Time variability of the solid particulate matter transport in the Malamocco inlet

The backscatter signal recorded by the ADCP ('Acoustic Doppler Current Profiler'), and properly calibrated, has provided an estimation of the time variability of the suspended particulate matter (SPM) in the Malamocco inlet. Both the data from the ship-mounted ADCP and gravimetric data deriving from the water samples, collected during the campaign in January 2006, were used to determine the sediment concentration in the water column, above the bottom mounted ADCP, moored in the central part near the mouth of the inlet. Assuming that the relationship between the backscatter and the SPM concentration can be extended to a longer period, the calibration procedure was extrapolated for the time before and after the January campaign. Thus, the long term variability of the SPM concentration was obtained for the duration of four months (October 24, 2005 - February 21, 2006)., at the temporal and spatial resolutions of 10 minutes and 1 m, respectively. The evolution of a vertically averaged SPM concentration in the water column is depicted in Fig. 1, together with the vertically averaged axial current, and wind vector components. The currents are to a great extent tidally driven, with a prevalent semi-diurnal signal, whose range is modulated by a spring-neap cycle. Other long-term, non-tidal phenomena are of less influence. The concentration, on the contrary, shows a greater variability associated to the periods of strong winds, than to the tidal excursion. The wind influence plays a major role through the erosion induced by the waves. As observed, the analysed period is rich in strong wind events, particularly due to the bora (ENE wind). An additional aim of this study is to estimate the total SPM transport in the period of time across the inlet, on one hand, and, on the other hand, to derive a preliminary budget of the transport, in comparison with the other two inlets, Lido and Chioggia.