The river delta is the lowland, which is located at the mouth of the river, where it flows into the ocean or another reservoir. Delta plays an important role for both people and fish, or other animals. They tend to contain very fertile soils, and also support a wide variety of flora.
See also: What is the estuary?
Before considering the Delta, it is important to know the definition of the concept of "river". Rivers are natural aquatic streams that usually flow from an elevation and fall into the ocean, the sea, a lake or another river. Most rivers are formed from surface effluents as a result of precipitation, ice melting and snow.
The delta is formed in the mouth, where the river puts onto it the main sedimentary load and flows into the reservoir with slowly moving or standing water. This usually happens when the river is connected to the sea, the estuary, the ocean, the lake, the reservoir, or in rare cases - a slowerly moving river. River delta are usually very fertile areas. Therefore, some of the most densely populated cities were formed near River Delta. Examples of the largest Delta of the world are the River Delta in Egypt and Delta of the Ganges River in Bengal.
Formation of river delt
River Delta / National Oceanic and Atmospheric Research (NOAA)
There are several factors thanks to which the river forms a delta. First of all, the river must carry enough sedimentary rocks to deposition in the mouth to form a delta. Secondly, the tidal flows of the river must be weak so that it does not tolerate the precipitation in the reservoir in which it flows. Thirdly, the river must flush in a reservoir with standing water, or slow the flow to prevent the fastest aluminum outflow from the mouth.
When the river enters its last phase before connecting with another reservoir, as a rule, it is no longer limited to one channel, and its water applies. The propagation of the river reduces its speed, and this, in turn, reduces the ability to transfer a large number of deposits. Consequently, these deposits are deposited on the rods and banks of the rivers. As precipitation accumulated, heavy deposits prevent the flow of water. Thus, the river branches and forms the sleeves. All the sleeves continue to flow down to the water, in which the river merges its waters. Ultimately, a fan-shaped river delta is formed with various sleeves and land plots.
Delta is very diverse and differ in size, structure, composition and origin due to factors such as climate, geology, and tidal processes.
The world's largest river delta
Delta Ganges Brahmaputra / Wikipedia
Delta Ganges-Brahmaputra is considered the largest delta in the world. She falls into the Bengal Bay and is located on the territory of Bangladesh, and India. This delta covers an area of more than 105,000 km².
From 125 to 143 million people live in the Delta area, despite the risks associated with floods caused by monscons, strong drains from the melting of snow in the Himalayas and the tropical cyclones of the northern part of the Indian Ocean.
It is believed that more than 300 million people are supported by Delta Ganges-Brahmaputra, and about 400 million people live in the Gang River basin, which makes it the most densely populated river pool in the world.
Roll of River Delta for Man
River delta were important for people for thousands of years due to their extremely fertile soils. Today, delta are important, as they are the source of sand and gravel. These sedimentary rocks are very valuable and used in the construction of motorways, buildings and other infrastructure. In many regions of the world, delta play an important role for agriculture. For example, the Delta of the Sacramento-San Hoakin rivers in California is one of the most productive agricultural regions of the state.
Biodiversity and Delta value
Mississippi Delta, USA - Wikimedia
In addition to human needs, river delta are among the most biodiversity areas on the planet. They are necessary to preserve the habitat of many species of plants, animals, insects and fish living in them.
There are many different types of rare, under threat to the disappearance of species inhabiting in delta and wetlands. Every winter of the Mississippi River Delta is a house for five million ducks and other waterfowl.
In addition to biodiversity, delta and wetlands can serve as a buffer for hurricanes. For example, the Mississippi River delta is able to act as a barrier and reduces the impact of potentially strong hurricanes in the Gulf of Mexico. The presence of an open land can weaken the storm before it reaches in densely populated areas, such as New Orleans.
