Dispersion processes in weakly dissipative estuaries: Part 2. Multiple
constituent tides.
Abstract
In the present study, we extend the analysis of the dispersion processes
induced by tidal flow in weakly-dissipative estuaries discussed in the
companion paper. Here we focus the attention on the flow induced by more
realistic tidal waves provided by different combinations of semi-diurnal
and diurnal constituents. We employ a large-scale physical model of a
system composed by a large basin (open sea) and a compound tidal
channel, where tides are produced as volume waves with prescribed
shapes. Two-dimensional superficial velocity fields are used to study
the main Eulerian and Lagrangian properties of the flow, in terms of
absolute and relative particle statistics. The results suggest that the
mixed character of the tides strongly influences the shape of the
macro-vortices generated at the tidal inlet, whereas the overall
residual currents seem to be less sensitive. Moreover, for the present
tidal setting, longitudinal dispersion, the dominant dispersion process,
is enhanced when the semi-diurnal constituents prevail. Finally,
multiple particle statistics show regimes typical of non-local dynamics
for particle separation larger than a typical injection length scale,
which is the size of the tidal inlet. Non-local dynamics imply that the
dispersion is dominated by flow structures larger than the mean
separation length, i.e. the tidal wavelength and the size of the
macro-vortices. The present results together with those discussed in
Part 1, offer a thorough insight in the main dispersion processes
induced by tidal flows, which are extremely relevant in the case of
estuarine dynamics.