Hydraulic Characteristics Of A New Permeable Spur Dike And Its Effect On Fish Behavior

The development and protection of the Yangtze River,the mother river of the Chinese nation,has always been the greatest concern of the Party and the state.In developing the Yangtze River,we should give top priority to the restoration of the ecological environment along the Yangtze River and follow a new path of ecological priority and green development.The past in order to promote economic development,improve channel,channel management department a series of waterway regulation project,the spur dike is the most typical waterway regulation buildings,the traditional scattered stone spur dike improved the navigation condition,but also changed the local channel currents and topography,local habitat affect the channel,has certain influence on the fish migration and habitat.Therefore,it is of great significance to find a waterway regulation building which can not only meet the regulation function of waterway but also improve the local habitat of waterway and provide migratory passage and suitable habitat for fish.In this paper,by analyzing the traditional scattered stone spur dike on the structural stability and the influence on fish behavior limits,and draw lessons from the overflow weir overflow surface WES curve design a new type permeable spur dike,and uses the method of combining the theoretical analysis and model experiment,the traditional scattered stone spur dike for the control group,the new permeable spur dike on the system of channel scouring and silting in hydraulic characteristics,terrain feature and the fish back and live action mechanism,the influence of the following main research results:(1)Through the analysis of the flow field and turbulence characteristics near the spur dike,it is confirmed that the WES curved section can effectively reduce the flow velocity and turbulence intensity of the overflow dam;The dike seepage hole can reduce the concentration of water flow and the flow velocity and turbulence intensity at the dike head.The change law of the turbulence intensity at the dike opening is defined,and the calculation formula of the flow turbulence intensity before and after the dike opening is established,which verifies the feasibility of the dike opening as the upstream passage for fish.(2)According to the scouring and silting characteristics of the waterway terrain,the response law of scouring and silting area to the pervious rate of the spur dike is found out,and the coupling calculation model of the scouring pit depth at the dike head and the influencing factors such as the characteristic parameters of the dike head,the length of the dike bottom protection structure and the effective scouring time is established.(3)The response of juvenile grass carp to velocity factor was studied and the function relationship between swimming ability and body length of juvenile grass carp was put forward.With the increase of body length,the critical swimming speed increased in the form of power function,but the induction velocity did not change significantly.The preferred velocity is between the inductive velocity and the 60%critical travel speed.According to the upstream path of grass carp,the upstream behavior pattern of grass carp was identified,and the influence mechanism of traditional rippling buttress and new permeable buttress on the upstream behavior pattern and habitat selection of grass carp was clarified.(4)Based on Shannon entropy and landscape patch principle,the calculation methods of velocity-topographic diversity index,velocity-topographic diversity index and topographic diversity index were proposed.Combined with the hydraulic characteristics and topographic scouring and silting characteristics of the spur dike,the variation rules of the velocity-topographic diversity index under different flow rates and different permeability of the spur dike were analyzed.The greater the flow rate,the greater the velocity diversity index,and the more the topographic diversity index increased first and then decreased with the increase of the pervious rate of the spur dike.(5)Based on the analysis of the upstream success rate of grass carp and the collecting effect of spur dike,the functional relationship between the channel velocity-topographic diversity index and the upstream success rate of grass carp and the average aggregation degree of grass carp was established.When the velocity was within the preferred velocity range of grass carp,the retroactive success rate increased linearly with the increase of the velocity-terrain diversity index,and when the velocity exceeded the suitable velocity range of grass carp,the retroactive success rate decreased sharply.The average aggregation degree of grass carp increased linearly with the increase of the velocity-topographic diversity index.(6)Compared with the traditional scattered stone spur dike,the new permeable spur dike can not only slow down the scour around the dike,improve the structural stability,but also provide a upstream passage for grass carp migration,create the hydrodynamic conditions and topographical conditions conducive to the upstream and habitat of grass carp,improve the upstream success rate of grass carp,and increase the average concentration of grass carp near the spur dike.