Tidal asymmetry in an estuarine pycnocline: Depth and thickness

Tidal variations in estuarine stratification are revealed by the depth and thickness of the density interface. The depth of the interface may be predicted using an inviscid two‐layer model that combines baroclinic estuarine circulation with barotropic tidal currents [Helfrich, 1995]. Here we present results from a two‐layer model modified to include the effects of bottom friction and interfacial mixing. Modeled layer thickness and speed compare favorably with prior analytic studies [Farmer and Armi, 1986; Pratt, 1986]. We use a bulk Richardson number criterion to estimate the thickness of the pycnocline from two‐layer model results; the predicted pycnocline depth and thickness compare remarkably well with observations. We also investigate the effects of changing bottom friction and barotropic currents on the pycnocline thickness.