Effect of shrub-grass vegetation coverage and slope gradient on runoff and sediment yield under simulated rainfall

Evaluating the benefits of sediment and runoff reduction in different vegetation types is essential for studying the mechanisms of soil and water conservation on the Loess Plateau. The experiment was conducted in shrub-grass plots with nine levels of mixed vegetation coverage from 0% to 70%, three slopes (10°,15°, and 20°) and two rainfall intensities (1.0 and 2.5 mm/min). The results showed that the vegetation coverage and slope gradient significantly affect runoff and sediment yield. Shrub-grass vegetation coverage had a significant effect on the runoff start-time, runoff flow velocity, runoff rate, and soil erosion rate on hillslopes. Mixed vegetation coverage could effectively delay the runoff start- time and decrease the runoff flow velocity. However, the effects of the slope gradient on runoff and sediment yield are opposite to those of vegetation coverage. Shrub-grass vegetation coverage could effectively increase runoff and sediment yield reduction benefits, while their benefits were affected by the rainfall intensity. At the 1.0 mm/min rainfall intensity, the reduction in the sediment production rate was greater than that under the 2.5 mm/min intensity. However, when the shrub-grass vegetation coverage exceeded 42%, the runoff reduction benefit was more obvious at higher rainfall intensities. The cumulative sediment yield increased with increasing cumulative runoff, and the rate of increase in the cumulative runoff was greater than that of the cumulative sediment yield with increasing of shrub-grass vegetation coverage. Moreover, there was a power function relationship between cumulative sediment yield and cumulative runoff yield (P < 0.05). Our paper is expected to provide a good reference on the ecological environment and vegetation construction on the Loess Plateau.