Runoff scouring experimental study of rill erosion of spoil tips

The soil erosion of spoil tips seriously threatens the safety of people's lives and property and the surrounding ecological environment. Rill erosion is an important cause of water and soil loss in spoil tips. This study investigated the rill erosion on spoil tip slopes, the morphological changes of rills and the mechanisms of rill erosion. A field runoff plot (5 m long, 1 m wide and 0.5 m deep) with three inflow rates (1.6, 2 and 2.4 mm min-1) and three typical slopes (28 degrees, 32 degrees and 36 degrees) was used for runoff simulation experiments. Results showed that inflow rate was the most important factor affecting soil erosion, which contributed 68.87% and 60.54% to the runoff rate and soil loss rate, respectively. Rill development has three stages: formation, development and adjustment. The overall predominance of parallel-shaped rills suggested that rill formation was dominated by concentrated runoff. Inflow rate exerted the greatest effect on the average rill width and average rill depth, with contribution rates of 73.11% and 60.26%, respectively. Meanwhile, slope exerted the greatest effect on the rill width-to-depth ratio, with a contribution of 60.45%. The average rill depth was the best indicator of rill morphology for evaluating rill erosion. Reynolds number was the best hydraulic parameter for predicting rill erosion. Flow shear stress was the best hydrodynamic parameter to describe rill erosion mechanism, with a critical value of 1.98 Pa. These results contributed to elucidating the rill erosion mechanism of spoil tip slope and provided a scientific basis for its soil erosion control.