Southwestern Coast Tidal Flats

Description

Coordinates:

Suncheon Tidal Flats N34 52 55 E127 30 48

Muan Tidal Flats N34 58 15 E126 22 37

Buan Tidal Flats N35 43 35 E126 36 16

Boseong Tidal Flats N34 49 48 E127 22 41

Sinan Tidal Flats N34 49 31 E126 07 10

The Tidal Flats on the southwest coast of Korea, distributed in Gomso Bay, Yeoja Bay, and Hamhae Bay (seashores) and the Sinan archipelagos, are unique macrotidal flats where typical embayed tidal flats turn into open-coast tidal flats during the monsoons. They have no barrier islands like other tidal flats in the Yellow Sea. During winter, strong waves create sand flats, while in summer, the mud flats expand as tidal currents overpower the waves. The seasonal change is very clear along the coastlines. Although mud flats that develop in embayed tidal flats are found year-round in the area, monsoons transform the mud flats into sand flats, giving rise to open-coast sand flats on this site. During the course of the year, they shift from mud flats to mixed flats to sand flats. This distinctive feature of Korean tidal flats on the southwest coast has attracted global attention.

The tidal flats on the southwest coast of Korea were created when sediment began to accumulate along the coastline, beginning 7,000 years ago when the Yellow Sea began to level out, ending the rapid rise of the sea level from 20,000 years ago. On the outer parts of the tidal flats, cheniers formed and gradually moved to the seashore. The onshore sand flats possess well-developed sand dunes, and windbreak forests are distributed to protect land under cultivation. Because salterns and rice paddies lay behind the windbreak forests, people have naturally tried to protect pine forests and expand these windbreaks. Their efforts have contributed to preserving the Korean tidal flats.

The tidal flats in the southwest of Korea also serve as a stopover for migratory birds flying to Siberia on the East Asia Flyway. The birds feed in the tidal flats and stockpile the energy needed to fly great distances. Annually, about 1 million birds of 300 species stop by this site.

In addition, a variety of life forms are found in the southwest tidal flats. It is home to some 150 species of macrobenthos, and the once damaged colonies of halophytes are thriving on the land today. Diverse wild plants and animals live on the islands. Also located in this tidal flats area, Korea's largest salterns produce vast amount of salt.

Justification de la Valeur Universelle Exceptionelle

(vii) contain superlative natural phenomena or areas of exceptional natural beauty and aesthetic importance

The tidal flats (intertidal flat zone), surrounded by mountains, are typical Korean tidal flats that usually develop along the transgressed coast. When looking toward the land from the tidal flats, the landscape resembles mountains rising from a basin or a desert. On the tidal flats in the archipelagos, sand, mixed, and mud flats are distributed in all directions depending on the geographical properties of the coast and the direction of the wind. Although the site is a macrotidal coast, the flat zones are relatively narrow due to the steep and rocky coastline. However, there are also kilometers-long tidal flat zones where severe erosive transgression has created bays. The tidal flats in the southwest of Korea exhibit the unique natural beauty and distinctive features that distinguish Korean tidal flats from those of the Wadden Sea(Germany / the Netherlands / Denmark), the United States, and China.

(viii) be outstanding examples representing major stages of earth's history, including the record of life, significant on-going geological processes in the development of landforms, or significant geomorphic or physiographic features; and

(ix) be outstanding examples representing significant on-going ecological and biological processes in the evolution and development of terrestrial, fresh water, coastal and marine ecosystems and communities of plants and animals

The history of the tidal flats began in the Cretaceous Period when ash and sediments from volcanic eruptions accumulated in one place. From the Miocene Epoch, the mountain-like region began to erode, and the resulting gorges were filled with water as the sea level rose, beginning 20,000 years ago. Finally, about 7,000 years ago, the current seashore was formed and the tidal flat zone was created by tides. The emergence of Korean tidal flats in the southwest is distinctive from other tidal flats in the Wadden Sea and North America, which developed in gentle and even coastal areas under different geographical conditions. Unlike Europe, the Korean tidal flats in the southwest were formed without small variations in the sea level.

Déclarations d’authenticité et/ou d’intégrité

The southwest coast tidal flats of Korea include all types of intertidal flats, which have no barrier islands: open-coast tidal flats, embayed tidal flats, and estuarine tidal flats. Due to the surrounding mountains, they are not usually connected to rice paddies on the land. As a result, the southwest tidal flats have less reclaimed areas than well-developed others around the world. Still, the sites are outstanding in terms of their large scale and diversity of tidal flats, as the only tidal flats of its kind around the globe.

Comparaison avec d’autres biens similaires

The Yellow Sea of Korea is a typical epicontinental sea, taking on the overall shape of a gulf. The water is very shallow with a maximum depth of only 90 meters and gentle slopes. It was created by the rising sea level during the Holocene, and its transgression basin, which is spread over the entire area, is valued not merely for its tectonic features but as it is the world's only large marine basin developed by transgression. In addition, the components of terrigenous origin that flow into the Yellow Sea boast the world's largest volume, playing an important role in controlling the sea's overall marine ecosystem. Historically, the Yellow Sea has experienced a longer period of human activity than the northern shores of the Mediterranean Sea.

Although broad intertidal flat zones are distributed on both shores of the Yellow Sea, the tidal range is different between the two coasts. While the Korean shore to the west has a macrotidal setting with 4 to 10 meters of tidal ranges, the Chinese shore belongs to a mesotidal setting whose range only extends 2 to 4 meters. In terms of the scale of tidal flats and ecological diversity, the Korean shore stands high above its Chinese counterpart. In addition, in most Chinese sites, fine-grained tidal flats formed due to the great influx of fine suspended sediment from the Yellow River and the Yangtze River as a representative delta tidal flat.

