Each river is unique in its own way. Everyone has a source - the place where it originates. The point of inflow into a larger water body is the mouth. Large water arteries flow into the seas or oceans in different ways: an estuary or river delta is formed. The type and shape of the mouth depends on many factors: the nature of the flow, climatic conditions, terrain, the presence of tides.
In nature, the water cycle occurs constantly. From the seas and oceans, it evaporates, gathers in clouds and rains. On land, it is absorbed into the soil or flows down in streams. Water is collected in swamps, ponds, lakes, but sooner or later it falls back into rivers and returns to the world ocean again. The cycle ends. Rivers play an important role in this process.
Their source is sometimes difficult to determine reliably, but the place where it flows into a larger object is visible from afar. However, each river, due to its peculiarities, gives up its waters in different ways. The mouth can be straight and deep with a sharply delineated coastline. And it happens that it is small and is divided into two, three or many branches (river delta).
The territory adjacent to the mouth can be constant for many decades or flooded tens or even hundreds of kilometers each year during a flood. And also each river has a special flow pattern. The discharged water may be clear or turbid due to the presence of a large amount of organic particles. With a rapid flow, they descend from the headwaters or are washed out of the muddy bottom sediments in the lower reaches. If most of them are not carried away into the sea, then in such cases a delta is most often formed.
Mouth of the river: views
The degree of sediment deposition is influenced by tides. Often, the mouths of rivers that flow into the open seas or oceans form an estuary. Salty sea water is heavier than fresh water. Flows of its tidal wave are brought far along the channel. With the tide she returns. The constancy of the movement does not allow accumulation of sedimentary particles at the boundary of the watershed. The depth of the channel in such places reaches significant indicators. It often has sharply defined boundaries, the territory adjacent to the coastline is stable and relatively constant. Rivers with estuaries of this type are often navigable. On the shores of wide wedge-shaped estuaries, resembling a convenient bay, large port cities have been built.
A river delta usually forms when it flows into a lake, reservoir or sea of a closed type without pronounced tides. Most of the discharged organic particles remain in the coastal zone, where the flow is weakened. They settle, gradually accumulating. This leads to higher levels of the bottom. Alluvial islands arise, they turn into braids dividing the channel into parts. This is how sleeves are formed. Those in turn are divided - the river is constantly changing.
This type of mouth has the shape of a triangle. From the similarity with the Greek letter Δ, the river formation received such a name. It is believed that the pronounced form of the mouth of the Nile for the first time in antiquity was called the delta. The type and configuration of the coastline depends on the predominance of the force of the oncoming waves of the final reservoir or flow in the channel.
There are three characteristic types of deltas:
- Stretched when the density of the river water due to the abundance of alluvial particles is higher than in the receiving object.
- Cone-shaped with relatively equal density of water and moderate current (Nile).
- Finger-shaped multi-branch mouth (Mississippi).
Delta can be formed not only at the confluence of the river. Due to the peculiarities of the relief (when the channel reaches the plain) of this type, the formation can also be in the middle course. Delta in this case will be referred to as internal. Downstream, the ducts are connected, and the river carries water in a single stream to the confluence.
Changing the shape of the channel in the mouths of large rivers leads to the formation of special ecosystems on such territories. Often they are characterized by the presence of fluids, a wide species diversity of the animal and plant world, and the economic fish resource.
Much more often more than one sleeve is formed. In the delta of the Lena River, for example, with a formation width of almost 400 km in a total area of about 45,000 km 2 there are countless of them. The processes of neoplasm are constantly going on, so it makes no sense to calculate their exact number in such a vast territory. Only three main ducts are not interrupted to the sea, the rest branch out with the formation of a variety of sleeves.