Proyecto de regeneración dunar en Laida (Reserva de la Biosfera de Urdaibai): Seguimiento y evaluación geológica

Zusammenfassung

As a consequence of the erosional character of the coastline, coastal dunes represent a very scarce ecosystem on the southern Bay of Biscay. Following destruction and intense transformation of these sandy areas during the last 200 years and due to their important role in coastal protection and biodiversity conservation, preservation and regeneration of this unique ecosystem have become of great social interest. Recently the Governing Board of the Urdaibai Reserve of the Biosphere decided to regenerate the coastal dune field that existed until 1950s on the lower Oka estuary. In order to achieve this goal, a three-year geological study was implemented to identify and evaluate the different physical processes operating in the area. Throughout the study period wind regime has demonstrated to be the main control on the accumulation process and it showed a clear bimodal character with dominant NW-SE winds. A detailed analysis has allowed to distinguish two different 6-month periods that have been regularly repeated over time: a) Semester 1 (october-march), with dominant NW-S winds and daily average velocities generally greater than 4 m/s. Sandy sediment was deposited abundantly on the supratidal area; b) Semester 2 (april-september), with dominant SE winds, very low daily average velocities (0-3 m/s) and important local breezes. During this period no net sand accumulation was measured. Despite annual morphological differences, the total sand volume accumulated every year was similar and the regenerating sand dune always maintained a simetrical morphology as a consequence of the bimodal wind regime.