VERBI VEnice Research BIbliography

The origin of the sands in the Venice lagoon has been the subject of extensive field surveying in parallel with numerical modeling. Three transects along Treporti and Burano canals were conducted from which 33 bottom sediment samples were collected. These samples were analysed for grain size and sorting to examine any trends in the granulometry of these sediments that might shed light on transport paths.
The modeling study consists of two parts: the sediment transport model SEDTRANS96 was used with a finite–element, hydrodynamic model (SHYFEM) to simulate sand transport in Treporti canal. A type of linked box model was created by combining elements of the main model and subsequently computing water and sediment fluxes for the so-created boxes. Several grain size classes were simulated; the distribution before and after the simulation were examined. A variety of wind regimes were used to force the tidal flows, as well as a full year of measured tidal and wind data. Only a part of the Venice lagoon was covered by the simulation: a major channel running from the Lido inlet north towards the northern lagoon.
The total transport through all of the sections was computed for 1987 (a normal year in Venice lagoon). Sediment mass balance was determined and the resulting trends of erosion and deposition were computed.
There were no trends in the median grain diameter and sorting of bottom samples from Treporti canal; all sands were fine (106 microns, one outlier of 300 micron was removed).
The absence of a trend in grain size suggests that there is no significant import of sand to the lagoon through the Lido inlet. The results from the simulations seem therefore to confirm the hypothesis of reworking of sand within the lagoon. The computed erosion is some cm/year diagnostic of channel scouring and enlargement with time. The Treporti canal is subject to strong current velocities of around 1 m/s which hold fine sand in suspension and thus prevent sedimentation.