Optimization Of River Channel Section For Bionomic Control Of Medium And Small Rivers

Small and medium-sized rivers are an important part of river network,which are widely distributed in urban-rural areas and rural areas,and undertake important economic and ecological functions,such as water supply for urban and rural people’s life and industrial and agricultural production,absorption of sewage,purification of environment,regulation of land and water ecosystem and so on.Therefore,the control of small and medium-sized rivers should not only consider the needs of flood control safety,but also abandon the single channel section management mode of "channelization,hardening and whitening" from the requirements of giving full play to the function of the river,ensuring the health of the river and creating a beautiful environment.The Jiangxi Provincial Water Conservancy Department issues the notice on guiding the Management of small and medium-sized Rivers with the concept of Ecological Civilization,which must follow the requirements of adopting compound section,wide and shallow section and strengthening the protection of flood beach according to local conditions,but the design standard of ecological control section is not clear at present.Therefore,based on the analysis of economic analysis and river flow characteristics,this paper carries out the study of "optimization of river section of ecological control of small and medium-sized rivers".The main research contents and conclusions are as follows:(1)The research and analysis on the ecological management of small and medium-sized rivers in some areas are carried out,and the types of the channel section,the slope protection type and the slope of the bank slope adopted in the current ecological management of the small and medium-sized rivers are summarized and the main problems are analyzed.(2)Based on economic analysis,a compound section optimization method with the lowest cost of river ecological control is proposed.Methods the effects of ecological control interrupt surface width,slope and composite section combination length on the cost are considered synthetically.The example shows that this method can effectively reduce the cost of ecological compound section,which provides a certain basis and reference for the design of ecological compound section.(3)The analysis model of river flow characteristics is established,and the influence of river slope and ecological compound section combination on flow characteristics is studied and analyzed.It is found that when the river bank slope is slow,the erosion of water flow to the foot of the slope is greater;The steeper the riverbank,the smaller the influence on the intensity of transverse circulation,the slower the velocity of circulation formation,and with the gradual increase of the bottom width,the velocity decreases gradually,and the transverse circulation is gradually weakened.At this time,the scour of the flow to the bank slope is weak.In the compound section of different roughness ecological material combination,if the Gebin stone cage with high roughness is used at the bottom of the river,the velocity of the river can be slowed down and the flow conditions can be improved,but the high setting of the stone cage has little effect on the water flow.(4)Based on the analysis of river flow characteristics,the optimization of river ecological control compound section is put forward,that is,the steeper slope should be selected as far as possible under the premise of ensuring the stability of bank slope.Considering the characteristics and economy of water flow,the revetment types with good scour resistance but high cost should not be set up too high,and the height can be set up to meet the needs if the height is half of the constant water depth.(5)The effect of the shape of the direct channel on the water flow characteristics is studied.The results show that with the increase of the length and width ratio of the straight road,the influence of the flood plain on the water flow is reduced,the range of the low flow velocity area after the beach front beach is reduced,and the main flow velocity of the river channel is reduced.when the width-width ratio of the floodplain is 4,the effect of the water flow is better;the curve elliptical floodplain at the same area is arranged at the center of the channel,the slope is 45 degrees,the ratio of the long and short shafts is greater than 1,the effect effect of the floodplain on the water flow is better,and the wake area after the beach of the floodplain is larger,The arrangement of the floodplain breaks the cross-section circulation,so that the flow velocity of the convex bank is increased,the sludge can be effectively washed,and when the ratio of the long and short shafts is greater than 1.7,a wake area is formed near the convex shore after the river flows through the curve,and is not beneficial to the scouring and silting of the convex bank.(6)Based on the analysis of the flow characteristics of the floodplain,it is proposed that the optimal section of the floodplain is as follows: the aspect ratio of the straight floodplain is 4,the shape of the curved floodplain is elliptical floodplain,the floodplain is located in the center of the river,the slope is 45 °,and the ratio of long to short axis is between 1 and 1.7.