On the Effects of Turbulence Modulation Driven by Suspended Sediment Stratification in Emergent Rigid Canopies

Aquatic vegetation has the potential to increase suspended sediment capture while also increasing sediment resuspension and bedload transport. Suspended sediment can induce density stratification, which modulates the turbulence in the water column. We derive a Rouse-based formulation for suspended sediment concentration (SSC) including the effect of sediment-induced density stratification. We perform Large Eddy Simulations of vegetated and non-vegetated channels to explicitly highlight the effect of stratification on SSC profiles. We found that the impact of stratification is dominant in the near-bed region within the bottom boundary layer, affecting both sediment resuspension and bedload transport. Stratification reduces the likelihood of both dominant sweep and ejection events in the near the bed region which may affect sediment entrainment and bedload transport. Modifications to existing models of sediment entrainment and bedload transport are suggested to account for the effects of sediment induced stratification in vegetated and non-vegetated channels. One of the primary functions of rivers is to transport sediments due to the movement of water. Sediments come in different sizes- larger sediments are heavy and slowly move along the riverbed, while smaller lighter sediments are suspended in the water and move with the flow. Suspension of fine sediments in river is directly related to the amount of turbulence in the flow. Suspended sediments tend to settle under their weight, while the turbulence keeps them from settling. The balance of gravitational settling and turbulent mixing leads to an equilibrium suspended sediment concentration profile in the water column. This causes a variation in the density of the water-sediment mixture along the river's depth, which reduces the turbulence in the river. However, aquatic vegetation which is a natural part of the river increases turbulence in the flow. In this work, we study the effect of density stratification in channels with aquatic vegetation which has implications for sediment transport in natural waterways. We present a Rouse-type formulation including effects of sediment-induced stratification to predict suspended sediment concentration in vegetated channel flowsStratification effects are explicitly revealed using Large Eddy Simulations of vegetated and non-vegetated channelsStratification is relevant for near bed processes such as sediment entrainment and bedload transport