Abstract: The mountain tunnel drainage may change the ambient groundwater seepage field and even drain groundwater resources, which threatens terrestrial vegetation. In order to quantitatively analyze the impact of tunnel drainage on terrestrial vegetation, the soil water matric potential is selected as an indicator for plant survival state to build an analysis model of tunnelsoilplantatmosphere continuum (TSPAC). In the model, the Richards equation is utilized to describe the moisture movement in the root zone. The atmosphere and the groundwater seepage model are input to the Richards equation as top and bottom boundary conditions. Then, the soil matric potential distribution of the root zone is secured by solving the Richards equation. Based on matric potential distribution within the root zone, the plant dynamic wilting process can be evaluated and its survival state can be judged. The method is applied to Mingtangshan Tunnel in Dabieshan Mountains to analyze its drainage impact on terrestrial vegetation. The applicable results show that: (1) The response of matric potential in the plant root zone to variations in groundwater levels and atmospheric conditions is lagged and nonuniform, thus the plants wilt gradually instead of withering immediately after the groundwater table descends. (2) The atmospheric conditions play the dominant role in vegetation survival in this region. (3) The drainage impact of the tunnel on surrounding plants is relatively small and different for various vegetation. The TSPAC analysis method innovatively introduced tunnelgroundwater seepage model to traditional SPAC models. By integrating factors that represent tunnels and environment, the approach analyzed the whole process of “tunnel drainagegroundwater recessionvegetation withering”. The method integrates tunnel, soil, vegetation and atmosphere as a whole to analyze the ecoenvironmental impacts of tunnel drainage. The approach can provide a novel thought of facilitating tunnel engineering environmentally friendly.

Key words: mountain tunnel, drainage, groundwater table, terrestrial vegetation, TSPAC analysis model, soil water matric potential