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

Advection and mixing determine the scalar tracer fields of, for example, te mperature and salinity in a given flow through a set of kinematic equations comprising a 'forward' problem. It may therefore be possible to extract in formation about the flow from a knowledge of the tracer field by considerat ion of a suitable 'inverse' problem. A forward problem is formulated for tw o-laver flows using a set of algebraic relations that may be considered a g eneralization of the classic Knudsen relations. The equations are: transfor med in order to determine the exact relationship between a variety of nondi mensional parameters that characterize the flow and another set that charac terize the variations in the tracer field. It is shown that not all flow pa rameters can be determined through the inverse process and that additional assumptions must be made in order to find a unique solution for a given tra cer field (or fields). The sensitivity of the solution to various assumptio ns is explored and it is shown that many of the parameters are not sensitiv e 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 c irculation patterns are also used to make predictions of nutrient flux. Alm ost 90% of the deep nutrient inflow is entrained into the upper layer and r eturns to the Pacific. (C) 2001 Academic Press.