What Is River Erosion?

A basic definition of river erosion is that it is the wearing down of part of the Earth's crust by the action of water flowing along a river's watercourse. This can be caused by large rivers or even slight streams. Moving water is a powerful agent, capable of modifying the relief of various landscapes. This occurs both by wearing down material and by depositing it further down the watercourse.

When water from a river erodes surfaces, the current carries along sediment and other materials. This modifies the distribution of the materials. This process is known as river transport. Materials carried via river transport are known as the load and they can be classified as one of the following:

• Dissolution loads: particles that dissolve in water, meaning they are not visible to the naked eye.
• Suspended loads: particles that remain in suspension, causing cloudy water.
• Bed loads: larger fragments of rock or earth that remain at the bottom of the bed and are transported by rolling, dragging or saltation.

The causes of river erosion are related to the energy of the water when it is in motion. The speed of the water is not constant along the riverbed, so we will tell you about the different phases of river erosion:

• Mechanical phase: occurs at the highest levels of the body of water. Here the current has great speed and consequently the greatest wear of the rocks occurs due to mechanical action.
• Intermediate phase: as its name indicates, it occurs at the intermediate levels of the body of water. In this phase, erosion by mechanical action continues, but when the current speed is lower, sedimentation begins to act.
• Sedimentary phase: occurs at the bottom of the body of water. All the eroded material is deposited there due to the lower speed of the water current.

River erosion is only one type of geological erosion we can see in nature. Read our related guide to discover the other different types of erosion.

While river erosion is one of the many types of erosion, it can be further broken down into subtypes. We look at some of the different types of river erosion we can see in nature:

General erosion

It is a lowering of the river bed caused by an increase in the transport capacity of a current. This usually occurs during a flood or another reason for a deluge.

Erosion due to channel narrowing

It occurs mainly in the sections of a channel where some engineering work has been carried out, such as bridges or tunnels. When the channel is reduced, the speed of the current increases, as does the transport of sediments via the current.

Erosion due to channel bends

It is common for the centrifugal force of water to occur at bends in riverbeds. Consequently, this increases erosion of the bed. Greater depths are reached there.

Localized erosion

It is caused by changes or obstacles present in the watercourse. These can cause changes in the flow of water, increasing its erosive power. In this type of erosion the general conditions of the water flow are not modified.

Rivers are not the only bodies of water which can result in the eroding of materials. Check out our related article on the power of ocean currents with our article asking what is coastal erosion?

The reliefs formed by river erosion are one of the main consequences of this process. We must mention that due to various fluvial processes, floods can also occur. These are overflows of rivers that cause excessive water content around its channels.

River floods not only wear down the surface of the riverbanks. Depending on the geographical location where they occur, they can also cause great economic losses and even fatal disasters. Moving water has an enormous power that goes beyond the formation of the relief.

With this in mind, the effects of river erosion over time can have a great impact on both natural ecosystems and human settlements. They include:

• River feature formation: most valleys are a caused by water erosion from rivers which occur over many millions of years. Other valleys might be formed by glacial movements, something we explore by asking what is glacial erosion?
• Riverbank collapse: when the sides of the river are eroded by the watercourse, it can cause the banks to collapse. This can also result in landslides, as well as the loss of land and property located on the riverbank.
• Habitat loss: eventually, river erosion can destroy land which is home to a wide range of flora and fauna. This is particularly the case for semi-aquatic animals that live near rivers.
• Infrastructure damage: when river erosion destroys land beside the river, it can cause the damage or loss of infrastructure. This can include farmland, residential areas, businesses, bridges and roads, among others.
• Economic effects: the loss of agricultural land, homes or businesses can result in economic losses and the displacement of people.

One of the main effects of river erosion is the changes the river's watercourse experiences. Due to both the erosion of the riverbanks and the deposition of sediment, various landforms such as river deltas and estuaries are created. Learn more with our article explaining what is the difference between a delta and an estuary?

As we have seen, river erosion can have a great impact on local ecosystems. The breaking down of material and the deposition of sediments can create various features on a landscape. Features formed by river erosion include the following:

Meanders

Meanders are produced as a result of sediment drag. Sediment begins to be deposited in the middle course, where the speed of the water begins to decrease. Under certain circumstances, erosive force also acts on these deposits, wearing them away and transporting them to other parts of the course. As a result, sinuous deposits are formed that we call meanders.

In a related article we explain more by looking at the formation and types of meanders.

River deltas

Deltas coincide with the end of the erosion process and occur at the mouth of watercourses. This is where most of the sediments carried along are deposited and the formation of this feature occurs. In this sense, deltas can be described as sedimentary terrains.

River terraces

Also called fluvial terraces, river terraces are sedimentary platforms of land in river valleys. They are formed by the deposit of sediments in the parts of the watercourse where there is a slope. This causes the speed of the current to slow and results in the creation of incremented terraces.

Now you have a definition of river erosion, as well as knowing its causes and effects, you may want to know more about how rivers created landforms with our article asking what is a wadi in geography? We also share with you what are the longest rivers in the world?

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