Long-term evolution of Danube delta barrier islands under the influence of storms, floods and big breaches

This work describes the main evolutionary stages of the Sacalin barrier island developed in the last 125 years in relation to storminess variability, river supply, accommodation space, and the establishment of the morphodynamic feedbacks operating in association with the occurrence of extensive breaches. This deltaic barrier is highly mobile due to its low elevation and high wave and currents exposure, recording a continuous elongation (of ca. 150 m/yr) and progradation in the downdrift sector (South Sacalin) but rapid retreat (20-70 m/yr) of the updrift sectors (North and South Sacalin). We found a contrasting behavior of the barrier characterized by fast shoreline retreat and small elongation during high storminess intervals but slight retreat and rapid elongation during low storminess. The occurrence of a vast breach (ca. 2.5 km long) at the end of the 1976-1981 stormy interval changed the evolution of the central barrier by the onset of a cyclic pattern of the barrier retreat and (large) breaching triggered mainly by barrier width but a pace influenced by storminess. The overall barrier coastline evolution is highly correlated with storminess, but the (alongshore) inter-sector analysis also highlights the influence of i) the river supply, which large oscillations (i.e. floods) are transmitted via mouth bar morphometric amplitudes to the North Sacalin and of ii) the significant breaches and related feedbacks for the Central and South Sacalin.