Spatial Pattern And Formation Of Gullies System In Yuanmou Dry-hot Valley

Soil erosion is a common geographical phenomenon. However, with the soil erosion getting more and more seriously, which made significant influence and damage to the coordinated development of ecosystem environment and social economic development. Gully is the result of development of soil erosion and the advanced stage of erosion gullies sequence. Spatial pattern types of gully system have a certain influence on the settlements, land planning and the layout of agriculture and industry. This system can help to understand the regularities of gully system development and formation mechanism, the pattern and law of soil erosion under a large scale system, and provide a scientific basis for the practical application for gully erosion prevention and treatment. In recent years, the Chinese and foreign scholars tend to study relatively small plots of land scale, such as surface erosion and rill erosion, instead of a larger spatial scales research. At the same time, they tend to study gully landscape and ecological interaction, instead of the spatial pattern types for gully system.In this paper, Yuanmou Dry-hot Valley area, with the most typical characteristic of dry, was chosen as the study area. Thousands of gullies and bad land of this area provides authentic materials for study of the severe gully erosion. In this paper, In Yuanmou Dry-hot Valley of visual interpretation of high resolution image extraction of gullies, and field investigation to verify the interpretation of results. Using the ArcGIS 3D Analyst in a software module in the "create a TIN" tool in Yuanmou basin to convert the 1:50,000 contour maps into digital model of the triangulated irregular network(TIN). Further more, converting TIN into a digital elevation model(DEM). Thirdly, using the ArcGIS software for hydrologic analysis tools to deal with the dates DEM and select the appropriate threshold and extract gully system and division of small watershed. The gully from DEM was used to verify the accuracy of the visual interpretation of gully. Depending on the different intersection angle of course of adjacent gully to divide into spatial pattern types of gully system in Yuanmou Dry-hot Valley, On the basis of the classification, typical gully system, including the geographical position, morphological characteristics, structural characteristics(quantity, length, density characteristics,direction and fractal features), landscape pattern were analyzed, and reveals the gully system of different formation condition. Main conclusions are as follows:(1)The gully system of Yuanmou Dry-hot Valley area is divided into six kinds of typical spatial pattern, including parallel gully system, dendritic gully system, radial gully system, lattice gully system, pinnate gully system and comb gully system. In the gully system of Yuanmou Dry-hot Valley area, the vectorial gully amount to 20598.the number of dendritic gully system is 49, the number of parallel gully system is 40,the number of lattice gully system is 36,the number of radial gully system is13,the number of pinnate gully system is15, the number of comb gully system is 7. It can be concluded that dendritic gully system, parallel gully system, lattice gully system, are dominant in the spatial distribution.(2)Each kind of gully system can be classified: parallel gully system can be divided into 7 grades(from 1 to 7), dendritic gully system can be divided into 6 grades(1, 2, 3, 4, 5, 7), radial gully system can be divided into 5 grades(1, 2, 3, 4, 7), lattice gully system can be divided into 7 grades(from 1 to 7), pinnate gully system can be divided into 5 grades(from 1 to 5), comb gully system is divided into 4 grades(from 1 to 4). Grades from 1 to 4 are dominant for shaping the morphological characteristics of these six types of gully systems. Based on the landscape ecology analysis and the characteristics of different type of gully system, the parallel gully system belongs to uniform pattern of the landscape; dendritic, radial, pinnate and comb gully system belong to gather pattern of the lands cape; lattice gully system belongs to combination pattern of the landscape.(3) As per the amount of the six types of gully systems, grade 1, 2, 3 is the most. However, the length of grade 1, 2 of gully system accounts for more than 65% of the total length, which occupies the absolute dominance. In short, all the six types of gully system structures belong to low grade of gully system; and for six types of gully system, their average length, total length and the amount are in pairs for linear relationship with their corresponding grades. All the six types gully system belong to intensive gully system with their densities all above 0.8. As per the direction,parallel gully system and lattice gully system are mainly to the west and northwest; radial gully system and comb gully system are mainly to the northwest and northeast; dendritic gully system is to northeast and southeast; and pinnate gully system is to east and southeast. It was found that when different types of gully system are in the same region, their trends are consistent.(4) The fractal dimension for the dendritic gully system is 1.34, 1.88 for the pinnate gully system, 1.29 for both parallel gully system and lattice gully system, 1.31 for both radial gully system and comb gully system. It was observed that the same fractal dimensions of gully system are at the same location. In short, in the same mountain family of Yuanmou Dry-Hot Valley, each forms of gully system fractal dimension are similar or identical, with little difference within a certain range.(5) On the basis of the hot-dry climate, the topography, soil, vegetation and human activities should be taken into consideration for spatial pattern types and the forming conditions of gullies system in Yuanmou Dry-Hot Valley and the topography is the key factor.