Downslope runoff and erosion response of typical engineered landform to variable inflow rate patterns from upslope

Downslope wash-scour erosion driven by upslope inflow from compacted platform plays an important role in the acceleration of water and soil loss from engineered landforms. To explore the quantitative effects of variable upslope runoff on downslope runoff and erosion, a typical abandoned spoil deposit derived from the construction of Shenfu Expressway was selected to conduct a set of field runoff scouring experiments on steep slope (72.7 %). Four types of upslope inflow rate patterns including constant inflow rate pattern and earlier, intermediately, as well as later peak inflow rate patterns were designed dependent on different rainfall patterns and the timing for peak inflow rate (total inflow amount was kept constant). Thus, the downslope runoff and erosion response of the selected abandoned spoil deposit under variable upslope inflow conditions were investigated, and the results reveal that: (i) Maximum peak runoff intensity and the timing for the maxima were greatly impacted by upslope inflow rate patterns; however, little impact was exerted on total surface runoff; total runoff from the inflow events with earlier, later, and intermediately peak inflow rate increased by 20.6, 11.7, and 8.5 % in comparison with that from the uniform inflow event. (ii) Runoff events induced by variable inflow rate patterns altered the sediment-yielding process as well as the spatial distribution of sediment yield in the downslope direction, and thus produced more soil loss. Total soil loss from inflow events with earlier, later, and intermediately peak inflow rate increased by 79.7, 78.2, and 14.2 %, respectively, in comparison with that from the uniform inflow event. Statistically, sediment yield from designated control section decreased as a negative exponential function of slope length downslope. (iii) Among the selected runoff erosivity factors, runoff depth, unit runoff erosivity, and stream power are effective indicators for predicting the area-specific sediment yield from individual upslope inflow events, regardless of inflow rate pattern. (iv) Area-specific sediment yield performs remarkable power function correlation with unit runoff erosivity; the unit runoff erosivity can represent the variation in runoff erosion dynamics from individual inflow events, regardless of upslope inflow rate patterns. The results may provide evidence for soil erosion degree assessment, erosion model construction in drastically disturbed areas, as well as the prevention of newly arising water and soil loss from engineered landforms.