Difference between Aggradation and Degradation

Aggradation and degradation both involve changes in the base level of a river. They are also both impacted by the amount of sediment in a river and the kinetic energy of a river. Read this article to learn more about Aggradation and Degradation and how they are different from each other.

What is Aggradation?

Aggradation, in geology, is the gradual accumulation of silt along the bed of a river or other similar setting. Rivers shape the terrain by both eroding and depositing sediment. When rivers' energy reserves are depleted, they start depositing silt because they can't keep it suspended. As sediments are washed down a river, they gradually elevate the water's overall elevation. The lowest point at which a river's current stops cutting into the riverbed and deepening it is known as the base level.

Sediment builds up during aggradation, lifting the riverbed. The sediment load in a river determines how much sediment it can entrain before it begins to deposit material, and if the river is nearing this limit, settling of sediments is likely to occur as a result of a progressive loss of kinetic energy.

A braided stream or river is an example of an environment where tensions tend to rise. When a river has a lot of silt entangled in it, we call it a braided river. As the river speeds down, the surplus silt is quickly deposited as the riverbed settles. The name "braided river" derives from the way the river looks after sediment has been deposited in the form of bars that cut it up into smaller channels.

Many braided river systems are located near glacial regions, where the rivers are nourished by glacier melt water. We know that glaciers may move and acquire a great deal of stuff. Braided river systems are more common as glaciers begin to melt because the melt water is full with debris.

A river's gradation can also be affected by the local ecosystem. Riverine and aquatic plants, for instance, can take hold in a river, providing a stable surface onto which other silt might accumulate to form a bar or platform.

As not just Earth but also certain other planets have liquids running across their surfaces, Earth is not alone in having problems. An ancient river system on Mars probably contained aggradation. The methane rivers of Titan may potentially show signs of aggradation.

What is Degradation?

Degradation, in geology, is the process through which a riverbed becomes flatter as a result of sediment loss. Degradation takes place when a river's kinetic energy rises to the point that entrained silt is unable to settle to the river's bottom.

Erosion causes sedimentary particles to be scraped or dragged down the riverbed and the river's margins during the degradation process. This will cause the river to gradually deepen as sedimentary particles that were deposited are hacked away by the river's current. Degradation occurs when the base level, the point below which the river cannot cut farther into the underlying bedrock or sediment, drops. Rivers with light sediment loads are more vulnerable to degradation. If rivers are not actively eroding their banks or depositing new sediment, they are in a state of balance. The term "river grade" might be used to describe this stable point.

There is usually not much of a difference in the base level equilibrium between a tributary and the stream or river to which it contributes since rivers and their tributaries have the same grade. A waterfall forms if there are significant disparities across grades. Grading variations are the result of events, including glaciers, that change the gravitational potential levels of the land surface. Grading disparities may also be brought on by a layer of exceptionally hard rock.

In most cases, fluctuations in the speed of a river are to blame for its deterioration. An increase in glacial melt water is one possible explanation of this. Long-term, it may also be induced by a river's steepening as a result of tectonic uplift. Degradation in a river can be affected not just by natural processes that modify the river's kinetic energy, but also by human activities. For instance, dams can have a major impact on the rate of deterioration. Geomorphological change is becoming more influenced by humans, surpassing natural processes like uplift and erosion.

Differences: Aggradation and Degradation

The following table highlights the major differences between Aggradation and Degradation −

Conclusion

Sediment accumulates in a river over time due to deposition by a river whose velocity decreases, a process known as aggradation. This raises a river's groundwater level. Because of sediment erosion, the base level of a river decreases over time as degradation progresses.

An increase in the river's kinetic energy leads to degradation. The sediment carried by a river and the river's kinetic energy both influence the rate of degradation and aggradation. Furthermore, there are significant distinctions between the two.

Aggradation raises the water table, takes place in rivers that are clogged with silt, is linked to the deposition of material, and reduces the river's kinetic energy. Degradation causes a river's base level to drop, occurs in rivers that are low in sediment, is linked to erosion, and is often accompanied by an increase in the river's kinetic energy.

Vineet Nanda

Updated on: 01-Mar-2023

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