Most people imagine what a river delta is, but not everyone thinks about the role that it plays in the life of all representatives of flora and fauna. What is she like? A river delta is a lowland formed by river sediments, located in its lower reaches. Most often, it is heavily cut through by a network of ducts and arms. 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 form strongly resembled the triangular delta of the ancient Nile.
In the process of long-term interaction of
river flows, sea or ocean waves, surging currents, tides, and also sediment runoff, a unique delta is formed at 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, and the Amazon - 100 thousand sq. km.
A river delta can begin hundreds of kilometers from its mouth. The deltas of some rivers extend into the seas or oceans, while others do not. Under the influence of ebbs and flows, such rivers as the Amazon, Amur, Ob, Taza, Pura have deltas that do not extend beyond their root shores.
When the water in the river has almost the same density as sea water, the delta takes on a conical shape (for example, at the Nile). If river water is rich in precipitation, it becomes more dense than sea water, therefore, under its influence, the delta takes an elongated shape. With a reduced density of river water, deltas are formed with a large number of branches and ducts (Mississippi River).
Most rivers of the world have deltas with developed alluvial (alluvial) activity. Such are the Volga, Lena, Terek, Northern Dvina, Kuban, Neva. Many southern rivers have developed “floodplains” with rich vegetation and a diverse wildlife. They have significant fish resources. The vegetation is represented by various herbs, thickets of reeds and reeds, shrubs and trees. They like to settle birds and various species of animals.
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 crops is grown. Succulent grasses in humid meadows located downstream are excellent livestock feeds. The valleys of the Ganges, Nile, Yellow River, Danube are areas with intensive agriculture.
The Neva River Delta , which flows along the swampy and flat Prievskaya Lowland, is peculiar. This river is conditionally divided into 2 parts (by the nature of the regime): the upper (source - Ivanovo rapids), 30 km long, and the lower (Ivanovo rapids - estuary), 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 canals. It arose as a result of surges and driving water from the sea and under the influence of flowing waters. The largest islands in the Neva Delta are Krestovsky, Vasilyevsky, Petrogradsky, Dekabristov. Her sleeves are Malaya and Bolshaya Neva, Malaya, Srednyaya and Bolshaya Nevka. The most famous channels are Obvodnaya, Morskoy, Kryukov, Griboedova.