Research Theme

Turbulence and Sediments

We develop physics-based theories of sediment transport that link turbulence across scales to particle settling, suspension, and exchange with boundaries—revisiting classical assumptions from first principles.

Sediment Transport Multiscale Turbulence Boundary Effects

Why turbulence matters for sediment transport

A long-standing assumption in sediment transport theory is that the settling velocity of particles in turbulence is identical to that in still water. This simplification underpins classical models such as Rouse’s equation.

Our work shows that turbulence fundamentally alters settling dynamics: even weak fluctuations can reduce effective settling velocity through history and inertia effects.

Using perturbation analysis, we derived one of the first analytical models for sediment settling in turbulent flows, explicitly accounting for:

Basset history force
Virtual mass effects

These mechanisms explain persistent discrepancies between classical theory, observations, and formulations based on the turbulent Schmidt number.

A multiscale theory of settling and suspension

🧪 Turbulent settling theory

A comprehensive settling-velocity formulation that integrates turbulence from bulk flow scales down to the Kolmogorov scale.

📉 Scaling and limits

Reveals explicit scaling with Reynolds number and clarifies the limits of local mixing-length models for suspension.

🔁 Classical theory as a limit

Demonstrates that Rouse’s equation emerges as a special case under restrictive assumptions.

Turbulence, roughness, and vegetation–sediment interaction

Sediment transport is strongly modified by boundary roughness, including aquatic vegetation and engineered structures.

We link microscale turbulence physics to field-scale sediment and contaminant dynamics in vegetated and rough-bed flows.

Key contributions include:

Development of an asymmetric eddy diffusivity model for vegetated channels
Derivation of a universal velocity distribution using asymptotic analysis
Numerical reactive transport modeling of contaminant uptake by vegetation
Quantification of floating treatment wetland efficiency, validated against field data

What this framework enables

Physically grounded sediment settling models in turbulent flows
Unified interpretation of suspension theory, beyond empirical fits
Improved predictions of sediment and contaminant transport in vegetated systems
Scalable links from turbulence physics to ecosystem-scale performance

Representative Publications

Li, S., Bragg, A. D., & Katul, G. Reduced sediment settling in turbulent flows due to Basset history and virtual mass effects. Geophysical Research Letters, 50(22), e2023GL105810.
Li, S., Bragg, A. D., & Katul, G. A co-spectral budget model links turbulent eddies to suspended sediment concentration in channel flows. Water Resources Research, 58(3), e2021WR031045.
Li, S., & Katul, G. Cospectral budget model describes incipient sediment motion in turbulent flows. Physical Review Fluids.