Monitoring the implementation of a dredging plan in the Óbidos Lagoon (Portugal)

Abstract

The Óbidos lagoon (central west coast of Portugal) is a small coastal system exposed to intense wave action. Because its inlet is highly dynamic and closes occasionally, frequent interventions have been carried out by local and national authorities. However, their results have been ephemeral, and the interventions’ efficiency needs to be assessed. A monitoring program was applied to understand the morphodynamics of the lagoon during the implementation of a dredging plan in its downstream sector. Topo-hydrographic surveys, airborne and satellite images, wave parameters and water levels data acquired between March 2015 and March 2016 are analysed. Results show that the objectives of the dredging plan were reached regarding the increase of the sandy barrier crest height and the tidal channels deepening. The tidal range inside the lagoon increased significantly as a result of the inlet enlargement and the channels deepening, and the flood dominance decreased leading to a significantly more stable inlet mouth