Ephemeral gully erosion in concentrated flow channels induced by rainfall and upslope inflow on steep loessial slopes
Hongliang Kang, Mingming Guo, Wenlong Wang
Abstract
Abstract Ephemeral gullies (EGs) play a crucial role in hydrological connectivity, soil erosion, and land degradation. However, little research has focused on flow hydraulics in concentrated flow channels and their effects on EG erosion on steep loessial slopes. A simulated experiment of rainfall (60–120 mm hr −1 ) and upslope inflow (0.45–2.25 m 2 hr −1 ) were conducted on concentrated flow channels with loess at 15°–25° slope gradients. The concentrated flow was turbulent and subcritical in most cases. The flow shear stress, stream power, and unit stream power in the concentrated flow channels varied from 32.65 to 109.40 N m −2 , 10.85 to 38.66 N m −1 s −1 , and 0.08 to 0.16 m s −1 , respectively. The EG depth, width, and width‐depth ratio varied within 14.8–24.6 cm, 18.5–33.8 cm, and 1.13–1.83, respectively. Moreover, the EG depth and width increased in a power function with the runoff rate ( R 2 = 0.82–0.83; p < 0.01). The sediment yield rate (Ys) varied within 15.94–94.44 g m −2 s −1 under the different treatments and had a good linear relationship with the runoff rate ( R 2 = 0.78; p < 0.01). Furthermore, the flow shear stress and stream power can be used to predict Ys by linear functions. The critical runoff rate and shear stress to initiate EG erosion were determined to be 0.09 m 3 hr −1 and 2.66 N m −2 . However, the coefficient of determination for the linear relationship between Ys and shear stress was low (0.58). The results indicate that the flow shear stress mechanism might not be enough to explain sediment load variation for EG erosion, and headcut erosion mechanism should be taken into account.