| In terms of solving the problem of river connectivity under the influence of water conservancy construction,the construction of fish facilities is currently the main engineering measure to repair the aquatic environment of rivers.In this paper,a new multi-level traceable fishway model is used to study the water flow and fish-passing effectiveness.In order to provide a theoretical reference for the study of fish passage facilities in the middle and high head water conservancy hubs,it provides technical solutions for repairing fish habitats and improving river connectivity.The main research contents and conclusions of this paper are as follows:1.Optimizing the physical model of the fishway.Compositions of the fishway model include several fishway pools,the traceback structures of the fishway,the energy dissipation structures of the fishway,the monitoring system for fish-passing effectiveness and the ecological measures of the fishway,through the coordination between various system structures and the proposed operational methods,fish are traced back.Structural optimizations include optimizations of the fishway tailgate structure,the fishpond floor roughening and the fishpond fall structure.The water flow structure of the fishway model is improved by optimizing the structure to create a water flow condition suitable for fish migration.2.Carrying out the hydraulic characteristics test of the fishway model.the water flow characteristics are studied by carrying out water flow tests in the fishway units during the operation of the first-stage arched baffle and the secondary arched baffle.By comparing flow velocities of the cross-section under multiple cases,it was found that when the primary baffle was raised to a height of 25 cm(case 5),the hydraulic conditions created in the first-stage fishway unit facilitated fish migration;when the secondary baffle is raised to a height of 15 cm(case 8),the hydraulic conditions created in the second-stage fishway unit facilitate fish migration,and detailed analysis of the corresponding velocity field is performed.3.Carrying out fish passing tests of the fishway model.In order to evaluate fish-passing effectiveness of the above-mentioned two cases in the combined operation,the relevant tests of fish-passing efficiency was carried out.The test results show that the fish-passing efficiency of the fishway model is 13.40%.The main reasons for analyzing the low efficiency of fish migration are: 1.There are differences in physical and swimming abilities between individual fish;2.The water flow in the fishway is not a uniform water flow,and eddy currents appear in local areas.In this area,the fish are stimulated to swim quickly,but the correct migration direction cannot be found,resulting in excessive consumption of physical energy and inability to achieve migration;3.Due to objective reasons,the size of the fishway constructed was small,resulting in a reduction in the fish rest area,and the flow of water near the upstream of the baffle is greatly affected by the backwater that is raised and lowered by the baffle.This paper is only a preliminary exploration study on water flow tests and the fish-passing efficiency through the new fishway model.In the later stage,it is still necessary to further optimize structures of the fishway through a large number of experimental studies to improve fish-passing effectiveness.Figure [32] Table [7] Reference [82]... |
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