Measurements of Aeolian Mass Flux Distributions on a Fine-Grained Beach: Implications for Grain-Bed Collision Mechanics

Saltation is the primary mechanism of sediment transport responsible for supplying sand to coastal dunes. Of the several sub-processes involved in saltation, the collision-rebound process is generally considered the most poorly understood. This study presents measurements of the vertical and horizontal distributions of sand mass flux collected on a fine-grained beach at Mustang Island, Texas, USA, immediately downwind of five test beds containing narrow ranges of pre-sieved sand. Measured mass flux distributions were increasingly stretched in the vertical and horizontal dimensions with increasingly large grain-sizes in the test beds. It is inferred that the effective inertia of the target bed grains imposes a limit on the rebound/launch velocity of saltating grains, such that impact energies in excess of the effective inertia are transferred to the target grains (and possibly adjacent grains) thereby setting them in motion. The characteristic scales of particle trajectories are thus substantively controlled by bed texture.