The majority of the world's tidal flats are developed in 1) an area linked to a river or its neighboring delta (e.g. the Yangtze river delta in China, Kakadu Park in Australia, and Sundabans mangrove forest in Bangladesh), 2) the inner part of a bay (e.g. The Wash in Great Britain), 3) an area surrounded by mountains (e.g. Gros Morne National Park in Canada), 4) a quiet lagoon having no waves due to barrier islands (e.g. East Coast of USA), or 5) an inland sea where sand tidal flats formed under the high influence of waves despite the presence of barrier islands (e.g. Wadden Sea in Germany, the Netherlands, and Denmark). But the intertidal flats in the west coast of Korea are significantly different geographically and geologically from the other sites. In addition, while the Chinese tidal flats along the coasts of the Yellow Sea are mostly mud flats that are related to big estuaries and deltas, the Korean sites have been highly affected by the correlation between the tides and waves,  creating sand, mixed, and mud flats together along the coastlines in various scales and shapes. The Korean Tidal Flats are similar to those in the Wadden Sea in terms of their development scales and function as a migratory flyway, but the two are considerably different when it comes to the geography, geology, habitats, and ecological history accompanied by human activity. In contrast to those in the Wadden Sea, the U.S., and China, high mountains are distributed in the hinterlands of the Korean tidal flats, whose shores are mostly rocky. Unlike the Wadden Sea and the east coast of the U.S., no barrier land has developed on the Korean western shore, which means no windbreaks to block waves from coming into the tidal flats. Moreover, the fact that the tidal flats are widely spread despite the lack of salt marshes makes the seashore more important as a site distinct from others around the globe.

The western tidal flats are directly influenced by monsoons from the south and southeast in summer and from the north and northwest in winter due to the absence of barrier islands. That is, the tidal flats are exposed to the wind from the outer sea and heavily affected by waves in winter, while weak waves generated by weak winds, mostly blocked by the land, promote the accumulation of sediment with growing influence of tidal currents during summer. These features are reflected in the tidal sediment and its evolution. Fine mud builds up in the zone during summer, but erodes in winter, transforming the zones into sand tidal flats. Furthermore, the coarsening upward sequences get underway as the sea level elevates, and the arenaceous stratums are mainly comprised of sediment formed by windstorms during winter. Such are the unique features of the Korean tidal flats as a rare and representative type of intertidal flat zones around the world.

The tidal flats in Jeollabuk-do province and Gomso Bay, Yeoja Bay, and Hamhae Bay in Jellanam-do province are typical macrotidal flats, whose tidal range is 6.8 meters. The sites have open-coast tidal flats, embayed tidal flats, and estuarine tidal flats that are typical of Korea's west coast. The outer tidal flats in the areas are open-coast tidal flats, consisting of sand tidal flats only. They feature distinctive seasonal change, depending on waves and tides. In the upper parts of the outer tidal flats, cheniers are formed and move medium-grained sand to the coastline in strong wind, resulting in the expansion of sand tidal flats on the seashore. This proves that the border lines of open-coast sand tidal flats move into the inner part of bays along with the rise in sea level. Meanwhile, in the mid-tidal flat zones, the offshoreward-coarsening process gradually creates embayed tidal flats that consist of permanent mud, mixed, and sand flats from the upper to lower parts. Near the coastlines of this mid-tidal flat zone, small estuarine tidal flats are formed. The inner part of tidal flats typically develops semi-enclosed mud flats, and Sueda japonica is dominant as a halophyte living on the west coast of Korea.

The southwest and south coasts of Korea are archipelagos that were originally mountain areas before being transgressed. The mountain ranges were created by weathering and erosion during the Miocene Epoch on the deposit massifs and granite massifs of the Cretaceous Period, granites of the Jurassic Period, and amorphic sedimentary rocks of the Paleozoic Era and the Precambrian time. The region has been tectonically stabilized since the Cretaceous Period, and the tectonic history of the coasts is different from other archipelagos (e.g. Western coast of Canada, Coast of Croatia). The mountains had gentle slopes and valleys before transgression, similar to those discovered on the mainland of Korea at present. Based on this topographical feature, the Holocene transgression caused by the rising sea level on the broad continental shelf created the unique coastlines of archipelagos and tidal flats. The tidal flats in Sinan located at the southeastern part of the Yellow Sea are representative of the archipelago-type tidal flats of the Yellow Sea.

The archipelago tidal flats in Sinan, Jellanam-do province, range from 3.8 to 5 meters as a typical macrotidal tidal flats. As tidal flats created in archipelagos possessing the characteristics of the coastal topography of the Korean southwest region, their widths are narrow compared to those on the land. But along the coastlines of the islands, various types of tidal flats develop depending on their geographical properties and directions. In the western and northwestern parts in the islands,  the typical open-coast tidal flats of the Korean sea in the west are common, while on the eastern and southern shores and the areas between islands, extremely fine-grained mud flats develop. The open-coast sand tidal flats share the types of sediment distribution and evolution with those on shore. The mud flats that developed in the inner parts and near tidal waterways transitioned to semi-enclosed mud flats. The Sinan archipelago looks similar to Halong Bay in Vietnam, but the two are actually very different as the Sinan tidal flats have developed along the islands' rocky coasts. Their geographic, sedimentary, and ecological characteristics are distinct from others around the globe. Along with the properties of an archipelago-type macrotidal flat, the tidal flats's location on uninhabited islands where the natural ecosystem is well preserved make the Sinan archipelago-type tidal flats highly valuable in terms of its unique characteristics and scales compared to other sites.