Program

Poster Presentations

Day 2, June 11（Thu.）　　Room P (5F 501+502)

2P-32

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Deciphering the Groundwater Flow System in the Kumagawa River Basin Using Multi-Isotope Tracers

(¹Univ. Tokyo, ²Kumamoto Univ.)
^oHirochika Sumino¹, Sakuya Maruyama¹, Tomohiko Tomita², Tomoko Minagawa², Kei Yoshimura¹

In Japan, climate change driven by global warming has recently increased the risk of flooding and landslides, as frequent torrential rains associated with the formation of linear precipitation zones during the rainy season have intensified. Notably, the July 2020 torrential rains caused catastrophic flooding in the Hitoyoshi Basin within the Kumagawa River Basin in Kumamoto Prefecture, claiming the lives of 50 people. Therefore, advanced monitoring of the water cycle and quantitative estimation of the water budget are essential for disaster prevention. In this region in particular, flood control plans are being developed to modify the land surface to facilitate precipitation recharge. However, it remains unclear what percentage of precipitation will be recharged and what percentage will flow over the surface without recharge—visualizing groundwater flow systems that both store precipitation and discharge into rivers is crucial in understanding the water cycle and budget.
From the time groundwater originating from precipitation recharges the underground aquifer until it emerges at the surface, the concentrations of major dissolved ions change due to leaching from rocks, and the ³H concentration changes due to radioactive decay to ³He, increasing ³He/⁴He. On the other hand, tracers such as ⁴He/²⁰Ne, δ¹⁸O, and δ²H (or δD), which retain information of the precipitation, also exist. We attempted to unravel the groundwater flow system in the Kumagawa River Basin by appropriately combining these geochemical tracers.

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