112 DESCRIPTION OF THE SISBAHIA HYDRODYNAMIC AND TRANSPORT MODELLING APPROACH VIII-1. INTRODUCTION The modelling approach follows the strategy of SisBAHIA, accordingly with a hierarchical database system, in the following way: (1) Selected Database: selection is made from the SisBAHIA interface from the many that might have been created. New databases can easily be created as required from the SisBAHIA interface. (2) Selected Modelling Project: selection is made from the SisBAHIA interface from those that might have been created within the Selected Database. New Modelling Projects can be created as necessary from the SisBAHIA interface. (3) Selected Domain/Mesh: selection is made from the SisBAHIA interface from the many that might have been created within the Selected Modelling Project. New Domain/Meshes can be implemented as required from the SisBAHIA interface and associated meshing tools. (4) Selected Hydrodynamic Model: selection is made from the SisBAHIA interface from those that may have been set up and associated with the Selected Domain/Mesh. Each Hydrodynamic Model which has been set up represents a given scenario of interest. The same mesh can be used for vertically averaged 2-DH and for 3-D models of the domain. New models can easily be created and set up as required from the SisBAHIA interface. (5) Selected Transport Model: selected from many that may have been set up and associated with the selected Hydrodynamic Model. New models can be created and set up as needed from the SisBAHIA interface. Transport models can be of three di?erent types, i.e general purpose Eulerian models; Eulerian models for water quality (salt, temperature, dissolved oxygen-biochemical oxygen demand (DO-BOD), nitrogen, phosphorous and biomass); general purpose Lagrangian models. In all cases pertinent to modelling the transport of water constituents and determining their fate during a time period, the focus will be in the far field, i.e. in regions su?ciently far from the water outlets, away from the active turbulent mixing zones typical of the jets that form in the near field of the outlets. In these far regions, the plumes of constituents, including those of heated water, are passively transported by the prevailing currents. Thus, in a far field sense, the considered water constituents, including heat and particulate substances, can be treated as passive scalars. The passive scalar approach allows decoupling of the transport modelling from the hydrodynamic circulation modelling. In this respect, the implicit hypothesis is that the hydrodynamic circulation in the far field is independent of the concentration distribution of a given constituent. The decoupling of the transport model from the hydrodynamic model allows the negligence of baroclinic forcing in the latter. VIII-2. GENERAL DESCRIPTION A comprehensive description of SisBAHIA can be found in various publications [VIII-1–5]. In summary, the current version of SisBAHIA has the following main features: ? Hydrodynamic model: It is a constant density 3-D/2-DH hydrodynamic circulation model optimized for natural water bodies. Results can be either 3-D or vertically averaged (2-DH) depending on input data. ‘Optimized’ is used in the sense of a model planned for optimal representation of ?ows in natural water bodies. The calibration process is