Study On Biological Habitats Reconstruction And Ecological Flow In Regulation Waterway

In the context of uneven distribution of water resources and significantly lower per capita water resources compared to the global average in China,the construction of water conservancy projects has provided strong support for social and economic development.River regulation projects have been widely applied in hydropower development,flood control and disaster reduction,urban water supply,agricultural irrigation,and other fields,in which curving cutoff is a common river regulation measure.Manual curving cutoff of meandering river can effectively improve the navigation conditions and flood discharge capacity of the river.However,while such projects bring corresponding economic benefits,they also alter the natural hydrological rhythm and hydraulic conditions of the river,resulting in reduced material exchange between the river and the floodplain,the simplification of biological community structure and the destruction of river ecosystem.To clarify the internal causes of fish habitat loss in channelized rivers and the influence of river regulation,and to explore the reconstruction effects of gravel groups and traditional spur dike on fish habitats,this study investigates the ecological flow of fish in different life stages before and after river reconstruction.The study focuses on the curved river section of the lower reaches of the Shaying River in Anhui Province,and selects grass,silver,and bighead carp of the four major Chinese carps were selected as the research targets.By combining fish habitat model and using numerical simulation methods,the study investigates the impact of river regulation on target fish habitats and the restoration effect of habitat in the reconstructed river.Furthermore,the ecological flow of target fish in the stages of juvenile,adult,migration,and spawning is calculated using the habitat method.The main research results are as follows:(1)After the river was cutoff,the waterway was able to meet navigation requirements,the flow velocity in the river increased,and the viscous force in the interlayer decreases.Under the condition of the 20-year flood discharge,the water level at the inlet and outlet decreased by 2.53m and 1.93m,respectively,indicating a significant improvement in the river’s flood control capacity.The hydraulic environment in the original river was similar to that of the artificially channelized river,the target fish spawning habitat is very limited,and the percent usable area(PUA)is only 1.26%,which is one of the important reasons for the scarcity of fish resources in the lower reaches of the Shaying River.The Froude number in the reconstructed river is larger than that in the original river,the shear velocity magnitude changes from the uniform distribution of the original river to the transverse gradient distribution,and the flow vortex in the lower reaches of the gravel groups was more intense,compared with the original river,the deep water,slope and shallow water transition zones increased by 26.86%,35.65%and 871.43%respectively,while the flat riverbed zones decreased by 55.39%.The flow pattern in the river became more diversified,which was beneficial to the improvement of the fish habitat structure.(2)By setting the dry season,flood season,and characteristic flow calculation conditions and plotting the Q-WUA curve,the minimum and appropriate ecological flows of the original and reconstructed rivers were estimated.For the grass,silver,and bighead carps spawning stage(March to June),the minimum ecological flow is30m~3/s and the appropriate ecological flow is 140m~3/s.For the migration period,the minimum ecological flow is 140m~3/s and the appropriate ecological flow is 240m~3/s.For the growth stage(July to November),it can be divided into the juvenile and adult stages,in which the ecological flow regulation of the river from July to August should be dominated by juvenile fish,the minimum ecological flow of the original and the reconstructed river should be 20m~3/s and 40m~3/s respectively.For the months of September to November,ecological flow dispatch should be focused on the adult fish,and the minimum ecological flow for both are 30m~3/s.The appropriate ecological flow for the original and r reconstructed rivers are 40m~3/s and 60m~3/s,respectively.The estimation of ecological flow has a certain indication for the water resources regulation of upstream dams and is of great significance for the protection of target fish habitats.(3)Under the condition of appropriate ecological flow,the weighted usable area(WUA)of peak habitats for target fish species in the reconstructed river(with gravel groups)increased by 168%,24%,and 581%for juvenile fish,migratory fish,and spawning fish habitats,respectively,compared to the original channel,while the area of adult fish habitat that preferred slow water environment decreased by 62%,but increased by 47.53%compared with the unarranged river,which effectively improved the spawning conditions for target fish species and made their habitat more balanced.The study compared the effect of habitat naturalization and flood control between gravel groups and traditional spur dikes.The WUA of juvenile fish with gravel group scheme was 17%higher than that of spur dike channel,and the WUA of adult fish was30%higher than that of spur dike channel.The concave bank of the river can form a continuous habitat,and the habitat quality is significantly improved.Moreover,the impact of gravel groups on fish eggs drift and migration channel was less than that of spur dikes.The habitat restoration effect was superior to the spur dikes.In summary,the navigation conditions and flood control capacity of the river after curving cutoff were significantly improved,and the arrangement of gravel groups can provide habitat for the whole life cycle of grass,silver and bighead carps in the waterway.The calculation of ecological flow at different growth stages can provide a theoretical basis for watershed ecological protection and upstream dam scheduling.