Simultaneous rejuvenation and aging of groundwater in basins due to depth‐decaying hydraulic conductivity and porosity

The age of groundwater is a manifestation of the temporal scale of groundwater flow in basins, whose pattern was recently found to be influenced by depth‐dependent hydraulic conductivity ( K ). In this paper, we show through numerical simulations how well‐documented depth‐decaying K and porosity (θ) influence groundwater age. In the unit basin, depth‐decaying K and θ cause aging in deeper parts and rejuvenation near the discharge zones, and the size of rejuvenated zones decreases with the decay exponent ( A ). In the Tóth basin, the geometry and size of rejuvenated zones, which are generally located at the interfaces between flow systems in the mid to lower reaches of the basin, are sensitive to A . In both basins, the maximum relative age and the relative age of groundwater at the lowest discharge point are dependent on A . Therefore, the depth‐decaying K and θ cannot be ignored when interpreting groundwater age distribution.