Research Highlight - Groundwater flow and age in topography-driven groundwater flow systems with geological barriers
“This study is the first to explore the effect of fault zones on groundwater age distribution in topography-driven groundwater flow systems. Using the HydroGeoSphere model, we elucidated the impacts of fault zones on groundwater age characteristics in both non-Tóthian and Tóthian models.”
Jia, L., Xie, Y., Love, A. J., Wohling, D., Dai, X., & Fu, R. (2025). Groundwater flow and age in topography-driven groundwater flow systems with geological barriers. Journal of Hydrology, 659, 133241. https://doi.org/10.1016/j.jhydrol.2025.133241
The research examines how groundwater age and flow systems are influenced by topography and geological barriers, using numerical simulations to clarify the interaction between surface-driven flow and subsurface heterogeneity. Traditional models of topography-driven flow often assume homogeneous geologic conditions, which can obscure the role of stratigraphic variations in shaping groundwater movement and age distribution. This study offers a detailed exploration of how structural barriers— such as low-permeability formations— interrupt or redirect groundwater pathways and affect the spatial and temporal distribution of groundwater age.
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By simulating a series of generic basin configurations with and without geological barriers, the researchers demonstrate how the presence and position of these features can significantly influence groundwater flow regimes. In systems without barriers, flow patterns closely follow the topographic gradient, producing predictable age gradients with younger water near recharge areas and older water in deeper zones or near discharge points. However, when geological barriers are introduced, these patterns shift: groundwater may be diverted laterally or forced upward, disrupting the expected age structure and creating zones of increased or decreased residence time.
The findings underscore the complexity of groundwater systems where both surface and subsurface controls are at play. Notably, the study finds that under certain conditions, groundwater can be much younger or older than predicted by simple topography-driven models, depending on how barriers affect flow connectivity. These insights have significant implications for water resource management, especially in regions where age-dating is used to assess sustainability, recharge rates, or contaminant transport potential.
To simulate these dynamics, the researchers used HydroGeoSphere (HGS)— a fully integrated, three-dimensional modelling platform capable of resolving complex interactions between surface and subsurface flow. HGS was used to build synthetic models representing various geologic and topographic configurations, allowing for precise control of boundary conditions and material properties. Through HGS, the team was able to track groundwater age distributions using an advection–dispersion approach and to test how different barrier scenarios influenced flow paths. The model’s flexibility in handling variably saturated conditions, heterogeneous media, and coupled hydrological processes made it ideal for evaluating how structural geology alters flow dynamics, reinforcing the importance of integrated modelling tools in understanding subsurface systems.
Abstract:
Faults in hydrogeological systems can act as conduits or barriers for groundwater flow. However, the effect of faults on groundwater flow and age has not been widely studied, particularly in topography-driven flow systems (i.e., Tóthian flow systems). This study established Tóthian models through HydroGeoSphere and compared age distributions between models with and without fault zones. Hydraulic conductivity of the aquifer was set at 1 m/d, whereas that of the fault zones (Kf) was varied at 0.001–0.75 m/d to simulate barrier effect and at 5–20 m/d to mimic conduit effect. Simple (aquifer thickness 100 m) and complex Tóthian models (aquifer thickness 1500 m) were both considered. Our results show that, when the fault zones act as conduits, the groundwater is slightly younger than it would be without the fault zones, regardless of simple or complex Tóthian models. When the fault zones act as barriers, in most simple Tóthian models, groundwater cannot flow across the fault zones, with new local flow systems forming on both sides. Groundwater age thus increases upstream but decreases downstream of the fault zones. In the other simple Tóthian models (Kf at 0.25–0.75 m/d), groundwater can flow across the fault zones at some depths. Age changes are more pronounced in parts with flow parallel to the fault zones than those in other parts. In all complex Tóthian models with fault zones as barriers, new local and intermediate flow systems are formed upstream and downstream of the fault zones. Age changes mainly occur in deep parts of the aquifer.