Surface Moisture Variations on a Multibarred Macrotidal Beach: Implications for Aeolian Sand Transport

Surface moisture contents measured on a macrotidal beach with multiple intertidal bars and troughs over three semidiurnal tidal cycles are strongly dependent on the cross-shore topographic variations induced by the bar–trough couplets. The bars show low to moderate moisture contents compared with the lower-lying troughs, with an overall seaward increase in contents with distance from the beach–dune contact. Neap tides are associated with lower moisture contents on the upper beach, but both topography and tidal range effects are less important on the lower beach below mean sea level (MSL), which is dominated by near-saturated conditions. In the upper beach zone, above MSL, where aeolian sand supply is critical to the foredune sediment budget, the topographically controlled cross-shore surface moisture pattern leads to segmentation of the aeolian fetch, with a narrow dry upper beach ramp and bar surfaces characterised by aeolian entrainment potential, alternating with troughs, which capture sand and act as aeolian-muting zones. Infill of the uppermost trough on the beach may lead to expansion of the upper beach ramp, and consequently, of the aeolian fetch zone.