Modeling wind erosion: detachment and maximum transport rate

In 1941, R.A. Bagnold published the basic laws goveming the detachment and transport of dune sand. Smce then, researchers modeling the sediment transport phenomenon have chosen to take a more empirical approach, especially when describing erosion processes on soils. Empirical modeling is accepted in many scientific circles. However, researchers seekmg extensive knowledge of wind erosion problems must understand and explain the fundamental processes of sediment transport, and not merely predict the magnitude of the sediment load carried by a particular wind energy.

Modeling and understanding wind erosion is essential to address present air quality concems. Dust generation, a byproduct of the saltation component of wind erosion, is explained by the physics of detachment and transport of particles from the action of wind forces and abrasion.

The Agricultural Research Service of the United States Department of Agriculture has developed several models to predict soil loss by wind on farm fields. These models, although of great mathematical and computational elegance, do not include key variables identified by Bagnold as early as 1941 and, therefore, are limited in value and applicability because the basic equations describmg the physical processes are incomplete. A need exists to clarify the processes of wind erosion and apply sensible understanding through modelmg to better predict and control wind erosion.

This study explores the basic erosion processes of soil and sand by wind, models the detachment process in terms of physical and temporal soil properties, describes the transition from aggregated soil particles to loose, noncohesive particles by the kinetics of abrasion down-wind with field length, and describes the maximum transport rate of this loose, noncohesive material as a function of particle size, particle size distribution, friction velocity, threshold friction velocity, and surface cover. Derived equations work equally well for sand and soil at different moisture conditions.

A wind tunnel study was conducted to veriíy the maximum transport rate equation, and the study provided msight into the contradictory findings of published results. The derived model, with assumptions and simplifications duly noted, provides the analytical framework from which wind erosion and dust generation models can be developed on the basis of physics, rather than statistical correlation.