The morphological evolution of shallow tidal systems strongly depends on gradients in transport that control sediment erosion and deposition. A spatially refined quantitative description of suspended sediment patterns and dynamics is therefore a key requirement to address issues connected with dynamical trends, responses, and conservation of these systems. Here we use a combination of numerical models of sediment transport dynamics, high temporal resolution point observations, and high spatial resolution remote sensing data to overcome the intrinsic limitations of traditional monitoring approaches and to establish the robustness of numerical models in reproducing space‐time suspended sediment concentration (SSC) patterns. The comparison of SSC distributions in the Venice Lagoon (Italy) computed with a numerical model with SSC retrievals from remote sensing data allows us to define the ability of the model to properly describe spatial patterns and gradients in the SSC fields. The use of point observations similarly allows us to constrain the model temporally, thus leading to a complete space‐time evaluation of model abilities. Our results highlight the fundamental control exerted on sediment transport intensity and patterns by the sheltering effect associated with artificial and natural intertidal landforms. Furthermore, we show how the stabilizing effect of benthic vegetation is a main control of sediment dynamics at the system scale, confirming a notion previously established in the laboratory or at small field scales.

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.

In a shallow dissipative tidal system, interventions that modify the local morphology in one location of the basin may quickly affect the surrounding areas, promoting strong changes in their morphology. If the localized modification persists over time, it may produce far‐field morphological modifications at delayed times. These modifications may have an impact on the local mean sea level and on tidal range, affecting the fate of salt marshes with implications for their survival. In this study, we investigate the effect of two anthropic interventions performed between the end of the nineteenth century and the beginning of the twentieth century in the northern Venice lagoon (Italy): the construction of jetties at one inlet and the removal of reed barriers protecting a fish farm in the inner lagoon. Using a 2‐D numerical model to reproduce the hydrodynamics of different historical lagoon configurations and a zero dimensional model of marsh vertical accretion, we investigate the effect of these interventions on the salt marshes of the northern lagoon basin. Interestingly, our results show that the increased depth at the inlet induced by the jetties lowered the local mean sea level of nearby areas and increased the tidal range, producing a temporary positive feedback on the stability of the marshes in proximity of the inlet. On the contrary, in the inner lagoon areas characterized by extremely low marshes, the removal of reed barriers delimiting a fish farm may have reduced the sediment fluxes thus contributing to the drowning of large marsh surfaces.