Characteristics of streamflow in the main stream of Changjiang River and the impact of the Three Gorges Dam

The assumption that natural system changes in a constant range runs through the practice of water resources application. However, under the changing environment, whether hydrological characteristics have changed is a crucial and important foundation for flood control and drought resistance. Based on daily water level, discharge, and precipitation for the last 100 or 60 years, this study analyzed the hydrological characteristics and their changes as results of the operation of the Three Gorges Dam (TGD) in the Changjiang (Yangtze) River. Results showed that the monthly precipitation did not significantly change for the longer period and the annual precipitation remained stationary during 1959-2018. However, the water level and discharge significantly increased during most months from January to March and significantly decreased from August to November. Yichang station, the nearest station to the TGD, changed the most, which annual runoff and water level series (1959-2018) showed obvious non-stationarity behavior. The same results were showed in period 1890-2018, while the process remained stationary for the period 1890-1970. 50.15% of the discharge at Yichang station decrease from June to November was attributed to water storage of the TGD and 57.57% of its increase during other months was attributed to recharge of the TGD. The TGD had a greater impact on the discharge, while the water level was affected by both the TGD and Gezhouba Dam. The trends of the water level and discharge were in perfect synchronization prior to 1980, but went out of sync in terms of a different direction or rate after 1980 given the operation of Gezhouba Dam. The non-stationarity behavior of discharge and water level and the change of their laws make it difficult to directly apply the relationship among precipitation-discharge-water level in the past, which brings great challenges to the planning and management of water resources.