| Soil erosion is the main reason of soil degradation, which has been the serious environmental problem during human development, and made destruction to many countries. Gully erosion, which was an important kind of slope erosion, made a big contribution to soil degradation. With the holding of "International conference of gully erosion under condition of worldwide changes" in 2000, Belgium and "International conference about gully erosion and worldwide changes" in 2002, Chengdu, P.R.China, there has been internationally an emphasis on characteristic, prevention and forecast model of gully erosion.Based on national "973" program "Environmental effects and its ecologic significance of soil application on gully erosion in area with longitudinal mountain and valley", this thesis was about the research on the characteristics of gully erosion in area with longitudinal mountain and valley. Wenshan County of Yunnan province is a typical region with longitudinal mountain and valley. As result of soil erosion, there have been some difficulties for local economic development and soil application, and a larger increase of silt concentration in rivers of its watershed. Under these conditions, two gullies in Xin Kaitian village were selected to study the soil penetrability and characteristics of erosion-proof through the determination of physical characteristics of soil in gullies. Changes of gully erosion happened in a rainy season was analyzed on basis of quantity of soil erosion which was determined through erosion nail, and three dimensional TIN graph which was generated through date from total station. Following results have been found out.(1) According to soil experiment, soil in gullies, compared with that in area with shrubbery, was identified with smaller density and larger pore ratio, and therefore a good penetrability. However, due to loose soil and its surface uncovered by plant, soil unit can be destroyed easily and converted into silt. Also, as result of low content of organic matter and poor erosion-proof characteristic, soil was easily taken away by runoff and rainfall. The organic matter of gully 1 was smaller than that of gully 2, and therefore a poor erosion-proof capacity and serious erosion.(2) According to observation of erosion nail in one rain season, gully 1 expend 3.2 cm on the whole and expend 21 cm at the front side of gully; gully 2 expend 1.56 cm on the whole and expend 7.23 cm at the front side of gully. Soil erosion of gully occurred mainly in the form of expansion of its front side, accompanied with slight erosion of side slope of gully. Erosion of gully bank, which happened mainly in form of partly dilapidation, was slower than that of gully slope. The rates of expansion of slope and front side of gully 1 were both fast than those of gully 2. This certified the relationship between soil characteristic and gully erosion, which means the more loose soil, lower organic content and poorer capacity of erosion-proof would result in more serious soil erosion.(3) Data of local rainfall was collected by rain meter. According to analysis, when the average rainfall was lager or the ration of number of 10 mm/h to total number of rainfall was lager, the soil erosion would be more serious. Also, there was more serious soil erosion in a day and month with lager rainfall. Further, serious destruction in the upstream of gully also made some contribution to the soil erosion of gully.(4) Three-dimensional TIN graph, which was regenerated through total station and Arc GIS, can definitely reflect the real form of gullies and the erosion changes during a rain season. There were soil erosion for both the front side and slope of the gullies. Also, there was a variation of gully bottom due to the successive flooding of runoff. According to pile-up analysis of three-dimensional TIN graph, the specific sites of erosion have been identified; gully erosion happened mainly in form of expansion of its front side, accompanied with erosion of gully slope and bottom. Furthermore, research method of total station combined with Arc GIS on gully erosion can be used for good references for further research.Principles and measures were provided on the basis of research conclusion mentioned above. They would made great contribution to the prevention of local gully erosion. |
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