Study On The Process Of Vegetation Control On Water And Sediment Of Slope Under Different Rainfall Conditions

In the process of rainfall runoff generation and sediment yield caused, is one of the most serious environmental problems currently in China and facing the world; because of the natural rainfall characteristics of new complex, is not conducive to control, artificial rainfall simulation has become an important way to study, but the two conditions the effects of vegetation coverage on the hillslope hydrological process is different. So the study of vegetation under different rainfall source has important practical value and practical significance to study on effects of hillslope hydrological process. This study used the simulated rainfall tests, in the experiment, we have set rainfall intensity 30mm/h, 60mm/h,90mm/h and slope 10°,20°, the surface vegetation selected as Chinese pine, Quercus variabilis, Vitex and Ryegrass, on the hillslope hydrological process under various conditions were studied; at the same time with the same area of the natural runoff rainfall runoff data, the source of vegetation under different rainfall role were analyzed. The main conclusions are as follows:(1) Firstly, the rainfall characteristics of QYJY-503C artificial simulated rainfall device and natural rainfall were studied, found that the rain of natural rainfall in diameter between 0.1mm-5.2mm, the majority of the rain diameter is less than lmm; the number diameter of the artificial rainfall in the 0.8mm-2.3mm, a handful of raindrop diameter will be greater than 3.0mm, it is also found that the average diameter of raindrops increases gradually with the increase of rainfall intensity. At the same time, in all the experiments, the rainfall uniformity can reach more than 85%, high degree of uniformity. The relationship between on rainfall kinetic energy and rainfall intensity, The natural rainfall: E=83.61Ⅰ0.28, R2=0.665;artificial rainfall simulation device by rainfall:E= 15.12-75.6/1, (10≤Ⅰ≤90), R2=0.9819;E is the kinetic energy of rainfall, J·m-2·mm-1; I is the rainfall intensity, mm/h; at the same rainfall kinetic energy in the range of test, the relationship between artificial rainfall and natural rainfall intensity:Ⅰartificiai=5.57Ⅰnatural0.28+5.04.(2)The rainfall runoff slope under different experimental conditions with rainfall duration were increased gradually after the stable trend of artificial simulation, the sediment yield increased with the rainfall duration showed increased firstly and then decreased and reached a steady state. The slope runoff and sediment yield and rainfall intensity and slope is positive correlation, at the same time, runoff and sediment yield show a greater increase of growth rate with rainfall intensity; with the increase of slope, the sediment yield increase is relatively stable, the runoff increase declined. We can see the impact on runoff and sediment:rainfall intensity> slope.(3)The runoff 4 vegetation of the artificial rainfall simulation experiment:Chinese pine< Quercus variabilis< Vitex< Ryegrass, compared to the bare slope runoff was significantly reduced, the overall performance of runoff:Forest< Grassland. The time to reach stable runoff and runoff is inversely proportional:Chinese pine> Quercus variabilis> Vitex> Ryegrass. The slope sediment experiment of 4 kinds of vegetation:Ryegrass< Vitex< Chinese pine< Quercus variabilis, compared with the bare slope were also significantly reduced, and the decreasing trend is greater than the runoff, it can be seen that vegetation impact on sediment yield on slope is stronger than runoff flow; the overall performance of sediment:Grassland< Forest, In contrast with the Runoff Trend. Overland sand to reach stable time: Ryegrass< Vitex< Chinese pine< Quercus variabilis, with the same sediment trend. The regulation ability of visible vegetation on slope runoff yield:Forest> Grassland, the regulatory capacity of the sediment yield on slope:Grassland> Forest.(4)In the process of natural rainfall runoff total runoff shows:Chinese pine< Quercus variabilis< Pine and Oak Mixed< Vitex, Because of the different vegetation on slope runoff regulation mechanism, the surface runoff flow performance:Pine and Oak Mixed< Chinese pins< Quercus variabilis< Vitex, the flow in soil for abortion:Quercus variabilis< Vitex< Chinese pine< Pine and Oak Mixed. So that: the runoff mainly forms of Pine and Oak Mixed runoff for the surface runoff, Quercus variabilis and Vitex runoff plots mainly in surface runoff, the slope runoff plots of Chinese pine runoff component proportion compared to the average. Compared with the rainfall runoff lag time:Vitex< Quercus variabilis< Chinese pine< Pine and Oak Mixed, is inversely proportional to the surface runoff and runoff, the longer the premature flow, make the greater the total surface runoff runoff.(5)The two source of rainfall, in the natural rain, the total runoff for Chinese pine total rainfall of 0.42%,Vitex slope total runoff total rainfall of 2.05%; in the experiment of artificial rainfall,1.48% the total runoff for Chinese pine rainfall gradient of slope 20°under various conditions, Vitex slope total runoff total rainfall of 2.12%,Chinese pine runoff varies greatly of two difference of rainfall runoff, Vitex is similar to runoff, but the two vegetation affect the ability of the same trend. From the source of rainfall on the runoff:Natural rainfall< artificial rainfall, from the point of view of vegetation types: Chinese pine< Vitex, from natural to artificial rainfall rainfall, the runoff of large trees change more.(6) When the kinetic energy of the rainfall is equal, the runoff of the slope under different rainfall intensity is less obvious at 4 plantings. For the case of equal rainfall energy, the runoff change with rainfall intensity remained stable trend, at the same time the 4 vegetation slope in rainfall runoff energy under rainfall runoff and time is consistent, runoff all showed:Chinese pine< Quercus variabilis< Vitex < Ryegrass. It is found that the kinetic energy of rainfall can be used as an ideal parameter to study slope runoff; sediment yield is due to the increase of rainfall intensity, drop diameter increases, increased the splash erosion.