A simple expression for wind erosion threshold friction velocity

Threshold friction velocity u(*t) is the friction velocity at which wind erosion is initiated. While u(*t) is affected by a range of surface and soil properties, it is a function of particle size only for idealized soils. In this paper we present a simple expression for u(*t) for spherical particles loosely spread over a dry and bare surface. In this expression we consider the balance between the driving forces (aerodynamic drag and lift) and the retarding forces (cohesion and gravity) and assume that the cohesive force is proportional to particle size. It is found that u(*t) can be expressed as root Y(1)d+Y(2)1/d, with Y-1 and Y-2 being empirical constants. Tho new expression is both simple and effective.