Rainfall and Upslope Inflow Impacts on Ephemeral Gully Erosion: Topography and Rainfall Intensity Contributions.

Ephemeral gullies (EGs) are major contributors to sediment loss and soil degradation on cultivated lands. However, the topography and rainfall impacts on EG development processes are still unclear, especially on steep loessial hillslopes like the Loess Plateau. A series of laboratory rainfall simulation experiments were conducted to investigate the impacts of topographic and rainfall characteristics on EG erosion on a steep loessial hillslope. A large slope adjustable soil pan (8 m-long, 2m-wide, and 0.6 m-deep) and a side sprinkler rainfall simulation system were used in this study. Three representative rainfall intensities (50, 75, and 100 mm h^-1), three typical slope gradients (26.8%, 36.4% and 46.6%) and five upslope drainage areas (16, 32, 64, 96, and 128 m²) were tested. The product of the upslope drainage area and the square of slope gradient (AS²) was selected to reflect the topographic characteristic in this study. The results showed that the EG erosion magnitude corresponded well with changing of rainfall intensity, slope and upslope drainage area. Soil loss increased when rainfall intensity, slope and upslope drainage area increased. Upslope topography and inflow had great impacts on downslope EG erosion. The upslope inflow rate was more effective than rainfall intensity in increasing runoff velocities in EG channels and thus caused more EG erosion when upslope inflow was applied. Soil loss equations based on rainfall intensity and AS² were established and validated, which showed satisfactory accuracy and could be used to predict the EG erosion in various topography and rainfall conditions on the steep loessial hillslope.