Delta ecosystems change significantly as a result of human activity, such as creating dams and hydroelectric power plants. Dams affect the natural flow of rivers and the speed of sedimentation in the delta. Then the lower amounts of precipitation reach the delta, which leads to its gradual erosion. Some of the most affected Delta of the world include the Nile Delta and the Colorado River Delta.
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Delta is an area where the river flows into the sea or the lake, branched on the set of ducts. Once, the ancient Greek farmers noticed that the mouth of the Nile in the form resembles the Delta's capital letter, fourth in their alphabet. It was depicted in the form of an extended an-free triangle. Greeks, and for them and the Romans began to call this area of Egypt, too, Delta. After a century, this term has consolidated for the river guests of this type.
Why is it like this?
The fact that Delta is lowland is not surprising. It is clear that the place of failure should be a reduced section of the bed, otherwise the river will simply won't flow here. But why does this site resemble a triangle? How is the labyrinth duct?
The river always carries hard particles, and sometimes there are a lot of them. Some are deposited on the way, other water comes to the flat plain of the mouth. From year to year without stopping, all this good spreads and settles. The level of the plain increases, it slows down the current and causes the stream to spread more wider. In the end, precipitation becomes so much that the flow is unable to maintain its integrity. It is broken down on the sleeves, which, one, make their way to the sea. In the Volga Delta up to 500 sleeves, some can be considered small rivers.
If the river is full and rich in precipitates, the delta can be huge. At the Siberian Lena, it takes 45.5 thousand km², it could be placed a small state with Denmark's size!
Part of the sediment is taken out into the sea and the fan falls on the bottom. Waves, tides and flows, hooking and a water sagon dispel the river brought. If the sea is especially "trying", the outlines of the coast in this place are practically not changed. The base of the "triangle" remains quite direct. But often the sea area is calm (for example, this is a shallow bay). It does not cope with what carries and carries the mighty river. Then the inclined stranded is formed near the mouth. It grows on the sides and up, and then rises above the water. At first, it may be small islands. Then they are connected to one array. The delta grieves towards the sea, loses the classic contours of the Greek letter and becomes like a fan. Dance Dance takes 11 meters per year by the sea.
Often along the edges of the delta, where the ducts fall, small, but growing braids are formed. Then the delta reminds the bird paw with hopping fingers. "Fingers" of large sleeves of the Mississippi delta (USA) are lengthened for a year by 15 meters.
Delta and man
The huge clusters of the alley, which centuries are deposited in the delta, make these land extremely fertile. In the delices of large rivers, the largest cities and whole civilizations arose - for example, ancient Egypt in the Nile Delta. In the world's largest Delta Ganga now lives over 145 million people!
True, grandiose floods happen in the same delta. First, due to the fact that the ducts can no longer break through the thickness of the precipitation and are forced to look for new channels. A, secondly, because in the mouths of Réka, collecting the water of all the tributaries, the most centuries.
Delta is convenient for the construction of ports. On this "crossroads", cargo delivered by the river can be overloaded for transportation by the sea. Market shipping goes up on the river. In the River delta, the world's largest ports are Rotterdam, Hamburg, Vancouver, St. Petersburg, Alexandria, Osaka.
In the delta, lace is often formed by lace and thick thickets (smooth) - a real paradise for fish, birds and other animals. Here people hunt, catch fish, rest. Delta Danube, where tens of rare and endangered species live, declared the UNESCO World Natural Heritage Site, an international biosphere reserve "Delta Danube" was organized here. Ancient delta places where the course has once sorted and laid huge sand and gravel reserves. Careers arrange here and produce these materials.
The irrational human activity is the construction of hydropower plants and irrigation systems, the creation of reservoirs, the disintegration of the rival land, the discharge of wastewater - destroy the delta ecosystems. Now, no one thousand years old mans that they give him. It is time to realize that these resources are not infinite.
