梯田对侵蚀地形指标的影响——以黄土丘陵第2副区为例

Influence of Terrace on Erosional Topographic Index-Taking the Second Sub-region of Loess Hill as an Example

[目的]探究人工地形(梯田)对地形指标的影响,分析修建梯田对土壤侵蚀过程的影响,为土壤侵蚀评价中梯田措施因子的确定提供科学依据。[方法]通过无人机航空摄影测量,获取纸坊沟流域高精度DEM数据,通过模拟原始坡面数据和构建水平梯田数据,并对这些数据提取坡度、坡长、坡度坡长因子、单位汇水面积和地形湿度指数,分析了这些因子的变化情况,认识梯田对侵蚀地形的影响。[结果](1)梯田的修建使得坡度减缓、坡长截断、LS因子变小,随着梯田面积占比的增加,坡度、坡长、LS因子均呈减小趋势;梯田区,坡度、坡长、LS因子大致沿等高线呈条带状分布,非梯田区,坡度、坡长、LS因子从分水线向下逐渐增加,到沟底又逐渐变缓。(2)梯田的修建使得单位汇水面积减小、地形湿度指数变大;单位汇水面积的空间格局与坡长比较类似,较高部位单位汇水面积较小、低洼部位较大;梯田区地形湿度指数与坡度有相反的空间分布格局,非梯田区地形湿度指数与单位汇水面积类似。(3)微观尺度上,坡长、LS因子、单位汇水面积以及地形湿度指数均沿田面坡降方向呈增加趋势,在修建梯田或维护梯田时,应尽量保持田面水平或有微小反坡。(4)根据梯田对LS因子的影响,研究区梯田的工程措施因子值可取0.26~0.37。[结论]修建梯田对黄土高原丘陵地区水土保持有较大贡献,可为黄土高原丘陵区修建梯田和土壤侵蚀评价提供参考。

[Objective]The aims of this study are to explore the impact of artificial terrain(terraces)on topographic indicators,analyze the impact of building terraces on soil erosion process,and provide scientific basis for the determination of terraces measures in soil erosion assessment.[Methods]The high-resolution DEM data of Zhifanggou watershed were obtained through UAV aerial photogrammetry.Through simulating the original slope surface and constructing horizontal terraces,slope,slope length,slope length and steepness factor(LS),specific catchment area(SCA)and topographic wetness index(TWI)from these data were extracted,and the changes of these factors were analyzed to understand the impact of terraces on erosional terrain.[Results](1)The construction of terraces reduced the slope,cut off the slope length and decreased the LS factor.With the increase of terrace area ratio,slope,slope length and LS factor all showed a decreasing trend.In the terraced area,the slope,slope length and LS factors were roughly distributed along the contour line in a strip;in the non-terraced area,the slope,slope length and LS factors gradually increased from the water dividing line downward,and then gradually slowed down to the valley bottom.(2)The construction of terraces reduced the SCA and increased the TWI.The spatial pattern of SCA was similar to that of slope length,the value was smaller in the higher part,and was larger in the lower part.The spatial distribution pattern of TWI in terraces was opposite to that of slope,and the spatial distribution pattern of TWI in non-terraces was similar to that of SCA.(3)At the micro scale,the slope length,LS factor,SCA and TWI all tended to increase in the direction of slope decline of the field surface.When constructing or maintaining the terraces,the field surface should be kept as horizon as possible or a slight reverse slope.(4)According to the influence of terraces on the LS factor,the engineering measure factor value of terraces in the study area should be taken as 0.26~0.37.[Conclusion]The construction of terraces has a great contribution to soil and water conservation in the hilly areas of the Loess Plateau,and can provide a reference for the construction of terraces and soil erosion assessment in the hilly areas of the Loess Plateau.