Study On Effect Of Vegetation Distribution Pattern On Slope Flow Resistance

Soil erosion of slope surface has become a major environmental problem in China.Vegetation plays an irreplaceable role in reducing slope erosion.Due to the different distribution pattern and growth status of slope vegetation,the internal structure of overland flow is changed to a certain extent,which increases the loss of kinetic energy and has the effect of retarding and intercepting the overland flow,making the overland flow complex and changeable[1].However,as far as the distribution pattern of vegetation on the slope is concerned,the research direction and purpose of the researchers at home and abroad are different.There is no uniform definition of the vegetation distribution pattern,which makes the research on the effect of slope vegetation pattern on resistance is not representative,resulting in research confusion.This study summarized the vegetation distribution pattern from the aspects of adjacent vegetation and individual vegetation.Because of the influence of planting and planting methods and topography on the vegetation,the direction of the stripe of the vegetation is different from that of the adjacent vegetation,thus leading to the overall vegetation distribution pattern.For a single vegetation,due to the different growth periods and species of the vegetation,the thickness of the vegetation stem varies.Therefore,the organic combination of the three important indicators such as the orientation of vegetation,the vegetation diameter,and the spacing between rows and columns was used to characterize the pattern of vegetation distribution.Flow resistance on slope is a parameter that reflects the condition of surface runoff that can hinder surface runoff.It is an important index in the process of simulated slope runoff production.It has important guiding significance in harnessing hydraulic erosion and protecting ecological slope.Discrimination of flow regime is a prerequisite for analyzing water flow properties,studying water scour and sediment transport,and is an important precondition for calculating flow velocity and turbulence intensity.It plays a crucial role in ecology,flood control and agricultural production.Importantly,the flow pattern of slope surface is directly related to the resistance characteristics of slope flow and is an important parameter to characterize the flow dynamics of slope surface,Therefore,it is necessary to carry out a deep research on the vegetation resistance and the fluid response of the slope,and to establish a distributed hydrological model combined with the actual situation to carry out the experimental simulation closer to the actual conditions.In order to optimize the distribution of vegetation on the slope and prevent the erosion of soil erosion,Flood control and disaster mitigation provide scientific basis.In order to systematically study the effects of vegetation on overland flow resistance and flow regime of slope surface,flume simulation experiments were conducted using three different plant row directions δ(15°、45°、90°),three different plant diameters d(3mm、4mm、5mm),and three row spacing a×a(40mm×40mm、50mm×50m、60mm×60mm)simulated vegetation distribution changes.Experimental slope is fixed,slope ratio of 1.0%.Simultaneously,studying the changes of hydraulic parameters of vegetation in submerged,transitional submerged and submerged state,and study the effect of vegetation distribution on the overland flow.The main conclusions of this topic are as follows:(1)In the non-submerged state,the vegetation distribution pattern has a significant impact on the flow resistance and flow pattern of the slope.When the angle(θ)between plant row and water flow directions decreased,the plant diameter(d)increased,or the row spacing(a×a)decreased,the Darcy-Weisbach resistance coefficient(f)for water flow became larger.Simultaneously,the Reynolds and Froude numbers(Re and Fr)both became smaller.In experimental condition,the change rate of f,Re and Fr were analyzed by linear regression,the θ decreased every 10°,the average increase rate of f was 6.6%,the average decrease rate of Re and Fr were 2.0%and 3.0%.The d increased every 1 mm,the average increase rate of f was 41.6%,the average decrease rate of Re and Fr were 11.2%and 12.2%.The a × a decreased every 10 mm,the average increase rate of f was 45.2%,the average decrease rate of Re and Fr were I 1.7%and 10.7%.The flow depth h increased every I cm,the average increase rate of f and Re were 13.6%and 25.2%,and the average decrease rate of Fr was 10.4%.(2)With the increase of water depth,the submerged state of vegetation is transformed from non-submerged to completely submerged.The the Darcy-Weisbach resistance coefficient f and Reynolds number Re continue to increase with the increase of water depth.The Froude number Fr decreases with the increase of water depth.The effect of vegetation distribution patterns on flow resistance and flow pattern on the slope gradually diminishes.From non-submerged to fully submerged transitions,that is,when the submerged water depth reached the height of the vegetation itself,the the Darcy-Weisbach resistance coefficient f reached the highest peak.(3)When the vegetation is completely submerged,with the increase of water depth,the Darcy-Weissbach resistance coefficient f is negatively correlated with the water depth h,and the Froude number Fr decreases with the increase of water depth.The number Re continuously increases with the increase of water depth,and the growth rate or decrease rate of hydraulic parameters is relatively stable.When the vegetation is completely inundated,the distribution pattern of vegetation has little effect on the flow resistance and flow pattern of the slope.