以雪山隧道導坑水之地球化學參數瞭解地表─地下水之交互作用

Surface water-groundwater water interactions play key roles on understanding the regional hydrological cycle. However, most the relevant studies investigate the interactions using models instead of the field experiment. The Hsuehshan Tunnel provides a great opportunity investigating the issues regarding velocity and celerity. In this study, we collect and analyze the amount of rainfall and discharge in the tunnel, and the hydrogen and oxygen isotopes of rainfall and tunnel water, understanding the response of tunnel water to rainfall events and calculating the contribution of rainfall to groundwater. The hydrogen and oxygen isotopes of rainfall reveal distinct seasonality among the wet and dry seasons, and the isotopic values of the groundwater remain in between and vary in a limited range. The LMWL is δD = 8.9δ18O+18.3. We estimate that the ~63.4%-75.2% and ~24.8%-36.6% of the tunnel water is from rainwater in the wet and dry season, respectively. By using theΦindex to separate infiltrated rainwater from rainfall, it is found that ~24%-34% and ~75%-96% of annual rainfall infiltrating to the groundwater, respectively, according to rainfall-runoff relations and the isotopic data. We believe that such discrepancy could be attributed to the velocity and celerity. From the time-lag analysis, it is found that the discharge of tunnel water rose in <1 month after a rainfall event. However, there is lag time, ~couple of months, between the isotopic values of rainwater and tunnel water. The understanding of the surface water-groundwater interactions will be the key for the joint operation of surface water and groundwater.