Studies on the Properties of Hydraulic Dynamics of the Overland Flow at the Different Surface Roughness
|School||Hunan Agricultural University|
|Course||Agricultural Soil and Water Engineering|
|Keywords||Overland flow Hydrodynamic characteristics Slope Flow Surface Roughness|
Water and soil of human survival and development of the most important natural resources, but because of steep terrain, concentrated rainfall eroded rock formations, the rapid growth of the world population, irrational production and business activities, deforestation, cultivation on steep slopes, etc. natural factors and human factors combined effects of soil and water resources suffered a serious loss and damage, leading to a deteriorating ecological environment. In all types of soil erosion, water erosion is the most widely distributed a way that the source water erosion overland flow, therefore, to grasp the erosion of water erosion will carry out regular overland flow law of hydrodynamic characteristics. Rainfall, slope shape, slope geotechnical structures, vegetation, human activities are affecting overland flow erosion of important factors. In this paper, experimental study and theoretical analysis of a combination of methods, the use of soil mechanics and hydraulics of the basic principles of variable slope indoors fixed bed flume experiment to study the same and different soil types underlying surface material composition on the slope, gradient, flow rate and surface roughness of three factors on the impact of overland flow dynamics to analyze its role in the process, through regression analysis, predictive modeling, in order to establish a national model for providing basic resources of soil erosion, soil and water conservation work to provide scientific theoretical basis. (A) under the same underlying surface slope variation of flow dynamics parameters of velocity, Reynolds number and the drag coefficient by more significant impact on the flow, the flow rate can be a power function V = KqaSb the form of the Reynolds number Re with exponential = 1447.428q1.081 to represent. In the same slope, the drag coefficient decreases with the flow, the flow is smaller, the more obvious changes, the power function between the two negatively correlated. Drag coefficient with exponential f = 0,4488 q-1.076 representation. The Froude number and flow by the combined effect of slope steeper the slope, the more urgent the overland flow. This paper studies under the same slope Froude number, drag coefficient and Reynolds number relationship. Froude number and the Reynolds number and the Froude number and flow relationship is very similar to that in the same slope, the two power functions showed a good positive correlation between the expression of Fr = 0.0012Re0.5427, while drag coefficient with Reynolds number decreases, both showed a good correlation between the negative power function, expressed as f = 350.48Re-0.912. About the relationship between flow rate and hydraulic roughness discussion found under the same slope, roughness between velocity and hydraulic power function decrements in 5 ° ~ 20 ° range, the slope of the trend on the flow rate is insignificant, when slope increases to 25 °, the flow rate decreasing trend increase, decrease faster. (2) under different underlying dynamics of overland flow parameter variation on the same slope, the surface roughness on hydrodynamic parameters of the slope, the flow is very similar factors were investigated. Velocity, Reynolds and Froude number and surface roughness was positively correlated with all three surface roughness increases. Drag coefficient and surface roughness were negatively correlated with surface roughness increases. Surface roughness on the hydrodynamic characteristics of runoff by soil properties. But in either the underlying surface, and surface roughness Froude number between power function can be used both Fr = aDb representation. Through regression analysis of experimental data, combined with the principles of statistics obtained three underlying surface water dynamics parameters of a simple prediction model, the basic expression is Y = aDbgcSd (3) the variation of surface roughness use of soil The direct shear test to get red loam, sand, earth and gravel mixture than 7:3,1:1,3:7 shear strength. Internal friction angle changed little, but the cohesion of soil samples with sand, soil content changes, and the variation range of 3.8 ~ 6.1Kpa. Surface roughness by soil physical and chemical properties, rainfall or runoff conditions and other factors over a great impact, with randomness. Surface roughness and soil there is a link between the shear strength, and showed a negative correlation. Using the contact stylus method was different underlying changes in surface roughness range: red surface is 0.3644 ~ 1.4320, sand the surface of 0.2125 ~ 0.9046, surface debris 7:3 mixture of 0.3216 ~ 1.1385, debris ratio 1: a mixture of surface is 0.2554 ~ 0.9424, surface debris than 3:7 mixture of 0.1643 ~ 0.8432. Under the same slope, surface roughness changes with the flow was normal at the same flow rate, the slope at 200 before, surface roughness change of state with a positive slope, 20 °, the negative change of state, indicating that 20 ° ~ 25 ° between, there is a change in surface roughness affect critical gradient. Surface roughness and slope, flow relationship can be a power function D = KqaSb to express. Hydraulic roughness of surface roughness on the role of a dynamic process, not always present a variation, in the middle there is a critical value, the critical value, the variation between the two tend to be stable. This paper initially been critical value of 0.6315 gravel slope, red slope threshold is 0.9337.