Effects of polysaccharides on the hydrodynamic parameters of sheet erosion on loessial slopes

The variations in hydrodynamic parameters at different polysaccharides rates and the relationships between sheet erosion modulus and hydrodynamic parameters were analyzed to reveal the hydrodynamic mechanism of sheet erosion on loessial slopes. Artificially simulated rainfall experiments were carried out under three slope gradients (10°, 15°, and 20°), three rainfall intensities (1.0, 1.5, and 2.0 mm·min^-1), and four dry-spreading rates of polysaccharides (0, 1, 3, and 5 g·m^-2). The results showed that (1) four hydrodynamic parameters (flow velocity, shear stress, stream power, and unit stream power) all increased with both rainfall intensities and slope gradients at four rates of polysaccharides. (2) Polysaccharides could effectively reduce hydrodynamic parameters. In contrast to the bare slope, the average flow velocity, shear stress, stream power, and unit stream power diminished by 27.11~41.18%, 9.53~18.67%, 31.82~50.24%, and 27.11~41.18%, respectively. (3) Polysaccharides could effectively reduce the growth rate of the sheet erosion modulus with hydrodynamic parameters, and there were few differences among the different rates (1, 3, and 5 g·m^-2). The increasing rates of the sheet erosion modulus with flow velocity, shear stress, stream power, and unit stream power were 14.0~65.7%, 14.8~33.9%, 7.8~23.7%, and 9.7~29.5%, respectively. (4) At different polysaccharides rates, the relationships between sheet erosion modulus and hydrodynamic parameters were all in logarithmic functions. Moreover, flow velocity (R² ≥ 0.920) and stream power (R² ≥ 0.876) were better hydrodynamic parameters than shear stress (R² ≥ 0.598) or unit stream power (R² ≥ 0.537). Polysaccharides decreased the hydrodynamic parameters and the response rates of sheet erosion to hydrodynamics.