Investigation into the Impacts of the Gezhouba and the Three Gorges Reservoirs on the Flow Regime of the Yangtze River

The flow regime of the Yangtze River (Changjiang) has been altered to some extent by intensified human activities over the past decades, particularly dam construction. To assess the impacts of dam building on the flow regime in the Yangtze River, two of the largest reservoirs on the upper reach, i.e., the Gezhouba and Three Gorges reservoirs, have been selected as case study sites. To analyze the changes in flow regime between predam and postdam periods, the whole study period was divided into three subperiods according to the years when these two reservoirs started to store water. On the basis of the time series of daily flow discharge from four key hydrological stations, i.e., Cuntan, Yichang, Hankou, and Datong, the alterations in annual, seasonal, monthly, and daily flow regimes and water rising or falling regime in different subperiods were investigated and the driving forces were explored. The results revealed the impacts of the two reservoirs on their downstream flow regime varied with reservoir storage capacity and the distance between the target reservoir and the case study site, the Gezhouba and Three Gorges reservoirs imposed various impacts on different time scales of downstream runoff regime, and the operation of these two reservoirs altered the water rising and falling regime to some degree, which is particularly critical for the spawning of Chinese sturgeon and the four major domestic carp. The output of the paper could provide references for the assessment of impacts of dam construction on the health and stability of the Yangtze River ecosystem.