Water flow in the inlets of the Marano-Grado lagoon system (NE Italy)

Water flow in the inlets of Grado and Lignano of the Marano- Grado Lagoon system was measured between July 2010 and September 2011, to study the water exchange between the lagoon and the Adriatic Sea. The average magnitude of the flow is about 500 mm/s in Grado and 400 mm/s in Lignano. The tidal forcing accounts for about 90% of the variability, with the semi-diurnal M2 and S2 contributing over 75%. They behave almost in phase with Lignano leading Grado by about 20 seconds. K1, the strongest diurnal constituent, contributes 7.4% to the energy, and shows a phase difference of about 10 minutes with the Grado response leading Lignano. Adriatic Seiches are found with periodicities of 21.14, 10.92, 7.04, 5.24, 4.29 and 3.59 hours, accounting for most of the non-tidal energy

Long-term changes in the kinematics of inlets of the Venetian Lagoon (NE Italy)

Long-term variations of the water flow through three Venice lagoon inlets are analysed seeking for the possible impact of structures under construction for the mobile gates for defending Venice against flooding. Time-series of monthly mean flow and standard deviations show long-term variations, mainly on the seasonal time-scale. An important increase in the water flow variance due to an increase in amplitudes of major tidal constituents in the Chioggia inlet can probably be explained as a consequence of the structures constructed recently that narrowed the channel

Vorticity Patterns Offshore of the Venetian Lagoon from HF Radar Observations

A network of high frequency (HF) radar systems was used to produce maps of surface velocity offshore of the Malamocco inlet during the 12-month period from November 2001 through October 2002. Inspection of the sub-tidal residual flow fields revealed frequent occurrences of small-scale (~10 km) eddy structures both north and south of the inlet. In addition, several monthly averaged velocity maps indicate the presence of a persistent meander in the mean current patterns. A more objective technique, based on vorticity, was developed to search the data set for the presence of eddies near the inlet and to separate those features from the larger-scale meander pattern. The vorticity at scales of 5-10 km was computed each hour using the low-passfiltered data set and year-long vorticity statistics were investigated at selected locations surrounding the inlet. The vorticity histograms and temporal variability changed significantly as a function of location relative to the Malamocco inlet. Both north and south of the inlet, the mean vorticity was weakly negative reflecting the larger-scale meander pattern whose crest is aligned, approximately, with the inlet. However, the range of vorticity north of the inlet was much greater than it was south of the inlet. A minor peak (or shoulder) in the year-long histogram of vorticity north of the inlet highlighted frequent occurrences of strong (~ 5 × 10-5 s-1) positive vorticity events in that area. A similar statistical behaviour was not seen south of the inlet. This observation was used to define a conditional sampling criteria that lead to a map of the typical flow field associated with strong eddy events. The vorticity time series were also used to investigate the relationship of eddy events to external forcing parameters. Strong winds, for instance, acted to destroy vorticity in the surface current field since they lead to a strong but horizontally uniform response in the surface currents. The roles of sea level variability and offshore current velocity were also investigated

Analysis of the inlet currents of Grado-Marano Lagoon system and comparison with the Venetian Lagoon (northern Adriatic Sea).

The flow through the Grado-Marano lagoon inlets is tidally driven: more than 90% of the energy is due to the astronomical forcing [1]. The second source of variability is due to the Adriatic seiches accounting for 7% of the total kinetic energy. Local winds are responsible of the variability in the ,residual currents (tides and seiches removed). NE Bora wind increases the residual inflow into the lagoon through the easternmost inlet and favouring the outflow through the westernmost inlet. Such a behaviour is similar to what has been reported for another Northern Adriatic lagoon, namely the Venetian lagoon

Water flow in the inlets of the Grado-Marano Lagoon System, Northern Adriatic Sea

The water flow in two inlets of the Marano-Grado Lagoon, the second biggest lagoon in Italy, has been monitored during 2010/2011 with Acoustic Doppler Current Profilers. The flow is highly polarized along the channel axis (99% of the variance). A barotropic regime prevails along the water column; therefore the vertical average is representative of the total variability. All the major tidal constituents of the Adriatic are present in the flow, accounting for more than 90% of the total energy. Seiches account for about 80% of the non-tidal energy. Low-frequency variability is related predominantly to the non-linear wind forcing, with Bora (from NE) exerting the highest influence