The Yangtze basin is rich in water and biological resources, providing essential natural conditions for economic development in the southern region of China. Various water conservation facilities have been constructed in the basin to perform water resource scheduling and electrical energy conversion. By 2009, there were 46000 reservoirs built in the basin, with a total irrigation capacity of more than 120 billion m³. These projects were associated with benefits in terms of drought flood control, power generation, shipping, breeding, and so on, but also had both positive and negative effects on runoff. Therefore, watershed water security not only affects economic development and ecological security in the southern region of China, but also is an inevitable requirement for sustainable development. We participated in an academic conference on soil and water conservation and disaster prevention and mitigation in the Yangtze River economic belt, during which several scholars and experts extensively discussed the current problems in the Yangtze River basin. Some experts pointed out that the construction of the Three Gorges project and other water conservancies would lead to an advance in the timing of the dry season in the middle and lower reaches of the Yangtze River, resulting in increased water pollution, changes in the habitats of migratory birds, and a series of ecological problems. Although low water levels and floods are classified into the extreme hydrology category, early drought has no significant impact on human activity, and is not as well studied as floods. With the growth of the social economy and population explosion, the gap between the supply and demand of water resources is increasing. Especially in the dry season, several ecological problems are experienced, including increased water pollution caused by the reduction in runoff and river blanking caused by excessive use of low water resources. Thus, it is necessary to study the effects of water conservancy projects on the dry season. After the conference, we conducted a field visit and a survey along the Yangtze River area, with a view to use the data to effectively assess the impact of water conservancy construction during the dry season. Since the construction of the Three Gorges project has attracted greater attention, its water security and ecological benefits have always been the focus of discussions. Therefore, we selected Yichang station as the study area and analyzed the impacts of the Gezhouba hydro-project and the Three Gorges project on hydrological dynamics. Based on the runoff data of Yichang station from 1890 to 2014, the effects of water conservancy construction on the distribution of runoff and the dry season were analyzed using runoff concentration degree and period and phase difference analysis. The results showed that the runoff concentration of Yichang station tended to decrease, with a mutation occurrence in 2004. After 2003, the runoff concentration decreased by 0.06 (a decrease of 12.98%) from that before 2003. This indicated that after the completion of the Gezhouba water conservancy project and the Three Gorges project, the runoff distribution in Yichang station over the year became gentle and the peak floods were effectively weakened. The rate of contribution of the Three Gorges project toward decreasing the runoff concentration degree in Yichang station (92.03%) was greater than that of the Gezhouba water conservancy project (7.97%). After the Gezhouba and Three Gorges projects were completed, the runoff concentration period and beginning of the dry season in Yichang station have advanced (with advances of 8 and 20 days, respectively). Following completion of the water conservation projects, changes to the water-carrying capacity of the environment and wetlands in the lower reaches will take place earlier than previously, resulting in increased water pollution, changes in wetland biodiversity, and several ecological problems. Our results revealed the influence of the water conservation projects on hydrological processes and their potential ecological efficiency, providing a scientific basis to better understand the influence of water conservation projects on runoff.