Rivers and landforms

Rivers and landforms

Rivers play an important role in shaping the Earth's surface: they cause erosion as well as carrying and depositing sediment.

Geography

Keywords

river, terrain shaping, Watercourses, river bed, river mouth, upper course, middle course, lower course, river delta, estuary, erosion, alluvion, backwater, bend, bar, island, valley, topography, water, hydrography, water cycle, nature, nature study, physical geography, geomorphology, geography

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Scenes

Rivers

  • upper course - Rivers with steep gradients have more energy than is necessary to carry their load of sediment. Therefore the channel becomes deeper and deeper and a V-shaped valley is formed.
  • middle course - The energy of rivers with gentle gradients is balanced. They carry and deposit sediment produced by lateral erosion.
  • lower course - Rivers with barely any gradient have low energy which is not enough to carry the sediment, which is deposited, forming bars (islands).
  • delta - Rivers carrying large amounts of sediment deposit the remaining sediment at the mouth, thus splitting up into several distributaries, and the islands between them expand at the expense of the sea.
  • estuary - It is a body of water that has only a small amount of sediment or that flows into seas with high tidal range. High tides continually make it bigger and deeper.

As an external force, rivers play an important role in shaping the Earth's surface: they cause erosion as well as carrying and depositing sediment. The four main forms of river erosion are: hydraulic action, abrasion, attrition and solution. These can change along the length of the river depending on the terrain the river flows through.

Upper course

  • V-shaped valley - A valley created by the vertical eroding effect of a fast-flowing river.
  • erosion - The process by which the surface of land or rock is gradually damaged by exogenic forces.

Flowing bodies of water have a certain amount of energy, a portion of which is used to carry sediment, while the remaining energy is used to erode the stream bed. Rivers with steep gradients have more energy than necessary to carry the sediment. Fast-flowing rivers deepen their beds with the erosive effect of the sediment they are carrying, forming a V-shaped valley over time.

Definitions:

Gorge: A deep, narrow ravine, usually between mountains, with steep, almost vertical, rocky walls, with a stream running at the bottom.

Canyon: A very long, deep valley with steep, rocky sides, carved out by the river running at the bottom.

Waterfall: A part of a river or stream where the water flows over the edge of a vertical or steep cliff. It occurs where there are harder rock platforms in the river bed. The softer rock layers, located above and beneath the harder rock, is eroded faster, producing a step in the gradient over which the water cascades or falls vertically.

Middle course

  • meander - A meander is a winding curve or bend in a river. The speed of flow is higher on the outside of the bend than on the inside, therefore here erosion takes place. On the inside, the water flows more slowly and deposits sediment, gradually increasing the curve of the bend.
  • oxbow lake - It is a body of water that has been cut off from the main stem of a river. During a flood, the river cuts through the necks of the meanders, thus straightening its course.
  • alluvium
  • eroding bank - The speed of flow is higher on the outside of the bend, therefore erosion takes place here.
  • point bar - The speed of flow is lower on the inside of the bend, therefore deposition takes place here.

The energy of rivers with gentle gradients is balanced, which means that they carry and deposit as much sediment as they produce by erosion. As they meander over a decreasingly steep gradient, they shape the course of the water. Bars (or elongated islands) are built up gradually near one bank, while the opposite bank is eroded, creating a bend. The speed of flow is higher on the outside of the bend, which causes the erosion and increases the curve of the bend, until its neck becomes so narrow that it becomes blocked by sediment deposited by the water flowing more slowly on the inside. This process creates what are called oxbow lakes.

Definitions:

Channel line: An imaginary line that connects the fastest flowing points of a river. In bends it is situated along the eroding bank; in straight sections it is located in the middle of the channel.

Lower course

  • distributaries - Forming islands and bars, the river deposits the sediment and splits into several streams.
  • alluvium

Rivers with barely any gradient have low energy which is not sufficient to carry sediment. As a result, deposition becomes dominant, though the process of carrying sediment continues to some extent. The alluvium deposited forms bars (or islands) and the channel splits into branches. The river’s continuously changing course and deposition of sediment lead to the formation of alluvial plains and alluvial fans.

