Surfaces geosciences (Hydrology-Hydrogeology) Miscible transfer of solute in different model fractures: From random to multiscale wall roughness Transport miscible de solutes dans differentes fractures modeles : influence de la rugositealeatoire ou multiechelles

Miscible tracer dispersion measurements in transparent model fractures with different types of wall roughness are reported. The nature (Fickian or not) of dispersion is determined by studying variations of the mixing front as a function of the distance travelled but also as a function of the lateral scale over which the tracer concentration is averaged. The dominant hydrodynamic dispersion mechanisms (velocity profile in the gap, velocity variations in the fracture plane) are established by comparing measurements using Newtonian and shear thinning fluids. For small monodisperse rugosities, front spreading is diffusive with a dominant geometrical dispersion (dispersion coefficient