A two-dimensional mathematical model for the study of hydrodynamic and sediment transport in the Venice Lagoon

For a long time Venice Lagoon has been investigated but the link between hydrodynamic and sediment transport is still not well understood: in particular, the morphological effects of the major interventions in the past and in the future are not known exactly. A two-dimensional hydrodynamic model (depth averaged and full non linear), designed to simulate partially dry areas, has been developed merging a 1D network to simulate the minor channels. The proposed hydrodynamic model is based on an existing framework developed at the IMAGE Department of Padova University in the middle 90’s. The present model follows those contributions but contains a new formulation of convective acceleration and Reynolds stresses, non considered in the existing framework. A sediment transport module, considering both suspended sediments and bed load, has been coupled to the hydrodynamics. The model has been tested on some geometric configuration where the flow behaviour is known: the problem of a sudden lateral expansion and the formation of free bars on a straight flume. Concerning the Venice Lagoon, discharges and tide level in some sections in a boundary region has been compared with the available measurements. We studied then the hydraulic behaviour of the three mouths in the actual situation and in the past; in particular, we examined the lagoon in the early 1800’s (from Denaix’s chart) and in the early 1900’s (from chart of Ufficio Idrografico del Magistrato alle Acque), pointing out the differences in the tide propagation and in the sediment dynamic.