Sand bypass and updrift beach evolution after jetty construction at an ebb-tidal delta

Garel, Erwan; Mendes da Silva de Sousa, Carlos A; Ferreira, Óscar

http://hdl.handle.net/10400.1/10902

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Authors

Garel, Erwan

Mendes da Silva de Sousa, Carlos A

Ferreira, Óscar

Abstract(s)

The evolution of an ebb-tidal delta (Guadiana, South Portugal) and its updrift beach after jetty construction (in 1972e1974) is analysed based on 24 ortho-rectified aerial photographs (1940e2012) and 13 bathymetric maps (1969e2014). The objectives are to evaluate the re-establishment of the sand bypassing process and if the disruption of the historical delta may affect the updrift beach evolution. Post-jetty progradation of the updrift beach resulted from two large accretion events. The second (largest) event (110 m progradation in 1985e1994) was due to beach attachment of a shoal produced by the erosion of a broad shallow area relict of the historical delta. The reworking of sand from this relict area also enables the individualisation of a lateral updrift bar simultaneously with the new ebb shoal proper formation. Both morphological features were close to (volume) equilibrium in 1995, indicating that most of the sand was transported towards the downdrift side of the inlet at that time. This study shows that erosion of the historical delta may enhance significantly the updrift shoreline progradation and may promote the re-establishment of sand bypassing after jetty construction.