The Anatomy of a River
Learn about how a river is formed…
No two rivers are exactly alike. Yet all rivers have certain features in common and go through similar stages as they age.
Flow from Source to End:
The beginning of a river is called its source or headwaters. The source may be a melting glacier, such as the Gangotri Glacier, the source of the Ganges River in Asia. The source could be melting snow, such as the snows of the Andes, which feed the Amazon River. A river’s source could be a lake with an outflowing stream, such as Lake Itasca in the U.S. state of Minnesota, the source of the Mississippi River. A spring bubbling out of the ground can also be the headwaters of a river. The source of the Danube River is a spring in the Black Forest of Germany.
From its source, a river flows downhill as a small stream. Precipitation and groundwater add to the river’s flow. It is also fed by other streams, called tributaries. For instance, the Amazon River receives water from more than 1,000 tributaries. Together, a river and its tributaries make up a river system. A river system is also called a drainage basin or watershed. A river’s watershed includes the river, all its tributaries, and any groundwater resources in the area.
The end of a river is its mouth. Here, the river empties into another body of water—a larger river, a lake, or the ocean. Many of the largest rivers empty into the ocean.
The flowing water of a river has great power to carve and shape the landscape. Many landforms, like the Grand Canyon in the U.S. state of Arizona, were sculpted by rivers over time. This process is called weathering or erosion.
The energy of flowing river water comes from the force of gravity, which pulls the water downward. The steeper the slope of a river, the faster the river moves and the more energy it has.
The movement of water in a river is called a current. The current is usually strongest near the river’s source. Storms can also increase the current. A swift current can move even large boulders. These break apart, and the pieces that are carried in the moving water scrape and dig into the river bottom, or bed.
Little by little, a river tears away rocks and soil along its bed and carries them downstream. The river carves a narrow, V-shaped valley. Rapids and waterfalls are common to rivers, particularly near their sources.
Eventually, the river flows to lower land. As the slope of its course flattens, the river cuts less deeply into its bed. Instead, it begins to wind from side to side in looping bends called meanders. This action widens the river valley.
Sediment:
At the same time, the river begins to leave behind some of the rocks, sand, and other solid material it collected upstream. This material is called sediment. Once the sediment is deposited, it is called alluvium. Alluvium may contain a great deal of eroded topsoil from upstream and from the banks of its meanders. Because of this, a river deposits very fertile soil on its floodplain. A flood plain is an area next to the river that is subject to flooding.
An oxbow lake starts out as a curve, or meander, in a river. A lake forms as the river finds a different, shorter, course. The meander becomes an oxbow lake along the side of the river. Oxbow lakes usually form in flat, low-lying plains close to where the river empties into another body of water. On these plains, rivers often have wide meanders.
Ox Bow Lake:
An oxbow lake starts out as a curve, or meander, in a river. A lake forms as the river finds a different, shorter, course. The meander becomes an oxbow lake along the side of the river. Oxbow lakes usually form in flat, low-lying plains close to where the river empties into another body of water. On these plains, rivers often have wide meanders.
Channel:
The deepest part of a riverbed is called a channel. The channel is usually located in the middle of a river. Here, the current is often strong. In large rivers, ships travel in channels. Engineers may dredge, or dig, deeper channels so more water can flow through the river, or the river can transport larger ships.
Delta:
The deepest part of a riverbed is called a channel. The channel is usually located in the middle of a river. Here, the current is often strong. In large rivers, ships travel in channels. Engineers may dredge, or dig, deeper channels so more water can flow through the river, or the river can transport larger ships.
Near the end of its journey, the river slows and may appear to move sluggishly. It has less energy to cut into the land, and it can no longer carry a heavy load of sediment. Where the river meets the ocean or a lake, it may deposit so much sediment that new land, a delta, is formed.
Not all rivers have deltas. The Amazon does not have a true delta, for instance. The strength of the tides and currents of the Atlantic Ocean prevent the build-up of sediment. Deltas almost always have fertile soil. The Nile Delta and the Ganges Delta are the chief agricultural areas for Egypt and Bangladesh, for instance.
