Classification of Estuarine Circulation

Estuarine circulation represents the interaction among the contributions from gravitational circulation, tidal residual circulation, wind-driven flow and circulation driven by the tidal covariance between tidal variations in vertical shear and tidal variations in eddy viscosity, or simply ‘eddy-shear covariance.’ In turn, gravitational circulation is driven by river discharge and density gradients. Gravitational circulation tends to be dominant in many estuaries and can be classified according to the basin‘s morphology or origin, to its water balance, or to the competition between tidal forcing and river discharge. Such classification as well as the circumstances under which the residual circulation induced by tidal flows and the eddy-shear covariance are discussed in this chapter. Also presented is a more comprehensive framework that considers the dominant dynamic balance between driving forces (per unit mass) and balancing (or counteracting) forces. The main forcing agents considered in such framework are baroclinicity, tidal stresses and wind stresses.