Study On The Characteristic Of Fish Habitat And The Impact Of Waterway Regulation On Fish Habitat In The Fluctuating Backwater Area Of The Three Gorges Reservoir

The inland waterway transportation is an important part of comprehensive transportation system and efficient utilization of water resources,and an important strategic resource to promote the economic and social development of river basins.With the rapid development of inland waterway transportation in China,the influence of waterway construction on river ecological environment becomes increasingly prominent.However,the influencing mechanism of waterway construction measures on river ecosystem in China is still unclear,and effective evaluation theories and methods need to be further studied.Therefore,under the strategic background of promoting ecological civilization construction in China,the study on the theoretical system of impact assessment of waterway construction on river ecosystem is the prerequisite for the smooth progress of waterway regulation project,which is of great significance to promote the sustainable development of regional shipping.After the impoundment of the Three Gorges Reservoir,the navigation condition of the three Gorges reservoir area has been greatly improved.However,the waterway condition of the fluctuating backwater area of the Three Gorges Reservoir is still poor in the water level drawdown period,which restricts the development of navigation in the upper reaches of the Yangtze River.It is urgent to improve the navigation condition through waterway regulation project.At the same time,the fluctuating backwater area of the Three Gorges Reservoir（chongqing Jiangjin to Fuling reach）has unique natural conditions and rich fish resources.In 2007,the Ministry of Agriculture set up the Siqiongyu National Aquatic germplasm resources protection Zone in Chongqing section of the Yangtze River according to the"Aquatic Germplasm Resources Protection Zone Demarcation Work Specification（Trial）".In order to coordinate the contradiction between upstream navigation construction and ecological environment protection,promote the sustainable development of navigation in the upper Reaches of the Yangtze River,explore the characteristics of fish habitat in the fluctuating backwater area of the Three Gorges,and reveal the influence mechanism of waterway regulation project on fish habitat,these are the urgent problems to be solved in the waterway construction of the Chaofu section of the upper Reaches of the Yangtze River.Therefore,this study by monitoring the fishes distribution and habitat characteristics in the fluctuating backwater area of the Three Gorges,inductive analysis fish preference of hydrodynamic index range,the fish habitat suitability evaluation model is established,the quantitative evaluation of waterway regulation effects on fish habitat,providing theoretical basis for engineering construction related department.Based on the above research objectives,the main results of this study are as follows:1.The spatial distribution and habitat characteristics of fish in the fluctuating backwater area of the Three Gorges Reservoir area were observed synchronically with hydroacoustic detector and multi-parameter water quality analyzer,and the key habitats of fish in the fluctuating backwater area of the Three Gorges reservoir area were identified,and the key factors affecting the distribution of the key habitats were screened.The monitoring results showed that the pool and backwater areas with large water depth and low flow velocity were the perennial habitats of fish in the fluctuating backwater area of the Three Gorges,and the water depth and flow velocity were the key habitat factors affecting the spatial distribution of fish.2.The characteristics of water and sediment in the key habitats of fish in the fluctuating backwater area of the Three Gorges Reservoir area were analyzed,and the hydrodynamic indexes（velocity and depth）thresholds of the key habitats were proposed.The monitoring results show that fish in the fluctuating backwater area of the Three Gorges reservoir reside in the pools with a depth of more than 20m.Considering the hydrodynamic characteristics of fish habitat,1.2m/s was selected as the upper limit of suitable velocity index,and 0.6m/s sediment non-silting velocity was selected as the lower limit of suitable velocity index considering the stability and sustainability of fish habitat.3.Based on the mechanics principle of fish swimming behavior,the mathematical expression of fish critical swimming ability is derived:U_crit=α（gL）^0.5,and a method was proposed to determine the maximum response curve of target fish to habitat factors of velocity based on critical swimming capacity.Based on the hydroacoustic investigation of the cumulative frequency curve of fish body length distribution,the velocity corresponding to the critical swimming capacity of fish with the maximum body length was considered as the upper limit of the survival velocity,so the maximum velocity response curve of target fish to the habitat factors of velocity was determined.4.Based on the hydrodynamic requirements of fish habitat,a habitat suitability evaluation model was established in the fluctuating backwater area of the Three Gorges Reservoir area.Based on the characteristics of fish biology and key habitat,the response curves of four fishes to key habitat factors were established,and the habitat suitability evaluation model was built based on the two-dimensional water flow model in the fluctuating backwater area of the Three Gorges Reservoir area.The fish habitat evaluation model was verified by using hydroacoustic fish habitat survey data,and the verification results showed that the simulation results of fish habitat evaluation model had good reliability.5.The effects of waterway regulation on fish habitat were quantitatively analyzed by habitat suitability evaluation model.The simulation results show that the habitat suitability of the main waterway is generally low,and the location with high habitat suitability is mainly located in the backwater area with low velocity.The dredging and reef-clearing projects for waterway regulation in the fluctuating backwater area of the Three Gorges Reservoir area have little influence on the habitat suitability of fish.The influence of waterway regulation project on fish habitat in the fluctuating backwater area of the Three Gorges reservoir area is mainly reflected in the dam construction project in the water level drawdown period and the ballast piling project in the water level drawdown period and flood period.