Effect of the gravel-vegetation combination on shear-stress partitioning and sand transport rate

The existing research mainly focuses on the influence of a single type of roughness element on shear-stress partitioning and sediment transport. However, when the two types of roughness elements (such as gravel and vegetation) coexist, the laws of shear-stress partitioning and sediment transport are still unclear. Two different types of roughness elements are selected (one is the cylindrical gravel model, and the other is the flexible plant model). The distribution of surface shear stress, total shear stress and sand transport rate on different gravel-vegetation surfaces were measured in a wind tunnel. The results show that the shear-stress partitioning on gravel-vegetation surfaces is expressed as a function of the gravel lateral cover and the plant lateral cover, and the model parameters can be approximately characterized by the model parameters of gravel-only surface and vegetation-only surface. The sand transport rate on gravel-vegetation surface is related to the probability density function of surface shear stress which is expressed as a normal distribution function. For gravel lateral cover greater than 0.025, the parameter C in the model of sand transport rate decreases linearly with increasing gravel lateral cover and increases linearly with increasing plant frontal area, but is not influenced by plant lateral cover. The non-dimensional sand transport rate of gravel-vegetation surface decays exponentially with total lateral cover, and its decay rate is smaller than that of gravel-only surface, but larger than that of vegetation-only surface. The present research is helpful to improve wind erosion model in the future.