Assessing the performance of conservation measures for controlling slope runoff and erosion using field scouring experiments

Slope runoff acts as a driving force for soil erosion on the Loess Plateau but is also an important water source for alleviating water shortages and maintaining vegetation growth. Identifying how to regulate runoff can help solve the problems of water shortages and soil erosion. This study aimed to determine the effectiveness of conservation measures on controlling slope runoff and soil loss in a 20° runoff plot using scouring experiments. The treatments included plots with bare slope (CK) and three typical soil and water conservation (SWC) measures—engineering measures (fish-scale pits, FSPs), vegetation measures (grass revegetation by alfalfa, GR), and agricultural measures (straw mulching, SM). The results showed that the SWC practices significantly (P < 0.05) controlled runoff and soil loss. The GR, FSPs, and SM significantly delayed runoff start time by 150–250%, 200–300%, and 250–400%, respectively, compared with CK, and reduced runoff coefficients by 25–60%, 7–50%, and 40–80%, respectively. The runoff reduction rate (RRB) and sediment reduction rate (SRB) averaged 33.6% and 82.1%, 43.7% and 76.4%, and 82.3% and 94.0%, respectively, for the GR, FSPs, and SM treatments. However, the effectiveness decreased with increasing inflow rate, especially for the FSPs as they were gradually destroyed and lost their ability to control runoff scour at 7.0 m³ h^–1. The RRB and SRB were most affected by SM compared with FSPs and GR. All three SWC measures increased the Darcy-Weisbach friction coefficients (f) and reduced the velocity (V), Reynolds (Re), and Froude (Fr) numbers. Except for FSPs at 7.0 m³ h^–1, all SWC treatments had a laminar flow regime and subcritical flow state. Gray correlation analysis (GRA) showed that stream power and Reynolds number had better relational degrees with erosion rate for conservation measures, followed by shear stress, indicating that they may be preferred descriptors of the erosional process. These results provide meaningful guidance on measures for preventing soil erosion on sloping farmland in the Loess Plateau.