Water Drop Impact Angle and Soybean Protein Amendment Effects on Soil Detachment

Abstract

To improve soil erosion prediction technology, the mechanics of each erosion process must be understood sufficiently to predict soil loss on an event basis. The mechanics of the initial erosion process, soil detachment caused by falling raindrops, requires greater understanding to improve mechanics‐based prediction. This laboratory study addressed the effect of soil shear strength and raindrop impact angle on soil detachment. Loess (fine‐silty, mixed, superactive, mesic Typic Hapludoll) and glacial till (fine‐loamy, mixed, superactive, mesic Aquic Hapludoll) A and C horizon soil materials were used. To vary soil shear strength, soybean protein material was added to each soil material at concentrations of 0.0, 0.5, and 1.0% by weight. Soil shear strength and soil detachment were measured on preformed soil cores. Soil detachment tests were performed at water drop impact angles of 90, 80, 70, and 60°. Soil strength increased and detachment decreased with increasing soybean protein concentrations. Shear strength of the loess C horizon increased 0.61 to 1.85 Mg m−2, while that of the till C horizon material increased 0.57 to 0.98 Mg m−2 with addition of 1% soybean protein. A 1%–soybean protein addition reduced soil detachment 26% compared with unamended soil. Significant soil detachment interactions existed between waterdrop impact angle and the other variables. These interactions were due to different mechanical behavior of the soils and changing strength caused by soybean protein additions. Interactions observed are explained based on differences in the lateral jet for varying impact angles and for elastic vs. inelastic impacts.

Sand detachment under rains with varying angle of incidence

“…Also, apart from being the radial, splashes tend to be unidirectional in the favor of prevailing action of wind (De Lima, 1989) or slope (Poesen, 1985;Erpul et al, 2005). Cruse et al (2000) and Erpul (2001) reported that the angle of incidence of raindrop impact varies significantly and would greatly depend on wind speed and slope aspect of topography during most rainfall.…”

“…Although "soil" is used as a more general term that also includes "sand", in the process of soil detachment by the raindrop impact, Erpul (2003) and Erpul et al (2005) distinguished both in terms of cohesion since cohesive soils are generally characterized by smaller particle sizes than cohesionless sand. Cruse et al (2000) showed that there were significant soil detachment interactions resulting from different mechanical behavior of the soil surfaces and the lateral jets of varying impact angles. Their fairly divergent results of soil detachment accounted for the differences in elasticity of waterdrop-soil collision and influence of drop impact angle on lateral jets.…”

“…For example, with the weak loess soil and perpendicular raindrop impacts, lateral jet development, other than shear strength, restricted measured detachment, and it appeared that soil detachment increased at lower impact angles since lateral jets were more efficient in detaching particles from the point of impact. Depending on elasticity or rigidity of the surface (Huang et al, 1982(Huang et al, , 1983, soil detachment varied with the development of lateral jets (Cruse et al, 2000). Huang et al (1983) reported that the lateral jet of water from raindrop impact would be greater on rigid surfaces and for lower impact angles than that on a soft, elastic surface with raindrop impact at a perpendicular angle.…”

“…Huang et al (1983) reported that the lateral jet of water from raindrop impact would be greater on rigid surfaces and for lower impact angles than that on a soft, elastic surface with raindrop impact at a perpendicular angle. Obviously, in the situations where the increased lateral jetting by wind drive exists, as the raindrop impact angle decreases (Cruse et al, 2000;Erpul, 2001), greater force components act parallel to the surface and lower force components act perpendicular to the surface. This study examines sand detachment under wind-induced lateral jetting and investigates the relative effects of the different components the raindrop incidence vector on sand detachment.…”

Sand transport under increased lateral jetting of raindrops induced by wind

“…Explicitly, E tx was as good as E tz at the process of RD in contradiction to the fact that D RD varied only with the normal component of impact velocity (Ellison, 1947;Heymann, 1967; Springer, 1976; Gilley and Finkner, 1985;Erpul et al, 2002Erpul et al, , 2003bErpul et al, , 2004Cornelis et al, 2004a,b). Therefore, this article is specifically intended to quantify the effect of the components of compressive and shear stresses (Huang et al, 1982(Huang et al, , 1983Al-Durrah and Bradford, 1982;Cruse et al, 2000;Erpul et al, 2005Erpul et al, , 2008 of obliquely striking wind-driven raindrops on sand detachment to model RD-WDT. The role of these two stress components in entraining sand particles into the splash droplets to be subsequently traveled with the wind is presented in this article.…”