Baroclinic and wind-induced circulation in Tarragona harbour (northeastern Spain)

The sustainability of harbour management from an environmental standpoint is a current concern for port authorities. It includes dealing with problems that may affect the quality of in-harbour waters. In semi-enclosed basins, the characteristics of the circulation pattern are one of the main factors influencing the water quality, since they determine the residence time of pollutants inside the basin and govern the interaction between inside waters and the cleaner outside waters. Although harbour hydrodynamics are affected by the constant traffic of vessels and the physical constraints imposed by harbour structures, the water dynamics in ports are generally governed by three mechanisms: tidal forcing, wind surface stress, and baroclinic effects. This study presents the characterisation of winter circulation features in Tarragona harbour (northeast Spain), based on both field data and numerical simulations. Due to the microtidal nature of the Mediterranean Sea, three-dimensional water density distribution and local wind are expected to be the most relevant driving mechanisms. The results obtained suggest that, although wind effects may be important in determining the water flow in and out of the harbour for small time-scales, in the long term the most important water exchange mechanism is related to the waterbody’s baroclinic structure, with wind forcing playing only a second-order role.