Effect of polyacrylamide concentration on runoff redistribution and sediment yield control from karst spoil heaps under simulated rainfall

Soil erosion in karst regions exhibits a dual-structure nature, involving both surface erosion and subsurface leakage. Therefore, for spoil heaps sites in these areas, it is essential not only to mitigate surface erosion but also to prevent groundwater contamination caused by rainfall infiltration. In this study, artificial simulated rainfall experiments were conducted to investigate the effects of polyacrylamide (PAM) solutions at different concentrations on the runoff generation processes and sediment transport characteristics on spoil heaps slopes. The results demonstrate that PAM application increased surface runoff by an average of more than 17%, while reducing the proportion of subsurface and underground runoff. Compared to the control group, PAM reduced the sediment transport modulus for surface and underground flows by an average of 29% and 48%, respectively. PAM concentration showed a positive correlation with surface runoff volume, but a negative correlation with runoff from other soil layers and sediment yield. Although higher PAM concentrations (5‰) significantly reduced underground runoff, they also limited water availability for plants. Taking all factors into account, a PAM concentration of 3‰ is recommended as the optimal application rate for the comprehensive soil and water conservation management of spoil heaps sites in karst regions.