The transport of water and particulate matter at the Venice Lagoon inlets

Tidal exchanges are, the chief controlling factor for processes affecting the life and evolution of lagoon ecosystems. Among these, we can cite: o thermal exchanges between the lagoon and the open-sea and their effects on the biological communities and algae production; o sediment transport within the lagoon and exchanges of materials with the sea and the nearby littorals and their effects on the erosion-deposition balance; o oxygen supply in the shallows and marginal areas; o supply of nutrient substances to lagoon organisms and the removal of decomposition products; o reproduction and migratory cycles of the fauna. For the Venice Lagoon, the tidal excursion strongly affects also the human activities in the urban areas and minor isles which are located within the lagoon basin. The quantification of the water and sediment exchanges through the inlets of the Venice Lagoon is therefore a fundamental requirement for designing interventions aimed at protecting the lagoon environment against exceptional tides and erosion processes. Acoustic Doppler current profilers (ADCP) are now being extensively used for the continuous monitoring of the flow by a research project entitled "Quantita e Qualita degli Scambi tra Laguna e Mare" (CO.RI.LA - Consorzio Ricerche Lagunari, Venice) and a three years-long time series of discharge is available for the three inlets. A CNR-ISMAR and APAT research project is also investigating the hydrodynamics and suspended sediment transport in the cross-section of the three inlets. The transport mechanisms are studied with conventional techniques and by applying the Sediview software procedure to the ADCP transect acquisitions which permit a better spatial resolution. The evaluation of the suspended load is performed by converting the acoustic backscatter data, recorded by the profilers, in estimates of the suspended sediment concentration through a calibration obtained by the direct measurement of concentrations in a large number of samples collected on-site. The results obtained in the preliminary investigations are described and discussed.