| Vegetation plays an active role in consolidating soil,reducing soil erosion and purifying water body,which can effectively alleviate land desertification and other natural environmental problems.However,vegetation can not only protect and repair the ecological environment,but also delay the surface runoff.This will make the surface infiltration and rainwater storage capacity increase,and the flood discharge and navigation capacity of river channel weaken,which will have a strong impact on the formation and confluence process of slope flow,and the response relationship between rainfall and slope runoff become abnormal,which will have a significant impact on the hydrological process of the basin.However,over time,vegetation types in the same watershed are changing.To a certain extent,the vegetation in nature presents different levels of distribution.If we can understand the relationship between hierarchical vegetation and slope water flow,and master the influence of hierarchical vegetation on the flow characteristics of slope water,it will make slope runoff simulation more accurate,and provide theoretical basis for slope water and soil control in natural watershed.In this study,a hydraulic model was established in the laboratory.The water flow resistance simulation test was carried out by adjusting the plant height,distribution form of high and low plants and the slope of the bottom slope.The vegetation height combinations were 7 cm and 9 cm,6 cm and 8 cm,5 cm and 7 cm respectively.There were two types of high and low plants:linear arrangement and staggered arrangement.The slope gradient was set as 5 gradients:0.0%,0.5%,1.0%,1.5%and 2.0%.14 groups of tests were carried out under each gradient,and 70 groups of tests were carried out in total.Through the analysis of the test data,the main conclusions are as follows:(1)Compared with the homogeneous vegetation,the flow velocity v of the stratified vegetation is higher with the increase of the water depth h.under the same water depth,the flow velocity of the homogeneous vegetation is higher than that of the stratified vegetation;the difference of the energy loss hf along the way is the largest when the water depth submerges the low plants of the layered vegetation,and then the difference decreases slowly with the increase of the water depth,and finally tends to be the same.When the low level vegetation is submerged,the resistance coefficient f of Darcy-Weisbach will suddenly decrease;when all plants are submerged,the growth rate off is higher than that of the low level plants when the high level plants are submerged,which indicates that when all plants are above the water flow surface,the water blocking effect is obvious,which has a timely inhibition effect on the surface runoff erosion,and also verifies the distribution density of vegetation and the specific surface area also has an effect on the f-value;when the vegetation is partially or completely submerged,the higher the plant height is below the water flow surface,the greater the f-value of the corresponding Darcy-Weisbach resistance coefficient,the greater the growth rate and reduction rate off.(2)Under the same water depth condition,the flow velocity of linear arrangement of vegetation is higher than that of staggered arrangement of vegetation;the flow pattern of linear arrangement of vegetation and Freud are higher than that of staggered arrangement of vegetation;the flow pattern of linear arrangement of Reynolds and Freud are higher than that of staggered arrangement of Reynolds and Freud;in the two distributions In the model,the difference of hf energy loss along the way is the largest when the depth of water submerges the low plants of the hierarchical vegetation,and then the difference gradually reduces with the increase of the depth of water,and finally tends to be the same;the distribution model of the hierarchical vegetation plants has an effect on the resistance coefficient of Darcy-Weisbach,on the whole,the resistance coefficient f value of the staggered arrangement of plants under the same depth of water is greater than that of the linear arrangement of plants Resistance factor f value.(3)The larger the surface slope is,the greater the flow velocity is.With the increase of water depth,the effect of slope decreases gradually.The larger the slope is,the larger the Reynolds number Re value is.The effect of slope on Froude number Fr and the energy loss hf along the path exists a boundary water depth,which is less than 0.05 m,under the same water depth,the larger the slope is,the larger the Froude number Fr value is,the faster the flow is,and the greater the energy loss hf value is,and the water depth is greater than 0.05 m,the Fr value of each slope has little difference,and tends to be stable,which indicates that the effect of surface slope change on Froude number will decrease with the increase of water depth,and the corresponding hf value of energy loss along the way will gradually become consistent and keep flat;with the increase of slope,especially in the case of large slope,when the water depth submerges the low plants,the sudden drop of resistance coefficient f is more and more unknown It is obvious that the effect of water depth on resistance coefficient is greater than that of slope. |
