Residual circulation, mixing, and dispersion

This chapter covers tidally-averaged circulation, salinity structure, and dispersion in estuaries. It begins with a discussion of volume and salt conservation for full estuarine systems. This leads to a focus on volume and salt fluxes through a cross-section near the estuary mouth. Techniques for calculating various parts of these fluxes are reviewed, leading to the classical "exchange" and "tidal" parts of the up-estuary salt flux. A simple description of the physics leading to the exchange flow is given, with some discussion of the many factors ignored in its derivation. The tidal salt flux term is then discussed, somewhat more informally with comments on along-channel dispersion. Along the way we use specific examples from observations and numerical simulations. There is a bias toward our own work in U.S. Pacific Northwest estuaries, but hopefully we have indicated some sense of the scope of work globally. Estuarine residual flow and dispersion have also been reviewed extensively by other authors. In particular we recommend the excellent textbook by Fischer et al. (1979), as well as the textbooks by Dyer (1997), and Lewis (1997), and review articles by Geyer and Signell (1992), Chant (2010), Monismith (2010), and MacCready and Geyer (2010).