A Discrete Particle Modeling Framework for Exploring the Evolution of Aeolian Sediment Transport on Moist Sand Surfaces

Aeolian sand transport on beaches is strongly affected by surface moisture, but its influence on transport evolution remains poorly understood. We present a novel discrete particle modeling framework to systematically investigate how moisture from liquid bridges affects the development of transport toward steady state after initiation. Moist sediment particles are modeled using a particle-based approach with evolving liquid bridges coupled to a one-dimensional airflow solver. The model captures realistic grain-scale collision dynamics under moist conditions and reproduces key features of aeolian transport in the dry limit. Simulations reveal two distinct behaviors: In steady state, the transport rate remains insensitive to moisture as lower saltation concentrations are compensated by higher saltation velocities; in the transient phase, however, increasing moisture prolongs the growth phase and delays the peak in transport rate. This delay arises because sand concentration peaks increasingly later than mean saltation velocity as moisture content increases. By projecting the temporal model results into a spatial representation, the position of peak transport is found to scale linearly with wind shear velocity, showing greater sensitivity at higher moisture levels. A preliminary test suggests that evaporation is essential for the initial grain dislodgement by wind alone but is unlikely to affect steady-state transport. This study explains the longer fetch distances observed on moist beaches before transport equilibrates and provides a physics-based tool for predicting sediment transport under varying moisture conditions.