Amplification factors to estimate wind erosion of piles of soil with different heights: Numerical simulation and structure-from-motion photogrammetry verification

Abstract

In this study, we propose amplification factors of single conical piles with different heights and sizes to describe wind erosion acceleration effects of piles compared to flat erodible surfaces. It is not difficult using traditional wind erosion models to estimate wind erosion of flat agricultural land or pastoral surfaces. However, in the current form these models cannot be used for elevated surfaces such as dunes or piles, which may lead to more serious dust emission and air pollution. A computational fluid dynamics simulation was used to refine a wind erosion estimation method of pile from the US Environmental Protection Agency (USEPA) by dividing the pile surface into multiple subareas with constant wind speed for each subarea and then obtaining ratios of pile erosion to the corresponding flat surface by calculating the total erosion rate of the pile and that of a flat surface with the same floor area. The ratios as amplification factors, E_amp, for six pile sizes (from 1 to 12 m) and five wind speed scenarios covering most erosive daily wind speeds from 824 stations throughout China were analyzed and fitted to equations to enable consideration of other heights and wind speed conditions. The changing patterns of the factors were verified using experimental surveys of two plots via the structure-from-motion photogrammetry method, which generated high-resolution digital elevation maps and detected detailed erosion changes. The erosion from a stockpile surface was found to be 2.52 to 7.16 times that from a flat surface with the same floor area, and the influence of pile height on amplification factor could be expressed by a logarithmic equation. These factors can be easily applied to estimate pile erosion by multiplying them by wind erosion results for flat surfaces obtained from other indexes or models. The procedure described in this paper can be extended to consider amplification or reduction effects of dunes, hills, piles, pits, and gullies with different shapes or configurations in relation to wind erosion. Furthermore, the reliability of wind erosion estimation over complex surfaces can be improved to implement specific soil conservation practices.