Study On Waterway Regulation And Its Impact On Fish Habitat In The Wanglongqi Beach In The Upper Reaches Of The Yangtze River

With the rapid development of inland shipping,the construction of waterway has been continuously promoted.Waterway construction may involve fish resource protection areas and have an impact on fish spawning grounds,hydraulic habitats,etc.Following the concept of ecological priority and green development,waterway construction needs to take into account ecological protection.Therefore,it is of great significance to study the impact of channel construction project on fish habitat.Wanglongqi reach in the upper reaches of the Yangtze River is located in the National Nature Reserve of rare and unique fish.The local navigable water depth of this reach is insufficient,the cross flow is strong,and the moraine head water is turbulent.It is necessary to improve the navigable flow conditions and upgrade the channel grade through channel regulation.Aiming at the regulation of wanglongqi beach dangerous channel,this paper uses the method of combining numerical simulation and theoretical analysis to explore the navigation obstruction characteristics and causes of beach danger,studies the implementation effect of channel regulation scheme,and analyzes the influence law of beach dangerous channel regulation on the distribution of fish hydraulic habitat indicators.The main conclusions are as follows:（1）Wanglong moraine is a low flow shallow and dangerous beach,which is mainly caused by wide and shallow water surface and scattered water flow in the beach section;The backwater of the side beach leads to the decrease of the velocity of the beach section and the obvious cross flow;The beach section is a bend inlet and relatively straight,with weak circulation intensity and insufficient sediment transport capacity.（2）In view of the characteristics and causes of beach hazards hindering navigation,combined with the regulation principles of taking advantage of the situation and giving overall consideration,the channel regulation scheme is put forward.The navigation channel layout of scheme I and scheme II is the same.The shallow area in the navigation channel is dredged,and one spur dam is arranged in the moraine head of wanglongqi.The difference is that one spur dam is built on the left bank of scheme I,and two spur dams are arranged on the right bank of scheme II.After the implementation of the scheme,under the design flow,the 3.5m contour line in the navigation channel of the two schemes can be completely connected,the cross flow at the moraine head is weakened,the navigable flow conditions are significantly improved,and the regulation effect is good.（3）Before the scheme,the confluence velocity um of the project reach gradually decreases from the river center to the bank,the flow Q increases,and the increase range of U_m decreases.The impact of schemes I and II on the velocity of spawning ground is similar.U_m changes significantly near the spur dike.There is a high velocity area on the dam crest,and the velocity increases by 0.4～0.8m/s on average after regulation.（4）Before the scheme,the transverse velocity gradient G_x is distributed in strips on the section,and the maximum value appears on the bank,and G_x is about 0.009～0.048s^-1.Compared with scheme II,G_x near the center of the river in scheme I is larger,which is mainly due to the joint action of the left bank and qinao spur dike,resulting in the disordered change of water flow between spur dikes.（5）The distribution law of longitudinal velocity gradient G_y before and after the scheme is similar.G_y is distributed in layers along the water depth and gradually decreases from the bottom to the surface.G_y before the scheme is about 0～0.4s^-1.After the implementation of schemes I and II,a high value area of G_y appears near the project area,and G_y increases by 0～0.22s^-1.With the increase of flow Q,the area of high value area increases.The difference between G_y and G_x in section distribution is about 10 times.（6）The variation law of vorticityΩ_z is similar to that of velocity gradient.The larger values appear at the bottom of the river and around the spur dike,about 0.045～0.06s^-1.Q increases,the variation ofΩ_z at the center of the river is not obvious,and the vorticity is 0～0.05s^-1.The distribution law of flow velocity suitability S_u section is similar to that of flow velocity.Under the design flow,the area with S_u>0.8 in the center of the river is the largest.