On the appropriate “equivalent aperture” for the description of solute transport in single fractures: Laboratory‐scale experiments

Three distinct definitions of “equivalent aperture” have been used in the literature to describe variable‐aperture fractures; however, significant inconsistencies exist in the literature as to which “equivalent aperture” is appropriate for simulating solute transport. In this work, a systematic series of hydraulic and tracer tests was conducted on three laboratory‐scale fracture replicas, and the cubic law, mass balance, and frictional loss apertures were calculated. The analytical solution of the one‐dimensional advection‐dispersion equation was fit to the experimental breakthrough curves. Additionally, one of the experimental aperture fields was measured directly using a light transmission technique. The results clearly demonstrate that the mass balance aperture is the only appropriate “equivalent aperture” for describing solute transport in a single variable aperture fracture and that the mass balance aperture is an excellent approximation of the arithmetic mean aperture. Previously, these conclusions have been reached based only on theoretical and numerical analyses.