Numerical modelling of cohesive sediments transport in the Ria de Aveiro lagoon, Portugal

Abstract

The main goal of this work is to implement a cohesive sediments transport model for the Ria de Aveiro and study the dynamics of the suspended cohesive sediments of the lagoon. It is carried out in the scope of the project Eicos, which main objective is to study the interaction between fine cohesive sediments and chemical and biological contaminations of the lagoon waters. Ria de Aveiro is a very shallow and well-mixed lagoon dominated by tidal currents. It presents a complex network structure composed by several sub-systems, dominated by tidal asymmetries, resulting in areas of ebb and flood dominance and weak gravitational circulation. Tidal currents are the main forcing in the transport of suspended sediments of the lagoon. The effects of the Vouga river input on the suspended concentration in the lagoon are enhanced during the spring tides and high rivers runoff. Wind stress enhances the bottom erosion and the advection of sediments when the induced residual current is in phase with the tidal current but may contribute to a decrease of sediments concentration in the case of phase opposition as can occur in the S. Jacinto channel. The S. Jacinto and the Espinheiro channels as well as C. Bico, are the most important areas of the lagoon, from the point of view of hydrodynamics and sediments transport. They are the most affected by the ocean as well as by the two major lagoon freshwater contributors, the Vouga and the Antuã rivers. High turbid zones, induced by strong tidal currents, tidal asymmetries and river's runoff, are observed in those areas during the spring tides. In most areas of the lagoon, namely the shallow ones, the deposition is the dominant process, evidencing a long-term trend leading to the mean water depth decrease.