To get a reasonable idea of how does running water cause erosion, it is better to understand the term erosion. Erosion is explained as wearing away of any surface. In this case we are considering erosion, caused by coming in contact with moving water. Erosion by running water refers to the detrition of surfaces by water that does not get absorbed or evaporated. This water that is left running over the earth is called runoff water.
Runoff water is deemed malicious for farming and different methods are applied to stop it from running across cultivated land. The worst disadvantage of runoff water is that it washes away surface soil. This soil is most productive and holds the entire plantation. In days of flood, famine sometimes follows if reasonable measures are not taken to avert runoff water.
Water erosion takes place in three ways.
- Raindrop impact erosion.
- Rill erosion.
- Gully erosion.
- Sheet erosion.
When rain falls on the ground, the direct impact causes surface erosion, or raindrop impact erosion. If it pours, a considerable amount of surface soil is detached. This usually unhinges roots of saplings, causing them to wither.
Rill Erosion happens when runoff water flows on the ground for a considerable duration it forms trickles. This water forms channels, cutting soil and forming rills. Ground when cut in places becomes unfit for cultivation for a while. This is the most important problem of running water causing erosion.
Running water causes gully erosion when it flows in channels, sometimes accumulating to form larger canals. Water when washes over land, forms larger ducts. Broader channels are formed, cutting cultivable land severely. Gully erosion is basically rill erosion on a bigger scale.
Sheet erosion occurs when water, after traveling a considerable distance, starts losing its energy. At this stage it starts pooling. Water leaves residue behind, which covers the soil surface in the form of a sheet. It is also defined as water flowing unrestricted over plain area. This kind of erosion removes the upper thin layer of soil.
Erosion can be avoided by growing plants and shrubs around cultivated land. This blocks water from entering and also binds soil firmly to the ground. In some areas where erosion occurs regularly the farmers make holes in the ground over which water passes before reaching the crops. Another method is providing land with proper drainage to cut down the flow.