5:15 PM - 7:15 PM
[AHW23-P02] Groundwater Flow at Boundary Area between Upland and Lowland, Northeast Tokyo
Keywords:Groundwater flow system, Upland-lowland boundary, Inorganic solutions, Stable isotopes, Tokyo
The groundwater flow becomes complicated generally in the boundary area of deferent geomorphic units due to drastic change of ground surface gradient and heterogeneity of hydro-geological structure in this area. In addition, some studies focus on the changes in the solutes of groundwater at the boundary of the geomorphic units. There are, however, few studies on groundwater flow process at the boundary of the geomorphological units. This study aims to clarify the groundwater flow at the boundary area between upland and lowland, northeastern Tokyo with application of inorganic solutions and stable isotopes of deuterium and oxygen-18 as tracers.
Spring water, groundwater and river water samples were collected in northeastern Tokyo from May to October 2024. The concentrations of inorganic solutions and stable isotopic ratios of hydrogen (δ2H) and oxygen (δ18O) were determined on all water samples. In addition, existed data of hydraulic head of groundwater and borehole logs of the sampling wells were also collected.
Spatial distribution of hydraulic head and solute concentration of groundwater in a vertical cross-section shows that the groundwater characterized by Ca-HCO3 type flows from upland to lowland and discharges at lowland area in the northern part of upland-lowland boundary. In addition, it shows that the shallow groundwater characterized by Ca-HCO3 type flows continuously from upland to lowland in the upland-lowland boundary. Also, the deep groundwater characterized by Na-HCO3 type flows from the zone at the depth of approximately 200 m toward to the zones at the depth of approximately 50 m in the same boundary.
In addition, spatial distribution of δ18O of the precipitation in highland, upland, and lowland and that of groundwater shows that the groundwater characterized by Ca-HCO3 type in the northern area could be recharged by the precipitation fallen on the western area of upland, and the groundwater characterized by Na-HCO3 type in the eastern area could be recharged by precipitation on highland area.
These results show that the groundwater flows in tens of kilometers scale in the northern part of upland-lowland boundary, and the groundwater flows in over 50 km scale in the eastern part of boundary, which suggests complicated groundwater flow structure in this area with different scale groundwater flow systems.
Spring water, groundwater and river water samples were collected in northeastern Tokyo from May to October 2024. The concentrations of inorganic solutions and stable isotopic ratios of hydrogen (δ2H) and oxygen (δ18O) were determined on all water samples. In addition, existed data of hydraulic head of groundwater and borehole logs of the sampling wells were also collected.
Spatial distribution of hydraulic head and solute concentration of groundwater in a vertical cross-section shows that the groundwater characterized by Ca-HCO3 type flows from upland to lowland and discharges at lowland area in the northern part of upland-lowland boundary. In addition, it shows that the shallow groundwater characterized by Ca-HCO3 type flows continuously from upland to lowland in the upland-lowland boundary. Also, the deep groundwater characterized by Na-HCO3 type flows from the zone at the depth of approximately 200 m toward to the zones at the depth of approximately 50 m in the same boundary.
In addition, spatial distribution of δ18O of the precipitation in highland, upland, and lowland and that of groundwater shows that the groundwater characterized by Ca-HCO3 type in the northern area could be recharged by the precipitation fallen on the western area of upland, and the groundwater characterized by Na-HCO3 type in the eastern area could be recharged by precipitation on highland area.
These results show that the groundwater flows in tens of kilometers scale in the northern part of upland-lowland boundary, and the groundwater flows in over 50 km scale in the eastern part of boundary, which suggests complicated groundwater flow structure in this area with different scale groundwater flow systems.