Seasonal climate affects the shape of the mouth-bar in the Yangtze Estuary, China. Wind-waves play a big role in shaping the mouth-bar outside the river mouth. River flow affects the area inside the mouth. Tides and waves reshape the shallow areas, while deep channels erode the mouth-bar. Shallow shoals are stable in summer but erode in winter. Deep channels export sediment all year. Understanding these processes is important for managing coastal areas.