Long-term bathymetric changes in the submerged delta of the Turia river since the nineteenth century (Western Mediterranean) and their drivers

Abstract

Deltas and estuaries are formed through periods of marine transgression and regression, which are the continuity of a river and provide key information about its evolution. However, many of the world's deltas are increasingly exposed to the impacts of human activities. While changes affecting the subaerial parts of deltas have been intensively studied, much less is known of their subaqueous parts, the understanding of which is important in gauging overall potential delta vulnerability. This research evaluates the bathymetric changes in the submerged delta of the Turia river (Western Mediterranean, Spain) before and after the extreme flood event of 1957, after which the riverbed was diverted. Three nautical charts were processed (1878, 1988 and 2022), including georeferencing and Digital Elevation Model (DEM) generation. In order to evaluate changes before and after the event, models for 1878–1988 and 1988–2022 were compared and differences were quantified in order to assess erosion and aggradation trends. The results indicate a more aggradated submerged delta in the surroundings of the old river mouth, favored by the high sediment availability since the end of the Little Ice Age (LIA), and the presence of a smaller delta next to its current river mouth to the south of the harbor of Valencia. Bathymetric reconstructions also made it possible to map some incisions in the inner continental shelf as river channels that migrated eastwards when the sea level was lower during MIS 2. Finally, the comparison of bathymetric models also revealed the scarcity of sediments on the current shelf since 1988, which is attributed to anthropogenic action. The successive extensions of the harbor are increasingly distorting the distribution of sediments along the coast and are thus remodeling seabed sediment distribution. Knowing the sedimentation in deltaic systems means better predicting future alterations due to increased anthropization and of the climate change.