不同覆盖位置下草地坡面水流路径长度变化特征

为深入探索植被覆盖及其格局的减水减沙的水动力学过程及其机理,该研究利用室内放水冲刷试验,分析了不同植被盖度及其覆盖位置在不同冲刷流量下水流路径长度的变化,以及水流路径长度与植被覆盖度、水动力学参数和产流产沙量之间的关系,探讨坡面水流路径长度作为表征植被格局参数的可行性。结果表明:1)植被覆盖度可有效影响水动力参数的变化,并且随着植被覆盖度的增加,流速和单位水流功率呈线性减小趋势(P0.01);而糙率系数、阻力系数和径流剪切力则呈指数增加趋势(P0.01)。坡面水流受阻可能性增加,动能减弱,进而导致产流产沙量不断减少,并且冲刷流量越大,减小幅度越大。2)在不同冲刷流量下,水流路径长度与植被覆盖度、水动力参数和产流产沙量之间均存在显著的相关关系(P0.01)。同时随着水流路径长度的增加,一方面,流速和单位水流功率呈对数式上升,坡面水流动能增强;另一方面糙率系数、阻力系数和径流剪切力分别呈对数式和指数式减小,坡面阻滞能力下降,水流侵蚀力增强。最终导致坡面侵蚀状况发生变化,产流产沙量呈对数式增加。因此,水流路径长度可作为反映植被减水减沙的动力学过程和预测坡面产水产沙的参数之一。该研究为深化理解植被格局与水文连通性的作用关系,建立合适的植被格局表征和植被减蚀效应评价提供依据,以期增强地区生态环境的质量和稳定性,为现代化农业发展,特别是保障农业生产环境做出贡献。

Variation characteristics of flow length of grass slope under different grass strip positions

Vegetation cover and its pattern generally determine the hydrodynamics process and mechanisms in the runoff and sediment reduction. In this study, an indoor scouring experiment was carried out to investigate the variation characteristics of flow length index under different vegetation coverage and patterns. A relationship was established for the flow length index with the hydrodynamic parameters, yields of runoff and sediment in different vegetation patterns and coverage under different flow rates. Furthermore, the flow length index of the slope was proposed to serve as an indicator for measuring the effects of vegetation patterns on soil erosion. The results showed that: 1) The vegetation coverage significantly affected the hydrodynamic parameters. There were different trends of hydrodynamic parameters with the increase of vegetation coverage. The velocity and unit stream power presented a linear trend of increase relationship (P<0.01). There was an exponentially increasing trend in the roughness coefficient, resistance coefficient, and runoff shear stress. The increase of flow resistance and the decrease of kinetic energy can cause a gradual reduction in the amount of runoff yield and sediment production, where the greater the discharge was, the greater the reduction was. The vegetation reduced runoff yield and sediment production by changing the hydrodynamic parameters of water flow. 2) The flow length index, one of the important indexes of hydrological connectivity, was widely used in water and soil conservation. There were significant correlations between the flow length index and vegetation coverage, hydrodynamic parameters, as well as runoff and sediment production. Hydrodynamic parameters, runoff and sediment production varied with the flow length index. The velocity and unit stream power increased logarithmically, leading to the increase in the kinetic energy of slope flow. The roughness coefficient and the resistance coefficient presented a logarithmical decrease, indicating the decrease in the retardation capacity of the slope surface. But the runoff shear stress decreased exponentially, leading to the increase in the unit stream power of runoff. Obviously, the ability of slope block was declined, whereas, the erosion capacity of water flow was enhanced. This case finally led to the change of erosion status of the slope. There was also a logarithmic increase in the runoff and sediment yield of the slope. Thus, the flow length index with the aid of the flow path change can be used to indicate the hydrodynamic parameters of slope surface water flow and sediment yield in the change. Particularly the flow length index can be expected to serve as an indicator for the dynamic process of vegetation runoff and sediment reduction, and thereby predict the runoff and sediment yield on the slope. This finding can provide a scientific basis for the relationship between vegetation pattern and hydrological connectivity, and further establish vegetation patterns and evaluate vegetation impacts on erosion. The simulation experiments can contribute to the effective distribution and utilization of water resources for the regional ecological environment in modern agriculture.