Simulation of groundwater flow paths under managed abstraction and recharge in an analogous sand-tank phreatic aquifer

Understanding the impacts of managed abstraction and recharge, i.e. artificial regulation of groundwater, on flow dynamics contributes to water resources planning and effective management of river basins. Based on the hydrogeological conditions of the aquifer in the Tailan River Basin, northwestern China, a two-dimensional sand-tank physical model and the corresponding numerical model were conceptualized and developed to investigate the influence of such regulation on the moisture content, groundwater flow patterns, groundwater age, residence time distributions, and groundwater flow paths in the groundwater reservoir. Four scenarios were examined at laboratory scale. The results showed that groundwater flow was influenced significantly by artificial regulation and that the depth of influence greatly increased depending on the regulation modes. Abstraction mainly alters the groundwater flow paths and moisture content at the ground surface in the core area of the depression cone and reduces the groundwater age in the entire aquifer. Groundwater flow lines are gradually parted by artificial recharge at different depths. Groundwaters of different ages have different behavior under the different artificial recharge depths and artificial recharge modes. Saddle points (kind of stagnation points) appeared at different locations, which were highly dependent on the modes of artificial regulation. Some of the lessons learned, and some management strategies, are proposed based on the results. Despite the dimensionality and scale of the model adopted, resulting in a relatively very large capillarity zone unrepresentative of field conditions, these findings nonetheless have important implications for understanding groundwater flow dynamics impacted by highly intensive human activities.