中文摘要：

地形是影响土壤侵蚀的重要因子,分布式土壤侵蚀学坡长是地形因子的重要参数。坡长与侵蚀过程相关,且受地形影响较大,在提取过程中,遇到沟道截断,坡长不再累计。由于沟头位置较难确定,通常沟道提取采用设置一定的汇水面积阈值来实现。然而,沟道对坡长提取结果的影响、不同阈值对坡长提取结果的影响、在无法确定沟头位置情况下如何更加合理地设置截断阈值等问题,亟待研究。本文以黄土高原县南沟和韭园沟流域DEM为数据源,对沟道引起的坡长截断进行对比分析。结果表明,沟道截断对坡长提取的平均值影响小于对坡长最大值的影响;不同区域对坡长的影响小于阈值设置的影响;黄土高原地区的沟道截断阈值可参考平均坡长降低的变化率为4%来设定。

英文摘要：

Topographic is one of the important factors affecting soil erosion. Distributed soil erosion slope length is an important parameter to evaluate terrain. Associated with erosion process, accumulation of distrib- uted soil erosion slope length should be stopped once cut off by channel. Channel head position is difficult to define, so threshold is always used to estimate channel networks. It is necessary to study the impacts of channel networks and different thresholds on slope length, and find the way to set a reasonable threshold in the case that the actual channel head cannot be determined. In this paper, the DEM data of Xiannan- gou and Jiuyuangou catchments in the Loess Plateau are used to extract slope length under different thresh- olds. The results show that the impact of channel cutoff on the maximum slope length is greater than that on the averages of the extracted slope length, and the impact of the different thresholds on the slope length is greater than that of the different areas. The threshold of channel cutoff in Loess Plateau area can be set as 4% of the average value of the slope length.