How Do Fractures Influence Hyporheic Exchange in Sedimentary Rock Riverbeds?

Bedrock rivers represent a hydrogeological environment in which surface water flows along an exposed bedrock surface. Studies of hyporheic exchange have exclusively involved composed unconsolidated fluvial sediments, leaving critical knowledge gap. This study evaluates the conditions that could support bedform-scale within fractured sedimentary river based on field data collected near Guelph, Canada. Hyporheic at was evaluated by numerically modeling migration conservative solute tracer through riverbed two-dimensional vertical cross-section flow direction. A stochastic discrete fracture-matrix framework developed to measured subsurface properties, producing probabilistic distribution potential pathways. Flow and transport model results indicate that: (a) exists with high fluid velocities fractures, yet long residence times due diffusion across boundary; (b) coincidence fractures hydrodynamic head gradients controls spatial extent exchange; (c) variability time is large (i.e., tens years) inherent facture network properties. Our field-based numerical indicates average (median) may not be good proxy for natural attenuation capacity has emplace contaminants porous rock matrix become long-term source trace contaminants.