A tracer method for determining transport in two-layer systems, applied to the Strait of Georgia/Haro Strait/Juan de Fuca Strait estuarine system

Advection and mixing determine the scalar tracer fields of, for example, temperature and salinity in a given flow through a set of kinematic equations comprising a 'forward' problem. It may therefore be possible to extract information about the flow from a knowledge of the tracer field by consideration of a suitable 'inverse' problem. A forward problem is formulated for two-laver flows using a set of algebraic relations that may be considered a generalization of the classic Knudsen relations. The equations are: transformed in order to determine the exact relationship between a variety of nondimensional parameters that characterize the flow and another set that characterize the variations in the tracer field. It is shown that not all flow parameters can be determined through the inverse process and that additional assumptions must be made in order to find a unique solution for a given tracer field (or fields). The sensitivity of the solution to various assumptions is explored and it is shown that many of the parameters are not sensitive to errors in assumed values for the depth-averaged transport or net fresh-water flux, as long as this is small compared with the layer transport. A detailed example of the application of this theory to summertime conditions in the Strait of Georgia/Haro Strait/Juan de Fuca Strait estuarine system is presented. Quantitative estimates of transport and mixing are found and indicate that entrainment into the surface layer occurs everywhere, whereas turbulent exchange processes occur mostly in the Hare Strait region. The circulation patterns are also used to make predictions of nutrient flux. Almost 90% of the deep nutrient inflow is entrained into the upper layer and returns to the Pacific. (C) 2001 Academic Press.