Hydrodynamic coastal processes in the North Adriatic investigated with a 3D finite element model |
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Authors: | Debora Bellafiore Georg Umgiesser |
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Institution: | (1) Institute of Marine Science, National Research Council (ISMAR-CNR), Castello 1364/a, 30122 Venice, Italy;(2) EuroMediterranean Centre for Climate Change (CMCC), Bologna, Italy |
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Abstract: | This paper deals with the interaction and small-scale processes occurring around the inlets that connect the Venice Lagoon
with the Northern Adriatic Sea. In a previous paper, barotropic processes have been investigated, whereas here, the focus
is on the baroclinic processes. The hydrodynamics of the area are studied by means of a 3D shallow water hydrodynamic finite-element
model, suitable to describe areas of complex morphology such as the coasts and the interaction channels. This is the first
work that models the 3D interaction between the Venice Lagoon and the Adriatic Sea. Three different sets of simulations have
been carried out to identify the physics behind the small-scale processes and the influence of the main forcings on the study
area. The first imposes different idealized forcings, such as tides, wind, and river runoff. The vorticity maps of the first
two layers show the predominance of wind forcing in the coastal area and tidal forcing in the three inlets of the Lagoon.
Bora wind acts homogeneously, increasing the littoral currents, while Sirocco wind mainly impacts near Chioggia inlet, with
a coastal current reversal, inducing its detachment offshore. Freshwater patterns are present along the coast, near the river
mouths. Rivers do not directly influence the circulation close to the coast in front of the Venice Lagoon, except for the
area near Chioggia inlet, where the Brenta river action can be seen. The second set of simulations deals with a sensitivity
analysis to define the importance of the advection and of the baroclinic pressure gradient terms in the creation of persistent
structures, such as small-scale coastal vortices seen along the littoral very close to the inlets. This analysis shows how
advection is the main physical process responsible for the persistence of the positive vorticity structures close to the coast
between the inlets, while the negative vorticity structures, also seen by the HF Radar, are due to the baroclinic-advective
interaction. Finally, a real case, year 2004, has been simulated both to validate the model with observations and to identify
the occurrence during the year of the characteristic hydrodynamic features attributable to the main forcings. The action of
Bora wind characterizes the surface current patterns of February and November 2004, while Sirocco influences the month of
May 2004. During periods of weak wind, the model reproduces the small-scale vortical structures close to the littoral. |
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