Hydraulic Simulation Study On The Connection Section Of The Outlet Of Nanmu River Imitating Natural Fishway

With the development and utilization of water resources,the masonry of water retaining structures such as weirs,dams and sluices in natural river channels not only destroys the connectivity of river channels,but also destroys the integrity of the original ecosystem,so that the survival,reproduction and execution of other biological functions are affected.Therefore,it is necessary to set up fishways on various water retaining structures to improve the connectivity of rivers and reduce the damage of buildings to the ecosystem as much as possible.The imitative natural fishway is a kind of fishway which imitates the hydraulic characteristics of river channel form,flow velocity distribution and flow pattern in the natural state.This fishway provides similar flow conditions to an undisturbed river without changes in nonbiological boundary conditions,and the fish will be easier to pass through.Therefore,the research on the imitated natural fishway has very important engineering application value and urgent practical significance.In this paper,through the analysis of hydraulic theory and physical model test research,the feasibility of the layout of the joint section of many kinds of imitating natural fishway exits is analyzed and demonstrated.The main work is as follows:(1)The transition and connection between imitated natural fishway and engineering fishway.By using physical model test,the transition area between the fishway and the simulated natural fishway is studied,and it is found that the flow at the outlet of the fishway falls seriously;the water surface gradient is too large,the water depth is shallow,and the flow velocity is high,which can not meet the flow requirements of fish migration.In view of the above flow characteristics,based on the concept of "dispersing the drop and reducing the head",a multistage submerged weir with three fish passing holes at the bottom is designed innovatively,which improves the flow pattern in the transition area.By using the existing stone resources in the area,the geometric scale can be scaled to reach the similar conditions,and the roughened stone can be made.Finding a suitable placement way near the orifice at the bottom of the fishway can achieve the effect of smooth water flow and reduced flow velocity.The research results have certain reference value for solving the shape design of the exit of the same type fishway.(2)The transition and connection between the imitated natural fishway and the ecological landscape lake.Using physical model test,the transition area between an ecological landscape lake and a simulated natural fishway is studied.This area is a hydrophilic area with landscape function,and the main channel is connected with the ecological landscape lake by a fan structure which gradually shrinks in the direction of downstream water flow.This requires that under the conditions of fish migration,as far as possible in the region to form fish temporary rest landscape area.Therefore,the bridge pier type wooden piles arranged with plum blossom piles are designed,one for tourists to walk through the fishway,and the other for fish to have a short rest in the relatively still water area behind the wooden piles.