Fan Delta vs. Estuary Delta? Difference Between Fan Delta and Braided River Delta and Delta

Both deltas and impact fans can be classified as alluvial plains.

Delta plain refers to the plain formed by the development of deltas. When a river is injected into the ocean or a large lake, the flow velocity decreases due to the slower slope, and the change of dynamic conditions such as the tidal support causes a large amount of sediment to be deposited in the river. Initially deposited under the surface of the water, it gradually accumulated due to the continuous supply of sediment, and finally came out of the water, where the sediment formed a triangular plain with the tip facing the land, which was named Delta.

This kind of delta that is dehydrated into land and advanced to the sea area gradually develops into delta plains, such as the Yangtze River Delta Plain. If a large river flows into the lake, a large amount of sediment can also accumulate into a lakeshore delta, such as the Dongting Lake Delta.

Alluvial fan plain: refers to the alluvial plain spread in a fan-shaped shape. Alluvial fans are not formed at the point where the river enters the sea or lake, but forms a fan-shaped accumulation landform at the outlet of a mountain river.

When the mountain river enters the open and flat area from the outlet of the foothill, due to the slowing slope of the riverbed, the flow velocity decreases, the water flow flows outward in a radial shape, the carrying capacity is weakened, and the detritus material is piled up, forming a fan-shaped alluvial pile that is narrow at the top and wide at the bottom, which looks like a fan, and is called an alluvial fan. Its top is facing the mountain pass, the outer edge is semicircular, from the top of the fan to the fan edge, the ground gradually decreases, the slope becomes smaller, the accumulation gradually becomes finer, and the sorting gradually improves, such as the alluvial fan at the foot of the Taihang Mountains.

Fan Delta and Estuary Delta are two beautiful places in China, and they are also very interesting places you said.

Fan Delta. The similarity with river deltas is that they are both located on land and sea.

Transition zone with a three-layer structure. The sand body at the front edge of the fan delta is modified by the wave sakura fiber, which indicates that it is located in the shallow water zone above the wave base, and most of the vertical sequences are anti-cyclical, and the bedding structure shows that it has the nature of traction flow, so it can also be considered that the fan-positive delta belongs to the delta category, but the front edge of the fan delta is poorly developed. There are also scholars who use coastal alluvial fans.

(Mial, 1983). Wu Zhengyun (1993) divides fan deltas into two types: backing type, that is, the fan delta is close to the root of the mountain.

The fan delta plain is the alluvial fan, and the outlet of the stream in the sector is the sea (lake), and the alluvial fan directly enters the water; By the fan type, that is, the fan delta formed by the water flowing into the lake at the end of the alluvial fan, and the top of the fan delta plain is by the alluvial fan. The differences between fan deltas (braided river deltas) and fluvial deltas are mainly reflected in the following aspects.

The topography of the fan delta (braided river delta) is a large slope from the estuary area of the long river delta to the meandering plain, and the slope is on the left and right, such as the Yangtze River Delta in China. The river slope (or fan slope) of the fan delta is generally several times to dozens of times that of the river delta, such as the southeast coast of Jamaica and Alaska.

The southeast coast is Erhai Lake, Yunnan Province, China.

Yangxi and other modern fan deltas are, Liao River.

The fan delta of the Tertiary in the lower rift valley is.

Adjacent sedimentary facies in the landward direction of the river delta The landward direction of the river delta is adjacent to the meandering river, the source is remote, the bank has a long gentle slope from the foothill to the lake shore, or the river comes from outside the basin. Braided river deltas (short river deltas) are adjacent to braided rivers to the landside, with shorter bank slopes and increased slopes. The landward side of the fan delta is an alluvial fan or source old mountain, and the shore slope is shorter and steeper, and even the water body reaches the root of the mountain.

Sand lithology The lithology of the river delta is fine, and the sedimentation of the delta ridge and flow plain resembles a meandering river or a reticulated river, but the detrital grain is slightly fine, mainly sand, and contains a small amount of gravel.

The subfacies of the delta front is dominated by fine sand and silt. The lithology of the fan delta sediment is coarse, and the sediment of the fan delta plain resembles a braided river, or even an alluvial fan, with a high gravel content. The subfacies sediments at the leading edge are also coarse, which can contain coarse sand and gravel, and the underwater channel is more developed, and the estuarine sand bar is poorly developed due to the usually unstable river channel.

Morphology and distribution of sand bodies The sand bodies in the river delta are large and few, often developed separately or a few adjacently, and distributed on the side of the minor axis gentle slope of the long axis or near the long axis of the lake basin. In the longitudinal section, it is a large lens, extending farther into the lake. The individuals of the fan delta are small and numerous, often appear in groups, and are distributed along the side of the short axis and steep slope of the lake basin. It is a thick, short wedge in the longitudinal section, which quickly sharpens in the direction of the lake.

Braided river deltas may be developed on the long axis of the faulted lake basin or on the gentle slope side of the short axis, and its lithology, morphology and distribution are between the river delta and the fan delta. The steep side of the short axis generally undergoes the evolution process from a mountain-type fan delta to a fan-shaped fan delta, and the growth of the bank slope slows down, and it will also evolve into a braided river delta.

An estuarine delta refers to a fan-shaped alluvial plain in the estuarine section.

When it flows into the sea, due to the decrease in the flow velocity, a large amount of sediment is carried by sedimentation, which extends in the estuary section, reclaiming the land, and gradually forming a fan-like accumulation during flooding.

From the perspective of the dynamic characteristics of the estuary area, within the range of the tidal boundary, the river is supported by the tidal current, and the flow velocity is small, which is most likely to form the heart beach and the river center island, which makes the river bifurcate. At the mouth of the estuary, due to the diffusion of the current, the flow rate slows down, and the sediment often accumulates into shallows, blocking the estuary.

