Upslope inflow, hillslope gradient and rainfall intensity impacts on ephemeral gully erosion

Ephemeral gullies (EGs) are major contributors to sediment loss and land degradation on cultivated lands. However, the topography and rainfall impacts on EG development processes are still unclear, especially on steep loessial hillslopes such as the Loess Plateau. A series of laboratory rainfall simulation experiments were conducted to investigate the impacts of topographic characteristics (3 typical slope gradients (S): 26.8%, 36.4%, and 46.6%; and 5 upslope drainage areas (A): 16, 32, 64, 96, and 128m(2)) and rainfall intensities (3 representative erosive rainfall intensities 50, 75, and 100mmhr(-1)) on EG erosion on a steep loessial hillslope. A large slope adjustable soil pan (8m-long, 2m-wide, and 0.6m-deep) and a side-sprinkler rainfall simulation system were used in this study. The results showed that soil loss increased when rainfall intensity, slope, and upslope drainage area increased. Upslope topography and inflow had great impacts on downslope EG erosion, and the contribution percentages ranged from 52.2% to 74.1%, from 48.3% to 71.4%, and from 29.5% to 66.7% for the 50, 75, and 100mmhr(-1) rainfall treatments, respectively. Runoff velocities with upslope inflow were 22.7% to 79.4% larger than those without inflow, and the upslope inflow was more effective than rainfall intensity in increasing runoff velocities in EG channels, thus caused more soil erosion. Soil loss equation based on rainfall intensity and AS(2) (product of the upslope drainage area and the square of the local slope gradient) was established and validated. The determination coefficient (R-2) and Nash-Sutcliffe simulation efficiency (E-NS) were 0.80 and 0.87, which showed satisfactory accuracy. This equation can be used to predict the EG erosion in various topographic and rainfall conditions on steep loessial hillslopes.