基于坡长效应的坡面侵蚀及室内外水土流失换算方法研究

Research on runoff, sediment yield and dynamics process is the breakthrough to reveal erosion mechanism on slope and is the basic problem to solve sediment transport mechanics, soil erosion and soil and water conservation, and whether the results from indoor experiments could be used to field exactly is the difficulty to conquer. Based on the indoor and field experiments in yangpo watershed of the Loess Plateau, this study analyzed the slope length scale effect on runoff, sediment yield and dynamics process and the changes disciplinarian of runoff volume and sediment yield with the same increment of slope length, constructed the sediment yield statistical model and sediment delivery ratio equation, thereby obtaining the critical slope length and critical rainfall intensity of erosive rainfall on sloping farmland for soil and water conservation measures distribution. Revealed the difference of soil loss between indoor and field experiments and calculated the conversion coefficients or established function to express the conversion coefficients according to plenty of experiment data. The conclusions of this study will provide theoretical support for further discussion of sediment yield dynamics process on different slope positions and construction of soil and water conservation measures, meanwhile, proposed the method to predict field soil loss objectively according to indoor simulated experiment results and will provide scientific basis for soil and water loss prediction and treatment decision making.

坡面径流侵蚀产沙及动力学过程的研究是揭示坡面侵蚀产沙机理的突破点，是泥沙运动力学、土壤侵蚀和水土保持学中亟待解决的基础问题，而室内按一定比例尺缩小的物理模型试验结果能否在实际中正确运用是目前需攻克的难点。项目以黄土高原阳坡流域为研究对象，通过野外与室内人工模拟降雨试验，研究坡耕地坡面水沙动力学过程在不同坡长尺度下的变化规律，分析坡长每增加相同长度，坡面产流产沙量的变化及其机理，构建不同坡长下坡面侵蚀产沙统计模型及泥沙输移比方程，从而得出该区坡耕地水土保持措施布设的临界坡长及侵蚀性降雨的临界雨强；揭示室内外水土流失量的差异性，求解出适合于黄土高原特点的换算系数或者根据大量试验数据将换算系数用函数表示出来。项目研究结论将为深入探讨坡面不同位置水沙动力学过程及坡面水土保持措施布设提供理论支撑，同时提出根据室内模拟试验结果客观预测野外实际水土流失量的方法，为水土流失预测及治理决策提供科学依据。

坡面径流侵蚀产沙及动力学过程的研究是揭示坡面侵蚀产沙机理的突破点，室内按一定比例尺缩小的物理模型试验结果能否在实际中正确运用是目前需攻克的难点。项目以晋西王家沟流域为研究对象，采用野外与室内人工模拟降雨试验方法，着重分析了3个问题：1. 坡长与雨强对坡面径流侵蚀的交互影响效应；2. 坡面径流侵蚀产沙动力学过程的坡长效应；3. 构建运用室内模拟试验结果预测野外实地土壤侵蚀的转换模型。主要得出如下结论：1. 坡面径流量、侵蚀产沙量及输沙率随着坡长、雨强的增大总体呈增加趋势，雨强60mm/h时径流侵蚀产沙量与输沙率明显增大，初步得出60mm/h雨强是该区水土流失重点监测的下限雨强；2. 同一雨强下坡长每延长相同长度，坡面径流量与侵蚀产沙量不呈比例增加，雨强越大坡长的延长对径流量与产沙量增量的影响越显著，坡面布设水土保持措施时其合理坡长应越短，因此，建议在晋西离石黄土区，雨强小于60mm/h时以4-5m为间隔，雨强大于60mm/h时以3-4m为间隔布设水土保持措施。3. 试验条件下坡面薄层径流为急流且属层流范畴，径流紊动性随着雨强、坡长的增大而增强，径流剪切力、径流深、流速等水力学参数与坡长、雨强呈正相关关系。4. 在室内与野外试验土壤性质、降雨特性及径流小区坡度基本相似的条件下，二者土壤侵蚀模数并非随面积呈倍数关系。因此，项目初步构建了考虑雨强、室内与野外面积比值的数学模型，从而根据室内数据预测野外土壤侵蚀模数。 项目研究结论将为深入探讨晋西黄绵土区域坡面径流侵蚀产沙过程及坡面水土保持措施布设提供理论支撑，构建的根据室内模拟试验结果客观预测野外实际土壤侵蚀量的方法，将为该区水土流失预测及治理决策提供科学依据。