考虑植被和地形对下坡侵蚀耦合影响的坡长因子研究

The mechanism is not clear and failed to be reflected in erosion prediction reasonably that vegetation on upslope segment and topography have coupling influence to downslope segment erosion by together changing the overland flow concentration and its hydrodynamic properties. This has become a main bottleneck of revealing the water erosion process on vegetation mosaic covering slope and carrying out large and meso-scale erosion prediction based on the empirical statistical model. Therefore, this project intends to build vegetation mosaic covering variable-slope flumes（runoff plots with mosaic surface cover） to carry out indoor artificial rainfall experiment and field in-situ observation. Then, by using statistical methods and erosion dynamics theory, we will take the improvement of slope length factor in the RUSLE as a breakthrough to analyze variation characteristics both of slope segment erosion intensity and hydraulic parameters in different conditions of vegetation on upslope segment and topography, and select the key parameters which can describe the response relation of the slope water erosion intensity to vegetation on upslope segment and topography. On this base, this project will reveal the mechanism of coupling influence of vegetation on upslope segment and topography to downslope segment erosion in the concentration process of the overland flow, develop a distributed slope length factor algorithm considering coupling influence of vegetation on upslope segment and topography to downslope segment erosion, and test its application. All of this have important theoretical and practical significances in revealing the process of slope water erosion process and predicting the water erosion of large and medium spatial scales based on distributed empirical prediction model.

当前，坡面内上坡植被和地形共同改变汇流及其水动力特性从而影响下坡侵蚀的机制尚不明晰，且未能在侵蚀预报中得到合理反映，成为全面揭示植被镶嵌覆盖的实际坡面水蚀过程和开展基于经验统计模型的大中流域侵蚀预报的主要瓶颈。为此，本项目拟搭建植被镶嵌覆盖的变坡水槽（复合地表覆盖小区），开展室内人工降雨试验和野外原位观测，以RUSLE中的坡长因子改进为突破口，综合运用统计学方法和水动力学理论，分析不同上坡植被覆盖和地形条件下，坡面坡段内的侵蚀强度与水动力参数的变化特征，遴选有效刻画坡面水蚀强度对此响应的关键参数，揭示坡面汇流过程中上坡植被与地形对下坡侵蚀的耦合影响机制，最终构建考虑上坡植被与地形对下坡侵蚀耦合影响的分布式坡长因子算法，并对其进行应用检验。对全面揭示坡面水蚀过程和基于经验预报模型的大中空间尺度水蚀预报具有重要的理论和现实意义。

上坡植被与地形共同改变上坡来水及侵蚀动力，影响下坡侵蚀，呈现典型耦合作用特征。然而，目前土壤侵蚀研究倾向于分析单因子在侵蚀产沙过程中的贡献，对耦合影响研究不足，制约了预报模型的应用。本研究基于人工模拟降雨实验，观测了变坡条件下（2 m、4 m、6 m和8 m坡长）不同草地和裸地组合方式坡段尺度上的径流量和产沙量及主要水力学参数特征，并分析了坡段尺度L因子与水力学参数的相关性。结果表明：1）裸地和草地水力学参数沿程变化趋势相似，除阻力系数和曼宁糙率外，草地水力学参数较低；2）总覆盖度一致的情况下，草地坡段越靠近坡面下部，全坡面产沙量越小；3）裸地实测L因子与USLE和RUSLE模型L因子接近，草地实测L因子随着坡长增加呈现轻微降低趋势；4）坡段L因子与本坡段水力学参数（流速、佛罗德数和单位水流功率）相关系数显著，且优于与上坡段水力学参数相关关系。本研究有助于进一步认识植被与地形耦合对侵蚀产沙的作用机制。