Hierarchical sedimentary architecture governs basin-scale solute dispersion: From pre-asymptotic dynamics to uncertainty propagation

Abstract. Real aquifers are structured as hierarchical sedimentary systems, where multi-scale heterogeneity and geometric connectivity jointly govern groundwater flow and solute migration. Although the general influence of heterogeneity has been extensively investigated, the scale-dependent effects of hierarchical organization, particularly under basin-scale flow conditions, remain inadequately quantified. In this study, we reconstructed a series of three-dimensional heterogeneous sedimentary architectures at the basin scale and performed numerical simulations to explore dispersion behavior. The results reveal that the geometry and connectivity of dominant lithofacies at macroform scales control macro-dispersion, while finer-scale heterogeneity has only a secondary influence on plume evolution. Furthermore, the evolution of macro-dispersion is characterized by a prolonged pre-asymptotic phase, far exceeding that observed at classical sites such as Borden, indicating that basin-scale solute transport remains non-ergodic over extended times and distances. Uncertainty analysis further identifies a distinct buffering effect inherent to basin systems, in which the aggregation of numerous flow pathways dampens realization-to-realization variability caused by local heterogeneity. When integrated with previously reported laboratory- and sandbox-scale results from the same site, these findings establish a mechanistic and transferable framework linking hierarchical sedimentary architecture to multi-scale dispersion and uncertainty. This framework advances theoretical understanding of non-Fickian transport and provides practical guidance for large-scale modeling and groundwater management in data-limited regions.