WATER EROSION: STAGES, CAUSES, EFFECTS, TYPES - ENVIRONMENT - 2024

Water erosion happens when water carries rocks away or separates and flattens soil particles. It is a process of separating compact masses (clays, mold, silt and sand) into individual particles. Although the causes of water erosion are generally natural, man participates in it.

The main cause of this type of erosion is the lack of vegetation. When an area has plants, roots that protect the soil and absorb water grow from these, increasing the permeability of the soil. On the contrary, if soils are lacking in vegetation, they can be waterproof and increase erosion.

On the other hand, climate is another factor that greatly affects water erosion. The more rainfall there is, and the more intense it is, the more erosion there is. This is more pronounced if the soils do not have vegetation, in areas of intensive agriculture or semi-arid regions.

Another important factor is the drops of water; those that have more speed and are larger, have more kinetic energy, therefore having a greater capacity to affect the soil than the smaller droplets and with less energy.

How does water erosion occur?

Water erosion occurs mainly by the force of raindrops or by the force of continental waters, such as rivers.

Erosive effect of rain: pluvial erosion

Rain erosion refers to the erosive effect of rain. A drop of rainwater is on average 1000 times greater than a particle of soil.

As a result, the force during the impact of a single drop is sufficient to dissipate soil particles. In arid or semi-arid areas, where the protection provided by plant cover is scarce, the low rainfall results in significant erosion.

As it flows on the ground, rainwater forms small channels, and if the slope allows it, erosion in furrows occurs. Precipitation crowds the soils on the slopes, causing the upper layers of soil and rock to slide away.

On the other hand, the constant heavy rains in areas of thin soil mean that the water is not completely absorbed and flows in torrents capable of wreaking havoc.

Inland water effect: river erosion

The flow of continental waters, mainly in the form of rivers, is an erosive agent of great magnitude. This flow wears out all the materials around it; in addition, they drag sediments towards the lowest parts of the relief.

Fluvial erosion can become terraces, dung cones, waterfalls, caves, gorges and canyons, among other geographical features.

Stages

The degree of erosion will depend on the soil material, the degree and length of the slope, the state and quantity of the topsoil, and the energy of the raindrops.

It consists of three stages: detachment, transport and sedimentation.

Detachment

Raindrops are the main factor in this stage. These drops fall with a kinetic energy that is dispersed on the ground and divides the clods and aggregates.

This action results in the detachment of particles that seal the small pores on the surface.

The transport stage

In this stage all the detached material is mobilized through the water that runs off the surface.

Normally it occurs in the form of a sheet or mantle with slow speed, although during natural disasters it can do so in a turbulent manner, with greater speed, transport capacity and detachment.

In this stage there is laminar erosion, groove erosion and gully erosion, each with its own particularities.

The sedimentation stage

Thanks to the decrease in energy, all the detached and transported material remains deposited, and eventually sedimented in a single point.

Causes

For water erosion to occur, there must necessarily be some source of energy. In this case it comes mainly from rain, which produces kinetic energy. This energy varies in intensity depending on the quantity, frequency and size of the drops.

For the effects of erosion, what is taken into account when analyzing its impact is the quantitative characteristic of the downpours; that is, intensity and duration take precedence over quantity and averages.

Although it is known that rain is the main factor, there are other actors that also influence the process. Such is the case of the topography, the insufficiency and percentage of organic material in the soil, and the type of plant cover.

Especially, the lack of vegetation, as discussed at the beginning of this article, is one of the most important causes. If the soil does not have plant roots, it will be less compact and will absorb less water.

These factors are compounded by some human activities, such as inappropriate cultivation techniques, modifications in hydrological systems, deforestation, and land marginalization or abandonment, which contribute to intensifying and accelerating erosion.

Compaction also plays an important role in water erosion and the main reason for this phenomenon is inadequate soil management.

Examples of compaction are the excessive density of livestock in a plot or the improper use of heavy machinery when cultivating a land when it is too wet. In these cases, damp soils do not offer sufficient resistance.

Effects edit

The effects of water erosion are divided into two: direct and indirect

Direct

It refers to when the fertility of the soil directly affects the result of the crop. The gradual but constant loss of fertile soils directly affects the results of the crops, until the land is abandoned.

As soils are eroded, their organic matter content decreases.

On steep terrain, heavy rains can lose newly sown crops. The formation of furrows, gullies or landslides in many cases prevent the work of the land.

Indirect

Sedimentation pollution is one of the most common in water.

It affects wildlife, increases the price of drinking water treatments, destroys irrigation canals, bridges and other works, contributes to flooding and affects the aesthetic and biological aspects of lakes.

When coming into contact with rivers, the particles reduce their quality both for human consumption and for irrigation.

Indirect impact can be measured directly through imbalances left by sediments in reservoirs and lakes, and in droughts and floods.

Types of water erosion

There are two main types of water erosion: sheet or stream. The latter has other subtypes.

In lamina or mantiform

The particles are entrained in the form of thin, uniform sheets. The most widespread of hydric erosions and the most difficult to observe occurs in soils with little decline.

As the process progresses, the decrease in nutrients is noticeable through a change in color in the soils towards lighter tones.

Stream erosion

It occurs when water concentrates its erosive power through a channel. In proportion to its kinetic energy, there are three types of erosion by streamlining:

Trickles

They occur through small channels that can be crossed and smoothed, depending on the tillage of the land.

Gullies and ravines

These form where the water descends.

Grooves

They are generated by the action of removing the soil or small stones by the action of the water.

References

1. Water Erosion. Compiled from Wikipedia.org on January 27, 2018.
2. Types of erosion. Compiled from Orton.catie.ac.cr on January 27, 2018.
3. Sustainable agriculture and soil conservation (2009) European Communities.