红壤坡面细沟横断面形态及水动力学特性研究

细沟是坡面侵蚀泥沙和养分流失的重要方式及输移通道，研究红壤坡面细沟形态和水流动力学特性对深入认识红壤坡面侵蚀规律和防治水土流失具有重要现实意义。以第四纪粘土发育红壤为研究对象，通过人工模拟降雨和放水冲刷相结合的室内试验，初步探讨了红壤坡面细沟横断面形态特征及其水动力学特性变化规律。结果表明：细沟横断面主要呈“V形”和“U形”，少数横断面侧壁呈向左或向右凹陷形态。细沟横断面宽深比在0.93～3.52，形态指数在0.30～0.60，且对同一细沟而言上坡位宽深比基本大于下坡位，而形态指数随坡长无明显变化。不同坡位的细沟流平均流速表现为：下坡>中坡>上坡，雷诺数和弗洛德数随坡长变化规律与流速基本一致。此外，细沟流平均流速和雷诺数仅与单宽流量呈极显著正相关（p<0.01），而细沟流从上坡至下坡的流速和雷诺数增幅则分别与雨强和横断面宽深比呈极显著正相关（p<0.01）。结果为进一步研究红壤坡面细沟侵蚀奠定一定的理论基础。

Characteristics of Rill Cross-Section Morphology and Hydrodynamics on Red Soil Slope

Rills have been recognized as main channels for both sediment and solute transport on slopes.Studies on rill morphology and hydrodynamic characteristics on red soil slopes can reveal the erosion mechanisms,and also have great significance on soil and water conservation in red soil hilly region.In order to investigate the rill cross-sectional morphology and the hydrodynamics of rill flow along the slope,an experiment considering the interaction of simulated rainfall(0,60,90,120 mm/h) and scouring flow(5,7.5 L/min) was carried out in a quaternary-derived red soil flume(10°,3-m length and 0.5-m wide and 0.4-m deep).The whole slope was divided into three parts,which represented the up-slope(1 m from the top slope),middle-slope(1-2 m from the top slope) and down-slope (2-3 m from the top slope).Rill cross-sectional width-depth ratios (C) and crosssectional morphology coefficient (η) were employed to quantify the rill morphology at three different slope positions.The results show that most of the rill cross-section presented a "V" or "U" shape,while a few of them presented a bowing bank shape.C varied from 0.93 to 3.52,and η varied from 0.30 to 0.60.The C values of up-slope were larger than those of down-slope for the same rill,while the η showed no definite trend with the rill length change.The mean rill flow velocity(V) along the slope was:down-slope＞middle-slope＞up-slope,Froude number(Fr) and Reynolds number(Re) were basically followed the same trend as velocity.Finally,V and Re were positively related(p＜0.01) to the unit discharge,while the increased value of V and Re from the up-slope to down-slope were positively related (p＜0.01) to rainfall intensity and mean C,respectively.The results can provide a reference for further studies on rill erosion in red soil hilly region.