Upslope and lateral inflow impacts on ephemeral gully erosion: contribution discrimination

Authors: XU, XIMENG - Institute Of Geographic Sciences And Natural Resources; ZHENG, FENLI - Northwest Agricultural & Forestry University; Wilson, Glenn; Zhang, Xunchang; QIN, CHAO - Northwest Agricultural & Forestry University; XU, GE - Northwest Agricultural & Forestry University

Submitted to: Journal of Hydrology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/23/2019
Publication Date: 9/23/2019
Citation: Xu, X., Zheng, F., Wilson, G.V., Zhang, X.J., Qin, C., Xu, G. 2019. Upslope and lateral inflow impacts on ephemeral gully erosion: contribution discrimination. Journal of Hydrology. 579:1-13. https://doi.org/10.1016/j.jhydrol.2019.124174.
DOI: https://doi.org/10.1016/j.jhydrol.2019.124174

Interpretive Summary: An ephemeral gully (EG) system includes the main EG channel and EG branches that flow into the main channel, along with flow from rills and interrill areas along the sides of the main branch. Lateral inflow from side of the EG creates the branches to the main channel for runoff and sediment discharge. The various branches to the EG drainage system are all interconnected. This EG system develops with time and contributes to different degrees to the EG erosion and local soil degradation. However, research quantifying the erosion due to flow into the main channel from upslope sources compared to the lateral inflow from the sides is still lacking. Thus, experiments under two representative rainfall intensities (50 and 100 mm h-1) and two typical slope gradients (15º and 20 º) were conducted with typical lateral and upslope drainage area conditions. The results showed that: 1) upslope and lateral inflow both contribute to the runoff connectivity of the EG system to the hillslope; 2) upslope inflow contributions (70-80%) to total runoff and soil loss were much greater than the lateral inflow contributions (10%). Lateral inflow was important in the formation of lateral rills contributing to runoff connectivity, and to the developed of side-slopes that are dissected with these small channels; 3) concentrated flow in EG and rills, as well as sheet erosion from interill areas, shifted the soil texture to be coarser, which may contribute to unproductive landscape areas. This work demonstrates the critical need of preventing both upslope and lateral drainage into EG channels to protect valuable soil resources from degradation.

Technical Abstract: Flow through an ephemeral gully (EG) system integrates flow through the EG channel (main branch) and the interconnected EG tributaries, as well as, lateral rills and interrill areas. Lateral inflow creates tributaries to the main channel for runoff and sediment discharge. The interconnected drainage system that develops with time contributes interactively to the EG erosion and local soil degradation. However, research quantifying the upslope inflow and lateral contributions to EG erosion is still lacking. Thus, simulated rainfall and inflow experiments under two representative rainfall intensities (50 and 100 mm h-1) and two typical slope gradients (15º and 20 º) were conducted with typical lateral and upslope drainage area conditions. The results showed that: 1) upslope and lateral inflow contribute to the runoff connectivity of the EG channel and lateral rills in the EG system; 2) upslope inflow contributions to total runoff and soil loss were 62% to 78% and 65% to 81%, respectively, while lateral inflow only contributed around 10% of total runoff and soil loss. Lateral inflow was important in the formation of lateral rills contributing to runoff connectivity, and to the lateral slope and imbricated landform formation process; 3) concentrated flow in channels and sheet flow in interill areas shifted the soil texture to be coarser, which may contribute to unproductive landscape areas. This work demonstrates the critical need of preventing both upslope and lateral drainage into EG channels to protect valuable soil resources from degradation.