Effects of vegetation cover and road-concentrated flow on hillslope erosion in rainfall and scouring simulation tests in the Three Gorges Reservoir Area, China

Abstract

Roads play a significant role in altering hydrological processes. Roads cause more erosion to be generated from the hillslope for both road-concentrated flow and rainfall. In this study, six treatments (Natural Restoration, Grass, Grass & Shrub, Sodded Strip, Grass & Farmland, and Farmland) were used to recolonize hillslope plants on a newly built unpaved road. Rainfall simulation (rainfall intensity of 90mmh−1 and 120mmh−1) and scouring simulation (scouring flow rate 15Lmin−1 and 20Lmin−1) tests were conducted to identify the effects of plants on soil erosion. In the rainfall simulation test, Grass & Shrub was more effective at reducing hillslope erosion than the other treatments, and Grass & Shrub also had a lower runoff coefficient, soil detachment rate, and higher efficiency in trapping runoff and sediment. The hydrological responses of all of the tested plots in the scouring test were much faster than in the rainfall simulation, as indicated by the lower lag time to runoff generation. The hillslope erosion in the scouring test was significantly higher than in the rainfall simulation. The water-stable aggregate, saturated hydraulic conductivity, vegetation cover, root length density, and root weight density were important factors that conditioned the runoff generation and sediment yield from the hillslope in both experimental tests. In the scouring test, in infiltration improvement and flow erosivity reduction, Grass was more effective at trapping runoff and sediment because of its dense well-developed system of fine roots. Therefore, except for an immediate surface cover, in the areas where the hillslope has a risk of road-concentrated flow scouring, the enhancement of topsoil roughness was also very important in weakening the impact of road-concentrated flow on the hillslope.