Impact of hydraulic engineering on hydro-ecology in middle and lower reaches of Hanjiang River

According to observed data before 1980,the impacts of the operation of Danjiangkou Reservoir on runoff,sediment,water temperature,water quality,and fish were studied.The results showed that the operation of the reservoir had reduced water quantity and homogenized annual runoff distribution,improved the flood control level,reduced sediment and water temperature during the flooding period,and reduced fish resources,and had no apparent influnce on water quality.The reason for worsening water quality and algal blooms in the middle and lower reaches of the Hanjiang River was increasing water pollution.After the South-to-North Water Transfer Project is built and in operation,runoff will be reduced much more,as will the water flow velocity.These will reduce the dilution and self-purification ability of water and the eco-environmental water supply,and lead the hydro-ecology in a negative direction.