Evaluation of runoff and sediment control by different measures from the perspective of hydrological-sediment connectivity on the Loess Plateau

Although previous studies have explored the effects of vegetation restoration and terrace construction on hydrological erosion processes, few studies have scientifically evaluated the regulation of runoff and sediment by different measures from the perspective of hydrological-sediment connectivity. In this study, field in-situ rainfall simulation experiments were conducted in combination with 3D laser scanning technology. Simplified hydrograph and relative surface connection function were utilized to characterize hydrological connectivity, while the index of connectivity (IC) was used to characterize sediment connectivity. Four measures configurations (i.e., terrace plot (Measure A), root system plot (Measure B), upper terrace and lower bare land plot (Measure C), upper terrace and lower root system plot (Measure D)) were set up. We explored the connectivity changes of vegetation and terrace patches, as well as the transport of runoff and sediment at the plot scale. Results showed that measure B has the lowest hydrological connectivity, and measure D has the lowest sediment connectivity. The transport of runoff and sediment mainly occurred in rills, and the connectivity within rill channels was much higher than that between rills. Compared with sediment, runoff responds more quickly to changes in sediment connectivity. In addition, measures A and B did not synchronize with changes in connectivity. The erosion process of integrated measure D was mainly divided into two stages. The first half depends on hydrological connectivity, while the second half relies on separation control. During continuous rainfall, the runoff reduction rate (RRE) and soil erosion reduction rate (SRE) of measure D were not the highest, but compared with other measures, its sediment connectivity reduction rate (ICRE) was as high as 12.1% ~ 12.3%. Therefore, we suggest that implementing comprehensive measures such as upslope terrace construction and downslope vegetation restoration can lead to better soil and water conservation outcomes.