草地植被覆盖度坡度及雨强对坡面径流含沙量影响试验研究

为研究植被修复状态下径流含沙量变化。该试验运用人工模拟降雨试验方法,分析了径流含沙量草被调控效益变化。结果:1)不同降雨强度或坡度下,平均径流含沙量随草被盖度的增大而减小,草被盖度从30%~70%,含沙量分别降低约10或5 kg/m3,可用线性方程显著描述。草被消减雨强对径流含沙量影响大于草被消减坡度的。平均径流含沙量随降雨强度或坡度的增大而增大,分别可用幂函数或指数函数方程显著描述,决定系数在0.5或0.8以上。2)基于单位水流功率建立幂函数模型决定系数为0.940,模型有效系数为0.986,说明模型模拟精度都较高。3)基于坡度、雨强和盖度建立指数函数模型决定系数为0.937,模型有效系数为0.894,说明模型模拟精度都较高。该研究可以预测草地坡面含沙量,为生态建设和流域管理提供指导。

Experiment on influence of cover degree, slope and rainfall intensity on sediment concentration of slope runoff in rangeland

Abstract: The purpose of this study was to model sediment concentration of sheet erosion on rangeland, which has a major impact on strengthening river basin management and controlling the source of soil erosion. The impact of herbaceous vegetation on sediment concentration under different slopes or rain intensities was studied by artificial rainfall experiment. The relationship of sediment concentration and slope gradient, rainfall intensity, and hydraulic parameters, such as shear stress, stream power and unit stream power, was investigated to derive an accurate experimental model. Each experiment soil pan with metal frames was 140 cm long, 120 cm wide and 2.5 cm deep. The experiment soil sample was collected from Ansai County, Shaanxi Province in China. After the soil was packed, herbaceous vegetation (Poa pratensis L.) was transplanted in a banded uniform layout. Poa pratensis L. was a gramineous plant, and the current year''s Poa pratensis L. was selected. The duration of all simulated rainfall events was 40 min. The experiment was conducted at 5 herbaceous vegetation cover densities (30%, 40%, 50%, 60%, and 70%), 5 rainfall intensities (0.7, 1, 1.5, 2, and 2.5 mm/min) and 5 slopes (7°, 10°, 15°, 20°, and 25°), respectively. All combinations were tested with 2 replicates of each run, a total of 90 experimental units. All statistical analyses were carried out using Excel or spss 18.0. Results show that: 1) Herbaceous vegetation not only decreases sediment concentration, but also reduces the effect of rainfall intensity or slope on it, which would increase with cover increasing. Cover increases from 30% to 70%, herbaceous vegetation decreases sediment concentration by more than 5 kg/m3, and reduces the effect of rainfall intensity or slope on it by more than 10 kg/m3. Under different slopes or rainfall intensities, sediment concentration decreases as linear equations with cover, and the relationship between sediment concentration and cover is significant (P<0.01). Under different covers, sediment concentration totally increases as power equations or exponential equations with rainfall intensity or slope, the relationship between sediment concentration and rainfall intensity is very well (P<0.01), and the relationship between sediment concentration and slope is also good (P<0.01). 2) Unit stream power is the parameter most suitably describing sediment concentration with an exponential equation among the 3 hydraulic parameters considered in this paper. Sediment concentration increases as shear stress or stream power increases, and both can be described by a logarithmic equation, but the relationship between sediment concentration and shear stress or stream power is poor. 3) Rainfall intensity, slope and cover can be used to predict sediment concentration with an exponential function accurately, which was satisfactory for predicting sediment concentration with the R2 value of 0.937 and the NE (Nash coefficient) of 0.894. Meanwhile, unit stream power also can be used to predict sediment concentration with a power function equation, which was satisfactory for predicting sediment concentration with the R2 value of 0.940 and the NE of 0.986. Vegetation species, layout and root morphology affect the simulation effect of sediment concentration on rangeland. In the later period, the vegetation species, layout and root morphology should be studied to quantify the sediment concentration and optimize the sediment concentration model.