Changes in grain size of sand in transport over a foredune

Suspended sand is sampled at several heights and positions on a beach and foredune, providing detailed insight into the vertical and horizontal variation in sand content in the air during landward transport. Grain-size analysis is used to study the changes in grain-size distribution during landward transport. Mean grain size and sorting decrease during transport. Changes in textural parameters follow a gradual and regular path when the sediment is transported into the foredune. Sediment trapped on the seaward slope at a height of 30-50 cm above the surface closely resembles the sediment trapped landward, which implies that changes in the direction of transport are related to vertical changes within the sediment transport profiles. The movement of sand over the vegetated foredunes is induced by turbulent forces created by the air flowing across the vegetation and the foredune, leading to a change from saltation on the beach to modified saltation and suspension on the foredune. Small grains are lifted higher and fall more slowly than coarse grains and therefore are transported further landward, resulting in a gradual decrease in grain size of the landward-deposited sediment.