Fish Migration Experiment And Layout Improvement In Vertical Slot Fishways

The contrastive experiments were conducted in vertical slot fishways of different flow pattern to study the relationship between the migration behavior of grass carp and the flow structure,and to seek for the type of flow pattern conducive to migrate and explore the internal mechanism.Based on the research results of the contrastive experiment,the optimization of the layout of the regular pool and turning pool of the vertical slot fishway was studied.The main conclusion can be summarized as follows:1)The relative length of lateral baffle P/B has a significant effect on the flow pattern in the vertical slot fishways.According to the difference of the observed changes in the mainstream and recirculation zone,it can be categorized as three different flow patterns Ⅰ,Ⅱ,III whose length of the corresponding lateral baffle,respectively,is in the range of P/B<0.2,0.2≤P/B<0.34,P/B>0.34.2)The juvenile grass carp,a kind of potamodromous fish,is selected as the objective specie to conduct experiments in three different typical flow pattern(P=0.1B,0.25B,0.5B).The results indicate that the success rate of grass carp juveniles in flow pattern II(Rr=73%)is significantly greater than that in the flow pattern Ⅰ and Ⅲ(Rr=55%in flow structure Ⅰ and Rr=64%in flow structure Ⅲ);The success time Tin the experimental fishway is presented withΓ distribution approximately,in which the success time T,no matter the median or the average,in the the flow pattern Ⅱ is significant lower than that in the flow pattern Ⅲ and flow pattern Ⅰ.So according to the success rate Rr and success time T,the flow pattern with P=0.25B is optimal for fish migrating.3)The software Zootracer is used to accurately and efficiently capture the trails of juvenile grass carps,and statistical analysis is used to generalize the scattered traces to three typical representative trajectories to describe the overall trajectory distribution.The results show that compared with the flow pattern Ⅱ,the unreasonable distribution of the mainstream and recirculation zones in the flow pattern Ⅰ and Ⅲ hinders the fish migration;the energy consumption for migration in the flow pattern Ⅰ is significantly higher than that of the other two flow patterns,and there are unobvious differences in energy consumption between flow patternⅡ and Ⅲ.According to the behavior of juvenile grass carp and the energy consumption for migration,the favorite flow pattern for the juvenile grass crap is that mainstream is centered and the recirculation zones are generally symmetrically distributed in the fishway.4)Based on the pattern Ⅱ,which is optimal for fish migrating,the layout of a streamlined head of baffle is put forward.The result indicates that the streamlined head baffle has unobvious effect on the flow pattern in the fishway pools,and the transversal diffusion of the mainstream increases while the deflection of mainstream slows down,which is beneficial to the attenuation of the velocity in the mainstream.The research also indicates that when the streamlined head of baffle is adopted,the local head loss is reduced at the vertical slot,so it is necessary to adopt small slope to control the velocity at the slot.In view of the fact that the streamlined head,a kind of fish-friendly structure,could avoid damage to fish that may be encountered during fish migration,so when conditions permit,the layout of streamlined head baffle may be considered to use in the hydraulic design.5)Based on the results of fish migration experiment in the regular fishway pools.The flow pattern in the turning pool is studied and the improvement measures are proposed to optimize the unfavorable flow pattern.For type I and type II turning pools,when the turning angles a are in range of 0°-45° and 0°-30° respectively,the turning pools can be rranged as the regular pools,in which the mainstream is roughly centered,and the recirculation zone is roughly symmetric.With the increase of the turning angle a,the flow ejects from the slot to the side wall and accompanies a relatively large scale recirculation zone,which is unfavorable flow structure for fish migrating based on the contrastive fish migration experiment,the optimization arrangement of combining the turning pools as the rest pool and adding the regulating plate at the corresponding position of side wall is put forward,which greatly improve the flow pattern.