Seasonal changes in the Qiantang Estuary in China affect the interaction between the river and tides. The study looked at how the river's flow and the estuary's shape impact water levels. They found that river floods can double the tidal range in the upper estuary, but this decreases as sediment builds up. The estuary's shape changes over time, affecting tidal dynamics. The relationship between water levels and tidal range varies depending on the season and river flow.