What is a river, knows every person. This is a reservoir that originates, as a rule, in the mountains or on the hills and, having done a way from tens to hundreds of kilometers long, flows into the reservoir, lake or sea. That part of the river, which departs from the main channel, is called a sleeve. A plot with a rapid flow running around the mountain slopes is the threshold. So what is the river? What components can be divided into it? Let's consider in more detail what we mean by such a simple and usual word as a "river".
What is the river?
The first fundamental knowledge of living and inanimate nature we get at school in the lessons of the surrounding world. Pupils get acquainted with such concepts as a stream, river, lake, sea, ocean, and so on. Naturally, the teacher cannot but tell about what parts of the river are. Grade 2 is too early to remember the many terms and concepts. Therefore, children seek help to parents. And, I must say, put them in a dead end. Because adults often can not answer such simple questions. So, not everyone can explain what the Delta of the river differs from the river, or how old people are formed. Or here is another example - what is the valley of the river? Let's reassure all these concepts.
The river is a permanent water stream. In the arid regions of the Earth, for example, in Africa and Australia, it can temporarily disar. Feed rivers with snow, underground, rain and glacier waters. This natural reservoir has centuries developed by its runaway. And the relationship between the climate and the river is very clear. And it is easy to trace. The flow mode depends on the climate: it is far from the same in different high-altitude, latitudinal and long-term zones.
The characteristic of the water resource under consideration is also directly dependent on the terrain and from the area in which it is located. The River Map shows that they can pass through the plains, descend on the mountain slopes. They can be discovered even underground. Plain rivers flow on flat wide territories. Here they prevail the blurred shores, that is, side erosion. The slopes of the podium reservoir, the channel, as a rule, winding, the flow is weakly pronounced. Very other characteristics of mountain rivers. Their channel is very narrow and stony. The valleys are weakly designed, with steep shores. Usually such water artery is not deep, but the speed of their flow is huge.
Also distinguish lake rivers. They can either flow out of the lakes, or lay the path through them. Such objects are characterized by a higher drain into the interlene. In the lake rivers a long period of flood. As a rule, they are not too long. Some other swamp rivers. They meet, of course, less often. They have a more stretched flood, there are frequent floods due to the characteristic flat terrain, where the channel passes, which is constantly slowly replenished with water from the swamp.
Karst rivers deserve special attention. They feed almost always from groundwater, which fill the so-called karst emptiness. Stocks in these rivers have increased.
The source of the river
The beginning of the river is called the source. This is the place where the constant channel is formed. The source may be different: stream, lake, swamp. The beginning of the big rivers often give some smaller reservoirs. At the same time, the source will be the place of their merge. For example, the beginning of the river Ob gives the Water Katun and Bii. Mountain rivers are almost always formed from the merger of a set of streams. Well, the plains start their way from the lake. It is worth remembering that the geography of each reservoir is individual. And the source of each river is also unique in its own way.
Before disassembled the names of the river parts, you need to stop at such a term as the "River Valley". If we speak scientific language, we are talking about the elongated depressions created by watercourses. They have a certain bias towards the flow. All parameters of the river valleys (width, depth and complexity of the structure) are completely dependent on the degree of power of the watercourse. Values also have the duration of its existence, the nature of the surrounding relief. The stability of rocks and the degree of tectonic activity of the area is taken into account.
All river valleys have a flat bottom and slopes. But, again, their characteristic depends on the relief of the territory. Mountain rivers are distinguished by steep slopes. They are deeper than the plain. At the same time, the valleys are not wide, but narrow. Often they have a stepped bottom. The plain valleys are completely different. They consist of an outstanding floodplain and beds. Young valleys are characterized by climbing slopes, and more ancient have stepped banks. Such slopes are called terraces. The older river, the speeds of the shores more and wider.
Young rivers do not have the terraces. Even the floodplains is not found everywhere. The bottom of such water bodies is trough, it is often due to the fact that the glacier once passed on this territory. But there are exceptions.
