Fish Habitat Distribution And Hydraulic Characteristics In The Upper Reaches Of The Yangtze River From Fuling To Fengdu

The development of shipping in the upper reaches of the Yangtze River is the strategic demand of the country‘s ―Belt and Road Initiative‖,and it is also an important support for Sichuan and Chongqing to build a comprehensive transportation hub in the southwest region and a shipping center in the upper reaches of the Yangtze River.Due to the presence of reefs in the upper reaches of the Yangtze River from Fuling to Fengdu that obstruct navigation during flood season,sea damage accidents frequently occur in some beach sections.However,this section of the river is also an important distribution area for my country’s rare and unique fish and four major domestic fish germplasm resources.On the one hand,the obstruction of navigation features such as reefs in the river and stone beams on the shore affects the development of shipping,but also creates a unique pattern in the upper reaches of the Yangtze River.The reef-deep habitat type,the contradiction between waterway regulation and fish habitat protection have become important factors restricting the development of water transport in the upper reaches of the Yangtze River.Therefore,to clarify the fish distribution characteristics and typical habitat characteristics of the engineering river section is an important guarantee for both shipping development and fish habitat protection.In order to strengthen the protection of fish resources in the process of waterway regulation,and provide basic information for the sustainable utilization of fish resources in the upper reaches of the Yangtze River.In May,August and December 2019,the method of hydroacoustics was used to investigate the distribution of fish in the upper reaches of the Yangtze River from Fuling to Fengdu,and the composition of fish resources was counted and identified.The distribution characteristics of fish habitat conditions and the characteristics of related factors of reef-deep tuo habitats were analyzed,and a two-dimensional hydrodynamic model was established to simulate fish under two typical flows and water levels during the ebb and flow period and the impoundment period.The distribution of habitat suitability,the main research results are as follows:(1)Through on-the-spot hydroacoustic monitoring of the study river section in 3periods in 2019,the distribution characteristics of fish in the study river section were obtained.In May,13 fish gathering areas were found,with an average density of 40.89 ind./km3 and an average TS of 40.89 ind./km3.was-49.38 d B;6 fish gathering areas were found in August,with an average density of 56.93 ind./km3 and an average TS of-47.71 d B;15 fish gathering areas were found in December,with an average density of62.95 ind./km3,The average TS is-48.13 d B.According to the water depth of the single fish target location,90% of the fish inhabit the water from 20 m to the bottom,mainly in the middle and lower layers or the bottom layer.(2)The significance and correlation of fish habitat related factors in the Fuling to Fengdu River section were analyzed,and the water depth,flow velocity,Froude number,aspect ratio,water passing area,wet circumference,hydraulic radius and A total of 8characteristic factors of water quality are used to describe the fish habitat in the upper reaches of the Yangtze River from Fuling to Fengdu.It is concluded that flow velocity and water depth are the main influencing factors of fish habitat in the study river section,Froude number,water passage area,wet circumference and hydraulic radius are secondary influencing factors,water quality and width-to-depth ratio are no influencing factors,and fish school Density and flow velocity were significantly negatively correlated,and significantly positively correlated with water depth,while Froude number,cross-sectional area through water,wet circumference and hydraulic radius had certain correlations in different periods.(3)The MIKE21 model was established based on the measured data to simulate the hydrodynamic distribution of the research river section under different flow and water level characteristics,and established a mathematical model of physical habitat.Combined with the results of the previous hydroacoustic survey,the suitability curves of water depth and flow velocity were obtained.By coupling the fish habitat suitability index,the spatial distribution of the fish habitat suitable area in the study river section under different average flow rates was obtained.The suitable area is an important habitat for the study of fish in the river section.