River

A river is characterized by its length, width, basin area, depth, gradient (slope along the stream), water level, flow velocity, water discharge (or flow rate), sediment load, chemical composition of its water, and so on.

Such changes in these hydrological elements over time are called river regimes. Rivers are typically divided into mountain and plain rivers based on their regime and valley structure. The place where a river first forms—its source (not «headwaters») — can be a spring, lake, sea, ocean, or another river. Many rivers in Central Asia are used for irrigation and are divided into irrigation canals that branch off downstream.

Most rivers originate from a spring. The spring flows into a stream, forming a river. Groundwater and rainwater also flow into the river. However, there are also rivers that do not start from a spring. For example, the Biya River flows from Lake Altyn-Kul in Altai, descending over a plateau. Its source has a high flow rate (or is a rapid), and its current is strong. There are also rivers that do not have rapids.

Depending on the climate and other physical and geographical features, river water is categorized by its main supply sources, which are typically four: rain, snow, glacial meltwater, and groundwater. Often, a river's water is formed from both snow and glacial meltwater simultaneously. In this case, one of them (snow or glacial water) predominates.

For example, the Murghab and Tejen rivers in Turkmenistan are used extensively for irrigation, so they often dissipate and do not flow anywhere (i.e., they are endorheic). Large rivers with abundant water, such as the Nile in Africa and the Mississippi in America, discharge a lot of sediment and silt into the sea.

In the estuaries and valleys, the river's flow slows down and sediment is deposited. This creates islands of silt or sand. The river's flow is divided into many distributaries and branches. This landform is called a river delta. The city of New Orleans, located in the Mississippi Delta, is situated below sea level (or below the riverbed).

The Mississippi River is prone to rising due to floods. The river flows along its banks. When snow or glaciers melt and water levels rise, the river overflows its banks and forms a floodplain—the plain along the main riverbed that becomes covered in water.

Usually, a lush green meadow grows there. The grass of such a meadow is excellent fodder for livestock. A river in a plain flows smoothly and slowly. Its flow only accelerates in sharp bends and rapids. However, these rivers sometimes change their course when the water enters, resulting in the formation of oxbow lakes (old channels).

An oxbow lake is a former river channel, where plants such as reeds and bulrushes soon grow. This is how lakes and swamps are created.

Other rivers flow rapidly, cascading from rock to rock, carving deep gorges through the rocks and creating waterfalls. When the snow and glaciers in the mountains begin to melt rapidly, they carry millions of tons of mud and rocks, sometimes overflowing their banks in torrents, sweeping away everything in their path.

Since ancient times, rivers have provided people with water, served as transportation routes and communication links. Rivers have also served as state borders and natural defensive barriers against enemies.

Rivers are now of great importance in people's lives. River water is essential for cities and villages, factories and plants. We build hydroelectric power stations on rivers, which provide cheap electricity. Passenger and cargo ships sail on rivers, and timber is harvested and transported.

The total volume of water flowing in a river over a period of time (ten days, months, seasons, years, several years) characterizes whether the water in the river is above or below the long-term average value for that period.

The importance of rivers in the national economy is vast and varied. The river is a source of drinking and industrial water; it is used to fill reservoirs for hydroelectric power plants and irrigation systems, water transport, fisheries, and more.

Rivers are also used to irrigate arid lands. Rivers are a great asset to humanity. They must be protected from pollution by oil, industrial, and domestic waste.

To prevent the river from decreasing in volume (or drying up), trees and shrubs on its banks and tributaries should not be cut down.