Sedimentary and geomorphological evolution of a young tidal flat in the northern part of the Po delta (Italy)

Due to anthropic activities of the last centuries, coastal wetlands worldwide lost wide portions of salt marshes. Since these ecosystems provide fundamental services and benefits to both natural and anthropic components, the natural restoration of these habitats is becoming one of the main objectives of these days, and the opening of new connections between land and sea is becoming a highly used technique to restore portions of intertidal areas. According to recent studies based on analysis of long-term satellite imagery datasets and bathymetric surveys, the Po River Delta (Northern Italy) is currently subjected to a positive sedimentation trend and a constructive process is ongoing at the main river branches. Following an evolution similar to restoration projects, new tidal flats are building up around the tip of the delta, where agricultural fields were inundated by strong floods in the 1950s and the 1960s. This study focuses on a young tidal flat of about 8 ha, located in the Southernmost part of the Barbamarco lagoon. Sediment granulometric distribution and sedimentary pattern were investigated be tween May 2019 and March 2021 through coring, sediment traps, and orthophotos. The results show that the system is undergoing a progradation and an extended crevasse splay is developing. This covers the central part of the flat and it has developed from the early 2000s, due to human intervention on levees as well as river floods. The levees of the eastern channel stabilized between 2008 and 2012 thanks to vegetation growth, allowing the floods to focus in the NW direction, leading to the development of this recent feature. The presence of the crevasse splay confirms the importance of the river floods on the tidal flat formation. The calculated depositional rates suggest that sedimentation is higher during summer (average 66.89 g/m2 per submersion event) and lower during winter (18.86–20.65 g/m2 per submersion event). These trends are opposite to the seasonal trends observed in the literature, showing that the deposition controlled by the tide is lower compared to the river influence and suggesting that the river is the dominant factor.