Deterioration of salt marshes may be due to several factors related to increased anthropic pressure, sea level rise, and erosive processes. While salt marshes can reach equilibrium in the vertical direction, adapting to sea level rise, they are inherently unstable in the horizontal direction. Marsh boundaries are characterized by scarps with bare sediment below the vegetated surface layer that can be easily removed by wave‐induced erosion. In this work, we explore the different mechanisms involved in the erosion of marsh borders through the interpretation of field data. The analysis is based on a systematic field monitoring of a salt marsh in the Venice Lagoon subject to lateral erosion. Measurements included horizontal retreat of the scarp at various locations and wave height in front of the marsh during three storm surges. Continuous erosion and mass failures alternated during the observed period, leading to an average retreat up to 80 cm/yr. The data, collected roughly every month for 1.5 year, indicate that the linear relation that links the observed erosion rate to the impinging wave power exhibits a larger slope than that already estimated in literature on the basis of long‐term surveys. Moreover, an increase in the gradient of erodibility is detected along the marsh scarp, due to the combined action of soil strengthening by vegetation on the marsh surface and the impact of wave breaking at the bank toe, which promote cantilever failures and increase the lateral erosion rate.

Coastal flooding prevention measures, such as storm-surge barriers, are being widely adopted globally because of the accelerating rise in sea levels. However, their impacts on the morphodynamics of shallow tidal embayments remain poorly understood. Here, we combine field data and modeling results from the microtidal Venice Lagoon (Italy) to identify short- and long-term consequences of flood regulation on lagoonal landforms. Artificial reduction of water levels enhances wave-induced sediment resuspension from tidal flats, promoting in-channel deposition, at the expense of salt marsh vertical accretion. In Venice, we estimate that the first 15 closures of the recently installed mobile floodgates operated between October 2020 and January 2021 contributed to a 12% reduction in marsh deposition, simultaneously promoting a generalized channel infilling. Therefore, suitable countermeasures need to be taken to offset these processes and prevent significant losses of geomorphic diversity due to repeated floodgate closures, whose frequency will increase as sea levels rise further.

Sea level (SL) forecast for the city of Venice, Italy, is of paramount importance for the management and maintenance of this historical city and for operating the movable barriers that are presently being built for its protection. In this paper, an ensemble prediction system (EPS; based on an ensemble of 50 simulations) for operational forecasting of storm surge in the northern Adriatic Sea is presented and applied to 10 relatively high storm surge events that occurred in the year 2010. It is shown that storm surge peaks correspond to the maxima of uncertainty (as described by the spread of the EPS members), which increases linearly with the forecast range. Further, the uncertainty in storm surge level is shown to be linked to the uncertainty of the forcing meteorological fields. The quasi-linear dynamics of the storm surges plays a minor role in the evolution of uncertainty, except it produces its oscillation with a period associated with that of the 11-h seiche of the basin. The error of the ensemble mean forecast (EMF) is correlated with the EPS spread. For these cases, the EMF accuracy is very close to that of the high-resolution deterministic forecast (DF) and is more robust than the DF (meaning that its error is consistently smaller than the error of the DF, as the lead time of the forecast varies).