Instability and mixing in a sediment-stratified shear flow

Stratified shear instabilities play an important role in the transport of heat, salt, momentum, and biogeochemical tracers in a variety of environmental flows. In estuarine and coastal flows, the stratification may arise not only from variations in heat and salinity (thermohaline stratification), but also from suspended sediment in the water column. Previous observations of sediment-stratified shear instabilities [Tu et al., J. Phys. Oceanogr. (52), 2022] have suggested that mixing parameterizations developed for thermohaline flows may significantly overestimate the turbulent fluxes. Here we use simulations of forced stratified shear layers with the inclusion of a settling velocity to mimic particle settling. We explore the impact of this settling velocity on both the primary instability (where it introduces asymmetry into the base flow) and subsequent mixing (where it impacts the turbulence energetics). By resampling the simulations to mimic observational data, we discuss how the proposed scalings for turbulent fluxes in thermohaline flows are modified, pointing to possible areas of improvement for mixing parameterizations.