Benefits of soil and water reduction on spoil heaps by vegetation under two driving forces

Soil erosion on spoil heaps has become an important environmental issue and it causes serious soil erosion, geological disasters and even limits land resources. The influence of grass on soil loss on steep spoil heaps remains elusive. This study aimed to investigate the effects of Artemisia gmelinii on runoff and erosion processes of spoil heaps with silt loam soil. The effects of vegetation on runoff and sediment reduction benefits were quantified. Field rainfall experiment and rainfall with scouring experiment were performed. A series of rainfalls at three rainfall intensities (0.8, 1.2, and 1.8 mm/min) and fixed discharge flow rate (15 L/min) were simulated in four plots (3 m × 2 m, including repeats). The spoil heaps were characteristics with the gravel content of 10% and slope gradient degree of 30. The characteristics and differences of vegetation's regulation of hydrological and erosion processes of spoil heaps under two driving forces were analyzed. The results showed: 1) Artemisia gmelinii reduced average soil loss rate and runoff rate by 57.28%-98.51% and 13.17%-83.11%, respectively, under the two driving forces, and the benefits of soil reduction and runoff reduction were decreased by 17.01% and 68.74%, respectively after adding the upper catchment flow. The vegetation not only decreased the erosion of the spoil heaps, but also made the erosion process of the spoil heaps smoother. 2) The benefits of soil and water loss reductions were decreased by 4.32%-21.10% with the increase of rainfall intensity for Artemisia gmelinii spoil heaps under rainfall experiment, and it was 26.85%-56.30% for runoff reduction benefits. However, the benefits of soil loss reduction were increased by 45.55%-46.35% and runoff rate reduction was decreased by 54.21%-55.54%, respectively, under rainfall and scouring experiment. Significant difference analysis also showed that rainfall intensity had a significant impact on soil and water yield of bare and Artemisia gmelinii spoil heaps (P<0.01) under the two driving forces, and the effect of discharge flow was significant than rainfall. 3) The soil loss rate was decreased with runoff duration for bare spoil heaps under rainfall and rainfall with scouring experiment, while it was increased for Artemisia gmelinii spoil heaps only under rainfall condition. The fluctuation of erosion and runoff on bare and Artemisia gmelinii spoil heaps was increased significantly with time as the driving force changed from rainfall to rainfall with scouring. The average soil loss rate was increased by 6.63-7.15 times and 4.92-192.81 times for bare soil and Artemisia gmelinii spoil heaps, respectively, when a fixed discharge flow was added. They were 4.96-10.81 times and 6.77-44.04 times for the average runoff rate. The change of driving forces had greater impact on Artemisia gmelinii than bare spoil heaps. 4) The average soil loss rate for bare spoil heaps during the early stage was 1.06-2.90 times that of the later stage under both driving forces, while it was 35.21%-59.30% for Artemisia gmelinii spoil heaps under rainfall condition. However, the stage with serious soil loss changed with rainfall intensity under rainfall and scouring experiment for Artemisia gmelinii spoil heaps. The results can provide guidance for the prevention and control of soil erosion and runoff loss in the spoil heaps of production projects. These results have significant value for guiding engineering practice.