Muddy coast

Geological terminology

The muddy coast is composed of silt Or mixed with Silty sand Is mainly composed of silt with particle size of 0.05-0.01 mm, which is mainly distributed in the input Fine particle A large river of silt Estuary coast.

Chinese name: Muddy coast
Composition: Silt or silt mixed with silt

Distribution: Along the estuary of large rivers with fine sediment input
Region: Western European Netherlands

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Coastal characteristics

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Western European Netherlands And Chinese Bohai Bay Coastal and Jiangsu The south central coast is the most famous（ Silty sand ）Muddy coast. The terrain here is flat and open, and the beach is several kilometers wide, even dozens of kilometers wide. When the tide exits, the small fish in the tide ditch Shrimp Crowds of clams, clams Marine earthworm They also keep crawling for food, just like a paradise for animals on the tidal flats. In recent years, the muddy coast along Jiangsu coast has been affected by reclamation, Tideland The width and area of.

Coastal distribution

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Coastal structure of China

The muddy coast is composed of silty sand, silt, etc Particulate matter A coast with a gentle slope. The muddy coast is rich in silt^[1] In areas with weak supply and tidal current carrying capacity, where the energy of waves passing through shoals is weakened and the tidal action is quite active, a large range of muddy shoals are developed, such as China Changjiang Estuary 、 Yellow River Estuary 、 Pearl River Mouth Northern Jiangsu Near the coast, Fujian coast, etc South America Of Suriname , Europe Netherlands Wait for the coast.

Causes

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The muddy coast of yancheng, jiangsu province

Due to most siltation Mudflat The fertile soil is often developed into a good place for beach aquaculture. The coast of Bohai Bay is rich in tender and delicious clams Xishi Tongue And other shellfish are famous at home and abroad. At the same time, the muddy beach is Sun salt The treasure land of Tanggu Saltern 、 Subei Saltern Are located in the muddy coastal area. The muddy coast is often developed with Tidal creek 。

Geomorphic morphology

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In terms of geological structure, the muddy coast is in the area of long-term subsidence, which is conducive to the accumulation of a large number of materials. As there are many rivers flowing into the sea along the coast, the sediment carried by the river estuary And coastal deposits, while pushing the coast outward. Only in a few sections, there are shell dykes composed of shell debris and sand in the muddy coast. The material composition of muddy coast is fine and the structure is loose Hydrodynamic force The change after the action is quite large, so it has the characteristics that the coast is rapidly eroded and retreated in a short period of time, or the coast is rapidly silted and expanded to the sea. The so-called hydrodynamic force here mainly refers to tidal current and waves, of which the influence of tidal current is the most important. At the same time, as the terrain changes from high to low from land to beach, the nature of tidal current action is also inconsistent, resulting in Geomorphic morphology , scouring and silting properties and ecological environment The characteristics have obvious zoning. Generally speaking, the muddy coast is divided into "high tide beach zone", "upper siltation zone"“ Washout zone ”And "lower siltation zone".

Three types

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Muddy coasts are widely distributed in China, which can be generally divided into three categories: muddy estuaries Delta Coastal and muddy Plain coast , muddy Harbour coast 。

Muddy estuary delta bank

There are many rivers flowing into the sea in China, among which the famous ones are Yellow River 、 Yangtze River 、 Pearl River , Haihe and Liaohe River Etc. The large rivers flowing into the sea have a long history, and the sediment brought from the middle and upper reaches is an important material basis for the formation of muddy estuary delta. Silty estuaries, deltas and coasts are hundreds of millions of tons of sediment brought by rivers Estuarine area It is formed by continuous accumulation. Under the condition that the river supplies abundant sediment, the muddy estuary delta grows rapidly, and the coast continues to move towards the sea. On the contrary, when the source of river material is reduced or interrupted, not only can a new muddy estuary delta not be formed, but also the outer edge of the original muddy estuary delta is scoured and eroded by waves and currents, and the coast is constantly retreating to the land. It can be seen that the relationship between the muddy estuary delta coast and the rivers entering the sea is very close.

Muddy plain coast

Rivers flowing into the sea not only create muddy estuaries and deltas, but also form an important material basis for the formation of muddy plain coasts. As far as China is concerned, the Yellow River and the Yangtze River are the two largest rivers that affect the muddy plain coast. The Yellow River flows into the sea south of Diaokou or during the period when the Yellow Sea flows into the sea the bohai sea Gulf Coast Beach surface The source of the above material is obviously reduced. Most of the coastal areas are dominated by waves Erosion Mainly, the silt is washed away, the beach surface material is coarsened, and the coast is mainly composed of silt, with a large number of Scapharca subcrenata and White clam etc. shellfish Biology. When the Yellow River enters the Bohai Sea on the coast north of Diaokou Fine particle The silt material covers the sandy and silty beach surface, causing a large number of shellfish on the beach surface to suffocate and die, and then the wave and tide shell From shallow water to High tide line Formed by accumulation nearby Shell dike 。 There are several long shell embankments along the coast of Bohai Bay, which proves that the Yellow River has entered the sea from this area many times in history. Every time the Yellow River enters the sea from here, it brings a large amount of sediment, which promotes the rapid siltation of the muddy plain coast along the Bohai Bay coast, the siltation of the beach surface, and the coastal movement to the sea.

Muddy bay coast

This kind of coast is usually in the harbor in the mountainous and hilly coastal section. Due to the tortuous coast and narrow harbor, this kind of coast is relatively small. The silt material in the bay mainly comes from the fine material brought by the rivers flowing into the bay in the land area, and also from the sediment output from the adjacent rivers. For example, the diffusion of the sediment from the Yangtze River into the sea has a certain impact on the formation and development of the muddy harbor coast in Zhejiang coast. In addition, there are also some ocean current Brought from the seabed Fine-grained material 。 Harbor internal environment It is relatively hidden. Some islands are distributed near the estuary of the harbor, acting as a barrier. The wave action of the sea outside the harbor can not affect the inside of the harbor, which is conducive to the rapid deposition of sediment in the harbor and also conducive to tidal flat The development of siltation, so that the muddy harbor coast continues to form and develop. Such as Zhejiang Huangyan Pingyuan Toutang was built in the early Qing Dynasty, New China was founded Six ponds were built before, and nine ponds were built after the founding of New China, which is a favorable place for reclamation.

Geomorphic significance

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The muddy coast is flat, with a large area of lowland Mudflat It is not only convenient to introduce seawater, but also not easy to make brine seep down. It is a very favorable place to open up a salt field; North China There is little rain, and the sunshine lasts for a long time. Use windmill to carry brine, sun or boil to evaporate water, and you can get a lot of white sea salt 。 Many areas of muddy coast in China have been opened up as salt fields. Salterns are mostly built on the coastal low-lying mudflats behind the high tide line. The great plain behind the salt farm is mostly low-lying and saline wasteland. If there are rivers passing by nearby, fresh water can be introduced for irrigation, so that the desolate saline alkali beaches can become fertile fields. Famous Tianjin“ Xiaozhan rice "It is produced on artificially transformed saline soil.

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