The main parts of the river-channel and floodplains are formed in different ways. In the militia to rapid erosion, they are much wider than in crystalline soils. Also, the main feature of the river valleys is that they are always gradually expanding to the mouths. Their slopes become stronger, and the terraces are expanded.
There are river valleys and special practical importance. This is the most convenient place to erect settlements. As a rule, there are cities and towns on the terraces, and the floodplains serve as excellent lands under the pastures.
If you translate literally, the "floodplain" is what water floods. And it is absolutely correct definition. This is part of the river valley, which during flood and floods completely pours with water. The floodplains has its own unique landscape. Often it is divided into two levels. Lower floodplains flooded regularly, from year to year. The upper part is only in those years when there is a high level of water.
Each flood leaves his imprint on the floodplain of the river. It blurs the surface soils, creates wins and forms old men. Every year, sand, pebbles and loams remain on the surface of the Earth. This leads to an increase in the flood level. At the same time, the process of deepening the bed is underway. Over time, low floods turns high, the insertion terraces are formed. They have a stepped character. The floodplains has coastal cliffs height in several meters. Often, it is formed by wins and old men.
At the plain rivers floodplains are wide. For example, the obi width reaches 30 kilometers, and in some areas more. Mountain rivers with the flooding territories cannot boast. Such sites are found only by scraps, and they can be found on the one hand, then on the other.
The value of floodplain lands is great. Such valuable areas are used as pastures and hayed meadows. The floodplain of almost any large river in the steppes, forest-steppe or taiga zone is a steady territory for the development of animal husbandry.
The lowest part of the river, or rather the valley, is called the river. It is formed by a continuous aqueous stream. It constantly moves the stock and most of the bottom nansions. Rouch, as a rule, has many branches. It is rarely straight, except for mountain rivers.
The channel, as it approaches the mouth, forms a lot of ducts and sleeves. Especially a lot of them in the delta. The duct in the floodplain of the river is formed during the periods of the flood, but in the summer hot months it can dry. Sleeves of plain rivers have a winding relief. They are noted by movable accumulations of fine-lumpy nans. The mountain rivers the ducts are formulated extremely rare, and the sleeves are more straight. Often you can meet the areas of thresholds and various heights of waterfalls. They can be cluttered with pebble and large boulders. Plesa - deep plots of sleeves - alternate with ruling. Often such transitions are marked in lower reaches. The width of the sleeves in full-water rivers, for example, such as Yenisei, Lena, Volga, Ob, can reach several tens of kilometers.
The river flow often forms the thresholds. Especially often they are found in line with mountain rivers. The threshold is a shallow water dressed in a pebble or boulders. It is formed in those places where it is difficult to bloated rocks. Here there are large flow differences. Thresholds, by virtue of its relief, make it impossible shipping and greatly make the alloy. Sometimes, because of them, the person is forced to build bypass channels. Often lower from the thresholds are elevated hydroelectric power plants. At the same time, the river drop and significant slopes are used with the maximum benefit. In an example, you can bring the Ust-Ilimsk hydroelectric station on the Angara River.
What is the river delta?
Delta is the lowland river. It is almost always characterized by numerous branched ducts and sleeves. Delta is formed exclusively in the lower reaches. It is also important to note that a special mini ecosystem is formed on this section of the reservoir. Each river is unique and unique.
Most of the major rivers of Russia have extensive delta with well-developed apparent activities. The Volga and Lena will always lead as classical examples. Their delta is huge and branched to a whole network of sleeves. In addition, they can be noted yet Kuban, Terek and Neva. A distinctive feature of the Delta located in the southern regions is developed smooth. There are a violent variety of vegetation, various mammals, amphibians and reptiles are found along the shores. Many bird species are waters in the forests and thickets from the water their nests. But these areas are especially valuable by fishery resources. Noting on the question of what Delta River is, it is safe to say that this is a unique microworld with its nature.
