Aeolian drift potential and coastal dunefield development in South Australia.

Graziela Miot da Silva
Flinders University, Adelaide, South Australia, Australia

The South Australian open coast is fully exposed to strong and predominantly onshore winds and to some of the highest energy waves in the world. These winds and waves have transported large amounts of carbonate sediments onshore from the continental shelf over the Holocene, building extensive coastal transgressive dunefields. This rocky and rugged coastline displays a series of embayments with strong curvature and abrupt changes in orientation in some cases. These changes cause coastal stretches to experience distinct variations in exposures to winds, waves and sediment supply and, consequently, dunefields display different degrees of development, orientation and migration patterns at local and regional scales. This study analyses wind data (direction and speed) from 40 meteorological stations along the South Australian coast, with the objective of characterizing local wind patterns, aeolian drift potential and dunefield migration patterns. The methodology includes the calculation of resultant drift potentials, construction of sand roses and analysis of dunefield orientation and migration rates using aerial imagery. Results show that the largest areas covered by transgressive dunefields are located where resultant drift potentials are at a maximum. At the local scale, dunefield position in an embayment and orientation is closely related to exposure to waves and onshore/alongshore winds. It is well established in the literature that maximum development of coastal transgressive dunefields can be expected in areas of sufficient-high sediment supply, wind exposure, and moderate to high wave energy dissipative beaches/surfzones. However, the relative importance of these factors in the degree of transgressive dunefield development on coastlines where these factors vary greatly has not yet been described, particularly in concert with a detailed analysis of aeolian drift potential. In low wave energy locations such as Gulf Saint Vincent and Spencer Gulf, as well in lee areas of headland embayments, transgressive dunefields may not be significant even when wind power and aeolian drift potential are substantial. In wave-exposed areas but with low aeolian drift potential, trangressive dunefields are developed but seem to be largely covered by vegetation in comparison to their high wave/high wind exposed counterparts. The findings of this study are of prime significance to understanding landscape change and coastal evolution in future climate scenarios where the contributions of wind and wave power to these changes are likely to increase.