黄土丘陵区植被作用下产流机制及侵蚀动力响应

Vegetation covers directly affect hydrological processes and have regulation effects on the runoff and sediment generation process. The average sediment yield of Yellow River of 1.6 billion ton reduced to 0.3 billion ton in recent years. Effect of vegetation coves on the decline of runoff and sediment of Yellow River is a hot scientific issue currently. Based on the better vegetation coverage and the sharp decline of runoff and sediment in the upper and middle reaches of the Yellow River, the vegetation effect on regulation of runoff generation mechanism was taken as the research mainline. So, the combined method of field plot observation, simulated rainfall experiment and theory analyse will be adopted to study the hydrology process and erosion dynamics of a coupled system of rainfall- vegetation-infiltration-runoff. The project aims to study the response of the nonlinear process of rainfall-infiltration to vegetation cover, the identification of changes in runoff generation mechanism, effect of vegetation cover on changes in runoff generation mechanism, the critical vegetation cover on changes in runoff generation, the response of the erosion dynamics to changes in runoff generation. The research results are important to reveal the mechanism of the decline of runoff and sediment of Yellow River in recent years, and provide an important scientific value for evaluating the effect of vegetation on reducing runoff and sediment.

植被覆盖变化状况直接影响到流域水文过程，进而对产汇流、产输沙形成调控作用。黄河输沙量由多年平均的16亿t减少到近年的3亿t左右，植被覆盖变化对黄河水沙减少的贡献是当前关注的热点问题。基于黄河上中游地区植被覆盖显著提高与同时期黄河水沙发生锐减的背景，以植被对产流机制的调控作用为研究主线，项目采用野外定位动态观测、野外与室内人工模拟降雨试验和理论分析相结合的方法，将降雨—植被—入渗—产流作为一个水文耦合系统，研究降雨入渗非线性过程对植被变化的响应，阐明植被覆盖变化对产流过程的胁迫作用，构建植被作用下坡面产流模式，辨识坡面产流机制胁变的被覆临界，诠释侵蚀动力对植被覆盖变化下坡面产流机制胁变的响应规律。本研究成果对于揭示近年黄河流域水沙发生锐减的机理具有重要意义，并可为科学评价植被对水沙过程的调控作用提供理论基础。

植被覆盖变化状况直接影响到流域水文过程，进而对产汇流、产输沙形成调控作用。基于黄河上中游地区植被覆盖显著提高与同时期黄河水沙发生锐减的背景，项目以植被对产流机制的调控作用为研究主线，采用野外定位动态观测、野外不同被覆坡面人工模拟降雨试验和理论分析相结合的方法，将降雨—植被—入渗—产流作为一个水文耦合系统，揭示了植被覆盖变化对产流过程的影响作用及其侵蚀动力响应机制。主要研究结果表明：（1）建立了天水罗玉沟流域大型野外人工模拟降雨试验基地，包括10个不同被覆坡面径流场和1套可移动式人工模拟降雨系统，获取了植被覆盖、土壤水力学、降雨、入渗和径流过程等3000多组参数；（2）天然状态下野外坡面水分动态监测结果表明，土壤水分的垂直变化可以划分为速变层、活跃层、次活跃层和相对稳定层，且0～40cm土层范围内差异较大；（3）模拟降雨作用下，土壤水分活跃性的影响主要表现在0～30cm土层范围内，且随土层深度的增加，降雨对土壤水分活跃程度的影响逐渐减弱，土壤水分在不同土层土壤中的流动存在梯度性差异和非均匀性特征；（4）草被覆盖度和降雨强度对土壤入渗存在交互性影响，自然草被覆盖度（约60%）草被增加土壤入渗系数的有效雨强在1～1.5 mm/min之间；（5）不同覆盖度和雨强条件下，利用4个入渗模型对土壤入渗速率与降雨时间的关系进行拟合，Horton公式能较好的模拟该区土壤入渗过程，该区域产流模式以超渗产流为主；（6）产沙能耗可以作为表征侵蚀动力的指标，降雨强度对产流过程的影响存在着临界阈值，这个临界阈的降雨强度范围为1.5～2.5mm/min。本研究成果对于揭示近年黄河流域水沙发生锐减的机理具有重要意义，并可为科学评价植被对水沙过程的调控作用提供理论基础。