Gully Networks Extracting And The Regional Difference Analysis In The Loess Hilly-gully Region

The soil erosion is especially serious in the Loess Plateau,which has been paid much attention by many scholars,is one of the hotspots of current research.Eroison gully is a formation of the soil erosion,constitutes the main gully landform in the loess region,is an important carrier to characterize process and mechanism of the soil erosion.Based on the erosion gully,a series of researches on soil erosion in the loess region were carried out,which has obtained fruitful achievements.Taking the gully network as an research object,the extraction method and the regional differences have been studied in depth,which can provide reference for further exploration of soil erosion in loess hilly-gully region.Taking Wangmaogou watershed,Yangou watershed and Nanxiaohegou watershed in the Loess Plateau as the research areas,the 5m resolution DEM data and the high resolution image data were used to extract the gully network of three watersheds.Using the length and density as the quantitative indicators of the gully characteristics,we explored the region difference characteristics,analyzed the influence of terrain factors and surface material factors on the gullies' distribution and development.The main conlusions were listed as following:(1)In view of some deficiencies in gully networks were extracted by the traditional hydrographic method such as broken lines,pseudo and parallel lines etc,this study ameliorated the extraction process,Including using Agree algorithm and D8 algorithm to extract DEM flow direction,taking the average of gully heads' catchment areas as the threshold,adding postprocessing procedures etc.And we finally achieved the extraction results with high accuracy.(2)In the loess hilly-gully region,the development of the gully is not entirely in line with the slope's enlargement,but will decrease significantly When slope reaches to 45°.Gully will develop intensely in those region with slope between 15° and 35°.The development of gully is heavily dependent on the slope shape.The concave slope area is the most important site for its development.There are a few high-grade gully networks in the straight slope area,and there is basically not gully in the convex slope.In addition to the watercourse area,the density of gullies increases with the slope length's enlargement,especially when the slope length longer than 150 m.With the increasement of TWI,the distribution of gullies increased first and then decreased.low-grade gullies are largely distributed in those areas where TWI is in the range from 3 to 10.(3)The antierrodibility of the loessial soil is the worst in three kind of soils in the Yangou watershed.There are a large number of gully distributed on the shrub land,farmland,sparse wood land and natural grassland,especially low-grade gully.There are less development of the gully in closed forest land,terrace field and artificial grassland,Which indicated terrace,artificial forest and grass planting are effective measures to control and mitigate soil erosion.