What is Water Erosion?
Water is arguably the most powerful tool for erosion, thanks to its great ability to move objects from one location to another. So, water erosion is the detachment and transport of soil material by water. This process could be natural or facilitated by human activity.
For example, when humans cut down too many trees and plants, the soil remains bare and loose and hence more easily moved by water. Water erosion wears away the surface of the earth. Its rate ranges from very slow to very rapid, depending on various factors such as the soil type, prevailing weather conditions, and the local topography.
The process of water erosion encompasses discrete phases, from raindrop impact to the development of gully erosion. Each phase has its specific processes and characteristics. These phases give us the different types of water erosion.
Types of Water Erosion
While there are several types of water erosion, they can generally be grouped into four major types:
- Inter-rill erosion
- Rill erosion
- Gully erosion
- Bank erosion
Let’s have a detailed look at them.
1. Inter-rill Erosion
Inter-rill erosion describes the movement of topsoil by rainfall and its resultant surface flow. It is also known as raindrop erosion. While it is mainly caused by rainfall, inter-rill erosion can be accelerated by factors such as gradient, topography, vegetative cover, and climate.
This type of erosion is the first and most critical step in the entire process of water erosion. It depends largely on the kind of rainfall found experienced at any particular time or place. Inter-rill erosion includes the following sub-types of water erosion:
- Splash erosion – When raindrops fall on the soil, they may possess sufficient kinetic energy that their impact can cause detachment and movement of small particles of soil.
- Sheet erosion – When heavy rain falls on bare soil, the water flows as a sheet down a gentle-sloping land, detaching soil particles in somewhat uniformly thin layers.
- Runoff – When precipitation surpasses soil infiltration rates, the excess water flows as surface runoff. The precipitation could be in the form of heavy rainfall or melting snow. The turbulence of surface runoff has the potential to cause more erosion than the initial raindrop impact.
2. Rill Erosion
Rill erosion results from the concentrated flow of water in small streams. These small streams are normally started by rainfall and carry soil with them. Rill erosion is the second phase in the process of erosion as a whole.
3. Gully Erosion
Gully erosion describes the detachment and transportation of soil by larger streams of water. It digs at least one-foot deep channels in the soil. It is virtually impossible to smooth over these channels by normal agricultural mechanisms.
4. Streambank Erosion
Streambank erosion occurs when fast-running streams and rivers cut into the banks. This type of water erosion is common at the lower end of stream tributaries. It is also found in streams that have somewhat flat gradients. Streambank erosion can result in large masses of soil slipping down and damaging surrounding fields.
Examples of Water Erosion
A good example is the Grand Canyon, which was formed by the Colorado River. Specifically, it is an example of streambank erosion. Over the course of many centuries, the water erosion managed to create a natural spectacle that attracts thousands of tourists every year.
Flowing water curves out caves over thousands of years. It is worth noting that this process could be accelerated by carbonic acid contained in the water. Fresh water collects calcium carbide from the rocks as it leeches through the rock and sips through cracks. When this water passes through a rock, the resultant carbonic acid erodes the rock over time until a cave is formed.
3. Coastal Erosion
When waves hit the shoreline, the impact is sufficient to cause erosion of the coasts. Water can also dip into cracks in the rock during the impact. When the water in the cracks gets cold, it would expand, causing the rocks to disintegrate and be washed away.
4. River Banks
As water moves past the banks of rivers and creeks, they erode over time, carrying away sediment and dumping it elsewhere. The rocks in the river itself can also be worn down and smoothed, thanks to the constant rolling motion caused by the moving water.
Interesting Facts About Water Erosion
Fact 1: A single rainstorm can wash away 5 tons of soil per acre.
Fact 2: The water erosion process in the United States moves about 4 billion tons of soil every year.
Fact 3: Rivers and streams erode land in three ways depending on the velocity of the water. They erode soil by transporting sediment from one location to another. During the process, they dissolve ions in hard sediments and strike bedrock with fast-moving particles. The water’s hydraulic action gathers small particles and transports them downstream. The fast-moving particles gradually chip away at bedrock, promoting the erosion.
Fact 4: Deposition of the soil particles detached by water erosion is likely in any area where the water velocity is reduced. This can be behind plant and rocks, in places where the gradient is reduced, or in water bodies such as lakes and reservoirs.
Fact 5: A raindrop falls at a speed of about 20 miles per hour and it can splash wet soil up to two feet high and five feet away.