| Citation: | Zheng Xiaokang, Yang Zhibing. Numerical simulation of saturated-unsaturated groundwater flow and contaminant transport in a karst aquifer[J]. Bulletin of Geological Science and Technology, 2022, 41(5): 357-366. doi: 10.19509/j.cnki.dzkq.2022.0211
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Groundwater in karst aquifers is an important source of drinking water. Due to the complexity of hydrogeological characteristics, it is extremely challenging to analyze and evaluate the groundwater environment in karst aquifers by numerical modeling. In this study, a variable saturation flow equation is used to describe the saturated-unsaturated flow in the aquifer matrix, a pipe flow equation is used to describe the laminar and turbulent flow in karst conduits, and the convective dispersion equation is used to describe solute transport in the matrix and conduits. The accuracy of saturated-unsaturated flow simulation is verified by comparison with experimental data and simulation results from the MODFLOW-CFP code. The numerical model is used to explore the effects of karst conduits and unsaturated parameters on groundwater flow and contaminant transport. These results show that the numerical model can well reproduce the groundwater dynamics in saturated-unsaturated regions and in the karst conduit of the aquifer; furthermore, the karst conduit has a great influence on the seepage field of the aquifer. Relatively rapid flow in the conduit leads to the inflow of surrounding groundwater, affecting the local flow field. As a result, the contaminant is transported through advection in the conduit and is quickly discharged through the outlet(spring). Breakthrough curves show that the response of concentration at the spring is faster than the corresponding location in the matrix. Unsaturated parameters have different effects on the breakthrough characteristics. The model established in this paper improves the simulation methods of groundwater flow, pollutant transport and coupling of matrix-conduit flow with solute transport in the saturated-unsaturated region in karst aquifers. The work deepens the understanding of groundwater dynamics and contaminanttransport in karst aquifers and is thus of great significance to karst hydrogeology and groundwater environment protection.
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