Major sources of soil erosion or degradation are the intensity of rainfall, overgrazing, deforestation and continue tillage practices degrade the soil in all climatic regions.
Due to soil erosion reduce agricultural yield, lowered the animal production, biological activity and adverse effect on the natural ecosystem. In the past half of the century, land degrade by the activities associated with humans. This reduces the production level of soil and can’t provide benefits to the human being.
Soil erosion by water is a three-step process first is the detachment of soil particle from soil second is the transportation of detached particle by floating rolling and splashing and third is deposition of transported particle.
Effect of Raindrops on soil erosion
Erosion is started when the first drop of rain is falling on the soil surface. When raindrop fall on soil surface splashes occurred which detached soil from its origin. Larger raindrops fall faster reaching a terminal velocity about as fast as a person can run. As raindrops fall on soil surface they transfer their high kinetic energy to soil particles.
When raindrops fall on the soil it destroys soil granulation and sometimes beat granules to pieces. As dispersed material dries it may develop into a hard crust which caused a problem in the emergence of seedling indirectly effect on crop production. The intensity of raindrops also decreases soil fertility because it detaches upper fertile soil and transports it to another place such as rivers.
When raindrops strike with soil surface they detach soil from its origin this soil particle moves in all directions. Soil particle easily detached when a heavy splash of raindrops strike with the soil surface. So raindrop is a starting point of soil erosion that detached soil and movement from one to another place.
Effect of runoff water on soil erosion
Runoff water also plays a major role in soil erosion. When the rate of rainfall exceeds from a point caused detachment of soil. If the rate of rainfall exceeds the soil infiltration capacity water will pond and begin running downslope. Soil particles flowing with water which will carry them down the slope. When water is flowing smoothly on the soil surface it has little power to detach soil particles but in some cases when the velocity of water increased then the flow of water is developed in soil. So, runoff water transport soil particles downslope and caused a severe type of soil erosion.
Classification of water erosion
Three types of water erosion are generally recognized which is as follow:
Sheet erosion; heavy rain falls on bare soil, the water flows like a sheet down a sloping land detaching soil particle in a uniformly thin layer. In this type splashed soil removed from surface uniformly except that soil often remains where pebbles are present and interrupt raindrops.
Rill erosion; results from the intensive flow of water in a small stream. When sheet flow changes into tiny channels rill erosion started. Rills are common on bare land. This small stream started by rainfall and carry soil with them. Rill channels are small enough to be smoothed by tillage practices but the damage is that soil is lost.
Gully erosion; it describes the detachment and transportation of soil by a large stream of water .when rill changed into large channels termed as gullies. When the volume of runoff is more intensive the rushing water cuts the soil very deeply. It digs a one-foot channel in soil. It is impossible to smooth channel by agriculture practices. Gully erosion is responsible for most of the soil moved.
Streambank erosion; it occurs when fast-running streams or rivers cut into the bank. This erosion caused a large amount of soil to slip down and damaging the surrounding field.
Deposition of detached soil
Erosion transport soil to a thousand kilometer or more. Soil move from rivers to the ocean by erosion. There is 60% of eroded soil reach in the stream where the slope is very steep. It is estimated that only 5 to 10% eroded soil deposit in the sea and remainder soil is deposit in a reservoir, river or on a flood plain. With the passage of time soil level increased in rivers and canals by deposition of soil by erosion.
All rivers contain a large amount of soil and sediments which is deposit by soil erosion. When the river stilled behind a dam the sediment and soil it contains sink to the bottom of the reservoir. As the sediment and soil accumulate in the reservoir, dams losses their ability to store water for the purpose for which it was built.
Effect of water erosion
When rainwater falls it causes soil erosion. Water erosion exposed the natural element from soil. If the process of water erosion is slow then it is not always harmful to the ecosystem but if the process will be fast then it caused a negative effect on the ecosystem.
Effect on crop productivity by water erosion
Water erosion removes the topsoil which has an adverse effect on crop productivity. Water erosion causes a diminished water capacity which reduces the nutrient in the soil. When nutrients in the soil will be decreased crop productivity will be reduced.
Flooding by water erosion
Water erosion removes the topsoil so chances of flooding are increased because water not absorbed in the soil. Flooding can be extremely devastating and in severe cases, it destroys roads, buildings, and houses.
Effect on marine life by water erosion
Because the absence of topsoil reduces the water quality and increased water pollutants, fish and algae are negatively affected. There is a reduction in fish numbers due to soil erosion and pesticide runoff. Excessive topsoil could cover up fish breeding areas and pollute water.
Effect on water quality by water erosion
Water erosion not only affects plants and marine life but also affects the quality of water. When rainwater erodes the soil it can affect water quality. After erosion topsoil reaches in water sources it increases the amount of nitrogen and phosphorus in the water. Due to this oxygen level reduced in water which diminished water quality. Harmful chemicals such as pesticides present in topsoil can reach in lakes, rivers, and ocean.
Effect on soil structure by water erosion
Soil structure, quality, and texture can be affected by the loss of soil. The breakdown of soil aggregate and removal of the entire layer of soil or organic matter can weaken the structure and change the texture of the soil. Textural changes can affect the water holding capacity of the soil and making it more susceptible to extreme conditions such as drought.
Destruction of infrastructure by water erosion
Soil erosion can affect the infrastructure of dams and drainage. The accumulation of soil sediments in dams and drainage can reduce their efficiency. Soil erosion from surface water runoff often destroys roads and tracks.
Desertification by water erosion
Soil erosion is a major driver of desertification. It transforms the land into a desert. Erosion by water removes topsoil which can change fertile soil into the desert. This usually leads to the loss of fertile soil and huge economic losses.
Erosion at the construction site contributes to drainage system clogs due to the sediment that is washed off the site. Water erosion is controlled by vegetation. Plants root system protecting the soil from water erosion. Coir is a natural fiber that protects soil from water erosion. Soil erosion control by mulching and preventing tillage and construction. Soil erosion occurs by water runoff so we can control it by channel construction and terracing. In agriculture, tillage management is an effective way to control water erosion.