Purpose

Severe water erosion of coarse-textured soils, thereby exposing subsurface horizons at the surface, is a serious problem in southern China. Currently, there are few systematic studies on erosion processes and features as the various coarse-textured subsurface horizons are exposed.

Materials and methods

The main objective in this study was to investigate the effects of rainfall intensity and inflow rate on the runoff, soil loss, and erosion features of three horizons of a typical soil developed from granite (topsoil horizon, illuvial horizon, and parent material horizon) in the steeply sloped region. A series of laboratory simulation tests were conducted in a 0.8-m by 3-m flume using two combined rainfall and upslope inflow condition (90 mm h⁻¹ plus 2 L min⁻¹ and 120 mm h⁻¹ plus 2.66 L min⁻¹, respectively).

Results and discussion

Runoff coefficient and soil loss increased with the evolution of erosion phase from sheet erosion to rill advancement to rill maturity phase. Runoff generation increased as soil horizons with higher bulk density were exposed on the surface and as the rainfall-inflow rate increased. Additionally, rainfall-inflow rate and soil horizon had significant effects on soil loss rate, headward erosion rate, and rill density (p < 0.01). The hillslope roughness was dependent on the interaction of soil properties (clay content) and rainfall characteristics (rainfall intensity and duration). Despite the different hillslope roughness levels exhibited as result under the different rainfall-inflow treatments, the topsoil horizon always exhibited low soil loss. Moreover, as rainfall duration increased, coarse grains (quartz) were gradually enriched on the hillslope surface, which worked as “armoring” to protect the soil surface of interrill areas from further erosion, especially for the topsoil horizon. Due to the surface armoring, rill erosion was considered the main sediment source during the rill maturity phase.

Conclusions

These results suggested that coarse grains could be an effective on-site soil conservation practice controlling soil erosion, which should be considered in future erosion prediction and bare land restoration in coarse-textured soils.