Roundness of sand grains of longitudinal dunes in saudi arabia

Abstract

Thirty-nine sand samples were collected from two longitudinal dunes of different size (with their interdunes) and an alluvial fan at Wadi ash Shumaysi (in the western region of Saudi Arabia). Roundness of sand samples (1.50 and 2.50 φ fractions) was measured. Sands of the interdunes are better rounded than those of the adjacent dunes. Dune sands tend to be less rounded with increasing dune height. Dunes with higher and steeper windward slopes have more pronounced sand grain variation than those with gentle slopes. This is attributed to selective sorting by the wind and easier transport of less rounded grains over dunes. The source sediments are considered to be the major factors controlling the roundness characteristics of aeolian sediments of the dunes and their interdunes. This study confirms that increasing roundness is associated with increase in grain size. Lastly, the shape of dune sands is not influenced by dune form.