Barrier Islands Facing Sea Level Rise in the Northern Adriatic Sea

Because of the presence of a unique freely-developing sandy barrier system, the Marano and Grado Lagoon provides as a useful case study in the debate on barrier island responses to relative sea level rise. To analyze the multidecadal evolution of these 10-km-long landforms, the coastline configuration in 16 different years was examined using historical cartography, aerial photos and topographic surveys. After subdividing the coast into 50 cells, the differences in the subaerial barrier area (AREA) and shoreline position (SHO) were computed for each temporal step and examined as morphodynamic indicators. The results show that barrier islands have been preserved throughout time as the AREA has increased, along with a general pattern of coastal retreat, indicating a dominant rollover process as a response to sea level rise. This process becomes significantly more complex when the behavior of indicators is examined at various time scales. On a four-year time scale, there are both typical rotational trends and periods of significant variability due to the coexistence of transgressive process and intense longshore constructive dynamics. The multidecadal history of Grado barrier islands demonstrates the complexity of barrier island response to sea level rise, often resulting in contemporary small-scale opposite dynamics due to either erosive or depositional phenomena.