Windfeldstudien in Dünengebieten

Abstract

The field study of aeolian dynamics and dune patterns in remote areas is restricted by the general missing of specific wind data. In semiarid environments with some sparse vegetation the measurement and mapping of wind-shaped plants can be a helpful tool to find out the direction of the dominating airflow responsable for the sand drift and dune movement, and to register the mesoscale windfield. Two case studies of windfield mappings from dune fields on the Canary Islands (Spain) are presented in this paper. The results of the airflow studies are compared to morphometric and morphodynamic data in the dune fields and to the standard wind registrations of near-by meteorological stations. In the dune field near Corralejo (NE-Fuerteventura, Photo 3) the unimodal trade-wind regime with dominating airflow from NNE brings about a sand flow and dune transfer in southern direction (mean annual rates of dune movement 4.5 - 6 m). The results of the plant-based windfield mapping (Fig. 4), the morphometric and morphodynamic dune studies, and the wind data of the Fuerteventura Airport (Fig. 3) are in reasonable conformity. The dune field of Maspalomas with a transition of transverse dunes to an aklé pattern in the central part (Photo 4) is situated in the leeward position of southern Gran Canaria. The wind data of the meteorological station Gando Airport (eastern coast of Gran Canaria, Fig. 5) are not transferable to the Maspalomas dune field near the southern coast. The plant-based windfield mapping (Fig. 6) reflects the predominance of a diverted trade-wind flow from ENE to WSW (average direction from 80.5° ENE), that is in correspondence with the general direction of the sand and dune movement (about 2 - 5 m per year) and with the morphometric field data. Actually the Maspalomas dune field is subject to a complex wind regime, however, with the diverted trades from ENE and with sea breezes from W and S mainly in summer. The westerly breezes cause a temporary inversion of the asymmetrie direction at the top of the dunes. The complex wind regime with opposite airflows in part favours the formation of the aklé dune pattern. In conclusion, the windfield mapping based on wind-shaped plants proves to be not adequate for the correct recording of a complex wind regime, that needs additional field studies in different seasons of the year. Nevertheless, the plant-based airflow studies and mesoscale mappings give a reasonable and realistic information about the direction of the dominating winds and sand flow, while the calculation of wind speeds from the deformation rates of plants have the rank of gradual estimates only.