Geoderma (Jun 2024)
Effect of different headcut heights on the process of headcut erosion and sediment production in the granite hilly area of South China
Abstract
Granite hilly areas are among the most ecologically fragile zones in China, and are susceptible to backward erosion under conditions of prolonged heavy rainfall and steep slopes. However, the spatiotemporal dynamics governing sediment generation and energy dissipation during gully headcut erosion in hilly granite areas remain unclear. In this study, through a field in situ scouring test, we investigated the temporal and spatial variation rules of gully headcut erosion energy consumption, sand production characteristics and sediment sorting characteristics of different soil layers (the laterite and sandy layer) at different headcut heights (25, 50, 75, 100 and 125 cm). The results showed that the energy consumption in the sandy layer exceeded that in the laterite layer, and the energy consumption in the upstream area (UA), gully head (GH), and gully bed (GB) consistently and linearly increased with experiment duration (R2=0.765–0.999, P<0.01). Moreover, the energy consumption in the GH (∆EH) and the energy consumption in the GB (∆EB) increased with the headcut height and discharge rate, whereas the energy consumption in the UA (∆EU) was predominantly influenced by the discharge rate. The GH contribution exceeded 50.00 % when the headcut height was greater than 100 cm; this height was the critical drop height for causing a sudden change in the gully headcut erosion. The sand production rate (Sy) reached its maximum value within 10 min of runoff initiation. Additionally, Sy initially decreased and then stabilized as a power function of the test duration, and Sy was greater in the sandy layer than in the laterite layer. In the runoff scouring process, the soil loss (S0) was concentrated in the UA and GH, while S0 was low in the GB. The total of soil loss amount (ST) and the soil loss amount of the GH (SH) linearly increased (P<0.01) with increasing total energy consumption (∆ET) and ∆EH, indicating that energy consumption can be considered to assess the retroactive erosion. Significant differences in the sediment content and enrichment rate between the laterite and sandy layers occurred, and the 1–2 mm particles accounted for the greatest proportion of sediments in both layers. The fine particles exhibited an enrichment trend, resulting in coarser slope particles. At the later scouring stages, coarse particles exhibited reduced cohesion and were susceptible to transport, this contributed to a gradual increase in coarse particles. This study could provide a theoretical basis for the systematic prevention and control of traceable granite erosion.