Types of river mouths

  • delta - Rivers carrying large amounts of sediment deposit the remaining sediment at the mouth, thus splitting up into several distributaries, and the islands between them expand at the expense of the sea.

Delta
Most of the major rivers flow into seas. Deltas are formed at the mouths of rivers where there is an abundance of sediment and a low tidal range. Rivers deposit the remaining sediment at the mouth, thus splitting up into several distributaries, and the islands between them expand at the expense of the sea.

Estuary
The estuary is a body of water that only has a small amount of sediment or that flows into seas with a high tidal range. The high tide continually makes it bigger and deeper.

River terraces
The course of a river changes over time at a given location due to tectonic and climatic influences. Thus, this change, which occurs multiple times in the same area, forms river terraces above one another. Since these are not reached by floods, roads and settlements are built here.

Animation

  • middle course - The energy of rivers with gentle gradients is balanced. They carry and deposit sediment produced by lateral erosion.
  • lower course - Rivers with barely any gradient have low energy which is not enough to carry the sediment, which is deposited, forming bars (islands).
  • delta - Rivers carrying large amounts of sediment deposit the remaining sediment at the mouth, thus splitting up into several distributaries, and the islands between them expand at the expense of the sea.
  • V-shaped valley - A valley created by the vertical eroding effect of a fast-flowing river.
  • erosion - The process by which the surface of land or rock is gradually damaged by exogenic forces.
  • meander - A meander is a winding curve or bend in a river. The speed of flow is higher on the outside of the bend than on the inside, therefore here erosion takes place. On the inside, the water flows more slowly and deposits sediment, gradually increasing the curve of the bend.
  • oxbow lake - It is a body of water that has been cut off from the main stem of a river. During a flood, the river cuts through the necks of the meanders, thus straightening its course.
  • alluvium
  • eroding bank - The speed of flow is higher on the outside of the bend, therefore erosion takes place here.
  • point bar - The speed of flow is lower on the inside of the bend, therefore deposition takes place here.
  • distributaries - Forming islands and bars, the river deposits the sediment and splits into several streams.
  • alluvium
  • estuary - It is a body of water that has only a small amount of sediment or that flows into seas with high tidal range. High tides continually make it bigger and deeper.
  • delta - Rivers carrying large amounts of sediment deposit the remaining sediment at the mouth, thus splitting up into several distributaries, and the islands between them expand at the expense of the sea.

Narration

As an external force, rivers play an important role in shaping the Earth's surface: they cause erosion as well as carrying and depositing sediment. The four main forms of river erosion are: hydraulic action, abrasion, attrition and solution. These can change along the length of the river depending on the terrain the river flows through.

Flowing bodies of water have a certain amount of energy, a portion of which is used to carry sediment, while the remaining energy is used to erode the stream bed.

Rivers with steep gradients have more energy than necessary to carry the sediment. Fast-flowing rivers deepen their beds with the erosive effect of the sediment they are carrying, forming a V-shaped valley over time.

The energy of rivers with gentle gradients is balanced, which means that they carry and deposit as much sediment as they produce by erosion. As they meander over a decreasingly steep gradient, they shape the course of the water.

Bars (or elongated islands) are built up gradually near one bank, while the opposite bank is eroded, creating a bend. The speed of flow is higher on the outside of the bend, which causes the erosion and increases the curve of the bend, until its neck becomes so narrow that it becomes blocked by sediment deposited by the water flowing more slowly on the inside. This process creates what are called oxbow lakes.

Rivers with barely any gradient have low energy, which is not sufficient to carry sediment. As a result, deposition becomes dominant, though the process of carrying sediment continues to some extent. The alluvium deposited forms bars (or islands) and the channel splits into branches. The river’s continuously changing course and deposition of sediment lead to the formation of alluvial plains and alluvial fans.

Most of the major rivers flow into seas. Deltas are formed at the mouths of rivers, where there is an abundance of sediment and a low tidal range. Rivers deposit the remaining sediment at the mouth, thus splitting up into several distributaries, and the islands between them expand at the expense of the sea.

The estuary is a body of water that only has a small amount of sediment or that flows into seas with a high tidal range. The high tide continually makes it bigger and deeper.

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