SLIM: a numerical model to evaluate the factors controlling the evolution of intertidal mudflats in Venice Lagoon, Italy

Venice Lagoon is suffering from a deficit in sediment supply, which results in the progressive destruction of salt marshes and tidal flats [Consorzio Venezia Nuova, 1996]. Nevertheless, some of the intertidal areas are accreting showing morphological changes, which are in contrast with the general trend within the Lagoon. The morphological evolution of Palude della Centrega, a well-preserved and vegetated intertidal area located in the northern part of the Lagoon, was investigated over a period of 3 years. The short-term accretion rate was measured to be 1.52 cm/year and was used to calibrate a three-element box model, Simulation of LIttoral Morphodynamics (SLIM) constructed to predict which of the accounted factors are more relevant to the evolution of the accreting intertidal mudflat. Sensitivity analyses using SLIM on Palude della Centrega suggest that the evolution of the flats is controlled by the balance between wave erosion during Bora events and tidal sedimentation during fine weather. This balance is strongly affected by (1) turbidity of the waters flooding the tidal flats, (2) sea grass density that suppresses wave action and tidal flow and (3) biostabilisation due to microphytobenthos, which enhances stability.