Stratified shear instabilities in estuarine fluid muds

Stratified shear instabilities are an important physical process in a variety of environmental flows, and understanding their dynamics is key to modelling turbulent fluxes. In estuaries, the underlying stratification may arise not only from heat and salt, but also from suspended sediment. Here, we compare echosounder observations of shear instabilities growing on a lutocline in a tidally-driven estuarine flow with direct numerical simulations of Kelvin-Helmholtz instability. We explore the relationship between characteristic lengthscales describing to the height of the primary billow (measured from the echosounder data) and the corresponding initial Richardson number and turbulent dissipation rate. While we show that useful parameterizations can be found for both quantities, our estimates suggest that sediment stratification leads to altered scalings which remain to be fully explained.