Spawning Grounds Of Drift Spawning Fish In The Upper Reaches Of The Yangtze River Study On Hydrodynamic Characteristics

The hydrodynamic characteristics of fish spawning grounds are of great concern in fish protection,but how to scientifically reflect the hydrodynamic characteristics of the above key habitats,define their scope and realize the accurate positioning of spawning grounds has not been well solved.Taking the upper reaches of the Yangtze River as the research object,through the combination of one-dimensional and three-dimensional river hydrodynamic simulation,this thesis studies the geomorphic,water depth and hydraulic characteristics of the spawning ground of drift spawning fish in the river section of Zhutuo Town,Yongchuan District,Chongqing,Yibin City,Sichuan Province,which is the main stream of the upper reaches of the Yangtze River,so as to provide a scientific basis for the protection and ecological restoration of key fish habitats in the upper reaches of the Yangtze River reserve.The main research contents and results are as follows:(1)The geomorphic features of spawning grounds can be classified according to river regime(large-scale landform)and geomorphic unit(local landform).The geomorphic characteristics of the spawning ground of drift spawning fish are jointly affected by the river regime and geomorphic units.Its geomorphic characteristics include the top of the river bay,the deep grooves in the upstream and downstream of the river bay,the concave bank of the river bay,the deep groove in the center of the river and the deep groove in the narrow part of the river.(2)In the study area of the upper reaches of the Yangtze River,the water depth gradually increased from April to July,and the increase increased month by month.The bed shear stress is small in April and may,and the river section is rich in sediment and species;June and July,the bed surface shear stress in the mainstream area is large,the sediment is simple,and the biological species are single.The Froude number is small from April to July,and the flow pattern is relatively consistent.From April to July,the horizontal velocity gradually covered the river surface from slow to rapid,and increased compared with the previous month.There are upwelling and downwelling bands in the vertical velocity from April to July.The water depth,bed shear stress,Froude number,horizontal velocity and vertical velocity increase with the increase of flow.The minimum and maximum values of water depth,bed shear stress,Froude number,horizontal velocity and vertical velocity in the spawning period(April to July)of drift spawning fish spawning ground.(3)The habitat patches of the spawning ground of drift spawning fish can be divided into two types according to geomorphic unit and hydraulic unit.According to the classification of geomorphic units,there are large patches and small patches;According to the hydraulic unit,it can be divided into water depth habitat patch,bed shear stress patch,Froude number patch,horizontal velocity patch and vertical velocity patch.(4)In the study area of the upper reaches of the Yangtze River,the water depth and horizontal velocity showed regular large patches(strips)in April;may,June and July,the horizontal flow velocity is divided into river sections,Yibin Hejiang section presents regular large patches(strips),and Hejiang zhutuojiang section presents messy small patches(small fragments).The bed shear stress and Froude number showed regular large patches(strips)in April and may;June and July,there were regular large patches(strips)in Yibin Hejiang river section and messy small patches(small fragments)in Hejiang Zhutuo river section.The vertical velocity shows regular upwelling / downwelling patches from April to July.The habitat patch of the spawning ground of drift spawning fish in the upper reaches of the Yangtze River belongs to deep-water area;The bed shear stress habitat patch gradually transformed from a single area of sediment to a rich area of sediment;The Froude number of habitat patches is less than the average Froude number of the river section;The horizontal velocity habitat patch belongs to the slow velocity area;The vertical velocity habitat patch belongs to upwelling strip.(5)The location of upwelling patches in the three river sections(Nanxi-Jiang’an river section,Naxi-Luzhou river section and Hejiang-Zhutuo river section)with dense spawning grounds for drifting disordered fish is likely to be the spatial location of potential spawning grounds used by fish in the upper reaches of the Yangtze River reserve.The location of vertical velocity habitat patches,the general common judgment of water depth,bed shear stress,Froude number and horizontal velocity habitat patch statistics together form the habitat characteristic model of drift spawning fish spawning ground in the upper reaches of the Yangtze River.