Study On Mechanism Of Runoff And Sediment On Slopes And The Impact Factors In Karst Mountainous Area Of Guizhou Province

In karst mountainous areas of Guizhou,vulnerale eco-system,diverse landforms,high proportion of steep farmland,and shallow soil layer resulted in an outstanding contradiction of people and land.Natural factors and human factors together lead to serious soil erosion and rocky desertification phenomenon in the region.Land degradation threatens local food security and ecological security.Slopes are units which soil erosion occurring,they are the main sources of sediment in karst mountainous areas.Quantitatively evaluation soil erosion occurred on Karst mountain slopes is the key to prevent and control soil erosion and to ensure food security in the region.In view of the insufficiency research of mechanism of soil erosion and soil and water loss on slopes in in karst mountainous area of Guizhou province,based on the theory of hydrology,hydraulics,Soil erosion science,soil and water conservation and Environmental Science and the data of rainfall,runoff and sediment obtained from the field runoff plots in three small watersheds in Longli,Zunyi and Bijie of Guizhou,analysis of water erosion characteristics on slopes were carried out by using of mathematical statistics,regression analysis and comprehensive analysis of geography and other methods in this paper.The values of each factor of soil erosion in Guizhou are calculated and formulas to estimate the values of rainfall factor and topographical factors are constructed.The main conclusions are as follows:(1)Slope runoff and sediment yeild under heavy rain and rainstorms accounted for 16.6%and 59.8%of the annual runoff,10.1%and 65.6%of the annual sediment,respectively.The rainfall amount of high intensity rains only accounted for 28.8%of the total rainfall amount,runoff and sediment yield under this rainfall condition accounted for 44.1%of the total runoff and 61%of the total sediment.(2)Slope runoff and sediment yield increased with the increase of the slope gradientsbetween 5°to 15°,then they decreased significantly when the slpoe gradients increased from 15° to 20° and had a small increase when the gradients increased from 20° to 25°.(3)Slope runoff showed a trend of decreasing-increasing-decreasing with the increase of slope length.Annual average sediment yield showed a trend of increasing with the increase of slope length.(4)Different vegetation made different effects on runoff and sediment reduction.The result showed that runoff reduction effects of different vegetation were:economic fruit forest>grassland and no difference between protective forest and cultivated land.The sediment reduction effects of different vegetation were:economic fruit forest>grassland and protective forest>cultivated land.(5)The estimation formulas for rainfall erosivity is R=0,13P1.943 and topographic factor is LS =(0.348E1.04?)(7.301+sin1.426?).The values of soil erodibility are between 0.0072-0.0151,the values of vegetation cover and management factor are between 0.00047-0.00851 and the values of soil and water conservation factor are between 0.00047-0.0872.