When the river shift in the sea is often shallow bays are often formed. They are called limans. Such a bay in the lower rivers - the place is very unusual and picturesque. Liman occurs when flooding the plain rivers by the sea. It can be open - then it is called Gouget. In this case, the bay does not necessarily have to be connected to the sea. There are also closed estuans, i.e., separated from the seawater of the sushi strip - a narrow patch. As a rule, water limanov is salted, but not to such an extent as marine. True, with a small influx of fresh water, it can sing hard. The bay in the lower reaches of the river is not always formed. Many of them are located on the coast of the Azov Sea. Limans have a Dniester and Kuban rivers.
A place in which the river flows into the lake, a reservoir, a sea or other reservoir is called a set. It may be different. For example, in the territory adjacent to the mouth, Liman, lip or wide delta may form. But river water may disappear, and the reasons for this are somewhat - the fence on irrigation of agricultural plantations or simply evaporation. In this case, they say about the blind mouth, that is, the river does not fall anywhere. It often happens that at the end of its way of water just go into the ground, and the flow disappears. Therefore, it cannot be said that each river has a clearly defined mouth. For example, Okavanngo's river bed disappears in the swamps in the Kalahari desert. Thus, the source of the river and mouth is not necessarily pronounced, and they are not always detected.
Functions of the river
The influx is watercourse flowing into a larger river. From the latter it is usually characterized by smaller waters and length. But, as studies, conducted in recent decades show, this is not always the case. There are several rivers that violate this established law. For example, an eye flows into a Volga, which is inferior to it in terms of water. At the same time, a kama is also falling into this great water artery, which is also more complete. But on the Volga, all known exceptions do not end. Angara is recognized as the influx of Yenisei. At the same time, the part of the river that merges with the second object, has twice the volume of water. That is, with confidence it can be said that the hangar is larger. As a rule, the influx has differences in the direction of the valley, so you can accurately determine what flows.
But the rivers do not always merge with each other. Sometimes they fall into lakes or other reservoirs. The tributies are divided into right and left, depending on which side they are suitable for the bed. They are of different order: paramount and secondary. Some of them fall directly in the main drain. These are paramount tributaries. All rivers that are connected to them will be secondary. For example, the chest is a paramount influx for the Oka and secondary for the Volga.
The sleeve is also part of the river. It may be a branch or "splitting" of the bed. Note that the sleeve must be made again into the river. Sometimes it happens in a few tens of meters, but more often stretches a few kilometers. The sleeve is formed as a result of the deposition of the nanos. At the same time, the island is formed in line. Sleeves have many local names. On the Volga they are called "Volgs". On the North Dvina River, they are denoted by the word "hollow". On Don, local residents call them ancient. On the Danube River - "Girlo." Sleeves can be secondary. Then they are usually called ducts. Almost all the sleeves and ducts after some time become styrices. As the main channel changes, they are disconnected.
Staritsa is an elongated lake or a river area disconnected from the mainstream. Starks can be found in the float or on the bottom terrace. They arise at the overlap of sandy or clay flames of hoses, as well as during the breakthrough of the shek of meanders. The old man always has a characteristic horseshoe form. They are connected to the waters of the main channel only at the time of spill. Of the most part of the time they are separate reservoirs. Often they are called flood lakes. The scheme of part of the river, which marks all old men, can give an idea of how the river looked before. Over time, this object changes - it overcomes, its form is transformed. The styal turns into a swamp, and then at all in the raw meadow. After some time, there is no trace from it.
The level of the river is the height of the water surface. This concept is used almost for all natural and artificial reservoirs. Each river has low and high values mentioned. The maximum water level is observed during the flood, as a rule, in spring and summer. Farms also occur in the fall. The reason for this is the protracted rave rain. In winter, the water level is lowered to the minimum mark. Often the river becomes less fully and summer - during long-term droughts, when the streams flowing into the river drill. The mode of each river is strictly individual. A decrease and increase in water levels always depends on climatic and relief features.