[A-HW32] Material transportation and cycling in aquatic ecosystems; from headwaters to coastal areas

[AHW32-20] Understanding of Subsurface Flow Systems: Role of Environmental Tracers in Model Calibration

*A T M Sakiur Rahman¹, Takahiro Hosono¹, Yasuhiro Tawara², Dennis Boateng¹, Jun Shimada¹ (1.Department of Earth and Environmental Science, Kumamoto University, Japan, 2.Geosphere Environmental Technology Corporation, NCO Kanda, Awajicho, Chiyoda-ku, Tokyo 101-0063, Japan)

Keywords:Fully coupled tracer aided model, Multiple tracer simulation, Groundwater age, Uncertain boundary correction

Integrated watershed modeling techniques are being applied to examine the surface and subsurface interactions in recent years. Generally, modeling approaches heavily rely on the best fit of the hydrograph which alone cannot describe entire catchment water dynamics. For holistic understanding of hydrological processes, it is necessary to incorporate and simultaneously simulate tracers which can provide important inferences about water ages, flow paths and origin. Hence, this study incorporated multiple tracers like tritium (³H), Krypton-85 (⁸⁵Kr), and groundwater temperature in model calibrations and seamlessly simulated tracers coupled with surface and subsurface flows using a fully distributed physically based modeling approach (i.e., GETFLOWS) for detailed characterizations of Kumamoto water regimes in southern Japan. The first model developed using the regular hydrometric parameters could not characterize isotopic compositions and groundwater temperature, though it showed acceptable model performance for simulating surface water and groundwater hydrographs for several observation stations located in the area. The second model calibrated by integrating tracers with regular parameters well characterized hydrographs of surface water, groundwater as well as isotopic compositions and groundwater temperature. Hence, tracer-aided model was used for simulating groundwater storage, flow paths and groundwater age which showed a close agreement with estimation of water ages using isotopic approaches in previous studies. The findings of the novel approach proposed in this study prove the potential in the use of multiple tracers for details visualizations of subsurface water dynamics and findings can be used for local water resources management and planning.