The researchers studied the tidal patterns in the Han River estuary in South Korea. They found that the shape of the waterways and man-made structures like dams affect how tides behave. In shallow areas, the tides change more rapidly than in deeper waters. The tidal patterns in the estuary are different from those in the open sea. The researchers discovered that the tidal form number increases significantly as you move upstream in the estuary. This means that the tides in the estuary are influenced by both natural and man-made factors.