Study On Lake-River Migratory Obstacle Crossing Of The Four Major Chinese Carp Poyang Lake Project

With the rapid development of society and economy,in order to meet the human demand for water resources,various types of water conservancy projects have developed rapidly.However,the economic benefits of water projects in supply electricity,flood control and other aspects have been produced,they also obstruct the natural connection of rivers and lakes under natural conditions,change their original hydrological situation,and prevent the free migration of aquatic organisms such as fish upstream and downstream,thus affecting the structure and function of the watershed aquatic ecosystem and leading to the reduction of biodiversity.For this reason,many water conservancy projects have designed and constructed fishway and fish hoist at the same time.In order to improve the effect of fish and improve the natural connectivity of rivers and lakes,more and more attention has been paid to the research.The four major Chinese carps are important commercial fishes in China which mainly live in the Yangtze River.They have typical characteristics of river and lake migration.The construction of water conservancy projects at the estuaries of lakes connected with the Yangtze River may have an impact on the migration process of the four major Chinese carps.It is of great significance to explore the impact of the construction of water conservancy projects on the fish migration and barrier and the countermeasures,which will guide the design and operation of the fish passing facilities and improve the connectivity and ecological environment of the rivers and protect the fishery resources.According to the design drawing of Poyang Lake Water Conservancy Project,a three-dimensional numerical model is built to simulate the three-dimensional flow field of the water Conservancy Project and its fishway by ANSYS FLUENT.Selecting typical normal flow year.According to the proposed operation scheduling scheme,the flow field characteristics of the hub are simulated in the river-lake connection stage with the gate fully open.The suitable flow velocity of each j the four major Chinese carps was determined according to the characteristics of the time,proportion and body length distribution of the four major Chinese carps entering the lake,and the migration of the four major Chinese carps into the lake under the operation of the water control project was analyzed.The main research results are as follows:(1)The construction and operation of the hydro-junction have a remarkable effect on the change of the flow field in its vicinity,and the velocity of each gate chamber is obviously higher than that under natural conditions.Influenced by the topography,the velocity of each gate hole is different.The velocity of 4～6 hole in the first area of the sluice is larger than that of other gate holes.(2)Overall,the hub operation had the smallest impact on the grass carp juvenile entering the lake,and there were more areas to meet the velocity conditions.It has the greatest impact on the entry of juvenile black carp and bighead carp into the lake,and can hardly cross the barrier into the lake when the upstream inflow is large.However,in July and August of the peak period,the left and right sluice areas can meet the majority of the juvenile fish barrier into the lake.(3)During the period of simultaneous operation of fishway and sluice area,it is difficult to form stable flow field because the water level of upstream and downstream is almost flat,so it is not suitable for crossing fish.During the period when the fishway operates alone,because it is not the peak time for the four major Chinese carps to swim into the lake,and the speed of flow in the fishway is faster,it can not satisfy the passage of juveniles.From here we see that the fishway has limited effect on the entry of the four major Chinese carps into the lake.If we want to solve the problem of the four major Chinese carps entering the lake,the necessity of fishway construction needs to be further demonstrated.(4)Among the four major Chinese carps entering the lake,grass carp and silver carp account for an increasing proportion year by year.Because of their strong swimming ability,the construction and operation of water control projects have little influence on them.The swimming ability of black carp and bighead carp is weak,and the number of fish entering the lake will continue to decrease.With the operation of the hub,grass carp and silver carp may become the dominant species of the four major Chinese carps.