Experimental Study On The Comprehensive Resistance Of Zonal Vegetated Channels

Vegetation is commonly found in urban and natural rivers,and its presence has beneficial effects on enriching the riverbank landscape,purifying water quality,and effectively controlling soil erosion.However,vegetation also adjusts the water flow structure and increases water resistance,making water flow movements more complex.In natural river channels,vegetation is often partially covered and zonal distributed.However,existing theoretical studies on comprehensive resistance mainly consider factors such as vegetation coverage ratio and softness without considering the interaction between the flow in vegetated zones and non-vegetated zones.Therefore,it is of great significance for total roughness estimation,flood prediction,and river regulation design to conduct research on the flow characteristics in zonal vegetated river channels.The zonal distribution of vegetation in a channel was divided into four modes:equalfraction mode,one-bank mode,two-bank mode,and central mode.Experimental research is carried out on the influence of different distribution modes on comprehensive resistance,and the estimation method of comprehensive resistance is discussed based on theoretical analysis.Main work and achievements are as follows:(1)With the increase of vegetation resistance coefficient,coverage ratio,and flow,the distribution uniformity of velocity in a section will gradually decrease.The depth,water surface ratio,velocity difference between the two areas,and comprehensive resistance will increase.The submergence state of the flexible vegetation is an essential factor affecting the water-surface ratio and comprehensive resistance.In the non-submergence state,the water surface ratio and comprehensive resistance positively correlate with the flow rate.The water surface ratio and comprehensive resistance negatively correlate with the flow rate in submerged states.(2)When the vegetation coverage ratio and resistance coefficient are small,the effect of the distribution modes on the surface ratio,the velocity distribution,and the comprehensive resistance of the open channel are not apparent.However,when the coverage ratio and vegetation resistance coefficient are large,the water surface ratio,cross-section velocity distribution,and comprehensive resistance will significantly differ under different distribution modes.In general,the water surface ratio,velocity distribution uniformity,and comprehensive resistance of the two banks are the largest,the central one,and the one-bank one,and equalfraction mode is the least.(3)When the vegetation coverage ratio and drag coefficient are large,the "optimal"momentum transfer coefficient will significantly differ under different distribution modes:the two-bank type is the largest among all,the central type is second,and the one-bank type is smallest.However,the "equivalent" comprehensive momentum transfer coefficient calculated by some existing methods is too small to reflect the influence of different distribution modes.The comprehensive momentum transfer coefficient tends to decrease gradually with the increase of flow and water depth.(4)A calculation method of comprehensive resistance and zonal velocity is proposed in this paper.Based on the experimental data of the flume and the measured data of the Huaihe River channel,the calculation results of different methods are compared.The results show that the method in this paper has some improvement.