The changing morphology of the Volturno delta (northern Campania, Italy): geological architecture and human influence

The present geomorphology of the Volturno River delta system (northern Campania, southern Italy) is largely a product of complex, long-lived relationships between geological evolution and human impacts. In order to assess the main drivers of the changed landscape in the last centuries, a multidisciplinary study was carried out by combining geological and historical data. The study was based on geological and geophysical data, including about 1800 stratigraphic well logs to reconstruct the stratigraphic architecture of the delta plain and ca. 180 km of very high resolution single channel reflection profiles to image the stratigraphic pattern of the continental shelf and the offshore delta (Buffardi et al., 2021). Cartographic sources from the last 150 years were acquired, georeferenced and managed into a GIS environment, to support geomorphological interpretation. Bathymetric data acquired in 1887 and in 1987 were compared to extract seafloor changes in the delta offshore. Land use changes were also assessed since the 1957 up to present (Donadio et al., 2017; Ruberti et al., 2017; Ruberti and Vigliotti, 2017). The Volturno delta is characterized by a micro-tidal regime and moderate-to-high wave energy. The Holocene reconstruction of the Volturno coastal plain evolution evidenced the control of climatic changes (and consequently sediment supply and global eustatic variations) on the depositional history. Similarly to other Italian delta plains, 6.5 ky cal BP a coastal progradational phase established, allowing the formation of a wave-dominated delta system, with flanking strandplains forming beach-dune ridges partially enclosing lagoonal-marshy areas. Beach and lagoonal environments persisted along the present coastal zone up to the Roman age. The present landscape appears largely inherited by the past MIS5 and LGM landscapes. A progressive increment of anthropic forcing took place after 2000 yr BP but the strongest modifications of the landscape occurred since the end of the XVII century, when, during the Spanish vice-kingdom, it was subjected to major land reclamation aimed at elevating the land surface by filling the low lands with earth material settled by rivers' water that were diverted, canalized and branched into diversion canals reaching the inner parts of the sedimentation tanks. Progradation of the delta ended during the early-middle XIX century. A peak of major alterations of the deltaic environment, and retreat of the coastline was attained between the 1960s and the 1990s. It is evident that the transformations of the landscape that have taken place over the last millennium are largely caused by anthropogenic impacts (i.e. reclamation, development of drainage network, land use changes). The sediment input of the river to the Tyrrhenian Sea sharply decreased, thus resulting in a dramatic change of the deltaic morphology and significant coastal land loss. The coastal zone, considered as a dissipative-type shoreline, evolved to an irreversible non-dissipative inshore profile characterized by mean erosional rates of 5m/yr along the beaches and 24 m/yr on the delta mouth. The river delta changed from a cuspate, wave-dominate delta to arcuate and eventually delta-estuary type.