Forestry and Forest Products Research Institute), Machida Isao(Geological Survey of Japan, AIST)

3:30 PM - 3:45 PM

[AHW22-01] Distribution of Modern, Paleo and Formation water in Plains and Basins in Japan

*Isao Machida1, Reo Ikawa1, Masahiko Ono1, Atsunao Marui1 (1.Geological Survey of Japan)

Keywords:Groundwater age, Residence time, Groundwater flow system

Ground water research group in Geological Survey of Japan, have been carried out groundwater sampling in basins or plains in Japan and published hydrogeological maps, Water Environmental Maps. Recently, we started to re-analyze them from the view of groundwater age by using ion concentration, stable isotopes and radioactive isotopes in water. Groundwater age can be classified into three types, Modern water (younger than 20,000 years), Glacial water (older than 20,000 years), Formation water (very old, c.a. 1 million years) and their transition zones (Hasegawa et al., 2017). Demonstrating the distribution of such groundwater is important not only to consider a lower boundary condition of groundwater flow system but also to show the basic information for hydrogeology in Japan.

In the presentation, we will introduce several conceptual maps in middle and northern Japan. As a result, the boundary of Modern and Glacial waters locates at a shallower than 200 m, in where soft Quaternary sedimentary rock area with gentle topography. This result emphasized that even soft Quaternary rock (generally with high permeability) can form the lower no-flow boundary of the groundwater flow system in respect to the Modern groundwater. The Formation water locates at depths of deeper than 500 m but seems to have wide transition zones.

On the other hands, the Modern water presents deeper than 200 m at volcanic areas. In these areas, the steep topography and high permeable geology seem to induce a high driving force of groundwater flow and produce the large scale of Modern groundwater flow system. At the coastal zone at the foot of Mt. Fuji, the Modern water is found at a depth of 250 m. The result above is the actual demonstration of the relationship between topography and the distribution of the Modern water.