Effects of three plant root systems on rill erosion characteristics on coal dump slopes under simulated experiments

Dump slopes have experienced severe rill erosion and threaten the safety of the ecological environment. Although vegetation restoration has improved the ecological environments of mining areas, because dump slopes have unique soil properties, the mechanism by which roots impact rill erosion on dump slopes remains unclear. Based on the in-situ runoff scouring experiment of the dump slope and the use of bare land as the control (CK), the influence of roots on rill erosion characteristics (RECs) of the dump slopes were analyzed for three root types of vegetation, specifically, tap root–Artemisia ordosica (AO), fibrous root–Elymus dahuricus (ED) and tap + fibrous root–Artemisia ordosica + Elymus dahuricus (AE). The results indicated that, compared to the CK, the roots reduced the rill erosion rate (Ts) by 75.61%–86.64% and the rill depth (Rd) by 64.62%–81.06% on the dump slopes. However, they increased the runoff depth (h) and Reynolds number (Re) by 2.02%–37.14% and 36.1%–172.0%. Among them, AO significantly increased Manning roughness coefficient (n), Darcy–Weisbach friction factor (f) and shear stress (τ), whereas ED and AE were most effective in reducing h and Ts, respectively. 59.9% of the RECs of dump slopes were explained by roots and hydraulic characteristics together. Furthermore, PLS-SEM analysis revealed that roots affect hydraulic characteristics by changing surface roughness and runoff friction resistance, ultimately leading to differences in the RECs of dump slopes, which explained 98.5% of the RECs on dump slopes with a 72.2% goodness-of-fit. The above results further enhance the understanding of the role of roots in controlling rill erosion on dump slopes.