Grassed Waterways Reduce Soil Erosion in Rare Earth Tailings Through Runoff Moderation and Sediment Particle Sorting

Ganzhou City in Jiangxi Province, China, serves as a critical source and supplier of rare earth ions. However, rampant mining activities have resulted in severe soil erosion, persistent pollution, and serious land degradation. Grassed waterways offer substantial benefits in drainage, erosion resistance, and promoting sediment deposition. This study investigated the application of the waterways for soil conservation in rare earth tailings, focusing on how flow rate and slope gradient dynamically influence runoff processes, sediment transport, and particle sorting during multiple scouring events. The results showed that grassed waterways effectively reduced runoff rates and significantly controlled sediment yield. Both flow rate and slope considerably affected sediment yield, with slope exerting a more pronounced influence. Particle size distribution in waterways typically exhibited bimodal patterns under varying conditions, with dominant particles size of the 0–0.068 and 0.094–0.171 mm. Transport mechanisms, primarily suspension/saltation (> 50%) and rolling, controlled these particle sizes, respectively, while coarse particles (> 0.955 mm) were predominantly deposited. Grassed waterways enhanced particle separation by minimizing the loss of large particles, including both agglomerates and individual grains, thereby reducing overall sediment generation. This study provided valuable insights into the potential of waterways in mitigating runoff and sediment generation and optimizing deposition processes, offering practical implications for engineering applications.