We present here a new conductivity-based system for measuring concentrations and grain velocities in the sheet-flow layer. The system is equipped with a new technique that translates measured concentrations back into vertical sensor movement, which enables the measuring probes to track a dynamic bed level. The new CCM system was applied for the first time during a series of swash zone experiments with bichromatic wave conditions. The results show a rapid erosion event with an erosion depth of an estimated 5 mm at the start of the uprush, after which the suspended sediment is advected to the upper swash. Sediment is transported back and deposited to the lower swash mainly during the second half of the backwash. The sheet-flow behaviour clearly differs from observations for non-breaking waves, with both the vertical concentration gradient and its mean vertical position varying within the wave group cycle

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