| The gully asymmetrical characteristic is the difference in the shape and structure of the gully's two sides after complex development process. And it is one of the basic characteristics of the complex watershed unit, which reflect the developmental evolution procession. The research on the evolution of gully asymmetric has always been a hot topic in academic related fields. But it is not enough to study the morphological extraction and quantitative analysis of gully asymmetric characteristic .Based on the previous studies, this paper takes the loess hilly region of the two-basin Pianguan river and Xianchuan river in the northwest of Shanxi province as the study area, and uses the multi-level nested watershed as the scale sequence. Combined with the digital terrain analysis theory and method, multi-resolution DEM data, geological maps to analyze the gully asymmetric characteristic in northwestern Shanxi.The main contents and conclusions of this paper are as follows:1. Constructing the analytical method system of gully asymmetric characteristic in the region, watershed and slope scaleThe gully asymmetric characteristic are affected by many factors, and the internal stress of geologic tectonics controls the macroscopic pattern of the gully networks.Under the microscopic scale, various environmental factors make more detailed carving of the characteristics. In this paper,the gully asymmetric characteristic are analyzed on multi-scale watershed. In the big scale, the gully asymmetric characteristic are analyzed using Swath Profile; In the middle scale, the skewness of the main gully is measured by gully deviation indexes; In the small scale, the multi-index terrain factors are used to study the gully asymmetric characteristic. According to the results, the comprehensive watershed is more developed on the north slope, different parts represent different degrees of asymmetric characteristic . And in the watershed and slope scale, the small basins of the loess gully show a random, varying degree of asymmetric characteristic.2. Quantitative index and differentiation of asymmetric characteristics on the Loess PlateauConstruct factor system of asymmetric characteristic according to profile morphological, morphological and gully slope morphological and then analyze the quantitative factors of gully features by using the principal component analysis method.The results show that, at three different scales, the factors can describe the asymmetric characteristics of valley from different angles. At the micro scale, factors have strong scale dependency. The larger the spatial scale is, the lower the effect of asymmetrical factors on the valley is. In the aspect of regional difference, the average slope ratio, the gully erosion area ratio and the terrain roughness show obvious slope dependence. In terms of regional differences, the slope dependency is obvious in the average slope ratio,the gully erosion area ratio and the terrain roughness.3. The genetic mechanism's hypothesis and analysis on asymmetry characteristics of gully in small watershed of Loess Plateau in the northwest of Shanxi ProvinceBased on the differentiation rule of asymmetric characteristics of Loess gully in the northwest of Shanxi Province, assumes and elaborates the reasons causing asymmetric characteristic of gully in study area from the three aspects which includes the structure of the bedrock and the accumulation of loess, water and heat conditions and vegetation coverage as well as the interaction between the internal and adjacent watersheds. The result shows that the underlying rock structure and loess accumulation are the main causes of the gully asymmetry. While the asymmetric characteristics will be more significant in the watershed of Pianguan and Xianchuan effected each other under the existing conditions. However, hydrothermal conditions and vegetation coverage have relatively small influence on the asymmetry characteristics of large scale gully. |
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