Cycle analysis of extreme water level in the tidal reaches of the Yangtze River

The periodic characteristics of the time series of yearly highest water level and yearly lowest water level in the lower tidal reaches of the Yangtze River are analyzed by using periodogram analysis and maximum entropy spectrum analysis according to the data (1964 ∼ 1987) of Wuhu, Nanjing and Jiangyin hydrologic station. The results show that the period all obtained in the yearly highest water level of Wuhu, Nanjing and Jiangyin is 3.14 years, and the period obtained both in the yearly highest water level of Wuhu and Nanjing is 7.33 and 2.2 years, and the period also obtained in the yearly highest water level of Jiangyin is 5.5 years. The period obtained in the yearly lowest water level of Wuhu, Nanjing and Jiangyin is 2.44∼3.14 years, and the period obtained separately in the yearly lowest water level of Wuhu, Nanjing and Jiangyin is 2.2, 5.5 and 11 years. The result shows that for the Yangtze River estuary in which the inland runoff and tidal currents are both strong, its periods of the extreme water level in tidal reaches reflect the dual characteristics of both inland runoff and ocean tide It provides the foundation for further research of evolution of the lower tidal reaches of the Yangtze River.