Research On Response Of Fish Behaviour To Flow Field And Fish Movement Modelling

Hydraulic structures such as gates and dams caused the fragmentation of rivers and lakes,which blocks the upstream and downstream passages of aquatic organisms,making fish and other aquatic organisms unable to complete their life cycles,hindering gene exchange,and affecting biodiversity.With the country’s increasing emphasis on the ecological environment,some fish-passing facilities for restoring the connectivity of rivers and lakes and restoring habitats,such as fish passages,fish lifts,fish locks,and fish collection vessels,have been rapidly developed and applied.However,at this stage,the fish passing efficiency of most fish passing facilities is insufficient.In addition to the problems in operation and management,the most important reason is that the design basis of the current fish passing facilities is insufficient and cannot match the actual needs of the fish passing objects in the migration process.To seek an effective method to improve the efficiency of fish passage facilities,we studied the response mechanism of fish behaviour to hydraulic characteristics through water flume experiments and proposes and studies the hydraulic characteristics of vertical slot fish passages with different structures through physical model tests and CFD numerical simulations in this thesis.A fish movement model based on behaviour strategy was constructed,and different behaviour strategy parameters were given based on the results of fish behavioural experiments.Finally,the fish movement model was used to accurately simulate the upswimming route of fish in a vertical slot fishway.The main research results are as follows:(1)In this paper,a four-channel water flume with different flow rates was used to provide a freely selectable area with a particular flow rate gradient,and statistical analysis is carried out on the number of times the test fish enters each channel autonomously.A significant difference in the choice of flow rate was found,showing a preference of fish for different flow rates.Compared with the forced movement of fish in a uniform flow field in the traditional fish swimming ability test,the free movement of fish in a non-uniform flow field is more similar to the internal environment of natural river channels and fish-passing facilities;(2)In this study,Schizothorax oconnori showed different preferences for flow velocity at different times,showing a preference for high flow velocity at the end of July and a preference for low flow velocity at the end of August.Due to the different seasons,its behavioural strategy changes from "aggressive" to "conservative" to save physical strength;(3)We proposed a weir-hole-vertical slot fishway and a cylinder-structure-vertical slot fishway based on the research on the hydraulic characteristics of typical vertical slot fishways,for increasing the differentiation and diversification of fishway water flow field.Experimental studies on fish behaviour found that long-term swimming in a constant flow field would lead to fish fatigue or “burnout” and reduce activity.Quantitative evaluation indicators were proposed by water flow velocity and turbulent kinetic energy requirements for common fish in the migration process.It was found that the proportion of the area suitable for fish to migration increased significantly in the weir hole structure and the pile structure;(4)A fish movement model based on the behavioural strategy was proposed.Fishes are regarded as particles,perceive the surrounding water flow environment during the motion process,and decide the following motion through a particular behavioural strategy according to the acquired information.The reliability of the model was verified by the results of fish behavioural experimental research;(5)The two behavioural strategies of Schizothorax oconnori in the fish behavioural experiment were simulated,and the behavioural strategy parameters were given.The main difference is: when it adopts the "radical" strategy and chooses the upswimming movement,There is a 95% probability of choosing the direction of the maximum flow velocity,while when the "conservative" strategy is adopted,and the upswimming movement is selected,there is only a 20% probability of choosing the direction of the maximum flow velocity;(6)The fish movement model was used to simulate the upswimming movement of Schizothorax oconnori in typical vertical slot fish pass,weir hole-vertical slot fish pass and pile structure-vertical slot fish pass with the two behavioural strategies.The feasibility of applying the fish movement model to the fish passing facility is verified.Pass rate and pass efficiency are presented for quantitative evaluation of fish pass facilities.It was found that even if fish with the same swimming ability were distributed in the same flow field,the passing rate and passing efficiency were significantly different under different behavioural strategies.(7)Weir hole-vertical slot combined fish pass and pile structure-vertical slot fish pass can effectively improve the passing rate and passing efficiency compared with the typical vertical slot fish pass and adapt to the upward adaptation of fish with different behaviour strategies.The performance is better,demonstrating the necessity of the differentiation and diversification of the water flow of the fish-passing facilities.A complete system is constructed that include the mechanism of fish movement,the hydraulic characteristics of fish-passing facilities,and then predicting the movement path through the fish movement model,which provides a reliable basis for the design and effect evaluation of fish-passing facilities.A powerful tool was provided to link research on physiological,behavioural,and fish-passing facility hydraulics and engineering.