Quantifying surface moisture influences on aeolian transport (Invited)

Surface moisture plays an important role in determining sediment availability and aeolian transport in beach systems but is heterogeneous both spatially and temporally. The development of rippled aeolian sand strips and protodunes are particularly influenced by surface moisture and are inherently transient and therefore difficult to quantify using traditional point based sampling methods. Furthermore, these structures are influenced by saltation cloud formation and mutual feedback associated with surface characteristics and transport dynamics. Here we utilise terrestrial laser scanning (ground-based LiDAR) to accurately decipher beach surface moisture during transport events, elucidating the switch between erosivity and erodibility as the surface dries and saltation intensity increases. This technology is particularly useful at identifying surface moisture within 0-10%, precisely the range over which the aeolian transport threshold is found. The resolution of the instrument allows millimeter accuracy of surface topography, percent accuracy of surface moisture with short (minutes) data collection periods, enabling the examination of multiple relationships at unprecedented detail. Surface roughness and saltation cloud height increase over moist areas, particularly as saltation intensity increases, whilst deposition on the wet/dry boundary is a function of feedback between the surface properties and aerodynamic attributes which ultimately contributes towards protodune formation. These observed feedback mechanisms are incorporated into a cellular automaton-based algorithm to examine sand strip development and surface moisture interaction. Simulations suggest the development of differing mobility between small-scale ripples and larger sand strip is a function of the response of the surface moisture to sediment deposition and erosion. Our findings highlight the inherent complexity of surface moisture and sediment transport interactions, and the need to incorporate their heterogenic nature in aeolian sediment transport calculations.