基于单位汇水面积的地形因子特征评价

探讨了典型黑土区基于单位汇水面积的LS因子算法与传统基于径流路径长度算法的差异。研究表明,在研究区坡长坡缓的地形条件下,基于单位汇水面积的LS因子算法值普遍要大于基于径流路径长度算法的LS因子值;在有限的坡度范围内,不同算法的坡度因子相差不大,与之相比,不同算法的坡长因子值差别明显,特别是对于坡长指数采用定值的Govers算法更是如此。这说明在研究区坡长坡缓的地形条件下,坡长因子对LS因子算法的响应更为敏感。同时,侵蚀机理分析得出,坡长因子指数采用与坡度有关的变值更为合理,特别是在采用DEM进行大范围土壤侵蚀量预测时更应如此。

Evaluation of Topography Factors Based on the Unit Contributing Catchment Area

Topography factor is one of the main components for soil loss prediction in soil erosion model. Here topography factor includes slope length factor and slope gradient factor, which have been the emphasis and difficulty in related research. Although many of LS factor algorithms have been proposed in literatures, it is not yet clear for the differences between them. In this article, L factor is calculated based on the algorithm of Desmet,which evolved from the unit contributing catchment area. With S factor value calculated based on different algorithms, LS factors are presented, which are called the kind of LS factor from unit contributing catchment area. Then they are compared with the LS factor from modified AML program of Remortel. The AML program is designed to calculate the L factor based on the grid cumulative length in the runoff path. When compared to the LS factor value from modified AML program, the method of unit contributing catchment area yields broadly greater results. In the limited range of slope gradient in the study area, different methods yield similar slope factor values. In contrast, it is obvious for the difference of slope length factor from different algorithms. This is especially true for the algorithms of Govers, in which the slope length index is constant value. This indicated that with the condition of long slope length and low slope gradient in study area, different LS algorithms have more influence on the slope length factor. Meanwhile, through the analysis of soil erosion mechanism, we concluded that it’s more reasonable for the slope length factor index to use variable values related to slope gradient. With the introduction of the use of DEM in soil erosion prediction, it’s more possible to calculate the soil loss for a wide range of region. However, the calculation is based on cell, which means that the slope gradient is not the same for all cells, e.g. the slope of each cell has a larger range, esp. for the small area with large elevation difference. In this case, it’s especially true for the slope length index values to be variable values related to slope gradient.