Effect of high intensity soil and water conservation engineering measures on soil erosion and sediment transport

The middle reaches of the Yellow River (MYR) cover a significant portion of the Loess Plateau, rendering it among the most heavily impacted regions by soil erosion globally. Consequently, the MYR are characterized by high-intensity soil and water conservation measures, such as terracing and silt check dams, which exert a profound impact on soil erosion and sediment transport in this region. However, there is currently no accurate and clear assessment of sediment interception and sediment reduction contributions for large-scale and complex cascading silt check dams. This study enhances the Revised Universal Soil Loss Equation (RUSLE) model by coupling the processes of soil erosion, slope sediment production, and channel sediment transport. The study evaluates the slope erosion and sediment production through the combination of RUSLE and the Sediment Connectivity Index (IC). Additionally, it calculates the sediment interception and sediment output in the channel based on silt check dams sediment interception efficiency. Accurate classification of complex cascading silt check dams is crucial for assessing their sediment reduction contributions. The research employs a flow-based method for precise dam classification and incorporates the latest terracing distribution data to accurately assess the sediment reduction contributions of high-intensity engineering measures in the MYR. The research findings indicate: (1) The average annual soil erosion rate in the MYR from 1981 to 2017 is 13.32±31.94 t ha^-1 yr^-1, with moderate to severe soil erosion covering 15.1% of the area. (2) Over the past 40 years, there has been an overall decreasing trend in soil erosion in the MYR, with a significant reduction covering 8.65% of the area. Significant decreases in soil erosion began to appear after 2000, with an average annual soil erosion rate reduction of 0.34 t ha^-1 yr^-1. (3) Based on the cascading situation of silt check dams, the 2187 large silt check dams in the MYR are classified into 6 categories. Taking the initial siltation year as an example, for basins controlled by silt check dams, the sediment output rate without silt check dams is 3.444 t ha^-1 yr^-1, while with silt check dams, the sediment output rate is 0.468 t ha^-1 yr^-1, achieving a sediment reduction contribution of 86.4%. The upcoming tasks include: (1) investigating the interannual fluctuations in sediment reduction attributed to silt dams and validating the model; (2) formulating diverse scenario assumptions to evaluate the sediment reduction contributions from engineering measures and vegetation restoration. This study seeks to precisely evaluate the impact of high-intensity soil and water conservation measures on mitigating soil erosion and sediment transport in the MYR, offering insights for regional soil and water conservation practices and sustainable management.