Research On Manning Coefficient Of Different Vegetated Slope

Manning coefficient is an important parameter for representing water flow characteristic of slope surface. Surface runoff velocity, flow pattern, penetration and erosion ability is the significant response indicator for surface roughness coefficient.Surface runoff velocity, flow pattern, penetration and erosion ability is the significant response indicator for surface roughness coefficient. Investigation of surface roughness coefficient play a important role on quantitative analyzing onthe ability of surface erosion, slope movement of water and sediment, improving the surface hydrological processes and implementing reasonable soil and water conservation planning and measures. In this study, we construct artificial slopes for simulating vegetated slope to research bared land, Salix alba var.Tristis, grass, Populus tomentosa and Buxus sinica five kinds of land-use types, which located in Changping District of ecological restoration experiment base Machi Town Pavilion Environmental Protection Research Institute. Beside, we gauged hydraulics and sedimental characteristics based on constant flow and variable flow, namely average velocity and Manning coefficient. We also set up artificial runoff plots with different vegetation and three slope degree next to the standard plot in order to research on correlation analysis of vegetated slope roughness coefficient. The results showed that:(1)When changing the flow volumn with slope degree of45,we found that the flow velocity of the grassland is always the smallest slope, bare slope flow velocity is relatively large; grass slope face slope has a good effect on blocking the flow velocity. The landuse type with maximum average roughness coefficient is grassland, the landuse type with smaller average roughness coefficient were bare land(0.0424), Populus tomentosa(0.414); when the flow volumn is0.25cm2/s, Reynolds nmuber is mainly ranged between21.34and23.49,Froude number is mainly between0.35and2.55; Darcy-Weisbach resistance coefficient ranged between1.03and54.43, which contain grassland with maximum coefficient and poplar with minimum coefficient.(2)Soil erosion is inversely correlated with Manning roughness, while coefficient infiltration rate have a positive correlation with Manning coefficient to some extent;(3)In light of three vegetation types, namely Festuca elata, Amorpha fruticosa, Coronilla varia+Humulus japonicus, under different flow volumn of5,10,15,20,25,30ml respectively, the overland flow velocity increased as the flow volumn increases. Surface roughness coefficient changes are:when the slope degree is15°and45°, the surface roughness coefficient decreases with flow volumn increasing; when the slope degree is30°, the surface roughness coefficient increased with flow volumn increasing.(4)According to correlation analysis, the study shows that Manning and Darcy-Weisbach resistance coefficient, capillary porosity, soil bulk density, soil erosion rate was significantly positive correlated, while roughness coefficient and soil erosion rate was significantly negative correlated; the relationship between Manning coefficient and soil erosion rates shows that:Ms=2.2777n-0.278(R2=0.3059)。Finally, this paper proposed some suggestions on vegetated slope surface for further study about Manning coefficient, in order to provide a theoretical basis and experimental research for guidance.