Seasonal variations and controlling factors of aeolian transport at Atlantida Sul Beach, Rio Grande do Sul, Brazil

This study evaluates the seasonal pattern (spring/summer of 1999-2000) of sediment supply from the beach to the foredune and the factors controlling transport rates at Atlantida Sul, an exposed microtidal beach, northern coast of Rio Grande do Sul, Brazil. In spring regional winds reach their annual maximum rate of energy due to an increase in their speeds (over 5m/s) and frequency from the northeast quadrant. This is the main cause of inland sand transport. In the mean net variations in deposited volumes, two periods were distinguished: a) deflation in all experiments from September to October; b) deposits from the second half of spring to a summer, with peaks in November (0.017m(3).m(-1).h(-1)) and a secondary peak in January. These results are consistent with the resultant drift potential (RDP) along the axis formed by the dune system. The transport increased with the distance from swash zone limits and reached its maximum on upper backshore, close to the foredune base (0.052 to 0.006 m(3).m(-1).h(-1)) and diminished significantly on the foredune top due to vegetation (Panicum rasemosum and Senecio crassiflorus) and to the deflection of the winds to the height. The increase wind drift potential of winds blowing inland is the most important variable controlling sediment supply to the foredune, and secondarily, beach width and sediment humidity levels.