Effects of coal mining and tunnel excavation on groundwater flow system in karst areas by modeling: A case study in Zhongliang Mountain, Chongqing, Southwest China

Abstract

A karst groundwater system ranks among the most sensitive and vulnerable types of groundwater systems. Coal mining and tunnel excavation can greatly change the natural hydrogeological flow system, groundwater-dependent vegetation, soil, as well as hydrology of surface water systems. Abandoned coal mine caves and proposed highway tunnels may have significant influences on groundwater systems. This study employs MODFLOW, a 3D finite-difference groundwater model software, to simulate the groundwater system's response to coal mining and tunnel excavation impact in Zhongliang Mountain, Chongqing, from 1948 to 2035. The results show a regional decline in groundwater levels within the study area following mining and tunnel construction. The groundwater flow system in the study area evolves from the Jial-ing River groundwater flow system to encompass the Jialing River, Moxinpo highway tunnel, Moxinpo, and the Liujiagou coal mine cave groundwater flow systems between 1948 and 2025. With the completion of tunnel construction, the groundwater level at the top of the tunnel is gradually restored to the water level in the natural state. The model also predicts groundwater level variations between 2025 and 2035. The groundwater level will rise further initially, however, it may take about 10 years for the system to stabilize and reach a new equilibrium. In light of these findings, it is advised that changes in groundwater flow systems caused by tunnel construction should be modeled prior to the practical construction. This approach is crucial for evaluating potential engineering and environmental implications.