黄土塬沟头溯源侵蚀动力过程及形态演化试验研究

Runoff over the upland in the gully area of the Loess Plateauis extremely intensive, which often violently scours gully head. Sometime, a rainstorm event can cause gully head to move upward several meters to tens of meters and consequently, severely damage farmland, road and town residence. However, few research works have been done on headward erosion in the region. The project is proposed to study headward erosion in use of simulated rainfall combined with field adding-water test, three-dimensional terrain laser scan, MX-2010-G landscape instrument and GIS techniques. Specifically, the relationship between gully head forwarding rate and the factors affecting headward erosion will be investigated and the relationships among hydrodynamic and soil mechanic parameters will be clarified. Moreover, the mechanisms of gully head forwarding, trench wall collapse and ravine expansion by the super imposed water and gravitational erosion will be understand to relate the evolution characteristics of gully head features in headward erosion to the factors and the hydraulic and soil mechanic parameters. At the same time, the proportion of gully headward erosion to soil erosion on tableland surface will be calculated to find headward erosion module and its formula. Finally, the frequency and volume of gravitational erosion will be separated and calculated using MX-2010-G landscape instrument and GIS techniques. The approach of indoor simulation validated by field experiments can reveal gully headward erosion and its form evolution on the Loess Tableland. The project proposed may provide a scientific basis for the “controlling gullies to protect tableland” and regional eco-environmental construction.

黄土高塬沟壑区塬面径流强度大，常剧烈冲刷沟头，一次暴雨可使沟头溯源数米或几十米，对道路、农田、民居等产生很大威胁，但关于溯源侵蚀的研究仍十分薄弱。本项目以黄土塬沟头溯源侵蚀为研究对象，采用室内与野外模拟降雨+放水试验，三维激光扫描、MX-2010-G地貌仪监测及GIS技术相结合的研究方法。阐明黄土塬沟头溯源侵蚀及前进速率与影响因素的关系；探讨溯源侵蚀量与水动力、土力学参数的关系，揭示在水力与重力叠加作用下沟头前进、沟壁崩塌及沟谷扩张的机理；建立溯源侵蚀沟头形态演化特征与影响因素、水动力、土力学参数的关系；计算沟头溯源侵蚀相对于塬面侵蚀的比例关系，确定沟头溯源侵蚀系数及其计算式；使用地貌仪结合GIS技术分离并计算重力侵蚀发生的频度和体积。野外试验验证室内模拟结果，揭示黄土塬沟头溯源侵蚀及形态演化的规律。为黄土高塬沟壑区“固沟保塬”与区域生态建设提供科学依据。

黄土高塬沟壑区塬面汇水面积大，暴雨条件下极易形成洪水，常剧烈冲刷沟头，一次暴雨可使沟头溯源数米至几十米，对道路、农田、民居等产生很大威胁，但关于溯源侵蚀过程与机制的研究十分薄弱。本项目阐明了黄土塬沟头溯源侵蚀产沙及前进速率与影响因素的关系；探讨了溯源侵蚀量与水动力、土力学参数的关系，揭示了在水力与重力叠加作用下沟头前进、沟壁崩塌及沟谷扩张的机理；建立了溯源侵蚀沟头形态演化特征与影响因素、水动力、土力学参数的关系；计算了沟头溯源侵蚀相对于塬面侵蚀的比例关系，确定了沟头溯源侵蚀系数及其计算式。最终揭示了黄土塬沟头溯源侵蚀及形态演化的规律。项目取得的重要结果如下：沟头溯源侵蚀产沙量随放水流量、塬面坡度和沟头高度的增大而增大，沟头前进速率随放水流量的增大而增大，与塬面坡度和沟头高度并无明显相关性。沟头溯源侵蚀产沙与径流能耗关系最为密切，启动沟头侵蚀产沙的临界能耗为0.68 J/s。沟头溯源距离均随跌水出射流速、入潭流速、剪切力及能耗增大而增大，随跌水入潭角度增大而减小。重力崩塌使侵蚀模数增加22.75%～324.59%，占沟头前进距离的6.95%~36.29%。孔隙水压力随试验时间呈显著线性或对数函数关系，孔隙水压力的上升是影响溯源侵蚀崩塌发生的关键因素。塬面侵蚀沟宽度、深度、切割度及弯曲度在试验初期快速增大后逐渐稳定，而宽深比发育则呈逐渐减小至稳定的过程；侵蚀沟宽度、深度、切割度、弯曲度分别为29.6~52.0 cm、1.76~3.80、19.7%~34.7%、1.15~1.32，且随流量增大而增大，宽深比变化为9.91~23.75，随流量增大而减小，沟头前进对塬面侵蚀沟的发育影响较小。沟头长度随试验时间呈指数增长，当沟头与集水区沟道相连或侵蚀到临界状态后不再增长，此时，发育形成二级沟头和三级沟头。溯源侵蚀系数变化范围为0.16~0.77，其与沟头高度呈正相关关系，沟头高度每增加0.3 m，溯源侵蚀系数增加0.07~2.48倍。研究结果可为黄土高塬沟壑区“固沟保塬”与区域生态建设提供科学依据。