Towards simulating solute transport in complex, regional-scale fracture networks: a rapid upscaled approach

Currently, the most common approaches for simulating solute transport in fractured aquifers are the single- or dual-continuum and the discrete fracture network (DFN) methods. However, continuum approaches often lack accuracy due to averaging, whereas DFN approaches may be computationally prohibitive for large-scale fracture networks. To address these challenges, this study presents an Upscaled Fracture Network (UFN) model, developed by discretizing complex fracture networks into elementary volumes, identifying solute transport flow channels and calculating breakthrough curves within an elementary volume. The identified flow channels within the micro-scale DFN are collectively employed to construct the residence time at the macro-scale DFN. Validated against a random walk particle tracking (RWPT) DFN-based approach, the UFN model accurately captures solute transport processes in saturated fracture networks at the macro scale, and represents a significant advancement in simulating solute transport in complex, regional-scale aquifers due to its computational efficiency, simple implementation, and high level of accuracy.