Quantification of upslope and lateral inflow impacts on runoff discharge and soil loss in ephemeral gully systems under laboratory conditions

摘要

Overland flow through an ephemeral gully (EG) system integrates flow from upslope areas and lateral side slopes. Lateral overland inflow creates tributaries to the main EG channel for runoff and sediment discharge which exacerbates the EG erosion and local soil degradation. However, research concerning tributary formation by overland flow, especially contributions of overland upslope and lateral inflows to EG erosion, are still lacking. Thus, simulated rainfall and inflow experiments under two erosive rainfall intensities (50 and 100 mm h(-1)) and two typical slope gradients (15 degrees and 20 degrees) were conducted under representative lateral and upslope overland inflow conditions using an 8-m long, 2-m wide and 0.6-m deep soil pan. The results showed that upslope and lateral inflow both contributed to the runoff connectivity of the EG channel and lateral rills in the EG system. For these simulated conditions, upslope inflow contributions to total runoff and soil loss were 62-78% and 65-81%, respectively, while lateral inflow only contributed around 10%. The contribution differences could be attributed to flow hydrodynamic characteristics in that shear stress and stream power in the EG channel were 4.9-8.6 times greater than those on the lateral slopes. Lateral inflow was important to lateral rill formation, which contributed to imbricated landform and lateral gradient formation process, and consequently promoted runoff and sediment connectivity of the EG system. Soil erosion induced by concentrated flow in channels and sheet flow in interill areas coarsened soil textures, soil particles lager than 0.02 min increased 12.6% on average, which may contribute to reduction of local soil productivity. This work demonstrates the critical need of preventing both upslope and lateral drainage into EG channels.