Statistical characterization of erosion and sediment transport mechanics in shallow tidal environments. Part 2: suspended sediment dynamics

Abstract

A proper understanding of sediment transport dynamics, critically including resuspension and deposition processes of suspended sediments, is key to the morphodynamics of shallow tidal environments. Aiming to account for deposition mechanics in a synthetic theoretical framework introduced to model erosion dynamics (D'Alpaos et al., 2022), here we investigated suspended sediment dynamics. A complete spatial and temporal coverage of suspended sediment concentration (SSC) required to effectively characterize resuspension events is hardly available through observation alone, even combining point measurements and satellite images, but it can be retrieved by properly calibrated and tested numerical models. We analyzed one-year-long time series of SSC computed by a bi-dimensional, finite-element model in six historical configurations of the Venice Lagoon in the last four centuries. Following the peak over threshold theory, we statistically characterized suspended sediment dynamics by analyzing interarrival times, intensities and durations of overthreshold SSC events.Our results confirm that, as for erosion events, SSC can be modeled as a marked Poisson process in the intertidal flats for all the considered historical configurations of the Venice Lagoon because exponentially distributed random variables well describe interarrival times, intensity and duration of overthreshold events. Moreover, interarrival times, intensity and duration describing local erosion and overthreshold SSC events are highly related, although not identical because of the non-local dynamics of suspended sediment transport related to advection and dispersion processes.Owing to this statistical characterization of SSC events, it is possible to generate synthetic, yet realistic, time series of SSC for the long-term modeling of shallow tidal environments.

Statistical characterization of erosion and sediment transport mechanics in shallow tidal environments – Part 1: Erosion dynamics

“…The present findings, together with the statistical characterization of suspended sediment dynamics (Tognin et al, 2024), represent a step towards the set up of a synthetic statistically based framework which can be used to model the long-term morphodynamic evolution of shallow tidal systems through the use of independent Monte Carlo realizations, thus possibly exploring a large set of equally likely lagoonal configurations.…”

“…Consequently, to effectively model bed level variations, it is essential to accurately describe both BSS and SSC. This contribution focuses on characterizing BSS, while the analysis of SSC is presented in the companion paper (Tognin et al, 2024).…”

Statistical characterization of erosion and sediment transport mechanics in shallow tidal environments – Part 2: Suspended sediment dynamics

“…All data presented in this study and used for the analysis of the suspended sediment concentration are available at https://doi.org/10.25430/researchdata.cab.unipd.it.00000729 (Tognin et al, 2022b). Competing interests.…”

“…But, because of the explicit description of the shortterm interaction between hydrodynamics and sediment transport, the application of process-based models to the longterm timescale is often computationally expensive or even prohibitive. A widespread solution to overcome this limitation is to upscale the effects of short-term sediment transport on bed evolution by means of the so-called "morphological factor", which is basically a multiplication factor to accelerate the computation of the effects on the morphology (Lesser et al, 2004;Roelvink, 2006).…”