Modeling sand-mud transport induced by tidal currents and wind waves in shallow microtidal basins: Application to the Venice Lagoon (Italy)

In this study we present a mathematical model for sediment entrainment, transport and deposition caused by the combined action of tidal currents and wind waves in shallow micro-tidal basins. The model uses a bi-granular mixture made up of cohesive and non-cohesive sediments thus considering clay, silt and sand, all of which commonly characterize the sediment bed composition of estuaries and tidal basins. The model also describes the evolution of bed elevation and evaluates the variation of bed sediment composition distinguishing cohesive from non-cohesive behavior. A stochastic approach is proposed to evaluate sediment entrainment close to incipient sediment motion. Particular attention is also given to the problem of reconstructing a reliable initial bed composition as this has a significant impact on sediment entrainment. The model was applied to the test case of the Venice lagoon (Italy) and good agreement was found when comparing model results to a series of turbidity measurements collected inside the lagoon. The model was then used to predict the actual net amount of sand and mud flowing through the inlets and the bottom evolution in terms of elevation and composition.