砾石对坡面土壤侵蚀水动力学机制的影响

Rock fragments on the soil surface or in the soil top layer play an important role in soil erosion. Rock fragment is one of the most sensitive factors influencing soil erosion. To study the hydro-dynamics mechanism of rock fragments on soil erosion by water has important scientific significance for accurately understanding the mechanism of soil erosion and improving soil erosion model prediction. The objective of this study is to better understand the role that rock fragments on the soil surface play in concentrated flow hydraulics and erosion. Laboratory flume experiments were conducted with soil material by varying the rock fragment cover, size and location under different rainfall intensities. Based on screening the key hydrodynamic parameters which affect the slope erosion process, the erosion dynamics equation that contains erosion dynamic, flow resistance, flow parameters and rock fragment structure parameters would be established, and then the hydro-dynamic mechanism of the slope erosion process affected by rock fragment would be revealed from the following aspects of flow resistance and erosion dynamic. This study can provide a theory basis for soil and water conservation and improve the simulation accuracy of the soil erosion model.

砾石是土石山区坡面土壤侵蚀最敏感的影响因素之一，对土壤侵蚀过程具有重要的调控作用。开展砾石坡面土壤侵蚀水动力学机制研究，是建立土壤侵蚀物理模型的重要基础，对于准确认识坡面土壤侵蚀机理和提高侵蚀模型预报精度具有重要的科学意义。本研究采用室内模拟降雨的实验方法，通过不同砾石结构坡面侵蚀过程对比实验，在分析坡面侵蚀过程和识别关键水动力学参数的基础上，以砾石对坡面流侵蚀动力和水流阻力的作用机制为研究核心，构建基于砾石结构、侵蚀动力、水流阻力和水流参数的侵蚀动力学方程，揭示砾石坡面土壤侵蚀的水动力学机制。研究结果可为北京土石山区构建土壤侵蚀模型和开展水土保持生态环境建设提供理论基础。

砾石是北京土石山区坡面土壤侵蚀最敏感的影响因素之一。项目采用室内人工模拟降雨实验和模拟径流冲刷实验等方法，对不同砾石结构坡面土壤侵蚀过程及水动力学特性进行了系统研究，从坡面流侵蚀动力和水流阻力2个不同的角度，阐明了砾石对坡面土壤侵蚀水动力学机制的影响，揭示了砾石对坡面土壤侵蚀的影响机理。研究结果表明：（1）砾石对坡面侵蚀过程具有重要的调控作用，砾石能够通过促进土壤入渗、延缓坡面产流时间、增加土壤表层粗糙度、防治雨滴击溅和径流冲刷等方式，来减少地表径流量、减轻土壤侵蚀量和有效控制水土流失。（2）砾石存在改变了坡面流在坡面上的分布，坡面流流经砾石后发生了明显的绕流现象，使得砾石具有明显的阻滞水流的作用，延缓了坡面流流速，雍高了坡面流水深，使得水流流型由急流趋向于缓流发展。（3）不同砾石结构下坡面流水力参数相关性分析表明，雷诺数Re是最敏感的水力学参数，而径流水流功率 则是最敏感的侵蚀动力参数。（4）砾石能够明显增大坡面流水流阻力并改变了坡面流阻力构成，在不同砾石覆盖条件下，绕流阻力占总阻力的77.4%，表明绕流阻力占主导地位，它是坡面流阻力的主导因素。通过阻力叠加的方法，构建了砾石坡面径流阻力模型，该模型中包含了雷诺数、淹没度、弗劳德数及砾石覆盖度因子。项目研究结果对深入认识砾石坡面侵蚀过程具有重要意义，可为北京土石山区构建土壤侵蚀模型和开展水土保持生态环境建设提供理论基础。