Research Effects Of Vegetation Lodging On Overland Runoff Resistance And Flow Regime Characteristics

In the study of overland runoff,the movement characteristics of the water flow under vegetation cover have always been the focus of people's attention.The vegetation has changed the original flow structure,increased the roughness of the surface,and greatly reduced the erosion of water to soil.Under the scour of current,vegetation will lodging due to its flexibility.Lodging phenomenon is more common in nature.which not only exists in farmland and rivers,but also has a significant impact on overland runoff.In order to further explore the inherent law of water flow structure under the condition of vegetation lodging and reveal the mechanism of soil and water loss prevention and control,the study on the influence of overland runoff characteristics of lodging vegetation was carried out.In this study,the bend-shaped rigid vegetation was used to simulate the flexible vegetation in the lodging state.Seven groups of slope,five groups of lodging angle and three groups of stem diameter were set for indoor open channel flow simulation test.In the process of data processing,the regression fitting method,the list interpolation method and the comparison method are mainly used to study the relationship between lodging angle,stem diameter,slope and flow resistance and flow regime.The research results show that:(1)The quantitative relationship between flow resistance,Reynolds number,Froude number and lodging angle was analyzed by regression fitting method.Under the condition of fixed slope and vegetation stem diameter,when vegetation is in the same water depth,Darcy-Weisbach resistance coefficient decreases with the increase of water depth,which showing an obvious inverse proportional relationship.The Reynolds number and the Froude number increase with the increase of water depth,which is proportional to the relationship.When the vegetation is in the same lodging degree,the relationship between Darcy-Weisbach resistance coefficient and water depth is controlled by the degree of vegetation submergence.With the increase of water depth,the Reynolds number and the Froude number show different trends,and the Reynolds number increases,while Froude number decreases.For the above rules,the analysis is performed by the regression fitting method,and it can be known from the fitting equation.The relationship between Darcy-Weisbach resistance coefficient,Reynolds number,Froude number and water depth is relatively simple(Darcy-Weisbach resistance coefficient and water depth are exponential functions,Reynolds number and water depth are one-order functions,Froude number and water depth are power functions),and the relationship with the lodging angle is complex composite function relationship.(2)The Darcy-Weisbach resistance coefficient increases and then gradually becomes flat with the increase of water depth under any diameter condition with fixed slope and lodging angle.The Reynolds number increases linearly with the increase of water depth,and the Froude number decreases,and finally tends to be gentle.Under the same water depth,the Darcy-Weisbach resistance coefficient increases with the increase of diameter,while the Reynolds number and Froude number decrease.The above laws exist not only in the lodging state,but also in the state of the vegetation standing upright.According to the difference analysis,in the erect state,when the diameter increases by 1 mm,the resistance coefficient increases by 46.10%,the Reynolds number decreases by 2.07%and the Froude number decreases by 9.96%.In lodging vegetation,the resistance coefficient increases by 36.46%,the Reynolds number decreases by 1.44%and the Froude number decreases by 7.96%for every 1 mm increase in diameter.(3)At any slope,for the same lodging angle,as the water depth increases,the Darcy-Weisbach resistance coefficient increases gradually,then decreases,the Reynolds number increases linearly,and the Froude number decreases.The curves of Darcy-Weisbach resistance coefficient and water depth at different lodging angles are gathered with the increase of slope,and the curves is completely gathered until the slope is 3.0%,the increasing rate of Reynolds number and the decreasing rate of Froude number increase accordingly.When the lodging angle is fixed,the Darcy-Weisbach resistance coefficient is positively correlated with the slope at small water depth and negatively correlated with the slope at large water depth.