The Hidden Structure of Hydrodynamic Transport in Fractured Media: Velocity dynamics and intermittency

Slides presented at UPC, Barcelona, on 29 October 2026. The presentation examines how flow heterogeneity, Lagrangian velocity statistics and spatial memory govern purely advective transport in single rough fractures and discrete fracture networks. An upscaled Ornstein–Uhlenbeck continuous-time random walk (OU–CTRW) model uses three inputs: the velocity distribution, tortuosity and a spatial correlation length. Comparisons with direct particle tracking address breakthrough curves, mean displacement and plume spreading. In single fractures, the correlation length is calibrated on late-time breakthrough; in fracture networks, all three inputs are obtained from the resolved flow field without calibration on transport data. The presentation also examines limitations of the Gaussian memory model, including non-exponential correlations, velocity-dependent persistence and intermittent velocity increments.