3D modelling in the Sado estuary using a new generic vertical discretization approach

Sado estuary (Portugal) is a mesotidal well-mixed estuary. The flow however, displays strong three-dimensional features associated with bathymetry variations. The flow is simulated using a three-dimensional primitive equation model based on the finite-volume method and incorporating a new concept for the vertical discretization. The innovative features of the model are analysed and the advantages of the finite-volume method to implement the generic vertical discretization are put into evidence. The model was validated using water level, velocity and salinity measurements in several stations along the estuary. Results show the influence of main channel's strong curvature on the generation of secondary flows inside the estuary. The steep bathymetry of the outer platform gives rise to a recirculation flow in the vertical plane that lasts for most of the tidal cycle. This structure is considered important for the sediment transport in that region. The above mentioned non-linear effects leave their print in both the transient and residual velocity fields. The results obtained help to understand the role of three-dimensional structures on the water exchange and sediment transport in the estuary, The results also confirm the suitability of the approach used in this model to simulate estuarine and coastal flows with strong three-dimensional effects.