Abstract: To obtain the erosion dynamic mechanism of spoil heaps, we examined the effects of taproot system (Artemisia gmelinii) and fibrous root system (Medicago sativa and Cynodon dactylon) vegetation on the runoff velocity, hydraulic parameters, and hydrodynamic parameters of the spoil heaps through artificial rainfall simulation experiment. Results demonstrated that vegetation reduced the average soil loss rate of spoil heaps by 88.34%-92.88%, as compared with bare spoil heaps. Average runoff velocity decreased by 50.51% under taproot system vegetation, and 21.32%-35.61% under fibrous root system vegetation. Both the runoff patterns of bare and vegetated spoil heaps were laminar (Reynolds Number <40). Runoff flow of bare spoil heaps was rapid when rainfall intensity was not greater than 1.2 mm/min; however, under the protection of taproot system vegetation, the runoff flow was slow, while under fibrous root system vegetation, the runoff flow pattern varied between rapid and slow regimes. Taproot system vegetation had a greater retardation effect on runoff resistance coefficient than fibrous root system. The flow shear stress and stream power could better describe the dynamic process of erosion on the spoil heaps under vegetation protection, showing a significant linear relationship (R² was 0.63-0.96). Our findings offer scientific basis for revising the vegetation factors in the establishment of soil and water prediction model suitable for production and construction projects.

Key words: spoil heaps, runoff characteristics, rainfall experiment, runoff velocity, erosion dynamics, vegetation type