Abstract：[Background] In view of high and steep slope with frequent heavy rainfall, the measures against extreme soil erosion have been taken commonly on the cut-slope in mountainous areas. However, the characteristics, process and influencing factors of soil erosion on the earth cut-slope with or without soil and water conservation measures are rarely reported. The earth cut-slopes in four mountainous regions of Sichuan and Yunnan provinces, Southwest China were selected to evaluate the benefit of runoff and sediment reduction resulted from soil and water conservation measures under multiple rainfall intensity, and examine the effect of soil compactness on sediment yield.[Methods] Here, the effects of nine measures, i.e., bare slopes, step rills, gravel, three-dimensional (3D) network, vegetation plus 3D network, different vegetation coverage (25%, 50%, 75% and 90%) against soil erosion on runoff and sediment reduction as well as the relationship between surface soil compactness and sediment yield have been executed on forty-five road cut-slopes at 12 sites in Panlong and Qiling counties of Yunnan province and Wenchuan and Songpan counties of Sichuan province, southwestern China, by setting up micro-runoff plots with simulated rainfall. The surface runoff and sediment yields produced in 45 earth slopes under various measures were determined by runoff plots with an area of 2 m2. The soil pH, organic matter content, particle and aggregate size distribution on each earth slope also were analyzed.[Results] The tested slope soils generally have coarser texture relative to undisturbed slope soils, and are dominated with the particle size fraction of sand and silt, occupying an averaged range of 36.9% to 54.1%, and 18.3% to 50.4%, respectively. Structural failure rate of the soil aggregates varies greatly from 20.8% to 63.3%, indicating the erosion durability of soils with the highest rate in Songpan is relatively low. Except the treatment that the surface soil covered with gravels, the runoff and sediment yields on slopes with protection measures are significantly lower than those on bare slope, with the runoff and sediment yields of higher than 1 700 mL and 100 g, respectively. Among them, the measures, i.e., vegetation plus 3D network and vegetation with the coverage more than 75%, are the most effective in mitigating runoff and sediment yields. With the increase of vegetation coverage from 0 to 90%, in general, runoff and sediment yields on cut-slopes significantly declined. The compacted degree values of the bare soil within a depth from the surface to 10 cm on the earth cut-slope varied greatly, fluctuating between 400 and 2 000 kPa. After rainfall, the average compactness of the soil within a depth from the surface to 10 cm dropped by 4 to 373 kPa. The variation of soil compactness would cause the changes in porosity, grain cohesion, and other mechanical properties of soils. In case the soil compactness exceeds 200 kPa, sediment yields on the bare slope would reduce as the soil compactness increases.[Conclusions] The measure with the vegetation coverage more than 75% is the most effective in mitigating runoff and sediment yields, while the nonlinear relationship between soil compaction and sediment yield on bare slope is found.
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2023, Vol. 21 
