A flow constrained simplification method for high-resolution fracture networks in epikarst zone

High-resolution fracture networks extracted from outcrop images in karst areas often exhibit highly complex structures, which increases difficulty in numerical computation convergence and cost for flow and solute transport. To address this issue, we propose a flow‐constrained simplification method that integrates geometric refinement with hydraulic correction to preserve the macroscopic flow characteristics of the original networks. During the simplification of fracture structures, each potential geometric modification is evaluated with respect to the flow field to ensure that local flow reversals or disruptions of dominant channels do not occur; meanwhile, an aperture correction based on flow conservation is applied to compensate for the hydraulic deviations induced by geometric alterations. Three representative outcrop‐derived fracture networks from the epikarst zone in southwest China were used to evaluate the method. The results indicate that the simplification and optimization of geometric and topological structures improve network partitioning, thereby significantly enhancing computational efficiency. Flow constraints enable the simplified model to preserve the main flow paths and equivalent hydraulic permeability of the original model, while its prediction errors for solute transport are markedly lower than those of the unconstrained simplification method. Consequently, this approach can provide an efficient means for uncertainty quantification of flow and solute transport in large-scale fracture networks.