Preliminary Assessment of the Interplay among the Capillary Rise, Atmospheric Evaporation, and Aeolian Sand Erosion

Aeolian sediment transport reshapes coastal landscapes, influencing dune morphology and shoreline stability. A key predictor is the friction threshold velocity (FTV), the minimum wind shear stress required for particle entrainment, which depends on grain size, slope, and surface water content, yet near-surface moisture varies dynamically through evaporation and capillary rise, challenging predictions. This study examines how near-surface water supplied by capillarity influences the FTV. Wind tunnel experiments were conducted in the NHERI Boundary Layer Wind Tunnel using a 1D partially saturated sand column instrumented with water content and temperature sensors. Groundwater levels, wind speed, and relative humidity were monitored, and sediment entrainment was detected by pixel-intensity analysis of video recordings. Results show that most first-onset entrainment occurred close to the dry-sand threshold and consistently below moisture-dependent theoretical predictions. The mean FTV across tests was 0.35 m/s for water content below 5%, lower than the theoretical threshold for wetted specimens, reflecting surface desiccation. Transport persisted intermittently, indicating that instantaneous surface conditions, not final water content, govern erosion initiation and motivating time-resolved, surface-sensitive measurements.