覆沙黄土坡面侵蚀叠加效应及动力机制研究

The wind-water erosion crisscross region on the Loess Plateau had typical coupled wind-water processes where soil erosion were serious. At present the erosion research was mainly concentrated in the characteristics of erosion by wind and water erosion interaction; the soil erosion of the sand-covered slopes was several times to several dozen times higher than that of loess slope, however the mechanisms are still need to further study. Therefore, this project is intended to take the sand-covered slopes in the wind-water erosion crisscross region on the Loess Plateau as the research object, then we conceptualize the overlapping effect of wind and water erosion and sediment yield as the water erosion process on the sand-covered slopes. The rainfall simulation experiments were designed to investigate the runoff process and sediment yield process of the sand-covered slopes. And to analysis the characters of rill development. With the sediment size distribution to reveal the source of soil and the development of soil erosion of the sand-covered slopes. To analysis the reason of increased in the sediment concentration in initial runoff period. Then to quantify the overlapping effect, and to reveal the dynamic characters of the overlapping effect in the soil erosion process of the sand-covered slopes; and to explore the dynamic mechanism of soil erosion of the sand-covered slopes. The results provide an essential evidence that the soil erosion mechanism of the water soil erosion effected by wind erosion. Therefore provide a scientific basis on the governance in plentiful and coarse sandy area on the Loess Plateau.

黄土高原风蚀水蚀交错区具有独特的风水复合侵蚀特征，土壤侵蚀严重。目前该区侵蚀研究主要集中在风蚀与水蚀交互影响特征方面，在研究风蚀对水蚀的影响中发现风沙覆盖的黄土坡面侵蚀量高于黄土坡面几倍到几十倍，但是其侵蚀机理等研究仍需进一步加强。为此，本项目以黄土高原风蚀水蚀交错区的典型覆沙坡面为研究对象，将该区黄土坡面上覆盖的风蚀物质概化为覆沙坡面，研究风蚀对水蚀的影响机制。通过覆沙坡面的模拟试验，研究覆沙坡面径流形成的特征，分析覆沙坡面径流形成的条件，明确覆沙坡面侵蚀产沙的特征；研究覆沙坡面细沟发育的特征，结合侵蚀粒径特征，辨析泥沙来源，阐明覆沙坡面侵蚀过程的演变特征；研究覆沙坡面径流初期含沙量剧增的原因，揭示侵蚀过程的叠加效应，确定覆沙坡面侵蚀过程的叠加效应的动力特征，阐明覆沙坡面侵蚀过程的动力机制。研究成果有助于深化该区风蚀对水蚀过程影响的内在机理认识，为黄土高原多沙粗沙区治理提供科学依据。

通过室内模拟降雨试验，分析了覆盖坡面与黄土坡面侵蚀产沙的规律，量化了覆沙及坡度协同作用下对侵蚀产沙的贡献率，研究了覆沙坡面细沟发育的特征，揭示了覆沙条件下坡面产流产沙改变机制。主要取得如下研究进展：（1）覆沙坡面初始产流时间是黄土坡面的3倍，坡面覆沙对坡面降雨的初始产流时间具有延长作用。除第一场外覆沙坡面的总径流量略低于黄土坡面，其他场次的总径流量覆沙坡面是黄土坡面1.1-1.2倍；总产沙量均是黄土坡面1.1-9倍，显著高于黄土坡面（P<0.05）。（2）黄土坡面整体的平均产流速率要小于覆沙坡面。在前9 min迅速增长，9 min后趋于稳定直至试验结束；覆沙坡面的产流速率曲线呈“波动上升-相对稳定”的变化趋势，在15-32 min波动上升，32 min后趋于稳定直至试验结束。黄土坡面的产沙速率明显小于覆沙坡面的产沙速率且黄土坡面产沙速率的曲线变化和产流速率的曲线变化趋势大致相同，即曲线呈 “快速上升-相对稳定”的变化趋势。（3）相同的覆沙梯度下，坡度在25°-30°之间存在一个阈值，对侵蚀的贡献会达到最大，在之后会逐渐降低。从多元分位数回归分析结果来看，覆沙对侵蚀速率的贡献占23.2%，坡度对侵蚀速率的贡献占到18.8%。（4）测试土壤饱和含水量为46.8%，黄土坡面在第一场降雨过程中，由于土壤物理结皮的原因，入渗并没有达到10cm处，土壤含水量一直处于初始状态；而对于覆沙坡面，由于沙层的作用，使得土壤物理结皮很难形成，土壤达到饱和状态，产流方式发生了改变，从典型的超渗产流转变为蓄满产流。（5）土壤含水量在蓄满的状态下，当仍有水分压力时，类似于土壤渗流现象，使得土壤的内部结构发生变化，土壤的颗粒之间的内聚力减少，土壤可蚀性增加，细沟发育明显。在相同的降雨条件下且侵蚀开始启动后，覆沙坡面更容易发生侵蚀。