Tidal ats are classi ed into mud ats, sand ats, or mixed ats, depending on surface sedimentary facies. They can also be categorized according to geomorphological features as follows: open, which are strongly affected by tidal currents and waves; estuarine, located along the coast with large rivers owing into them; and bay, which are rarely affect- ed by waves due to their narrow mouths.

The Gyeonggi-man tidal at and the Taean tidal flat are mixed flats, where certain areas are com- posed largely of mud and sand. The Suncheon-man and Yeoja-man tidal flats include vast coastal wetlands and a variety of vegetation, and the Nak- donggang tidal at has a near-shore sand ridge due to the active in ow of sediment from the Nakdong- gang River.

Estuaries are ecological transition zones where freshwater and seawater meet. Although they are