Response of erosion rate to hydrodynamic parameters in sheet and rill erosion process on saturated soil slopes

Sheet erosion and rill erosion are two important forms of slope erosion. The initiation and development of those forms are significantly affected by erosive power of water flow. Identifying main erosion forms and exploring the relationships between hydrodynamic parameters and erosion rates, especially in a saturated soil slope simultaneous the development of sheet-rill erosion, are important to reveal erosion intrinsic mechanism. The objectives of this study were to quantify erosion rates, hydrodynamic parameters, and determine the relationships between hydrodynamic parameters and the soil erosion rate at sheet and rill erosion stages of saturated soil slopes. A series of indoor soil flume simulated rainfall experiments were conducted on a saturated soil slope at three rainfall intensities (30, 60, and 90 mm h−1), four slope lengths (1, 2, 4, and 8 m), and five slope gradients (2°, 5°, 10°, 15°, and 20°). Results revealed that erosion rates at sheet and rill erosion stages on a saturated soil slope increased from 5.31 to 22.31 kg m−2 s−1 and 23.91 to 140.35 kg m−2 s−1, respectively. The values of flow shear stress, stream power, unit stream power at those two stages were within the scope of 0.064–0.151 m s−1 and 0.175–0.327 m s−1, 0.77–2.97 Pa and 1.59–6.70 Pa, 0.24–0.80 W m−2 and 0.53–1.80 W m−2, and 0.041–0.12 m s−1 and 0.07–0.36 m s−1. Hydrodynamic parameters of flow velocity, shear stress, stream power, and unit stream power at rill erosion stage were 2.01 to 2.77, 1.18 to 2.31, 1.31 to 2.51, and 1.20 to 2.57 times those at sheet erosion stage. Furthermore, erosion rates at sheet and rill erosion stages increased linearly with the increase of flow velocity, shear stress, stream power, and unit stream power under different experimental conditions. The erosion rates at those two erosion stages were accurately predicted by stream power and flow velocity (R2sw=0.86, R2rv=0.92). This study is helpful for unraveling the dynamic mechanism of sheet-rill erosion process and establishing reasonable process-based soil erosion models.