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, 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 over-threshold 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 over-threshold events. Moreover, interarrival times, intensity and duration describing local erosion and over-threshold 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.