Interfacial Mixing in Stratified Channel Flows

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Abstract
Mathematical modelers of stratified channel flows require equations which can predict the onset of interfacial mixing and compute the rate of mixing. Experiments show that although certain equations can predict entrainment rates in wind‐driven lakes, no reliable experimental equations exist for estuarine flows. The problem appears to be that in laboratory channels, there is not always complete dynamic similarity between experimental and prototype flows. This is because the interfacial layer in the experiment may be in a quasi‐laminar state while that in the prototype may be completely turbulent, leading to different rates of mixing. In view of this, care must be taken to ensure that any experimentally derived mixing equation is compatible with the flow conditions in the prototype. In essence this means that any estuarine mixing equation, either for entrainment mixing or turbulent diffusion mixing, must be expressed not only in terms of the bulk Richardson number but also in terms of the interfacial and boundary friction factors.