Research On The Impact Of Dam Construction On The Spatial Distribution Of The Spawning Grounds Of The Four Major Chinese Carps In The Three Gorges Reservoir

Dam construction can bring huge social and economic benefits to human beings,but at the same time,the water flow and natural conditions of dam-built rivers have undergone significant changes compared with natural rivers,and the reproduction of aquatic organisms and the habitat environment are affected.Research on the ecological effects caused by dam construction is conducive to protection of river ecosystems and guidance of ecological regulation,thereby balancing the relationship between development and protection.As an important economic fish in my country,the four major Chinese carps(FMCC)are widely distributed in the Yangtze River Basin.The annual output of the FMCCs in the upper reaches of the Yangtze River is even more important in the annual catch.During the post-dam period,due to changes in water flow conditions,the spatial distribution of the spawning grounds of the FMCCs also changed dramatically compared to the pre-dam period.This study takes the Three Gorges Reservoir area(TGR)in the upper reaches of the Yangtze River as an example.A one-dimensional model of the reservoir area and a habitat suitability model of the FMCCs were established.Based on the stochastic simulation method,simulated and analyzed the spatial distribution and changes of the spawning grounds of the FMCCs during the pre-dam period and post-dam period in the Zhutuo-Zigui section of the upper reaches of the Yangtze River under complex incoming current conditions.The main results and conclusions are as follows:1)Establishing a habitat suitability model for the FMCCs in the TGR,and evaluates the suitability of different sections based on the HSI method and the suitability curve method.Using MIKE11,a one-dimensional unsteady flow hydrodynamic model of the TGR was established.This model is based on high-precision DEM data and takes into account the impact of the tributaries and river bays on the channel storage of water flow(bifurcation channel capacity),thereby reducing the flow simulation error.The calibration and verification results show that the hydrodynamic model has high simulation accuracy and can accurately calculate the flood evolution process.The hydrodynamic model is coupled with the habitat suitability model,and the actual measurement results show that the coupled model can better simulate the changes of the spawning grounds of the FMCCs.2)Based on stochastic hydrology and statistics,a periodic stationary autoregressive model of daily flow was established that can predict future water regimes based on actual hydrological data.The model generates 2,000 flood sequences that can reflect the changing characteristics and statistical laws of the measured flood sequence.According to the daily parameter pass rate of each station,the simulated value of the parameter fits well with the measured value.The simulated sequence generated by the periodic stationary autoregressive model of daily flow can well reflect the statistical properties of the measured sequence.3)Based on the combination of 2000 random floods,the flood simulation of different outflow conditions during the pre-dam and post-dam period.After calculation and evaluation by the habitat suitability model,the spawning ground of the FMCCs in the reservoir area has moved up significantly compared with natural water flow conditions during the post-dam period,The FMCCs tend to breed in the 60km long Zhutuo-Jiangjin section and the 255km long Banan-Zhongxian section.The reservoir area above Zhongxian section contains six spawning grounds for the FMCCs:Zhutuo-Jiangjin,Banan-Xiakouzhen,Xiakouzhen-Luoqi,Luoqi-Fuling,Fuling-Puzituo and Puzituo-Zhongxian sections.4)According to the water level conditions of different dam sites,simulate the impact of different sizes of dam heights on water flow conditions.Through the simulation of four scenarios—high dam,middle dam,low dam,and no dam—after the construction of the high dam,370 km of the FMCCs' spawning grounds in the TGR disappeared.In the low-dam scenario,the impact distance was 290 km.This shows that the ecological suitability of aquatic organisms in dammed rivers is affected to varying degrees,depending on the size of the dam.