Compared evolution and erosion of three beach / spit systems. Ortigueira, O Barqueiro and Viveiro Rías. Galicia, Spain

Abstract

In the general context of sea level rise and coastal erosion, three beach/spit systems are studied in North Galicia (North-west coast of Spain), corresponding to the mouth complex of estuaries situated in the inner part of the Rías of Ortigueira, O Barqueiro and Viveiro. The morphodynamic characteristics and the degree of human occupancy of every system is analysed, in order to compare the erosion vs accretion tendency to a ten years time-scale and the response to energetic conditions in winter when supposedly beaches tend to erosion. The Morouzos Beach, in the Ría of Ortigueira presents minor human occupation and the tendency is to an slight accretion. The profiles measured in the beach show an important cross-shore sediment exchange along the year, with berm erosion during the winter and reconstruction during the summer. The accretion tendency, contrary to a generalised erosive stage, is interpreted as the response to an increase in solid load in the rivers feeding the beach. The Area Longa Beach, in the Ría of O Barqueiro, although with few human interventions, is subjected to an intense erosion. The main reason is the very unfortunate location of a small harbour, which dramatically cut off the main source of sediments of the down-drift placed beach. The Covas Beach, in the Ría of Viveiro, is a totally different case. The human occupation of the system is almost complete, including dune urbanisation, river channelization and construction of a dock in the Celeiro Harbour. As a consequence, the beach lost part of the sedimentary source and was regenerated. The nourishment is repeated every year, transporting sand from the oriental to the occidental sectors, inversely to the beach sedimentary transport.