Statistical characterization of erosion and sediment transport mechanics
in shallow tidal environments. Part 1: erosion dynamics
Wave-induced bottom shear stress is one of the leading processes that
control sediment erosion dynamics in shallow tidal environments, because
it is responsible for sediment resuspension and, jointly with tidal
currents, for sediment reworking on tidal flats. Reliable descriptions
of erosion events are foundational to effective frameworks relevant to
the fate of tidal landscape evolution.
However, the absence of long-term, measured time series of bottom shear
stress (BSS) prevents a direct analysis of erosion dynamics. Here we
adopted a fully-coupled, bi-dimensional numerical model to compute BSS
generated by both tidal currents and wind waves in six historical
configurations of the Venice Lagoon in the last four centuries. e
one-year-long time series of the total BSS were analysed based on the
peak over threshold theory to statistically characterize events that
exceed a given erosion threshold and investigate the effects of
morphological modifications on spatial and temporal erosion patterns.
Our analysis suggests that erosion events can be modeled as a marked
Poisson process in the intertidal flats for all the considered
configurations of the Venice Lagoon, because interarrival times,
durations and intensities of the over-threshold exceedances are well
described by exponentially distributed random variables.
Moreover, while the intensity and duration of over-threshold events are
temporally correlated, almost no correlation exists between them and
interarrival times. The resulting statistical characterization allows
for a straightforward computation of morphological indicators, such as
erosion work, and paves the way to a novel synthetic, yet reliable,
approach for long-term morphodynamic modeling of tidal environments.