黄土坡面细沟演化的有效侵蚀力解析及作用机制研究

Rill erosion plays a significant role in the sediment yield and slope-scale geomorphic evolution, and therefore is pivotal to the prediction of soil erosion. Substantial reports have been dedicated to investigating the process, mechanism and environmental effects of rill erosion. However, the mechanisms driving rill development are still far from being fully understood. This project plans to conduct simulated rainfall experiments and mechanics analysis, with the aims at identifying the effective erosion force driving rill development on eroding slopes. By comparing the effects of raindrop impact, runoff drag force, runoff uplift force, gravity and soil adhesion to soil particle detachment, this project attempts to further distinguish and calculate driving force and resisting force during rill development. With the hydrodynamic data obtained from the rainfall experiments, this study will also compare the spatial and temporal variations of effective erosion force on different topographic positions. Following the principle of the effective erosion force imposed on soil particle detachment, this project intends to deduce the functional relations between effective erosion force and soil erosional responses during rill erosion (e.g., detachment rate, erosion rate and sediment yield). Furthermore, based on the quantitative relationships between sediment yield and rill morphology, this work aims at establishing a quantitative relationship between rill development and effective erosion force to reveal the underlying mechanisms of rill evolution process. The findings will help us to advance the current understanding of rill erosion mechanism and improve soil erosion prediction model.

细沟侵蚀对坡面产沙与地貌演化具有重要作用，是土壤侵蚀预报的关键。已有研究在细沟演化过程、机理及环境效应等方面取得了丰硕成果，但基于力学理论的细沟演化机制研究相对薄弱。本项目以黄土坡面细沟为对象，采用模拟降雨试验与力学分析相结合的研究方法，以土壤颗粒分离的受力分析为切入点，研究雨滴打击力、水流推力与上举力、土壤水下重力与粘结力等作用力对细沟侵蚀的动力与阻力分量，解析细沟有效侵蚀力（动力与阻力差值）及其计算公式；结合试验中的水动力学数据，分析不同坡位细沟有效侵蚀力的变化过程，揭示其时空分异特征；通过有效侵蚀力对土壤颗粒分离的作用原理，推导产沙率、产沙量、剥蚀率等细沟产沙参数与有效侵蚀力之间的函数形式；在研究细沟产沙与细沟形态变化特征及两者定量关系的基础上，建立细沟演化与有效侵蚀力的定量关系，阐明有效侵蚀力对细沟产沙及形态演化的作用机制，为细沟侵蚀机理的深化与土壤侵蚀机理模型的发展提供理论依据。

已有研究在细沟演化过程、机理及环境效应等方面取得了丰硕成果，但基于力学理论的细沟演化机制研究相对薄弱。本项目以黄土坡面细沟为对象，采用模拟降雨试验与力学分析相结合的研究方法，以土壤颗粒分离的受力分析为切入点，研究多源作用力对细沟侵蚀的动力与阻力分量，解析细沟有效侵蚀力（动力与阻力差值）及其计算公式；结合试验中的水动力学数据，建立细沟产沙参数与有效侵蚀力之间的函数形式；进一步建立细沟演化与有效侵蚀力的定量关系，阐明有效侵蚀力对细沟产沙及形态演化的作用机制。结果表明：本项目采用的间歇性降雨方法，可以准确模拟天然降雨下黄土坡面的细沟侵蚀过程，数据可靠；在空间上，细沟侵蚀与细沟平面形态参数关系密切，均沿坡长呈现出先增后减的规律，峰值均出现在坡面中部，主要是因为在坡面中部水流汇集，流速增加，径流侵蚀力增强，沟壁崩塌和下切侵蚀强烈；在时间上，细沟侵蚀与形态变化均在快速发展一段时间后进入相对稳定状态，侵蚀动力下降，侵蚀阻力增大，对应的有效侵蚀力显著下降，主要是因为坡面水蚀促使坡面微地貌发育，反馈影响径流的水力特性；有效侵蚀力可以代表驱动土壤分离的多源作用力综合作用，与细沟侵蚀量及形态均有显著的相关关系；在细沟防治过程中，可以通过减弱有效侵蚀力的方式防治侵蚀，如植被恢复、秸秆覆盖后，增加地表糙度减小侵蚀动力，同时增加土壤抗冲性增加侵蚀阻力，拦蓄径流减小侵蚀动力，促使动力与阻力平衡，削弱有效侵蚀力。研究成果不仅能为土壤侵蚀的理论深化与模型发展提供理论基础，而且对黄土坡面水蚀防治具有重要的实践意义。