Special circumstances

Of course, there are also rivers whose estuaries do not form deltas. For example, there is no delta at the mouth of the Qiantang River in China. This is because the sediment content in the Qiantang River is scarce, and the estuary is a very wide trumpet-shaped estuary, and the huge scouring force of the rising tide makes the sediment unable to be deposited, even if some sediment is lucky to stay.

Piled up at the mouth of the Qiantang River, it is also difficult to increase the height, and can only form an underwater sand barrier under the water surface, which cannot form a delta that is exposed to the water surface.

In addition, contrary to the delta formation process, the amount of sediment coming from the river is small, and the estuary is strongly scoured by the current, and there is no delta formation, and it is often trumpet-shaped, and this kind of estuary is called a triangle port or triangle bay.

For example, Hangzhou Bay is a typical triangular port. The Qiantang River carries less sediment, the estuary coast falls, and the tidal range is large, which not only makes the sediment carried by the river unable to accumulate in the estuary, but also causes a strong erosion, deepens and widens the estuary, and gradually forms a triangular port.

What is the difference between an estuarine delta and a tidal flat?

An estuarine delta refers to a fan-shaped alluvial plain in the estuarine section. When the river enters the sea, due to the decrease in the flow velocity, a large amount of sediment carried by it is silted up and extended in the estuary section, and the land is reclaimed from the sea.

Tidal flat is a general term for beaches, river beaches and lake beaches, which refers to the tidal flooding zone between the coastal high tide level and the low tide level, the beach between the normal water level of rivers and lakes and the flood level, the beach area below the flood level of seasonal lakes and rivers, and the beach area between the normal water storage level and the maximum flood level of reservoirs and ponds. Nowadays, tidal flats generally refer to mudflats along the beach.

1. The position of formation is different. The estuarine delta is at the mouth of the river, and the tidal flats appear on the banks of rivers and lakes.

2. The contour shape is different. The main part of the delta is located high above the water, forming a plain where the tidal flats are submerged at high water levels.

3. Different uses. Planting is mostly developed in the estuarine delta, and the tidal flats are mainly aquaculture.

How is an estuarine delta formed?

An estuarine delta refers to a fan-shaped alluvial plain in the estuarine section. When the river enters the sea, due to the decrease in the flow velocity, a large amount of sediment carried by it is silted up and extended in the estuary section, and the land is reclaimed from the sea. The small self-broadcast has this ** introduction.

What is the formation of estuarine deltas.

Sediment deposition is formed by flowing water.

It is formed by the combined action of flowing water and the deflection force of the earth.

It's a long-term process.

What is the largest estuarine delta in China.

Yangtze River Delta.

The estuarine delta is divided according to its genesis and what landform it belongs to.

The sand, gravel and soil brought by the Nile River eventually formed a delta at the mouth of the Rihai Sea, as was the case on Chongming Island.

The formation process of the estuarine delta is as follows:

The estuarine delta is the river at the mouth of the sea or at the mouth of the river, because the terrain is flat and the flow rate is slow, so the sediment carried in the river water, a large amount of sediment, a large amount of sediment is deposited, and the river water also obtains the top of the seawater, therefore, the river water compromises a large amount of sediment to form a land.

The location of the estuary should be low and flat, the flow speed of the river channel is slow, the sediment-carrying capacity of the river channel is weakened, and the sediment accumulation forms a delta, so the delta is usually low and flat.

Causes of estuarine delta formation.

Estuarine deltas are sedimentary systems fed by rivers, which are the products of the interaction of "dynamics-sedimentation-geomorphology" and other factors, and are distributed in areas where rivers flow into oceans or lakes. Its planar shape is mostly triangular, with the top pointing upstream and the bottom facing the open sea. It is composed of two parts: onshore and underwater.

The basic conditions for the formation of estuarine deltas mainly depend on the basic laws of water flow changes in the estuarine area. Therefore, factors such as rivers, marine tectonics, climate, and natural geography of the basin all profoundly affect the sedimentary characteristics and morphological types of deltas to varying degrees. According to the different geomorphological parts, from the continent to the sea, the delta is generally divided into the top layer, the prelayer and the bottom layer.

Estuarine deltas are a common surface topography. Delta, or estuarine alluvial plain, is a common surface topography. An estuary is the terminus of a river, where it flows into an ocean, lake, or other river.

An endorheic river that does not flow into a lake is called a tailless river and can have no estuary. At the estuary, the cross-section expands, the water flow rate decreases sharply, and a large amount of sediment is deposited to form a triangular sandbar, which is called a delta. The top of the delta points upstream of the river, and the outer edge faces the sea, which can be seen as the "bottom edge" of the triangle.

Geographical features:A delta is an alluvial plain that gradually develops into an alluvial plain when a river flows into an ocean, lake or other river due to the decrease in the flow velocity, and the sediment it carries is deposited. The delta formed by the confluence of lakes and rivers is also called the inland river delta.

However, there are some rivers that directly alluvial deltas on land and do not flow into other water systems, such deltas are called inland deltas, which are a type of inland river deltas.

The above content reference: Encyclopedia - Estuary Delta.

Reasons for the formation of estuarine deltas.

Soil erosion in the middle and upper reaches carries a large amount of sediment, and the river channel widens and the slope tends to be gentle at the estuary, coupled with the jacking effect of seawater, the river flow slows down, and the sediment is deposited at the estuary, forming a delta.

Soil erosion in the middle and upper reaches, sediment deposition due to slowing down in the downstream, sedimentation, and flowing water deposits.