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
home to the highest productivity on the planet, their ecosystem is increasingly impaired due to various development ventures. In response, Korea has been carrying out surveys of the current eco- system status of national estuaries with high bio- logical diversity and superior ecological functions. These surveys have been effective in the designa- tion of the estuaries as Ecosystem Conservation Areas or Wetland Protection Areas. From 2004 to 2014, the Ministry of Environment completed a detailed investigation for 28 main estuaries (such as the Hangang estuary and Tamjingang) through the 1st Intensive Survey on Estuarine Ecosystems. Currently, the National Wetland Center of Korea is in the process of conducting detailed and basic investigations for the other estuaries as well.