Formation and Change Trend of Large Flood in the Lower Tidal Reach of the Yangtze River

Hydrological factors of formation of large flood in the lower tidal reach of the Yangtze River are analyzed,and change trend of large flood is revealed.Obtained conclusions are:(1) Formation of large flood in the river reach is very complex; (2) Occurrence frequency of large flood in the river reach has been increasing since 1900; (3) The mean value of the peak stage has been rising since 1975; and (4) Above the charct eristics of occurrence of large flood in the river reach are primarily affected by human activity and rise of sea level.