Most people imagine what a river delta is, but not everyone thinks about the role it plays in the life of all representatives of flora and fauna. What does she represent? A river delta is a lowland formed by sediments of a river, located in its lower reaches. Most often, it is strongly cut through by a network of ducts and sleeves. A special ecosystem is being created on this lowland. The river delta got its name from one of the letters of the Greek alphabet, which in its shape strongly resembled the triangular delta of the ancient Nile.
In the process of long-term interaction of river flows, sea or ocean waves, surge currents, ebbs and flows, as well as sediment runoff, a unique delta is formed near each river, which can occupy up to one hundred or more thousand square kilometers. At the Ganges, it occupies almost 106 thousand square meters. km, while the Amazon has 100,000 sq. km.
A river delta can start hundreds of kilometers from its mouth. The deltas of some rivers protrude into the seas or oceans, while others do not. Under the influence of tides, such rivers as the Amazon, Amur, Ob, Taza, Pura have deltas that do not go beyond their primary banks.
When the water in the river has almost the same density as sea water, the deltaacquires a conical shape (for example, at the Nile). If river water is rich in precipitation, it becomes denser than sea water, therefore, under its influence, the delta acquires an elongated shape. With a reduced density of river water, deltas are formed with a large number of branches and channels (the Mississippi River).
Most of the world's rivers have deltas with developed alluvial (alluvial) activity. These are the Volga, Lena, Terek, Northern Dvina, Kuban, Neva. Many southern rivers have developed “floods” with rich vegetation and diverse wildlife. They have significant fish resources. The vegetation is represented by various herbs, thickets of reeds and reeds, shrubs and trees. Birds and various kinds of animals like to settle in them.
It is difficult to overestimate the importance of moisture and fertility of soils located in the river delta. In many countries of the world, it is on them that a significant part of agricultural crops is grown. Succulent grasses in moist meadows located in the lower reaches of the rivers are an excellent feed for livestock. The valleys of the Ganges, Nile, Huang He, Danube are areas with intensive agriculture.
The delta of the Neva River, which flows through the swampy and flat Neva lowland, is peculiar. This river is conditionally divided into 2 parts (according to the nature of the regime): the upper (source - Ivanovskiye rapids), 30 km long, and the lower (Ivanovskiye rapids - mouth), 44 km long. In the lower reaches (about 15 km from the mouth), the Neva forms a wide delta, replete with channels,arms, islands and channels. It arose as a result of surges and surges of water from the sea and under the influence of flowing waters. In the Neva delta, the largest islands are Krestovsky, Vasilyevsky, Petrogradsky, Dekabristov. Its arms are Malaya and Bolshaya Neva, Malaya, Middle and Bolshaya Nevka. The most famous canals are Obvodnoy, Morskoy, Kryukov, Griboedova.
