Modelling short-term dynamics of suspended particulate matter in Venice Lagoon, Italy

Sediment stability in the shallow Venice Lagoon was investigated by means of numerical modelling. Results from a hydrodynamic model allowed for the determination of the wave climate and bottom effective parameters so that simulations with a Lagrangian model for suspended particulate matter could be performed. A spring-neap cycle in summer 1998 was chosen as integration period since data for calibration and verification were collected within the European project F-ECTS between summer 1998 and spring 1999. Deposition on shallow mud flats as well as short term erosion during a strong wind event were reproduced and mass balances for two areas computed. A relation of patterns of SPM in the water and in the sediment was found and can be ascribed to the displacement of material during storm events from shallow areas to the bottom of very small channels. Assuming about 10 to 14 storm events during the year comparable to the Bora event during the integration time, estimates for long-term trends of sediment loss on shallow flats by Day et al. [Day, J.W., Rybczyk, J., Scarton, F., Rismondo, A., Are, D., Cecconi, G., 1999. Soil accretionary dynamics, sea-level rise and the survival of wetlands in Venice Lagoon: a field and modelling approach. Estuarine, Coastal and Shelf Science 49, 607-628] are met by the simulation results. Evidently, long-term sediment evolution of the lagoon is therefore not dominated by the average (residual) processes that occur in the lagoon, but by the few peak events that happen randomly over the year.