Morphological evolution of the tidal flat in the southern Barbamarco Lagoon (Po Delta, Italy) in the period 2020 – 2024

Coastal environments, such as tidal flats and salt marshes, are subject to rapid changes due to natural processes (waves, wind, and currents) and human interventions. These ecosystems play a crucial role in coastal protection, but they are increasingly threatened by degradation and erosion, making continuous monitoring essential. Remote sensing through drones has proven to be an effective method for analysing the morphological and sedimentary evolution of these areas. This study focuses on the evolution of a tidal flat in the southern part of the Barbamarco lagoon, in the Po Delta, between 2020 and 2024. The results were then compared with data from the 2018-2020 period obtained from previous studies. In February 2024, a fieldwork was conducted using a commercial drone and a GPS-RTK to obtain precise measurements. Nineteen Ground Control Points (GCPs) were placed to ensure the accuracy of the aerial images, and 60 GPS points (called “validation points”) were also collected to validate the Digital Surface Model (DSM) obtained from the drone’s orthophotos. Additionally, comparison of DSMs from different dates were performed to analyse morphological changes obtaining a DEM of Difference (DoD). The Geomorphic Change Detection (GCD) software was used to estimate vertical and volumetric variations by applying a threshold (TCD) to distinguish significant changes, considering the Root Mean Square Error (RMSE) and the propagated uncertainty. This approach was also used to analyse sediment accumulation in the northeastern area of the tidal flat, influenced by canal dredging, to assess its impact on sediment supply. The results showed a positive trend in sediment accumulation between 2020 and 2024. Notably, from February to October 2020, sediment accumulation was higher compared to subsequent years; this increase was attributed to significant river floods, which proved to be more influential than tidal currents. The latter phenomenon is visible through the presence of crevasse splays near channel entrances. Furthermore, the tidal flat is protected in the north by the barrier islands of the lagoon, which mitigate the influence of the waves. An important example of flooding occurred in November 2023, which promoted material deposition near the edges, especially around Spartina sp. patches and in the central part of the tidal flat. Meanwhile, erosive processes were less intense than in the past and mainly concentrated along the northeastern margin. Currently, the rate of vertical variation of the tidal flat is around 1.4 cm/year. If this rate remains constant, the interaction between sea level rise and subsidence could reduce the elevation by 1 cm compared to the current level in a pessimistic scenario, while an optimistic scenario predicts sediment deposition that could increase the elevation by 33.5 cm. However, the future of this area remains uncertain, highlighting the need for continuous monitoring and targeted management interventions.