[A-HW17] Near Surface Investigation and Modeling for Groundwater Resources Assessment and Conservation

[AHW17-P04] Groundwater connectivity between upland and lowland, eastern Tokyo, Japan

*Mugiho Miura¹, Maki Tsujimura¹, Qianyu Yang¹, Taiga Suzuki¹, Kei Matsuura², Teruaki Hirano² (1.University of Tsukuba, 2.Tokyo Metropolitan Research Institute for Environmental Protection)

Keywords:Spring, Groundwater, Upland, Lowland, Groundwater connectivity, Boundary area

This study aims to clarify the groundwater connectivity in urbanized area, Tokyo, where the strata type is different between the upland and the lowland, with a focus on shallow groundwater and spring water quality. From June to November 2023, spring water, river water, and groundwater were collected in the eastern part of Tokyo, and analyzed the concentrations of inorganic dissolved ion components and stable isotopic composition of hydrogen (δ²H) and oxygen (δ¹⁸O) in water samples. Then, spatial distribution of the concentrations of inorganic dissolved constituents and δ¹⁸O were investigated in the boundary area from the upland to the lowland, and the groundwater connectivity was discussed using topographic cross-sectional maps. Concentrations of dissolved ion components and δ¹⁸O of spring and groundwater were similar in the boundary area. The topographic cross sections with location of groundwater wells and springs suggest that groundwater connectivity exists between the upland and the lowland at a depth of 80 m in the eastern part of the study area. In the southern part of the study area, the groundwater connectivity is also indicated between the upland and the lowland in the shallow part, and the groundwater flows along the direction of the topographic slope. These results suggest that the groundwater connectivity exists in the boundary area from upland to lowland, where the strata type is different, by comparing the concentrations of inorganic dissolved ion components and δ¹⁸O of groundwater to the topography.