砾石对红壤工程堆积体边坡径流产沙的影响

为探究砾石对红壤工程堆积体边坡降雨侵蚀的影响，基于室内模拟降雨试验，在1.0、1.5、2.0、2.5 mm/min雨强条件下，以土质边坡为对照，研究了10%、20%和30%的砾石质量分数红壤工程堆积体边坡的径流特征、产沙过程及侵蚀动力机制。结果表明：1）砾石质量分数对稳定径流强度的影响存在阈值，在雨强 > 1.0 mm/min时稳定径流强度随砾石质量分数的增加先减小后增大，在1.0 mm/min雨强时则表现为先增大后减小，且均在10%砾石质量分数下达到极值；2）雨强1.0 mm/min时，径流为缓流，砾石促进径流流动，使弗汝德数增大24.5%-87.8%，雨强2.0、2.5 mm/min时，径流为急流，砾石延缓径流流动，使弗汝德数降低4.2%-13.0%；3）侵蚀速率随产流历时变化过程受砾石质量分数和雨强的影响，雨强越大，砾石质量分数越低，边坡越易发生细沟侵蚀且伴随重力崩塌现象，侵蚀速率呈多峰多谷变化趋势；4）1.0 mm/min雨强时，砾石存在加剧了土壤侵蚀，产沙增幅达28.7%-50.5%；雨强 > 1.0 mm/min时，砾石减沙效益为5.0%-64.4%；5）径流功率是描述红壤工程堆积体侵蚀动力机制最优参数，其可蚀性参数及发生侵蚀临界径流功率从大到小对应的砾石质量分数均为10%、0、20%和30%。研究成果可为红壤区开发建设项目水土流失治理及侵蚀预测模型提供科学依据。

Effects of gravel on runoff and sediment yield of red soil engineering accumulation slopes

Engineering accumulation slopes, a special geomorphological unit resulting from human disturbances, are characterized by a large slope gradient, lacking soil organic matter, and loose surface structure, which drives the engineering accumulation body to be prone to intensive soil erosion under heavy rainfall. To explore the effect of gravel on rainfall erosion occurring on red soil engineering accumulation slopes, a series of indoor simulated rainfall experiments were conducted to investigate the runoff characteristics, sediment yielding processes, and erosion dynamic mechanisms of red soil engineering accumulation slopes with different gravel mass fractions (0, 10%, 20%, and 30%) under different rainfall intensities (1.0, 1.5, 2.0, and 2.5 mm/min). The results showed that:1) the stable runoff intensity varied as a decreased-increased tendency with gravel mass fraction increasing under the rainfall intensity higher than 1.0 mm/min, whereas it varied as an increased-decreased tendency under 1.0 mm/min rainfall intensity, and both reached extreme values at 10% gravel mass fraction (maximal value or minimal value). 2) Under 1.0 mm/min rainfall intensity, runoff flowed in the regime of subcritical flow during the whole test. The Freund number increased by 24.5%-87.8% because of the existence of gravel, and the gravel promoted the runoff to flow. However, under 2.0 and 2.5 mm/min rainfall intensity, runoff flowed in the regime of supercritical flow. The Freund number was reduced by 4.2%-13.0% because of the existence of gravel, and the gravel slowed down the runoff flow. 3) The erosion rate variation during the rainfall test was affected by the gravel mass fraction and rain intensity. Red soil engineering accumulation slopes became more vulnerable to rill erosion and gravity collapse under higher rainfall intensities and lower gravel mass fractions, resulting in multi-peaks and multi-valleys in the erosion rates.4) Under 1.0 mm/min rainfall intensity, the gravel exacerbated soil erosion with the erosion rate increasing by 28.7%-50.5%. On the contrary, the gravel retarded soil erosion with the erosion rate decreasing by 5.0%-64.4% under rainfall intensity higher than 1.0 mm/min. 5) The stream power could serve as the optimal parameter for describing the hydrodynamic process of the red soil engineering accumulation slopes. The values of erodibility-related parameters and the critical stream power values ranged from large to the small corresponding with the gravel mass fraction being 10%, 0%, 20%, and 30%, respectively. The results may provide a scientific basis for soil erosion control and erosion modelling for the red soil engineering accumulation slopes.