**166**

**Stratification effects in sediment-laden air flow**

__Bailiang Li__
^{1}, Douglas Sherman^{2}

*
^{ 1}Xi'an Jiaotong-Liverpool University, Suzhou, Jiangsu, China,^{ 2}University of Alabama, Tuscaloosa, AL, USA*

Many laboratory studies have shown that velocity profiles in sediment-laden water deviate from the expected log-linear relationship. One common explanation for this phenomenon is that it results from flow stratification induced by a sediment concentration gradient. This stratification effect damps the development of turbulence and changes the structure of eddies. The process is often analogized to temperature-induced stratification in a stable atmosphere (Stull, 1976), which is often quantified by a form of Richardson number.

In sediment-laden flow, the modified velocity profiles should still obey the Law of the Wall, however, a correction parameter, Φ_{m}, is necessary:

du/dz=u_{*}_{Φ}_{m}/(*kz)*

where *u* is the streamwise velocity at elevation of *z*, *u _{*}* is the shear velocity,

*1/Φ _{m}=1-βR_{f}=1-αβR_{i}*

where *α* and *β* are constants. Note *α* is the Schmidt number, representing the ratio of eddy viscosity to eddy diffusivity, commonly assumed to approximate 1. In thermally stable flow, *R _{i }*and R

We developed depth-averaged, sedimentological gradient and flux Richardson numbers (*R _{ia} *and

This study explored the stratification effect on the streamwise velocity profile caused by saltation-flux gradients in sand-laden air flow, and quantified those effects using a pair of sedimentological Richardson numbers (flux and gradient). This study derived a range of estimates for the Schmidt number and the constant *β*. These results can help us better understand sand-air interactions, and improve our ability to represent sand flux and wind velocity gradients near the surface.