Suspended sediment dynamics at the inlets of Venice Lagoon: Unraveling the effects of storm surges and mobile barrier operations

This study investigates the effects of flow regulation by the floodgate system (MoSE: Electromechanical Experimental Module) on sediment and water exchanges between the Venice Lagoon and the Adriatic Sea, during two significant storm surges in 2022 and 2023. An integrated observation system, which combines satellite-derived products and data from in-situ instrumental networks, was implemented at the three lagoon inlets (Lido, Malamocco and Chioggia). The high spatial and temporal resolution of continuous in-situ data allowed to characterize the complex interactions between sediment fluxes driven by tidal flow and the repeated and prolonged activations of the floodgates, considering the intense particle resuspension within the lagoon and along the coasts by wind waves. Our findings reveal a quite similar net sediment loss from the lagoon during each event (∼13,880 tons and ∼ 14,850 tons), but with distinct spatial and temporal patterns in the four inlet channels. During the 2022 event, sediment export during ebb tides exceeded import during floods, leading to a net loss at all inlets (Chioggia ∼ 4,720 tons, Malamocco ∼ 3,360 tons, Lido ∼ 5,800 tons). By contrast, in the 2023 event, sediment import dominated in the northern basin (Lido ∼ 5,900 tons), while export prevailed in the central and southern basins (Malamocco ∼ 6,570 tons, Chioggia ∼ 14,160 tons). As observable in satellite images, this input at north is related to fine particles resuspended under northeasterly wind along the adjacent coast and transported in the lagoon by flood tidal currents. The presence of jetties at the inlets interrupts the natural coastal drift at south inhibiting such inputs at central and southern basins. Besides being effective in preventing high waters in Venice, this study suggests that the regulation operated by the barriers can potentially determine positive or negative short-term feedbacks on the lagoon sedimentary budget, minimizing sediment losses from the lagoon or blocking the inputs from the nearby coast. In an operational context, near real-time information deriving from the tested methodology can support an effective management of the MoSE system, adaptable to the evolution of meteo-marine conditions. In the long term, adaptive strategies are essential to prevent alterations of the sediment fluxes and the consequent loss of habitat in shallow tidal environments that are already threatened by natural and anthropogenic pressures.