102 FIG. V-1. 2-D mean annual circulation calculated by USEV model and sea surface set-up forced by a mean wind from the southwest (6 m/s). The scale colour is in meters (m). As an example, the calculated annual mean circulation and the wind set-up are presented in Figure V-1. Wind set-up is the sea surface displacement from the mean sea level caused by the wind. Since the wind blows from the southwest, the water is piled at the northeast borders of the sea, where the sea level is higher than in the southwest. V-2. SEDIMENT TRANSPORT Sediment dynamics is described in a very simple way, but still retains its main aspects. This has proven to be enough to satisfactorily simulate reactive pollutant dispersion. The transport of sediments is described by a 2-D advection–di?usion equation to which some terms are added. These are external sources of particles, terms describing particle deposition on the seabed and erosion from the bed to the water column. The formulation of these processes is based upon standard formulae. Thus, the erodability constant is used for the erosion term. Particle deposition is described using the settling velocity, which is obtained from Stokes’ law. Critical erosion and deposition stresses are applied as usual [V-3–5]. The equation for suspended sediment transport is: ?(??) ?? + ?(???) ?? + ?(???) ?? = ? ?? ???? ?? ?? ? + ? ?? ???? ?? ?? ? + (?? ? ???) + ? (V-7) where m is the suspended matter concentration, Kh is an e?ective horizontal di?usion coe?cient, S is the external particle source and ER and DEP are the erosion and deposition terms respectively. The deposition term is written in the following form: