Sediment transport processes on mixed beaches: A review for shoreline management

Mixed beaches are a comparatively neglected area of coastal research, other than for sedimentological investigations or relatively long-term geomorpho logical change. The paper reviews the progress of research into processes o f sediment transport on mixed sand and gravel beaches since 1980, including fieldwork, laboratory studies and modelling. First-order and secondary fac tors are identified. The hydraulic conductivity of the bulk sediment is fou nd to be an influence on swash and backwash infiltration and groundwater fl ow through the sediment. No existing transport model contains the most sign ificant factors for mixed sediment transport, which should include swash an d backwash hydrodynamics, infiltration, steep beach gradients, fractionatio n and differential hydraulic conductivity. Near-prototype scale physical mo del tests of profile response are needed, since mixed sediments cannot be s caled correctly for both hydrodynamic response and hydraulic conductivity.