黄土坡面片蚀过程稳定含沙量及其影响因素

Steady sediment concentration of sheet erosion on loess slope and influencing factors

黄土高原地区坡面土壤侵蚀具有明显的垂直分带性,溅蚀片蚀带是坡面侵蚀的最上方地带,研究片蚀过程含沙量变化有助于阐明坡面侵蚀规律。本文采用人工模拟降雨试验方法研究了黄土坡面片蚀稳定含沙量及其影响因素;试验处理包括2种质地的黄土(塿土和黑垆土),2个雨强(90和120 mm/h)和4个坡度(10°、15°、20°和25°)。结果表明:在不同质地黄土、降雨强度和坡度条件下,水流含沙量均呈现先减小后平稳的规律;稳定含沙量与土壤颗粒体积分形维数、降雨强度和坡度呈幂函数关系,稳定含沙量随土壤颗粒体积分形维数的增大而减小,随降雨强度和坡度的增大而增大,影响程度依次为土壤颗粒体积分形维数、降雨强度和坡度;所分析的水动力学指标中单位水流功率与稳定含沙量关系最密切,降雨强度对稳定含沙量的影响大于单位水流功率。

Soil erosion on the loess hillslope shows clear vertical zonal differentiation. From upslope to downslope locations, the erosion zones are sheet erosion zone, rill erosion zone, and shallow gully erosion zone. Sediment concentration of sheet erosion zone has important impacts on detachment, deposition, and transportation processes of rill erosion zone. The purpose of this study was to investigate the relationship between steady sediment concentration and different influencing factors including loess soil type, rainfall intensity, and slope gradient. The relationship between steady sediment concentration and shear stress, stream power, and unit stream power were also examined. The impacts of loess soil type, rainfall intensity, and slope gradient on sediment concentration in rain-induced sheet flow were examined by artificial rainfall experiment from June to August 2015. Two loess soils from Yangling and Changwu districts were subjected to simulated rainfall using a detachment tray under infiltration condition. Two rainfall intensities of 90 and 120 mm/h were simulated on slope gradients from 10° to 25°, resulting in rain-induced overland flow. The sediment was sampled at several time intervals and sediment concentration was determined. Different hydraulic parameters including flow velocity, shear stress, stream power, and unit stream power were measured. The results show that： （1） Sediment concentration demonstrated a similar trend under different conditions： first sharply decreased and then became steady. A new equation can be used to model changes of sediment concentration, with the minimum value of the equation as steady sediment concentration. Sediment concentration was greater at higher rainfall intensity and steeper slope gradients. With slope gradient increasing from 10°to 25°, sediment concentration increased from 4.3 to 6.25 kg/m3 and 9.56 to 18.53 kg/m3 at rainfall intensities of 90 and 120 mm/h on Lou soil hillslope; and increased from 4.76 to 12.42 kg/m3 and 9.72 to 19.08 kg/m3 at rainfall intensities of 90 and 120 mm/h on Dark loessil soil hillslope, respectively. The steady sediment concentration was lower with higher fractal dimension of loess particles. The impacts of factors on steady sediment concentration are in the following order： fractal dimension of loess particles 〉 rainfall intensity 〉 slope gradient; （2） Unit stream power was the hydrodynamic parameter that was most closely correlated with steady sediment concentration, and a new model including rainfall intensity, unit stream power, and fractal dimension of loess particles was advanced to calculate steady sediment concentration. The impacts of factors on steady sediment concentration are in the following order： fractal dimension of loess particles 〉 rainfall intensity 〉 unit stream power.