Return Period of Low Tide Level in the Yangtze Estuary based on Nonstationarity Analysis

Due to the influence of climate change and human activities, stationarity of hydrologic time series is being challenged. The Yangtze Estuary is a region with highly developed hydraulic structures and shipping. Stationarity analysis of water level in the Yangtze Estuary is of great significance. In this study, the return period of low tide level in the Yangtze Estuary is estimated with nonstationarity considered. Conventional frequency analysis and the time-varying moment method are used to analyze the annual minimum tide level (AMTL) records of Wusongkou Station and Baozhen Station on the basis of temporal change analysis. Abrupt changes are detected at 1996 and 1990 for Wusongkou Station and Baozhen Station separately. The GEV distribution with linear time-varying parameter fits best for Wusongkou Station and Baozhen Station. The AMTL series of both stations reveal a slight increasing trend. The 100-year low tide level of Wusongkou Station is approximately 0.261 meters, which is about -0.041 meters for Baozhen Station. The corresponding return period is 150 years and 119 years respectively, which indicates the existing channel standard more secure and the recalculation of design water level necessary in the Yangtze Estuary.